Capstone Learning Biology Book 1
Udo, K. W ( Raphael)
PGDE ( Uniuyo)
HND ( Microbiology)
C Capstone Learning
First Published 2018 by :
Jehub Publishers, Inc. ( Ubprint)
52 AfahaEket Road, Eket
ISBN: 978-9978-8509-4-7
Copyright information : The copyright of this book belongs to Raphael Udo (Kufre ).
The Copyright of this book is strictly prohibited. Anyone found in breach of the copyright without permission will be prosecuted.
Dedication
This book is dedicated to Almighty God, the giver of wisdom and to my lovely wife Sarah Raphael Udo.
Preface
The purpose of this book is to provide a brief summary and a standard textbook for Biology students in senior secondary schools.
Again, to guide learners to revise successfully and to receive adequate knowledge in Biology . In all the chapters of the book, basic concepts are clearly presented in a simple and readable way .
The book Capstone Learning stands out as an instructional tool for all learners.
This book gives basic foundations of what a student is needed to know in Biology
The author covered essential topics that will be of great benefit to both learners and teachers.
Revision Tips
The first important point about revision is that you need to be realistic about the amount of work that you need to do.
To revise successfully for any subject,( particularly for science) , you have to really get into it. You have to get your mind deep into the subject. That’s because science has some difficult concepts that require thought and concentration. For instance, you are right in the middle of that challenging topic and your phone rings. Your friend has sent you a message about something that he saw on either WhatsApp or Facebook. You reply and start revising again. Another message appears. This is from a different friend who has a meme they want to share. And so on and so on.
What I’m trying to tell you is that successful revision requires isolation. You need to shut yourself away from distractions and that includes your phone. Nothing that any of your friends have to say is so critically important that it cannot wait until you have finished. Just because your friends are bored does not mean that your revision has to suffer.
Again, it’s about you taking charge. There are different ways to revise and you have to find what works for you. I believe that active revision is the most effective. I know that many students like to copy out details notes. Personally, I don’t believe that this is a great way to revise since it’s not really active. A better way is to read a book and then try to answer the question from the book you read. If you can’t, then you might need to read the book again (or look carefully at the answers to check the part that you struggled with).
The human brain learned by repetition. So the more times that you go over a concepts, the more fixed it will become in your brain. That’s why revision needs so much time because you really need to go over everything more than once ( ideally several times) before the exam.
Introduction
Hello, this is my summary of capstone Learning Biology Book 1 For Senior Secondary Schools. As a teacher, I have always enjoyed teaching Biology and really want to make it a fascinating subject for all learners.
Please, don’t think of science as some sort of impossible mountain to climb. Yes, it could be challenging a bit, but it’s not as difficult as people think.
Take your time, work hard and believe in yourself. When you find a topic difficult, don’t give up. Just go to a different topic and come back to it later.
Finally, if you have any feedback on the book capstone Learning Biology Book 1 , you’re free to let me know (capstonelearning9@gmail.com). I’m always keen to make the book better so if you have a suggestion, I’d love to hear it.
Good luck on your journey, I hope that you skyrocket to get grade that you want.
About the Book
Capstone Learning Biology Book 1 is written to meet the need of students in Senior Secondary Schools. It covers the current examination syllabus of the West African Examinations Council
( WAEC), National Examinations Council ( NECO) and that of the united Tertiary Matriculation Examinations ( UTME).
This book is made easy for learrners who desire amazing results in the Senior Secondary School Examinations and entrance examinations into the University , Polytechnic and college of Education.
This book has four chapters, consisting of lessons that begin with learning objectives to let the learners know exactly what to expect. Each chapter is clearly presented and well summarized.
Contents
Dedication
Preface
Revision Tips
Introduction
Contents
Chapter One : CELL BIOLOGY
Lesson 1 : What is in a Cell?
Lesson 2 : Eukaryotes and Prokaryotes
Lesson 3 : Sizes of Cells
Lesson 4 : Order of Magnitude
Lesson 5 : Animal Cells
Lesson 6 : Plant Cells
Lesson 7 : Animal Cell Specialization
Lesson 8 : Plant Cell Specialization
Lesson 9 : Microscope
Lesson 10 : Cell Division by Mitosis
Lesson 11 : Stem Cells
Lesson 12 : Diffusion
Lesson 13 : Surface Area to Volume Ratio
Lesson 14 : Bacterial Division
Lesson 15 : Osmosis
Lesson 16: Active Transport
Required Practical 1 : Microscope
Required Practical 2 : Culturing Microorganisms
Required Practical 3 : Effect of Osmosis on Plant Tissue
Chapter Two : ORGANIZATION
Lesson 1 : The Digestive System
Lesson 2 : Digestive Enzymes
Lesson 3 : Effect of Temperature and pH on Enzymes
Lesson 4 : Absorption in the Small Intestine
Lesson 5 : The Heart and Circulation
Lesson 6 : Arteries, Veins and Capillaries
Lesson 7 : The Blood
Lesson 8 : Cardiovascular Diseases
Lesson 9 : Gas Exchange in the Lungs
Lesson 10 : Cancer
Lesson 11 : Communicable and Non-Communicable Disease
Lesson 12 : Correlating Risk Factors
Lesson 13 : Lifestyle and Disease
Lesson 14 : Plant Tissues
Lesson 15 : Transpiration
Required Practical 4 : Food Test
Required Practical 5 : Effect of pH on Amylase
Chapter Three : Infection and Response
Lesson 1 : Pathogen
Lesson 2 : Measles and HIV
Lesson 3 : Salmonella and Gonorrhea
Lesson 4 : Malaria
Lesson 5 : Non-Specific Defense System
Lesson 6 : The Immune System
Lesson 7 : Infectious Diseases in Plants
Lesson 8 : Vaccination
Lesson 9 : Antibiotic
Lesson 10 : Testing Medicine
Lesson 11 : Monoclonal Antibodies
Lesson 12 : Plant Disease
Lesson 13 : Plant Defense Response
Lesson 14 : Plant Hormones
Required Practical 6 : Plant Responses
Lesson 15 : Cloning Plants
Lesson 16 : Cloning Animals
Chapter Four : Bioenergetics
Lesson 1 : Photosynthesis
Lesson 2 : Limiting Factors
Lesson 3 : Respiration
Lesson 4 : Exercise
Lesson 5 : Metabolism
Required practical 7 : Photosynthesis
Lesson 6 : Monosaccharides
Lesson 7 : Diaccacharide
Chapter One : CELL BIOLOGY
Lesson 1 : What is in a Cell?
Learning Objectives :
By the end of this lesson, learners should be able to :
• Describe what is in a cell.
• Describe the scientists that discovered cell.
What is in a Cell?
Human being has about 73 trillion cells in their body. All living things comes from cells. Most cells are so small that you can only see them with the help of a microscope. According to the cell theory, the cells are the basic building blocks of all plants and animals . This simply means that the cell is the smallest unit of living things that can carry out all the activities necessary for life.
Inside cells are various structures that are specialized to carry out a particular function. Both plant and animal cells have these components;
• Nucleus : This controls what happens in the cell. It contains DNA, the genetic information that cells need to grow and reproduce.
• Cell Membrane : This surrounds the cell and allows nutrients to enter the cell and waste to leave the cell.
• Cytoplasm : This contain enzymes to carry out chemical reactions in the cell.
• Mitochondria : These are the power house of the cell, which release energy by respiration.
• Ribosomes : These make proteins in the cell.
Scientists that Discovered Cell.
1. Robert Hook, in 1665 discovered an empty space while working with a thin slice of cork under a microscope and called it ‘cell ‘. Robert Hook has been seen as the father of cells and that’s because he was the first man to discover the cell.
2. Dujardin, in 1835 discovered that cells are made up of living unit called “protoplasm “
3. Mathias Schleiden , in 1838 revealed that the bodies of plants are made up of cells.
4. Theodor Schwann, in 1839 also revealed that the bodies of all animals are consists of cells. The discoveries of Schleiden and Schwann led to the postulation of the cell theory in 1839.
5. Rudolf Von, in 1855 concluded in his research that all cells comes from previously existing cells.
Lesson 2 : Eukaryotes and Prokaryotes
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe the differences and similarities between eukaryotic cells and prokaryotic cells.
Eukaryotes and Prokaryotes
Both animals and plants are eukaryotes. The most obvious feature of an animal and plant cell is that they have a nucleus .
The nucleus contains the genetic material of these cells. In other words the DNA. So this brings us to the definition of eukaryotic cells.
Eukaryotic cells contains their genetic material (DNA) enclosed in a nucleus.
Eukaryotes
Animal and plant cells also have a cell membrane and It’s really critical that you don’t call this the cell wall as that’s not correct. Within the cell membrane we have the cytoplasm.
Prokaryotes
Now unlike animals and plants, bacteria are prokaryotes . In prokaryotic cells, the genetic material is not enclosed in a nucleus and again that’s a key definition that you need to learn.
The second key fact is that prokaryotic cells are much smaller than eukaryotic cells.
Remember that prokaryotic cells such as bacteria do not have a nucleus and their genetic information consists of a single loop of DNA.
Bacteria may also have small rings of DNA which are called plasmids.
Prokaryotic cells have a cell membrane, but they’ve also got cell wall. It’s important to remember that this is a bacterial cell wall. Don’t get confused with the plant cell wall which we’re going to look at in a later lesson.
Finally, prokaryotic cells also contain cytoplasm. Examples of prokaryotic cells include Lactobacillius bulgaricus ( a rod shape bacterium used in the production of yoghurt from milk) and Pneumococcus ( a spherical bacterium that causes pneumonia).
Lesson 3 : Sizes of Cells
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe the size of cells.
• Use the prefixes centi, milli, micro and nano.
Sizes of Cells
Size is how small or big an object is. All sizes in science are based on the meter. But the problem is that the objects in biology are often more smaller than that.
For instance a dog like German shepherd is around 1 meter and if we divide 1 meter into 100 equal parts, then we have 1 centimeter.
“ Centi “
The word “ centi “ means one hundredth.
1 centimeter is 1/100 th of a meter.
Using standard form : 1cm = 1 x 10-2 m
Also, the width of your little finger is around 1 centimeter. In biology 1 cm is large. If we divide 1 cm into 10 equal parts, then we have 1 mm.
“ Milli “
The word “ Milli “ means one thousandth.
1 millimeter is 1/1000 th of a metre.
Using standard form : 1mm = 1 x 10-3 m.
“ Micro “
The word “ micro “ means one millionth.
1 micrometer is 1/1000000 th of a meter.
Using standard form : 1um = 1 x 10 – 6 m
Remember, scientists often used standard form and you could be expected to use that in your exam.
Remember that a typical human cell is 10 – 20 micrometers in size. That means that biologists find a micrometer a very useful unit especially when looking at cells.
“ Nano “
The word “ Nano “ means one billionth
1 nanometer is 1/1000000000 th of a meter.
Using standard form : 1nm = 1 x 10 – 9 m.
You should know that nanometer is a very small size. Proteins and cells such as haemoglobin molecules are measured using nanometer.
Lesson 4 : Order of Magnitude
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe what is meant by order of magnitude.
• Carry out order of magnitude calculations.
What is Meant by Order of Magnitude.
Sometimes scientists want to compare the approximate size of the different objects and for this, we use the idea of order of magnitude.
If an apple and an orange for example have the same size , scientists say that these are around the same order of magnitude.
In the case of a pineapple and a small lemons , the pineapple is around ten time (10x) larger than the lemon. Scientists say that the pineapple is one order of magnitude larger than the lemon.
Therefore, one order of magnitude means ten times.
Another instances is between a dog and a woodlouse. You can see that the dog is around 100 times larger than the woodlouse. Scientists say that the dog is two orders of magnitude longer than the woodlouse.
The key idea is that every order of magnitude is ten times greater than the one before. An easy way we can work this out is to count the number of zeros. This tells you the order of magnitude. Therefore;
10 x is one zero.
One zero = one order of magnitude.
100x is two zeros.
Two zeros = two order of magnitude.
1000x is three zeros.
Three zeros = three order of magnitude.
Order of Magnitude Calculation:
Sample Question
A fox is around 40cm long. A tick living on a fox is around 0.4cm long. How many order of magnitude is the fox longer than the tick?
Working
Fox = 40cm
Tick = 0.4cm
40 ÷ 0.4 =100x
Therefore, the fox is 100x, which is two order of magnitude longer than the tick.
Lesson 5: Animal Cells
Learning Objectives
By the end of this lesson, learners should be able to :
• Correctly label a diagram of an animal cell.
• Describe the functions of the different parts of an animal cell.
Animal Cells
Animals are eukaryotes and their genetic materials (DNA) is enclosed in a nucleus.
Animal cells do not contain chloroplasts and are not able to carry out photosynthesis.
Animal cells have no cell walls. They often store carbohydrate as glycogen.
Remember that the cells are measured in micrometre and 1 micrometre = 1/1000000 th of a metre.
Functions of the Different Parts of an Animal Cell :
Nucleus : This is the center of the cell activities and it controls what happens in the cell. It also contain the genetic information (DNA and RNA) that cells need to grow and reproduce.
Cytoplasm : This is a watery solution, which contain enzymes and salt to carry out chemical reactions.
Cell Membrane : This controls the movement of substances in and out of the cell. That is to say it surrounds the cell and allows nutrients to enter the cell and waste to leave the cell.
Mitochondria : This is where aerobic respiration takes place. It is regarded as the power house of the cell.
Ribosomes : These are the tiny structures where protein synthesis takes place. Proteins are really important and they carry out lot of functions in cells example enzymes.
Remember that ribosomes are extremely small and can’t be seen using light microscope. Instead we need to use a powerful microscope called an electron microscope.
Lesson 6 : Plant Cells
Learning Objectives
By the end of this lesson, learners should be able to :
• Correctly label a diagram of a plant cell.
• Describe the functions of the different parts of a plant cell.
Plant Cells
Plant can use light to carry out photosynthesis. Plant cells have a regular shape. Unlike animal cells, which can easily change their shape.
Plant cells are packed full of green structure called chloroplasts.
Plants are eukaryotes and they have several structure in common with animal cells such as nucleus, cytoplasm, cell membrane, mitochondria, ribosomes etc.
Cells have cellulose cell walls. They store carbohydrates as starch or sucrose.
Examples include flowering plants, such as a cereal (e.g. maize) and a
herbaceous legume (e.g. peas or beans).
Functions of the Different Parts of a Plant Cell :
Plants have three main structures which animal cells do not and its really important you learn these.
Cell Wall : This is found only in plant. It is made from chemical called cellulose and this strengthen the cell and allows it to be turgid.
Permanent Vacuole : Plant cell also contain a large permanent vacuole. The vacuole is filled with a fluid called cell sap. The vacuole helps give the plant cell its shape and also acts as a store of water or sugars.
Lesson 7 : Animal Cell Specialization
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how sperm cells, nerve cells and muscle cells are specialized to carry out their functions.
Animal Cell Specialization
Most animal cells are specialized. This means that they have special features which help them to carry out their specific function.
When cells become specialized, scientists call that differentiation.
Differentiation occurs during development of a living thing. Remember that organism lose the ability to differentiate once the become specialized.
Different Types of Animal Cells
Sperm cell / ova or egg
Nerve cell / neuron
Muscle cell
White Blood Cells u
Red Blood Cells
Bone cells
Epidermal cells
Cone cells
Rod cells
Let discussed some of the functions of these animal cells:
Sperm cell / Ova or Egg
The job of a sperm cell is to join with an ovum (egg cell). We call that process fertilization. During fertilization, the genetic information of the ovum and the sperm combine.
Sperm cells are specialized for reproduction.
Sperm cells contain their genetic information in the nucleus.
However, sperm cells only contain half the genetic information of a normal adult cell.
Sperm cells have a long tail which allows them to swim to the ovum. They are also streamlined to make them swim faster .
Sperm cells are packed full of mitochondria and this provide the energy needed for swimming. They have enzyme in the tip of the head called acrosome.
Finally, sperm cells contain enzymes which allow them to digest their way through the outer layer of the ovum.
Nerve Cell / Neuron
The job of a nerve cell is to send electrical impulses / messages around the body.
The axon carries the electrical impulses from one part of the body to another.
Myelin insulates the axon and speeds up the transmission of nerve impulses.
The end of the axon has synapsis. Synapsis are junctions which allow the impulses to pass from one nerve cell to another.
Dendrite increase the surface area so that other nerve cells can connect more easily.
Muscle cell
Muscle cells are the fleshy part of the body. There are over 650 muscle cells in the body. The key feature of muscle cells is that they can contract. In other words get shorter . To do this, muscle cells contain protein fibers which can change their length. When a muscle cell contracts, these protein fibers get shorten, decreasing the length of the cell.
Muscle cells are also packed full of mitochondria to provide energy for muscle contraction.
Muscle cells are attach to bones and these gives shape to the body.
Muscle cells are used for movement. Now one important point that muscle cells do is that they work together to form muscle tissue.
White Blood Cell / Leucocyte
• White blood cells defend the body against disease.
• They produce antibodies and antioxidants.
• White blood cells are used for immunity
Red Blood Cell / Erythrocytes
• Red Blood Cells are specialized to carry oxygen from the lungs to the cells.
• They remove carbon dioxide from cells to the body.
• Large surface area to increase diffusion of oxygen.
• No nucleus so extra room for haemoglobin.
Lesson 8 : Plant Cell Specialization
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how root hair cells, xylem cells and phloem cells are specialized to carry out their functions.
Plant Cell Specialization
Most plant cells are specialized. That is to say they have special adaptations , which help them to perform their function.
Types of Plant Cells
1. Xylem
2. Phloem
3. Root hair cells
Xylem Cell
Xylem are found in the plant stem. They form long tube. These tubes carry water and dissolved minerals from roots to the leaves.
They have thick wall containing lignin. This provide support to the plant.
Because the cell walls are sealed with lignin, this causes the Xylem cells to die.
The end walls between the cells have completely been broken down. This means that the cells then form a long tube so that water and dissolved minerals can flow easily.
Xylem cells have no nucleus, cytoplasm, vacuole or chloroplasts. That makes it easier for water and minerals to flow.
Phloem Cell
Ploem tube carry dissolved sugars up and down the plant.
Phloem vessel cells have no nucleus and only limited cytoplasm.
The end walls of cells have pores called sieve plates. These features allow dissolved sugars to move through the interior cell. Each phloem vessel cell has a companion cell connected by pores. Mitochondria in the companion cell provide energy to the phloem vessel cell.
Root Hair cell
Water enters root hair cells by osmosis. The roots are full of minerals, which artificially lower the concentration of water inside the root cells, so water is always drawn into them from the soil. This enables transpiration to happen even if the soil is very dry.
The roots take the minerals up against the concentration gradient and is, therefore, an example of active transport.
The root hair increases the surface area of the root. It can absorb water and dissolved minerals more effectively. Root hair cells do not contain chloroplasts, because they are underground.
Lesson 9 : Microscope:
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe the advantages of an electron microscope over a light microscope.
• Carry out calculations based on magnification.
Microscopes
Microscopes are first invented hundreds of years ago. Modern microscopes are much more advanced. Microscopes use light to view specimen.
Now over the years, light microscopes have been used a lot to study cells. They’ve allowed us to make important discoveries about the structures inside cells. For example the nucleus and that’s because microscopes allow us to magnify. In other words, the image that they produce is much bigger than the actual object.
Now, there are couple of problems with light microscopes. Light microscope have a limited magnification. For example we cannot easily view structures inside the nucleus with a light microscope and that’s because the magnification is not powerful enough. Light microscopes have another big problem, which is that they have limited resolution. What is means is that the image is blurred. Even if we could increase the magnification we’d still get a blurred image and we’d not be able to see fine detail. Again, that’s because the resolution is limited.
Scientists realized that if they wanted to explore structures inside cells in detail then a light microscope is not that useful. So they invented the electron microscope.
Advantages of an Electron Microscope
Now, the key advantages of electron microscope is that they have a much greater magnification and resolution than light microscope and you could be asked that in your exam and because of the high resolution, we can now see detail in the nucleus that we could never see with a light microscope.
How to Carry out Calculations Based on Magnification
Remember that microscope use lenses to magnify the image of a specimen so that it appears larger.
To calculate magnification, simply use this formula:
Magnification = size of image
size of real object
Sample Question 1:
Use a ruler to measure the image size of the nucleus in mm. The diameter of the real nucleus is 0.01mm. Calculate the magnification. In this case, the size of the image is 45mm. Pause your reading and try this yourself.
Working
The size of the image is 45mm. The actual diameter of the real object is 0.01mm.
Magnification = size of image
Size of real object
= 45mm = 4500
0.01m
Sample Question 2
If we know the image size and the magnification then we can calculate the size of the real object. To do that, we need to use the triangle that we saw earlier. The size of the real object is the size of the image divide by the magnification. Here’s a question for you.
Measure the length of the cell shown. The magnification is 2000x. Calculate the real size of this cell in mm. The real size of this cell is 87mm. Pause your reading and try this.
Working
Size of the real object = size of image
Magnification
= 87 = 0.0435mm
2000
Lesson 10 : Cell Division By Mitosis
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe the importance of mitosis.
• Describe the stages of the cell cycle involving mitosis.
Importance of Mitosis
Plant and animal cells contain a nucleus. In the nucleus we find chromosomes which are made up of DNA. This cell contains chromosomes :
• Body cells contain two of each chromosome. They are paired with long and short chromosomes.
• Human body cells contain 23 pairs of chromosomes.
• Gametes have chromosomes which are not paired ( I.e. human gametes have 23 single chromosomes).
• Chromosomes carry a large number of genes which determine many of our features.
Stages Of Cell Cycle
Animal and plant cells contain a very large number of cells. That means cells have to be able to divide. That is called cell cycle. Cells can divide by either mitosis or meiosis. In this lesson we are looking at mitosis
The cell cycle including mitosis consists of three main stages :
In the first stage of the cell cycle, the DNA replicates to form two copies of each chromosome. The cell also grows and copies its internal structures such as mitochondria and ribosomes.
In the second stage of the cell cycle, mitosis takes place. One set of chromosomes is pulled to each end of the cell. The nucleus also divides.
In the final stage of the cell cycle, the cytoplasm and the cell membrane divides to form two identical cells.
In some textbook, you might see lots of different stages of mitosis but in this book I’m showing you three stages.
Functions of Mitosis
1. Mitosis is essential for growth and development. ( For example when a foetus grows and develops in the uterus ).
2. Mitosis takes place when an organism repairs itself ( For example when a broken bone heals).
3. Mitosis happens during asexual reproduction. This is when an organism reproduces without the need for a partner. We see this in a large number of plants and in some animals ( for example green fly ).
Lesson 11 : Stem Cells
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe what is meant by a stem.
• Describe where stem cells are found in animals and plants.
• Describe how stem cells can be used for medical treatment and plant cloning.
Stem Cells
Humans start when a sperm cell joins with an ovum (egg cell). This is called fertilization. The fertilized ovum now undergoes mitosis and forms a ball of cell called an embryo.
Overtime, these cells continue to undergo mitosis. They also change and begin to form specialized cells such as nerve cells and muscle cells.
When cells specialize like this, scientists call this process differentiation.
Finally, these cells form the adult organism .
Remember that cells in the early embryo do not differentiate. When any one of this cell is capable of differentiating into any type of body cell, scientists called it embryonic stem cells.
Meaning of Stem Cells
A stem cell is an undifferentiated cell which can give rise to more cells of the same type of cells and can differentiate to form other types of cells. Remember that differentiate means change to a cell which is specialized ( for example a muscle cell or neuron). Stem cells are undifferentiated ( in order words they have not yet specialized ). Stem cells can produce more stem cells by undergoing mitosis. Stem cells can also differentiate into specialized cells.
We can find stem cells in adult organisms example in bone marrow. Unlike embryonic cells, adult stem cells can not differentiate into any other type of cell.
Note; The stem cells in bone marrow differentiate to form cells found in our blood such as red blood cell, white blood cell and platelets.
How Stem Cells can be Used for Medical Treatment and Plant Cloning.
Stem cells are very useful in medicine:
Cancer of the bone marrow is called Leukemia . This is treated with a bone marrow transplants .
Treatments
To treat this, first the patient’s existing bone marrow is destroyed using radiation.
The patient then receives a transplant of bone marrow from a live donor.
The stem cells in the bone marrow now divide and form new bone marrow. They also differentiate and form blood cells.
Problems of Bone Marrow Transplants
There are two main problems of bone marrow transplants. These are ;
First, the donor has to be compatible with the patient otherwise the white blood cells produced by the donated bone marrow could attack the patient’s body.
Secondly, there is a risk that viruses can be passed from the donor to the patient.
• Therapeutic Cloning
In therapeutic cloning, an embryo is produced with the same genes as the patient.
Stem cells from the embryo can be transplanted into the patient without being rejected by the patient’s immune system.
Once inside the patient, the stem cells can then differentiate to replace cells which have stopped working correctly.
This technique could be useful for a range of medical conditions such as diabetes or paralysis.
However, some people have ethical or religious objections to this procedure.
• Plant Stem Cells
Roots and buds contain meristem tissue. These stem cells can differentiate into any type of plant tissue, at any point in the life of the plant.
We could clone a rare plant to stop it from going extinct or we could produce cloned crop plants for farmers. For example plants which are resistant to diseases.
Lesson 12 : Diffusion
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe what is meant by diffusion
• Describe the factors that affect the rate of diffusion.
What is meant by diffusion?
Diffusion is the spreading out of particles resulting in a net movement from an area of higher concentration to an area of lower concentration, down a concentration gradient. The word net means overall.
The cell membrane is where molecules enter and leave the cell.
One way that molecules can move in and out of cells is by diffusion and that’s what you will learn in this lesson.
Molecules which Move in and out of Cells by Diffusion :
There are three molecules which move in and out of cells by diffusion. These are oxygen, carbon dioxide and urea.
1. Oxygen
Cells need oxygen for respiration which is carried out by mitochondria. Cells are surrounded by a high concentration of oxygen above. This oxygen is then transported in the blood from the lungs.
From the diagram shown, there is higher concentration of oxygen outside the cell. What this means is that, the oxygen molecules move into the cell by diffusion from an area of higher concentration to an area of lower concentration.
The oxygen is used to generate energy in respiration and this produces the waste gas called carbon dioxide.
2. Carbon dioxide
Description
This diagram shows a higher concentration of carbon dioxide inside the cell than outside. So the carbon dioxide moves out of the cell by diffusion.
3. Urea
Urea is a waste product produced inside cells. It diffuses out of the cells into the blood plasma and is excreted by the Kidneys.
Factors that Affects the Rate of Diffusion
The rate of diffusion is affected by three main factors.
• The first factor is the Different in concentration.
I’m showing you here a molecule on the outside and the inside of a cell. As you can see, there is higher concentration outside the cell than inside. So that means the molecules will diffuse into the cell as shown above.
Remember that the different in concentration is called the concentration gradient. Therefore, the greater the concentration gradient, the faster diffusion takes place. So in this example, diffusion will be faster.
In this example , the concentration gradient is much smaller. That means that diffusion will be slower.
• The second factor that affects the rate of diffusion is Temperature . The higher the temperature, the greater the rate of diffusion. That is because the particles have more kinetic energy and are moving faster.
• The final factor is the Surface Area of the Membrane. Take a look at these two cells below ;
The cell membrane of the cell on the left has a much larger surface area than the cell on the right. This means that the rate of diffusion will be greater for the cell on the left.
Remember that the larger the surface area of the cell membrane, the greater the rate of diffusion.
Lesson 13 : Surface Area to Volume Ratio
Learning Objectives
By the end of this lesson, learners should be able to :
• Use the idea of surface area to volume ratio to explain why multicellular organisms require exchange surfaces and a transport system.
• Describe how gills increase the rate of transport of gases into and out of fish.
Recap
In the last lesson we saw that molecules move in and out of cells by diffusion. For example, oxygen diffuses into cells and carbon dioxide diffuses out.
Why Multicellular Organism Required Exchange Surface and a Transport System.
Description
I’m showing you amoeba here. Amoeba are singled – celled organisms. They have a huge surface area for their volume. Scientists called this surface area : volume ratio.
Singled – organisms such as amoeba can rely on diffusion to transport molecules in and out of their cell. For example all of the oxygen that the amoeba needs simply diffuses in through its membrane.
How to Calculate the Surface Area to Volume Ratio
Example 1.
Surface area of each side = 1mm × 1mm × 6mm = 6mm2
Volume = 1mm × 1mm × 1mm = 1mm2
6 ÷ 1 = 6
Surface area : volume ratio = 6 : 1
Example 2.
Surface area = 2mm × 2mm × 6mm = 24mm2
Volume = 2mm × 2mm × 2mm = 8mm3
24 ÷ 8 = 3
Surface area : volume = 3:1
Example 3
Surface area of each side = 3mm × 3mm × 6mm = 54mm2
Volume = 3mm × 3mm × 3mm = 27mm3
54 ÷ 27 = 2
Surface area : volume = 2 : 1
From the calculation shown above , you can see that as organisms get larger, the surface area : volume ratio falls sharply. This presents a huge problem for multicellular organisms (organisms with more than one cell). Their surface area is not large enough for their volume. Cells on the surface can get enough oxygen simply by diffusion.
However, not enough oxygen can diffuse into the cells in the center of the organism. They are too far away from the surface. Animals has solved this problem in two
ways :
Firstly, animals have special structures for gas exchange with a very high surface area for example lungs as in mammals.
Secondly, animals have a transport system to carry out gases around the body example fish.
Description
Fish get oxygen from the mouth. The oxygen – rich water passes into the mouth. It is then flows over gills, where the oxygen is transported into the bloodstream. The gills are covered in a very large number of fine filaments. This is where gases pass in and out of the blood.
Deoxygenated blood passes into the filaments. Oxygen diffuses from the water into the blood. Oxygenated blood returns to the body.
The filament has three adaptation to increase the rate of diffusion and these are :
1.The filaments give the gills a massive surface area.
2.The filaments also have a thin membrane to provide a short diffusion pathway.
3. The filaments have an efficient blood supply to take the oxygenated blood away.
This ensures that the concentration gradient is always high. All of these adaptations make diffusion as efficient as possible.
Lesson 14 : Bacterial Division
Learning Objectives
By the end of this lesson, learners should be able to :
• Calculate the number of bacteria in a population after a certain time.
• Express the number of bacteria using standard form.
Binary Fission
Bacteria multiply by simple cell division. That is to say bacteria cell splits into two bacterial cells. Scientists call this binary fission .
Bacteria can carry out binary fission once every 20 minutes as long as they have enough nutrients and the temperature is sustainable. Meaning that bacteria can increase very rapidly.
How to Calculate the Number of Bacteria in a Population after a Certain Time
Sample Question 1
Under ideal conditions, a type of bacterium divides every 20 minutes. Calculate the number of bacteria present after 3 hours. Pause your reading and try this yourself.
Working
To calculate the number of bacteria, we use this equation :
Number of bacteria = 2 n
Where n = number of rounds of division.
3 hours = 180 minutes
The bacteria divide in 20 minutes
180 ÷ 20 = 9 rounds of division.
Therefore, the number of bacteria = 2 9 = 512
This means that we have 512 bacteria present after 3 hours.
Using standard form
Number of bacteria = 5.12 x 10 2
Sample Question 2
Under ideal conditions, a type of bacterium divides every 20 minutes. Calculate the number of bacteria present after 8 hours. Pause your reading and try this yourself .
Working
First, calculate the number of rounds division.
8 hours = 480 minutes.
The bacterium divide once every 20 minutes.
480 ÷ 20 = 24 rounds of division
Therefore, number of bacteria = 2 24 =16,777216
Using standard form
Number of bacteria = 1.678 × 10 7 to 3 d. p.
Lesson 15 : Osmosis
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe what is meant by osmosis.
• Describe the effects of osmosis on animal and plant cells.
Definition
Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
Description
Dilute solution contain a high concentration of water whereas concentrated solution contain a low concentration of water.
As you can see, in concentrated sugar solution, we don’t have lot of water. Scientists would say that concentrated solutions contain a low concentration of water.
Partially Permeable Membrane
Partially permeable membranes allow water molecules to pass through but not sugar molecules. This result to a higher concentration of water on the left hand side and a lower concentration of water on the right hand side. The water then diffuses from the left hand side to the right hand side as shown. Therefore, osmosis is simply the diffusion of water.
Effects of Osmosis on Animal Cells
I’m showing you an animal cell here and this brings us to a key point:
The cytoplasm of cells is a relatively concentrated solution. In other word, it contains a relatively low concentration of water.
If we place this cell in water, then osmosis will take place. Water will move by osmosis from outside the cell to inside the cell as shown in the diagram .
In the case of an animal cell, the water moving in will cause the cell to expand and the cell could even burst.
If we place an animal cell in a very concentrated solution, then water will move out of the cell by osmosis and the cell will shrink.
Effects of Osmosis on Plant Cells
I’m showing you a plant cell here. If we place a plant cell in water, then water will move in into the cell by osmosis and the cell will expand.
The key point here is that ;
The cell wall prevent the plant cell from bursting. Instead, the cell become swollen and scientists call this turgid. Turgidity is when plant cells absorb plenty of water up to a point where the cell is fully stretch.
If we place the plant cell into a concentrated solution, then water moves out of the plant cell by osmosis. This causes the cell to shrink and scientists say that the cell has become flaccid. Flaccidity is when plants lose water to their surroundings faster than they absorb.
Lesson 16 : Active Transport
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how substances are absorbed by active transport.
• Describe examples of active transport in animals and plants.
Recap
Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration and the word net just means overall. The diagram above illustrate cell membrane with a high concentration of particles on outside and a low concentration of particles inside. Scientists call this a concentration gradient because we have a region with a high concentration and a region with a low concentration.
At this point, there’ll be a net movement of particles by diffusion down the concentration gradient .
How Substances are Absorbed by Active Transport
Description
There is a higher concentration of the molecules inside the cell than outside . This means that the molecules cannot diffuse into the cell. In fact they could diffuse out.
The question is, how can a cell bring these molecules in?
To do this the cell uses a process called active transport.
Active transport is the movement of molecules from low
concentration to high concentration against the concentration
gradient. Energy is required for movement to occur.
Difference Between Diffusion and Active Transport
Diffusion Active Transport
1.Particles move down the concentration gradient. Particles are moved against the concentration gradient
2.It does not require energy from respiration. It require energy from respiration.
Examples of Active Transport in Animal
Description
This shows the cells lining in the human small intestine. The cavity of the small intestine where food is digested is called the lumen and you can see that here from the diagram shown.
In the lumen, we find the molecules produced when foods are digested. Examples of these are sugars. You can see that the concentration of sugars in the lumen is lower than the concentration of sugars inside the cell.
These sugars cannot diffuse into the cell, instead the sugars are carried in by active transport.
Once inside this cell, the sugars can then be transported into the blood and carried around the body.
These cells contain lots of mitochondria and this allows respiration to takes place thereby providing the energy needed for active transport.
Examples of Active Transport in Plants
This shows the roots of plants. We saw these cells in lesson eight. Root hair cells transport ions such as magnesium into the plant from the soil. Plants need magnesium to make chlorophyll in the leaves. The concentration of ions in the soil is lower than the concentration inside the root hair cell.
Active transport is then used to move the ions into the cell as shown. These ions are then transported to the Xylem vessels and moved to the leaf.
Again, we can see that root hair cell contain lots of mitochondria to provide the energy for active transport.
Required Practical 1 : Microscope
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how to use an optical microscope to look at cells on a prepared microscope slide.
Microscope
This is a required practical so it’s really important that you learn the details. This could come up in the exam as a six mark essay question.
I’m showing you here an optical microscope and you should have used one of these at school. I should point out that some optical microscopes are slightly different to this and I’ll discuss that in a minutes.
Important Parts of the Optical Microscope
The centre of microscope has a stage. This is where we place the microscope slide.
The stage has clips to hold the slide in place.
Below the stage there is a lamp; Light from the lamp passes up through the microscope slide. As I said before, some optical microscopes are different to this. Rather than having a lamp, these microscopes have a mirror beneath the stage. The mirror is used to reflect light up through the microscope slide.
Okay, above the stage, we have a set of lenses and these are called objective lenses. Most microscope have three different objective lenses. These usually have a magnification of 4×, 10×, or 40×.
At the top of the microscope, we have the eyepiece and this is where we look through. The eyepiece contains the eyepiece lens which has a magnification of 10×.
The final parts of the microscope are the coarse focusing dial and the fine focusing dial. We’ll be discussing how to use these later.
How to use an Optical Microscope to Look at Cells on a Prepared Slide.
First, we place the slide onto the stage and use the clips to hold the slide in place.
We then select the lowest power objective lens. This is usually 4×.
We need to position the objective lens so it almost touches the microscope slide. To do this, we slowly turn the coarse focusing dial. It is really important that we look at the microscope from the slide while we adjust the position of the objective lens.
When the objective lens almost touches the slide, we stop turning the dial. If we look through the eyepiece while positioning the objective lens, there is a risk that we damage the slide. At this stage, we look down through the eyepiece.
Now, we need to slowly turn coarse focusing dial. This increases the distance between the objective lens and the slide. We do this until the cells come into focus.
At this stage, we use the fine focusing dial to bring the cells into a clear focus.
How To Calculate The Total Magnification
To calculate the total magnification… we multiply the magnification of the eyepiece lens by the magnification of the objective lens.
The eyepiece lens has a magnification of 10x. and the low power objective lens has a magnification of 4x.
Multiplying 10 by 4 gives a total magnification of 40x.
Mathematically :
Magnification = eyepiece lens x low power objective lens
= 10 x 4 = 40x
At this point, we can select a higher power objective lens example 10×.
Again, we will need to adjust the fine focusing dial to bring the cells back into focus
If we are looking at animal cells, we should see something like this. I should point out that this will depend on the type of animal cell on the slide.
At this stage, we can use a pencil to make a clear labelled drawing of the some of the cells.
Using an optical microscope, we can only see limited detail. We can see the nucleus, the cytoplasm and the cell membrane. These tiny flecks may be mitochondria. However, we definitely cannot see ribosomes.
If we look at plant cells, we might see something like these.
Again, this depends on the type of plant cells on the slide. Under the light microscope, we should be able to see the cell wall, the cytoplasm and the nucleus.
Now on your drawing, you should also include a magnification scale. To do this, we place a clear plastic ruler over the stage and we measure the diametre of the field of view in millimetre. Then we show this on our drawing using a scale bar like this
You should also write the magnification example 100×.
Required Practical 2 : Culturing Microorganisms
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how to prepare an uncontaminated bacterial culture using aseptic technique.
• Describe how to investigate the effect of antibiotics on bacterial growth.
Culturing
Culturing is the process of growing microorganisms in the laboratory using special medium called culture medium.
Material Used In Preparing Culture Medium
• Nutrient broth
• Petri dish with cover
• Wire loop
• Bunsen burner flame
• Incubator
• Autoclave
How to Prepare an Uncontaminated Bacterial Culture using Aseptic Technique
Recap
Bacteria reproduced by binary fusion. Given enough nutrient in a suitable temperature, can double bacteria in number every 20 minutes.
In this lesson I’m showing you how to culture bacteria.
Description
These bacteria grows in nutrient broth solution. This contains all the nutrient that the bacteria need to grow and divide. The broth is cloudy because it contain a very large number of bacteria. Another way to culture bacteria is to use an agar gel plate which I’m showing you here.
Agar gel plate contains nutrient broth but that’s been cycling to a jelly using a chemical called egg. This is important to a petri dish and allowed to set. On a gel plate, the bacteria grows the visible colonies as seen in petri dish.
When preparing nutrient broth solution, its really important to avoid contamination. There are lots of microorganisms such as bacteria and fungi, which naturally exist in the environment and this could easily contaminate the culture.
Technique for Culturing Microorganisms
Step 1. Sterilize all petri dishes containing bacterial nutrient broth and agar. This kills any unwanted microorganisms and it prevents contamination.
Bacteria are normally transferred into the culture using inoculating loop (wire loops).
Step 2. Sterilize the inoculating loop by passing it through a Bunsen burner flame before using it. Once the bacteria are transferred onto the petri dish, attach the lid of the petri dish using adhesive tape. This stop the lid from falling off and unwanted microorganisms entering.
Step 3. Then place the agar plate upside down into an incubator. This stops moisture from dripping down onto the bacteria and disrupting the colonies.
Step 4. In school laboratories, we normally incubate bacteria at 25 c. This reduces the chances that harmful bacteria will grow.
Effect of Antibiotics on Bacterial Growth
1. Clean the working bench with disinfectant solution. This kills microorganisms that could contaminate the culture.
2. Sterilize the inoculating loop by passing it through a Bunsen burner flame.
3. Open a sterile agar gel plate near a Bunsen burner flame. The flame kills bacteria in the air.
4. Then use the loop to spread the chosen bacteria evenly over the plate.
5. Finally, place sterile filter paper disc containing antibiotic onto the plate.
6. Incubate the plate at 25c.
7. .After 2-3 days, the plate should be observed and you will notice something like this.
The bacteria formed the layers on the surface of the agar gel.
Around the antibiotic disc, we have a region where the bacteria have not grown. This is called the zone of inhibition.
The effect of the antibiotic can be measured by calculating the area of inhibition zone and to do that we use this equation :
Area = pie r2 . Where R is the radius of the inhibition zone.
Sample Question
Required Practical 3 : Effect of Osmosis on Plant Tissue.
Learning Objectives
By the end of this lesson, you should be able to :
• Describe how to investigate the effects of osmosis on plant tissue.
• Calculate percentage change
Recap
This is a required practical so it’s really important you learn the details. In the last lesson, we looked at osmosis and we saw that osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
We saw that when a plant cell is placed in water, then water will move into the cell by osmosis and the cell will expand
However, if we place the plant cell into a concentrated solution , then water moves out of the plant cell by osmosis and this causes the cell to shrink. In this lesson we’ll look at how to investigate the effect of osmosis on plant tissue.
How to Investigate the Effect of Osmosis on Plant Tissue
Procedure:
1. Peel the potato. That is because the potato skin can affect osmosis.
2. Use a cork borer to produce three cylinders of potato. Using a cork borer makes all of the cylinders the same diameter.
3. Then use a scalpel to trim the cylinders to the same length (around 3cm).
4. Measure the length of each cylinder using a ruler and the mass of each cylinder using a balance.
5. Now, place cylinder into a test tube as shown . Add 10cm3 of 0.5 molar sugar solution to the first test tube.
6. Add 10cm3 of 0.25 molar sugar solution to the second test tube and 10cm3 of distilled water to the third test tube. The reason that the distilled water is used rather than tap water is because distilled water contains no dissolved substances and they could affect the weight of osmosis.
7. Leave the potato cylinders overnight to allow osmosis to take place.
8. Then remove the potato cylinders and gently roll them on paper towel to remove any surface moisture.
9. Finally, measure the length and the mass of the cylinders again.
How to Calculate the Percentage Change
To calculate the percentage change use this equation :
% change = change in value × 100
original value
Sample Question: 1
A potato cylinder has a starting mass of 1.56g. This increases by 0.25g. Calculate the % increase. Pause your reading and try this yourself.
Working
% change = change in value × 100
original value
% change = 0.25 × 100
1.56
% change = + 16. 03% to 2 dp
Sample Question : 2
A potato cylinder has a starting mass of 1.32g. This decreases by 0.19g. Calculate the % decrease. Pause your reading and try this yourself.
Working
% change = change in value × 100
original value
% change = 0.19 × 100
1.32
% change = -— 14.39% to 2 dp.
How to Draw a Graph of Percentage Change in Mass
Description of the Graph
In water, the potato cylinder gain mass as water moves into it by osmosis.
In concentrated sugar solution, the cylinder loses mass as water moves out by osmosis.
Where the line cross the x axis, there’s no change in mass. That is because the concentration outside the cell is the same as the concentration inside. So the overall osmosis takes place. This concentration is the approximate concentration inside the cell.
Chapter Two : ORGANIZATION
Lesson 1 : The Digestive System
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe what is meant by a tissue, an organ and an organ system.
• Identify the main organs in the digestive system and state their functions.
Recap
In the previous chapter, we saw that cells are often specialized. In other words, they have adaptations to help them carry out their functions. An excellent example of this is muscle cells.
Muscle cells can contract ( i.e. get shorter). They contain special protein fibres which can damage their length.
Muscle cells are also packed full of mitochondria which provide the energy needed for contraction. Muscle cell work together to form muscle tissue and this brings us to the definition of a tissue.
What is Meant by a Tissue, an Organ and an Organ System
Tissues
A tissue is a group of cells with a similar structure and function. That means that a tissue is when you have the same cells working together to give you muscle tissue. It really important that you learn that definition.
Organs of the Body
An organ is a group of tissues working together to carry out a particular function.
For example the stomach. The stomach is where food is digested. The stomach contains :
• Muscle tissue - contract and muscle cells become shorter.
• Glandular tissue - produces digestive enzymes and
• Epithelial tissue - covers the inside and outside of the stomach.
Other examples of an organs and their primary functions are :
• The Heart – pumps blood around the body.
• The Lungs – separate oxygen from the air and remove carbon dioxide from the blood.
• The Brain – controls thought, memory and other organs.
• The Liver – removes poisons from the blood.
• The Intestine – absorb nutrients from food.
• The Kidneys – filter blood and produce urine.
Organ Systems
Finally, organs are group into organ systems which work together to form organisms example digestive system, which we’re looking at in this chapter.
Organ System and their Functions are :
• The circulatory system which includes the heart, veins and arteries. Its function is to transport substances in the blood, around the body.
• The respiration system which includes the nose and the lungs. It takes in oxygen and removes carbon dioxide.
• The digestive system which includes the stomach and intestine . It breaks down food and absorbs nutrients.
• The reproductive systems which includes the uterus and vagina in women, and the penis and testes in men. Its function is to produce offspring.
• The skeletal system which includes bones and muscles. It supports the body and allows movements.
• The immune system includes bone marrow. It protects the body from infection.
Organs of a Plants
Plants are made up of organs, including roots, leaves, the stem and reproductive organs. In plants, each organ has several functions:
• Roots – keeps a plant in the ground. They also take in water and nutrients from the soil.
• Leaves – absorb sunlight, and make food for the plant by photosynthesis.
• The Stem – supports the leaves and flowers. It also transport water and nutrients between the roots and the leaves.
• Reproductive organs – such as male and female sex organs in flowers, examples ovary, anther and stigma allows a plant to produce new seedlings.
Together, the organs of a plant allow it to carry out the seven processes of life.
Life Processes
All living organisms carry these seven processes. The phrase MRS GREN
is one-way to remember them :
• Movement: All living things move.
• Respiration : Getting energy from food.
• Sensitivity : Detecting changes in the surrounding.
• Growth : All living things grow.
• Reproduction : Making more living things of the same type.
• Excretion : Getting rid of waste.
• Nutrition : Taking in and using food.
In addition, all living organisms contain nucleic acids (DNA) and have
the ability to control their internal conditions. Finally, all living
organisms can die.
Nutrients Found in Food
Food contains three main nutrients. These are :
• Carbohydrate ( e.g. starch)
• Protein ( e.g. milk) and
• Lipid (e.g. fat)
All of these are large molecules. They are too large to be absorbed into the bloodstream.
During digestion, large food molecules are broken down into small molecules by enzymes. The small molecules can then be absorbed into the bloodstream.
I’m showing you a picture of the human digestive system here.
Description
First, food is chewed in the mouth. Enzymes in the saliva begin to digest the starch into smaller sugar molecules.
The food then passes down the oesophagus into the stomach. In the stomach, enzymes begin the digestion of proteins.
The key point is that the stomach also contains hydrochloric acids which helps the enzymes to digest proteins.
The food spends several hours in the stomach. The churning action of the stomach muscles turns the food into a fluid, increasing the surface area for enzymes to digest. The fluid then passes into the small intestine.
At this point, chemicals are released into the small intestine from the liver and the pancreas.
The pancreas releases enzymes which continue the digestion of starch (started in the mouth )and protein (started in the stomach ). They also start the digestion of lipids ( fats ).
The liver releases bile which helps to speed up the digestion of lipids.
Bile also neutralizes the acid released from the stomach. This is important as the enzymes which operate in the small intestines work best under alkaline conditions .
In the small intestine, the small food molecules produced by digestion are absorbed into the bloodstream either by diffusion or by active transport.
Now the fluid makes it way through the large intestine, where water is absorbed into the bloodstream.
Finally, the faeces is released from the body.
Remember that in the digestive system, large food molecules are digested into smaller molecules and then the products of digestion are absorbed into the bloodstream.
Now the products of digestion are then used by the body to build new carbohydrates, proteins and lipids. Some of the glucose produced is used in respiration.
Lesson 2 : Digestive Enzymes
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe the enzymes in the digestive system.
• Describe the role of bile.
Recap
In the last lesson we looked at the digestive system and we saw that large food molecules are digested by enzymes into smaller molecules. These products of digestion are then absorbed into the bloodstream. In this lesson, we are looking at the enzymes involved in digestion.
Key Fact About Enzymes
• Enzymes catalyze ( speed up) chemical reactions.
• Enzymes are large proteins molecules and they have a groove on their surface called the active site.
• The active site is where the substrate attaches to and the substrate is the molecule that the enzyme breaks down.
• Enzymes are affected by temperature and pH and they are not used up in the reaction they catalyze.
• Enzymes are not living things. They are special protein that can break down large molecules into small molecules.
I’m showing you here the active site on the surface and the substrate molecule and you can see that it fits perfectly into the active site like this :
The enzymes now breaks down the substrate into the products
This shows the same enzyme and a different substrate. This substrate does not fit into the active site so the enzyme cannot break down this substrate.
Remember that enzymes are specific and the substrate must fit perfectly into the active site. Scientists call this the lock and key theory.
Specific Enzymes in the Digestive System
Proteins are broken down by enzymes called proteases and we find these in the stomach, the pancreatic fluid and the small intestine.
I’m showing you a drawing of the structure of proteins here.
Proteins are long chains of chemical called amino acids.
When we digest proteins, the protease enzymes convert the protein back to the individual amino acids which are then absorbed into the bloodstream.
When the amino acids are absorbed by the body cells, they are joined together in a different order to make human proteins.
Digestion of Carbohydrate
I’m showing you the structure of starch here. As you can see starch consists of a chain of glucose molecules. Carbohydrates like starch are broken down by enzymes called cabohydrases and in the case of starch, this is called amylase.
When carbohydrates like starch are digested, we produce simple sugar . Amylase is found in the saliva and pancreatic fluid.
Digestion of Lipids
A lipid molecule consists of a molecule of glycerol attached to three molecules of fatty acids. Lipid molecules are digested by the enzyme lipase. This produces glycerol and fatty acids and again you could be asked that in your exam.
Lipid molecules are digested by the enzymes lipase and this produces glycerol and fatty acids like this.
We find lipase in the pancreatic fluid and also in the small intestine. The digestion of lipids also involves bile.
The Role of Bile
Bile is made in the liver and it is stored in the gall bladder. Bile helps to speed up the digestion of lipids but bile is not an enzyme.
This shows a lipid droplet and lipase. Bile converts large lipid droplets into smaller droplets. Scientists say that bile emulsifies the lipid. This massively increases the surface area of the lipid droplets and this increases the rate of lipid breakdown by lipase.
Bile is also alkaline. This allows it to neutralize stomach acid, creating alkaline conditions in the small intestine and again this increases the rate of lipid digestion by lipase.
Uses of Enzymes in the Home and Industry
Many microorganisms produce enzymes which they release from their cells. These enzymes can be used in the home and in industry. For example, biological washing powers contain enzymes.
They contain protease to digest protein. They also contain lipase to digest fat and that’s because lots of stains contain protein and fat, and by using protease and lipase, we can digest the stain.
Advantages of Enzymes in the Home and Industry
• Enzymes wash better at low temperature than just using detergents. This means that we can do our washing at cooler temperature and get good result.
• Baby food contain an enzyme called protease, and protease pre-digest the protein in the baby food into amino acids. This is beneficial to the baby because they can access these amino acids more easily than when the baby had to digest all the protein itself.
• The enzyme amylase is used in industry to convert starch into sugar syrup and this is used to sweeten foods.
• Another enzyme called isomerase is used to convert glucose into fructose, which is much sweeter than glucose.
• Fructose is used in slimming foods because it gives the same level of sweetness but it must be used in small amount.
• Enzymes save money in industry. This is because they allow reactions to take place at cool temperature, which save energy.
Disadvantages of Enzymes in the Home and Industry
• Enzymes are very expensive.
• They stop working at high temperature.
1
Lesson 3 : The Effect of Temperature and pH on Enzymes
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe the effect of temperature and pH on enzymes activity.
Recap
We’ve been looking at enzymes and we saw that enzymes speed up chemical
reactions and to do this, they’ve got a groove on their surface called the active site. The substrate is the molecule that the enzyme reacts with and this fit perfectly into the active site like this. The enzyme now breaks down the substrate into the products. Remember that enzymes are specific and that’s because the substrate must fit perfectly into the active site. This is called the lock and key theory
The Effect of Temperature on the Rate of an Enzymes Catalyzed Reaction.
I should point out that this is a very common exam question so you need to learn it. I’ve got an enzyme catalyzed reaction and I gradually increase the temperature. At each temperature I measure the activity of the enzyme. In other words the rate of the reaction looks like this
As you can see, as we increase the temperature , the activity of the enzyme increases ( i.e. the reaction get faster). That’s because as the temperature increases, the enzyme and substrate are moving faster. So there are more collisions per second between the substrate and the active site.
At a cerntain temperature, the enzyme is working at the fastest possible rate and that’s called the optimum temperature.
At this point, there is the maximum frequency of successful collisions between the substrate and the active site.
For most human enzymes, the optimum temperature is 37. c which is human body temperature.
As we increase the temperature past the optimum, then the activity of the enzyme rapidly decreases to zero. In other words the enzyme stop working and that’s because at high temperature, the enzyme molecules vibrates and the shape of the active site changes like this :
Now, the substrate no longer fits perfectly into the active site. Meaning that the active site is denatured and you will be expected to use that word in your exam.
Also, the enzyme can no longer catalyze the reaction.
The Effect of pH on Enzymes
The enzyme has an optimum pH, where the activity is maximum.
If we make the pH more acidic or more alkaline, then the activity drops to zero and that’s because the active site denatured if the conditions are too acidic or too alkaline.
Each enzyme has a specific optimum pH. For example the enzyme shown above work best at an acidic pH. This could be a protease enzyme in the stomach. This enzyme works best at an alkaline pH and this could be an enzyme released from the pancreas into the small intestine ( example lipase).
Lesson 4 : Absorption in the Small Intestine
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how the small intestine is adapted for absorbing the products of digestion.
Recap
Over the last few lessons we’ve been looking at digestive system and we’ve seen that during digestion, large food molecules are broken down into smaller molecules by enzymes. For example starch is digested into simple sugars by the enzyme called amylase. The products of digestion are then absorbed into the bloodstream in the small intestine. So in this lesson, we’re looking at how the small intestine is adapted for absorbing the products of digestion.
Absorption in the Small Intestine
Firstly, a small intestine is very long for example the human small intestine has a length of around 5m. This provides a very large surface area for absorption of the products of digestion.
Villi in the Small Intestine
The interior of the small intestine is covered with million of villi like this .
Villi massively increase the surface area for the absorption of molecules.
This shows a close – up of villi. On the surface of the villi we find microvilli and we can see these here. Microvilli on the surface increase the surface area even further. Villi have a very good blood supply so the bloodstream rapidly removes the products of digestion and this increases the concentration gradient.
Finally, the thin membrane ensures a short diffusion path. All of these features means that there is a rapid rate of diffusion. Any molecules which cannot be absorbed by diffusion are absorbed by active transport.
Lesson 5 : The Heart and Circulation
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe the structure of the heart.
• Describe how the heart pumps blood around the body.
Fish : Single Circulatory System
Description
In order to understand how the heart works, we’re going to start by looking at circulation in fish.
Fish have a single circulatory system. Deoxygenated blood is pumped from the heart to the gills where it collects oxygen and becomes oxygenated. The oxygenated blood now passes straight from the gills to the organs where the oxygen diffuses out of the blood into the body cells. The blood then returns to the heart.
The problem of single circulatory system such as this one is that the blood loses a lot of pressure as it passes through the gills before reaching the organs. This means that the blood travels to the organs relatively slowly. So it cannot deliver a great deal of oxygen. Unlike fish, humans have a double circulatory system.
Humans : double circulatory system
Description
Here, deoxygenated blood is pumped from the heart to the lungs where it collects oxygen. This oxygenated blood then returns to the heart. The heart then pumps the oxygenated blood to the organs where the blood transfer its oxygen to the body cells.
The blood then returns back to the heart. The benefit of the double circulatory system is up because the blood passes through the heart twice.
It can travel rapidly to the body cells, delivering the oxygen that the cells need.
The Humans Heart
This shows a simplified picture of the human heart. The heart is an organ consisting mainly of muscle tissue. The heart pumps blood around the body. The heart has four chambers.
At the top, we have the left atrium and the right atrium.
At the bottom of the heart, we have the left ventricle and the right ventricle. The atria are separated from the ventricles by valves. You’ll notice that the heart appears to be back to front. That’s because diagrams of the heart always show it as if you’re looking at a person.
Blood Vessels
There are four main blood vessels entering and leaving the heart and again you are expected to learn these.
The vena cava brings in deoxygenated blood from the body. The blood now passes from the heart to the lungs in the pulmonary artery. In the lungs, the blood collects oxygen.
Oxygenated blood passes from the lungs to the heart in the pulmonary vein and then the oxygenated blood is pumped from the heart to the body in the aorta.
The Pattern Blood Flows Through Heart
First, blood enters the left atrium and the right atrium. The atria now contract and the blood is forced into the ventricles.
The ventricles now contract and force blood out of the heart. Valves stop the blood from flowing backwards into the atria when the ventricles contract.
The left side of the heart has a thicker muscular wall than the right side. This is because the left ventricle pumps blood around the entire body and it needs to provide a greater force. The right ventricle only pumps blood to the lungs.
Types of Blood Vessels
Coronary Arteries :
This branch out of the aorta and spread out into the heart muscle. The purpose of the coronary arteries is to provide oxygen to the muscle cells of the heart. The oxygen is used in respiration to provide the energy for contraction.
Peacemaker no
The natural, resting heart rate is controlled by the peacemaker as shown above . Sometimes the peacemaker stops working correctly. In this case, doctors can implant artificial peacemaker like the one seen on the palm.
An artificial peacemaker is a small electrical device and it job is to correct irregularities in the heart rate.
Lesson 6 : Arteries, Veins and Capillaries
Learning Objectives
By the end of this lesson, learners should be able to :
• Explain how the structure of arteries, veins and capillaries relate to their function.
The Circulatory System
In the last topic, we saw that humans have a double circulatory system. Blood is pumped from the heart to the lungs where it collects oxygen. The blood now returns to the heart and is then pumped around the whole body where it delivers the oxygen to the body cells.
In this lesson we’re looking at the blood vessels involved in this process and we’re gonna start with arteries.
Arteries carry very high pressure blood from the heart to the organs in the body.
Arteries
I’m showing you the structure of arteries here. The first adaptation is that arteries have got very thick muscular walls. This allows them to withstand the very high pressure of the blood.
Blood travels through the arteries in surges every time the heart beats.
To cope with that, arteries contain elastic fibers stretch when the surge of blood passes through and now recoil in between surges, which keeps the blood moving. Blood travels through the organs and the arteries but once it’s in the organs, the blood flows through the capillaries.
Capillaries
When the blood passes through capillaries, substances such as glucose and oxygen diffuse from the blood to the cells. Carbon dioxide diffuses from the cells back to the blood.
Capillaries have very thin wall, so the diffusion path is very short. This allows substances to diffuse rapidly between the blood and the body cells.
Once the blood has passed through the organs, it now makes its way back to the heart in veins.
The problem here is that, the blood is now travelling slowly and at low pressure. That means that it could stop or even go backwards.
Structure of Veins
I’m showing you the structure of veins here.
First, veins have a thin wall. That’s because the blood pressure is low so the wall does not need to be thick.
Secondly, many veins contain valves. The job of valves is to stop blood flowing backwards
.
When the blood is flowing in the correct direction, then the valves open to allow the blood to flow through like this :
When the blood starts to flow backwards, the valves shut and you can see that here.
Lesson 7 : The Blood
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe the different parts of the blood and then state their functions.
• Describe the uses of blood products and state the risks of these.
The Blood
Description
This shows a picture of human blood under a microscope. There are four important parts that you need to know.
First, plasma is the liquid part of the blood. In the plasma, we have two different types of blood cells.
Plasma also contain tiny fragments of cells and these are called platelets.
Functions of the Different Parts of the Blood :
Blood Plasma
Plasma is a liquid part of the blood and it’s job is to transport :
a. Soluble digested products (such as glucose) from the small intestine to other organs
b. Carbon dioxide ( produced by aerobic respiration) from the organs to the lungs to be breathed out.
c. The waste product urea from the liver to the Kidneys to be excreted in urine.
Red Blood Cells
Red blood cells transport oxygen from the lungs to the body cells and to do this they’ve three adaptations :
Firstly, the red blood cell contain the oxygen – carrying molecule called haemoglobin.
Haemoglobin + oxygen lungs oxyhaemoglobin
Here, haemoglobin combines with the oxygen in the lungs forming the molecule Oxyhaemoglobin.
The red blood cells then travel to the organs where the oxyhaemoglobin releases the oxygen like this :
Oxyhaemoglobin organs haemoglobin + oxygen
Secondly, red blood cell have no nucleus, which means that they have more room for haemoglobin and you can see that here.
Lastly, red blood cell have the shape as shown. In the center of the cell, there are dimples and scientists call this shape a biconcave disc.
This shape gives the red blood cells a greater surface area so that oxygen diffuses in and out rapidly.
White Blood Cells
White blood cells form part of the immune system for example by making antibodies. There are two main types; macrophages and lymphocytes.
White blood cells contain a nucleus. This contain DNA which encodes the instructions that the white blood cells need to do their job.
.
Platelets
Platelets are tiny fragments of cells and their job is to help the blood to clot
Donated Blood
Donated blood has many uses in medicine for example it is used :
• To replace blood lost during injury.
• Some people are given platelets extracted from blood to help in clotting.
• Proteins extracted from blood can also be used for example antibodies.
Problems in Using Donated Blood
In a blood transfusion, we have to make sure that the donated blood is the same blood type as that of the patient. Otherwise the body’s immune system will reject the blood and the patient could die.
Lots of different diseases can be transmitted via blood.
In Nigeria, blood is screened for infections so the risk is extremely low.
Lesson 8 : Cardiovascular Diseases
Learning Objectives
By the end of this lesson, you should be able to :
• Describe different cardiovascular diseases.
• Evaluate the different methods of treating cardiovascular disease
Cardiovascular Diseases
Cardiovascular diseases are diseases of the heart and blood vessels.
The key features of these is that they are non – communicable and they are not infectious. In other words they cannot be passed from person to person. Example of cardiovascular disease is coronary heart disease.
Coronary Heart Disease
Recap
In lesson five, we saw that the coronary arteries branch out of the aorta and spread out into the heart muscle. The purpose of the coronary arteries is to provide oxygen to the muscle cells of the heart. The oxygen is then used in respiration to provide the energy for contraction.
Description
In coronary heart disease, layers of fatty material build up inside the coronary arteries. This causes the coronary arteries narrow. The effect of this is to reduce the flow of blood through the coronary arteries. This result in a lack of oxygen for the heart muscle.
In extremely cases, this can result in a heart attack, where the heart is starved of oxygen and this can be fatal.
Different Methods of Treating Cardiovascular Diseases
There are two main common treatments of coronary heart disease.
Stains are drugs which reduce the level of cholesterol in the blood. This slows down the rate that fatty materials build up in the arteries.
Stains have been proven to reduce the risk of coronary heart disease. In other words, stains are an effective treatment.
However, stains have unwanted side – effects e.g. liver problems.
In some people, coronary heart disease can cause almost a total blockage of a coronary artery. These people can be treated using a stent.
A stent is a tube which can be inserted into the coronary artery to keep it open. The advantage of inserting a stent is that the blood can flow normally through the artery. However, a stent will not prevent other regions of the coronary arteries from narrowing. It does not treat the underlying causes of the disease.
The Heart Valves
Another type of cardiovascular disease concern the heart valves. Sometimes the heart valves do not fully open, so the heart has to pump extra hard to get the blood through. This can cause the heart to enlarge
Other time the valves are leaky which can cause the patient to feel weak and tired.
When heart valves are faulty, we can replace them either with a mechanical valves made of metal or a valves from an animal such as a pig.
Mechanical valves can last a lifetime but they increase the risk of blood clots. Patients have to take anticlotting drugs.
Valves from animals do not last as long and may need to be replaced. However, patients do not need to take drugs.
In some patients with cardiovascular disease, the heart cannot pump enough blood around the body. This is called heart failure. Patients are sometimes given a donated heart or a donated heart and lungs.
Two problems are involves here:
Firstly, there are not enough donated hearts available to treat every patient.
Secondly, the patient must take drugs to stop the donated heart from being rejected by the body’s immune system.
Sometimes a patient can be given artificial heart as a temporary solution while waiting for a heart transplant… or to allow their damage heart to rest
Artificial heart increase the risk of blood clotting. They are not a long – term solution to heart failure. They can only be used for a relatively short time.
Lesson 9 : Gas Exchange in the Lungs
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how the lungs are adapted for gas exchange.
Recap
In lesson five, we’ve been looking at the circulatory system and we saw that the heart pumps blood to the lungs where the blood collects oxygen. The blood then returns to the heart and is pumped around the whole body where it delivers oxygen to the body cells.
So in this lesson, we’re looking at how the lungs are adapted for gas exchange
How the Lungs are adapted for Gas Exchange
Description
Air passes into the lungs through a tube called trachea. Rings of cartilage prevent the trachea from collapsing during inhalation.
When we inhale, the trachea now splits into two smaller tubes called bronchi, with one passing to each lungs.
Further into the lungs, the bronchi subdivide into many smaller tubes called bronchioles. The bronchioles end in tiny air sacs called alveoli.
Alveoli any are where gases diffuse in and out of the bloodstream. In other words they’re the site of gas exchange.
How Alveoli are Adapted for Gas Exchange
Oxygen in the air diffuses into the bloodstream and carbon dioxide diffuses out of the bloodstream back into the air as shown. The alveoli have several adaptations to make the rate of gas exchange as fast as possible.
Firstly, the millions of alveoli means that the lungs have a huge surface area.
Secondly, the alveoli have very thin walls so the diffusion path is very short.
Lastly, the alveoli have a very good blood supply. Once the oxygen diffuses into the body, it is rapidly removed. This ensures that the concentration gradient is as steep as possible. These adaptations mean that oxygen diffuses rapidly into the bloodstream and carbon dioxide diffuses rapidly out.
Breathing
By breathing, we also increase the rate of diffusion. Breathing brings fresh oxygen into the alveoli and takes away the carbon dioxide. This makes the concentration gradients high for these gases and again that increases the rate of diffusion.
Lesson 10 : Cancer
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe what is meant by a benign and a malignant tumour.
• Describe the risk factors for cancer.
Recap
In chapter one , we looked at cell division by mitosis. Remember that in mitosis, one cell is copied into two cells. Cell division by mitosis occurs all over the body, especially during growth and during repair for e.g. after an injury. Mitosis is extremely tightly controlled.
Genes in the nucleus tell cells when to divide and when to stop dividing. Sometimes, changes take place in these genes and that leads to uncontrolled growth in mitosis This produces a tumour, ( growth). There are two different types of tumour. These are called benign and malignant.
Meaning of Benign Tumour
Benign tumour are growths of abnormal cells which are found in one area. Benign tumour are usually contained within a membrane.
They do not invade other parts of the body. They stay in one place.
Malignant Cells
Malignant cells invade neighbouring tissues and move into the bloodstream.
Malignant tumour cells are classed as a cancer. Once in the bloodstream, the malignant cells spread to different parts of the body and they form new tumours. Scientists call these new tumours secondary tumours. This shows the secondary tumours in a patient with prostate cancer.
Cancers Linked to Genetics
Some cancers are genetics. In other words we inherit an increase risk of these cancer from our parents. Examples of these are certain types of :
• Breast cancer
• Prostate cancer
• Cancer of the large intestine
Other cancers are linked to our lifestyle for example :
• Lungs cancer linked to smoking
• Skin cancer linked to ultraviolet light
• Mouth and throat cancers are linked to drinking alcohol
Certain cancers are caused by substances in our environment and an excellent example of this is radon.
Radon is a radioactive gas which increases your risk of developing lungs cancer and that’s because radon releases ionizing radiation which damages the DNA in our cells. This can cause our cells to undergo uncontrolled cell division, leading to cancer.
Lesson 11 : Communicable and non – communicable Disease
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe what is meant by communicable and non – communicable diseases.
• Describe how different types of diseases may interact.
Definition of Terms
Communicable Disease :This can be spread from person to person examples measles, chicken pox, tuberculosis, coronavirus etc. They are spread by pathogens such as bacteria or viruses.
Non – communicable Disease :These are diseases that cannot be passed from person to person examples coronary heart disease, stroke etc.
Health : This is defined as the state of physical and mental well – being.
Ill health : These are caused by both communicable and non – communicable diseases.. It can also be caused by poor diet, high level of stress and other life situations example working with harmful chemicals.
All of these can have a negative effect on both physical and mental health.
Again, one important idea that you need to understand is that different types of diseases can interact for example :
Tuberculosis (TB)
Description
Tuberculosis ( TB) is a communicable lung disease and TB can be fatal. In most people, the immune system can fight off TB.
However, some people have a defective immune system for example people with HIV. People with a defective immune system are much more likely to suffer from infectious diseases.
HIV increases the risk of contracting a different disease such as TB.
Human Papilloma Virus (HPV)
HPV is extremely common. In most people it is essentially harmless.
In some people, HPV can cause cervical cancer. Around 2000 women are diagnosed with cervical cancer every year in Nigeria.
Most cervical cancers are caused by the human papilloma virus which infects the cells of the cervix. Sometimes a disease can be triggered by the immune system example allergies such as asthma or dermatitis.
In this case, the body is affected with a pathogen which the immune system fights off but the person is then left with an allergy.
Sometimes a mental illness can be triggered by a physical illness. People with arthritis can find it very difficult to move and live a normal life.
In certain cases, this can make them feel isolated and depressed.
Lesson 12 : Correlating Risk Factors
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how we can determine whether a risk factor is linked to a non – communicable diseases.
• Describe how sampling can be used to determine correlation.
• Describe what is meant by a causal mechanism.
Recap
In lesson eleven of chapter two, we’ve already seen that many diseases are spread from person to person via a pathogen such as a bacterium or virus. Scientists call these communicable disease.
However, many non-communicable diseases are not spread from person to person. Instead, these are caused by risk factors and we’re looking at those in this lesson. Example of non - communicable disease is lung cancer.
Lungs Cancer
Description
In the 1930s, rate of lung cancer began to increase sharply and scientists could not explain this. Scientists could not carry out experiments on humans to try to work out what causes lung cancer. That would be unethical. Instead, scientists looked very closely at people’s lifestyle habits to see if they could link any of these with lung cancer. Studying the patterns of disease to determine risk factors is called epidemiology.
Scientists noticed that lung cancer is much more common among cigarette smokers than among non -smokers. Scientists then looked at how many cigarette people smoked each day and then how many of these people developed lung cancer.
Scientists were looking to see if there was a correlation ( a link ) between lung cancer and smoking.
In order to determine whether there’s a correlation, scientists plot a scatter graph like this :
As the number of cigarettes smoked per day increases, the risk of developing lung cancer also increases. Scientists call this a positive correlation.
One key that you need to remember is that ; A correlation does not prove cause. So this graph does not prove that cigarette smoking causes lung cancer. It simply suggests that they might be linked.
Causal Mechanism
Scientists began to look at how cigarette smoking could cause cancer and scientists call that a causal mechanism. They discovered that cigarette smoke contains chemicals which damage DNA and increase the risk of cancer and these are called carcinogen.
So now, and scientists had a strong correlation between smoking cigarettes and lung cancer and they had a causal mechanism. This means that now we accept that smoking increases the risk of lung cancer.
As I said before, epidemiology involves studying the patterns of disease to determine risk factors but there’s a potential problem with this and that is sampling.
Sampling
Imagine that we wanted to investigate whether a disease is linked to diet.
Ideally, we would look at every single person in a population. We’d look at what they eat and then the chances of them developing the disease. It is not possible to sample every single person.
Instead, scientists sample a group of people and then try to draw conclusions about the whole population.
Imagine we select our sample from only one town, it is possible that this does not represent the entire population of the country. In other words, the sample is biased, for example people in the town might take less exercise than average. or they might be exposed to a certain type of pollution only found in that town. That means that we could not use the results to draw conclusions about the whole country.
To avoid bias, we need to take as large a sample as possible and it must be as random as possible. We cannot draw conclusions from a small or non – random sample.
Lesson 13 : Lifestyle and Disease
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how your lifestyle can affect your risk of developing a non – communicable disease.
Lifestyle and Disease
Recap
Remember that non – communicable diseases cannot be passed from person to person. They are not pathogens example cardiovascular disease, type 2 diabetes and most types of cancer.
non – communicable diseases are the biggest cause of death in Nigeria. So in this lesson, we’re going to explore the risk factors for non – communicable diseases.
Risk Factors for Cardiovascular Diseases :
Cardiovascular diseases includes coronary heart disease. These diseases account for over a quarter of all deaths in Nigeria. Diet is a major risk factor for coronary heart disease. A diet high in fat and low in vegetables increases the levels of certain types of cholesterol in the blood. This increases the rate of fatty materials build up in the arteries.
A diet high in salt can increase blood pressure, increasing the risk of developing cardiovascular diseases. The risk of developing cardiovascular disease is also massively increased in people who smoke. But the risk is decreased in people who exercise.
Risk Factors for Lungs Disease and Lungs Cancer :
Smoking massively increases the risk of lung cancer.
Cigarette smoke contains a number of chemicals which can trigger cancer. These are called carcinogens. Smoking also increases the risk of other lung diseases example emphysema. These diseases are extremely unpleasant and can lead to a very poor quality of life.
Effects of Smoking on Unborn Baby
Smoking when pregnant increases the risk of miscarriage and premature birth.
It can also lead to the baby being born with a low body mass.
Effects of Drinking Alcohol on Unborn Baby
Drinking alcohol when pregnant can cause fatal alcohol syndrome.
Children born with fetal alcohol syndrome can have learning difficulties and other mental or physical problems. So to summarize, pregnant women are advised not to smoke at all or drink any alcohol. Both of these harm the unborn baby.
Effects of Drinking Alcohol on Adult
Adults who drink alcohol excessively increase their risk of liver cirrhosis and liver cancer.
Alcohol can also affect the brain, leading to addiction and memory loss.
Type 2 Diabetes
People with type 2 diabetes struggle to control their blood glucose level. Type 2 diabetes is a very serious diseases which can lead to blindness or require the amputation of a limb. Obese people have a much higher risk of developing type 2 diabetes.
Risk factors can interact for example drinking excess alcohol can lead to obesity diabetes. Now I should point out that some risk factors are not linked to lifestyle and these include substances present in your environment example radon.
Radon
Radon is a radioactive gas which increases your risk of developing lungs cancer and we find radon in certain parts of Nigeria. We looked at radon in lesson 10 on cancer.
Lesson 14 : Plant Tissues
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe the roles of the different tissues in a plant.
Plant Tissues
Recap
Now I need to be clear here. There’s a lot of detail in this lesson and the best thing you can do is to learn it. It’s very likely to be on your exam.
Remember that photosynthesis takes place in leaves.
The leaf is a plant organ. Like any organ, the leaf contains different tissues. We’ll be looking at the functions of these tissues in this lesson.
The Role of the Different Tissue in a Plant
Description
This diagram shows you a cross section of a leaf. In other words the leaf is been sliced from top to bottom.
The top and bottom of the leaf are covered with a layer of very thin cells. These are called epidermal cells and they form epidermal tissue.
• The epidermis protects the surface of the leaf.
• The upper epidermis is transparent. This allows light to pass through it, to the palisade mesophyll where it is used in photosynthetic cells. If the upper epidermis was not transparent, then this would prevent light from reaching the palisade mesophyll.
• The upper epidermis is also covered with a thin layer of oily material called the waxy cuticle.
• The waxy cuticle reduces the evaporation of water from the surface of the leaf and this helps to prevent the leaf from drying out.
• The lower epidermis has tiny pores called stomata. Stomata allow carbon dioxide to enter the leaf ,where it is used in photosynthesis. Oxygen gas (which is produced by photosynthesis ) can also diffuse out of the leaf through stomata.
• Stomata also help to control the amount of water vapour that can pass out of the leaf. On either side of the stomata we find guard cells.
• The palisade mesophyll consists of palisade cells.
• Palisade cells are packed full of chloroplasts. Remember that chloroplasts contain chlorophyll which absorbs the light energy needed for photosynthesis.
• Beneath the palisade mesophyll, we find the spongy mesophyll.
• The spongy mesophyll is full of air space. The air space allow carbon dioxide to diffuse from the stomata through the spongy mesophyll to the palisade cells through the spongy mesophyll to the stomata. There are two other tissues we need to look at and these are xylem and the phloem. We’ve already seen the adaptations of these in lesson eight on plant cell specialization.
Xylem Tissue
• Xylem tissue transports water from the roots to the stem and leaves. Some of the water is then used in photosynthesis.
• The xylem also transports dissolved mineral ions. These include magnesium which is used to make chlorophyll.
Phloem Tissue
• Phloem tissue transport dissolved sugars produced by photosynthesis from the leaves to the rest of the plant.
• The sugars can then be used immediately e.g. glucose is used in respiration
• The sugars can also be stored for e.g. as starch.
• The movement of sugars and other molecules through phloem tissue is called translocation.
Meristem Tissue
We find meristem tissue at growing tip example shoots and roots. Meristem tissue contains stem cells. These can differentiate into different types of plant tissue.
Lesson 15 : Transpiration
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe what is meant by transpiration.
• Describe the factors that affect the rate of transpiration in plants.
• Describe the roles of stomata and guard cells in gas exchange and in water loss
Transpiration
Recap
In the last lesson we looked at the different tissues found in the leaf. Two of the key tissues include the palisade mesophyll and the xylem. The palisade mesophyll is where photosynthesis takes place and xylem tissue transport water and dissolved mineral ions from the roots to the leaves. Remember that water enters the roots through root hair cells.
What is Meant by Transpiration
Water is constantly evaporating from the surfaces of leaves and this process is called transpiration.
Transpiration starts with the evaporation of water from cells inside the leaf.
The water vapour then diffuses through the air spaces in the spongy mesophyll and out of the leaf through the stomata.
Now, water passes from the xylem into the leaf to replace the water that has been lost.
Finally, water is drawn into the root hair cells and up the xylem vessels to the leaf and scientists call this whole process the transpiration stream. Transpiration is really important process:
1. Transpiration brings water to the leaf and the water is required for photosynthesis.
2. The transpiration stream transport dissolved mineral ions such as magnesium which play significant roles in the plant.
3. The evaporation of water from the leaf cools the leaf down especially in warm weather.
Factors that Affect the Rate of Transpiration
1. The rate of transpiration is greater at higher temperatures and that’s because evaporation is faster when temperatures are higher.
2. Transpiration is also faster under dry conditions, when the air is not humid. That’s because evaporation takes place more quickly under dry conditions.
3. The rate of transpiration increases in windy conditions and that’s because wind removes any water vapour, allowing more water to evaporate.
4. The rate of transpiration increases when the light intensity increases and that’s because high light intensity increases the rate of photosynthesis.
The Role of Stomata
Stomata are surrounded by two guard cells. When the light intensity is high for example during the day, the guard cells swell and they change their shape. This causes the stomata to open like this:
Now carbon dioxide can diffuse into the leaf and be used in photosynthesis.
Under hot conditions, the plant close its stomata to reduce water loss by transpiration. That means that the plant cannot photosynthesize.
Required Practical 4 : Food Test
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how to carry out chemical tests for carbohydrates, proteins and lipids (fats).
Food Test
Now this is a required practical and it contains a lot of detail. The key things you need to learn are the chemicals used to test for each food group and the positive results.
I should point out that all the chemicals on these tests are potentially hazardous so safety goggles and gloves must be worn before conducting the experiments.
Preparation of Food Sample
• Prepare the food sample and grind with distilled water using a mortar and pestle.
• Transfer the paste to a beaker and add more distilled water.
• Stir so that the chemical in the food will dissolve completely in water
• Filter the solution to remove suspended food particles.
• Use the decanted liquid as the test solution.
Test for Starch
• Place 2cm3 of food solution into a test tube.
• Add a few drops of iodine solution… which is an orange colour.
• If starch is present then the iodine solution will turn blue-black like this
• However, if there is no starch present… then the iodine solution will stay orange.
Testing for Sugars
• Place 2cm3 of food solution into a test tube.
• Add 10 drops of Benedict’s solution which is a blue colour and swirl.
• Place the test tube containing solution into a beaker… and half fill the beaker with hot water from a kettle like this
• Leave it for at least 5 minutes.
• If sugars are present, the Benedict’s solution will change colour.
• The colour of the Benedict’s solution… gives us an approximate idea of the amount of sugar present. But it cannot tell us the exact amount.
Interpretation / Result
• A blue colour shows that there’s no sugar present.
• A green colour shows that there’s a trace amount of sugar present
• A yellow colour shows that there’s low amount of sugar present.
• A brick-red colour shows that there’s high amount of sugar present
• The Benedict’s test only works for certain sugars example glucose and scientists call these reducing sugars.
• The Benedict’s test will not work for sugars which are non – reducing… for example sucrose
Testing for Protein
• Place 2cm3 of food solution into a test tube.
• Add 2cm3 of biuret solution which is a blue colour
• If protein is present then the biuret solution… will change from blue to a purple or lilac colour.
Testing for Lipids
• Transfer 2cm3 of food solution to a test tube.
• Add a few drops of distilled water … and a few drops of ethanol.
• Then gently shake the solution.
• If lipids are present, then a white cloudy emulsion forms like this
Sudan III Test for Lipid
• Place 2cm3 of food solution into a test tube.
• Add 3 drops of Sudan III.
• Shake the test tube gently to mix.
• If the food contain lipids, then a red stained oil layer will separate out and float on the surface.
• Remember that ethanol is highly flammable. It is very important that no naked flames are present.
Required Practical 5 : Effect of pH on Amylase
Learning Objectives
By the end of this lesson, you should be able to :
• Describe how to investigate the effect of pH on the enzyme amylase.
Effect of pH on Amylase
Recap
This is a required practical so it really important that you learn the details. We’ve already looked at amylase in the previous lesson. Remember that amylase breaks down starch into simple sugars. In this practical we’re investigating the effect of pH on amylase.
Procedure
We’re use iodine to test for the present of starch. Remember that iodine turns blue-black if starch is present.
• In the first stage we place one drop of iodine solution into each well of a spotting tile.
• We take three test tubes and in the first test tube, we add 2cm3 of starch solution.
• In the second test tube, we add 2cm3 of amylase solution.
• In the third test tube, we add 2cm3 of pH buffer solution.
• Buffer solution is used in biology to control the pH.
• We then place all three test tubes in a water bath at 30 degree Celsius as shown.
• We leave them for 10 minutes to allow the solution to reach the correct temperature.
• We then combine the three solutions into one test tube and mix with a stirring rod. We then return the solution to the water bath and start a stopwatch.
• After 30 seconds, we use the stirring rod to transfer one drop of solution to a well in the spotting tile which contains iodine.
• The iodine should turn blue-black showing that starch is present.
• We take a sample every 30 seconds and continue until the iodine remains orange as shown on the spotting tile .
• When the iodine remains orange, this tell us that starch is no longer present. Meaning that the reaction has completed.
• Then we repeat the whole experiments several times using different pH buffers for example pH 6, 7, and 8.
Problem
We are only taking samples every 30 seconds. This means that we only have an approximate time for the reaction to complete. We could address this by taking samples every 10 seconds.
We are looking for the time when the iodine does not go blue-black. This is not always obvious.
The colour change tends to be gradual. Some well might have a small amount of blue-black mixed with orange, so it can be difficult to see when the reaction has finished.
One way to address that problem is to ask several people to look at the spotting tile and decide when the reaction has completed.
Chapter Three : Infection and Response
Lesson 1 : Pathogen
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe what is meant by a pathogen
• Describe how bacteria and viruses cause illness.
• Describe how the spread of pathogens can be reduced or prevented.
Pathogens
Recap
Now we’ve already looked at non - communicable diseases in previous lesson, but in this lesson we’re looking at communicable disease.
Communicable diseases are spread from person to person. In other words they’re infectious. These diseases are spread by pathogens.
Meaning of Pathogen
Pathogens are microorganisms that cause infectious disease and it really important you learn that definition. Pathogens include bacteria and viruses, which we’re looking at in this lesson. They also include protists and fungi which we’re going to be looking at those in later lesson.
Bacteria
Description
Bacteria such as rod bacteria cause food poisoning. Around 300000 people in Nigeria get food poisoning from this type of bacteria every year. Fortunately, most people recover from food poisoning but sometimes it can be fatal. In fact, many bacterial diseases can kill us.
How do Bacteria make us Ill ?
The key fact is that once inside the human body, bacteria reproduce very rapidly. Under ideal conditions, bacteria can divide every twenty (20) minutes.
Bacteria can then release harmful chemicals called toxins. Toxins damage tissues and make us feel ill.
Viruses
Another type of pathogen that cause a lot of human diseases are viruses.
I’m showing you here the virus HIV which can lead to AIDS. Viruses cannot reproduce by themselves. They can only reproduce inside a host cell.
This shows a virus and a human cell. First, the virus invades the host cell. As you can see, the virus reproduces inside the cell. This is very damaging to the cell. When the virus leaves the cell, it can cause the cell to burst open and die like this
How do Pathogens Spread?
Some pathogens are spread in the air example in water droplets (influenza).
Other pathogens can be spread directly in water (e.g cholera).
Some pathogens are spread by direct contact between individuals (e.g HIV).
How to Reduce the Spread of Pathogen
1. Washing your hands before eating can prevent the spread of pathogens.
2. Providing people with clean drinking water can also reduce the spread of pathogens. In Nigeria, drinking water contains chlorine which kills microorganisms.
3. Using a condom during sexual intercourse reduces the spread of HIV.
4. Using hand sanitizer, covering of face mask and maintaining social distancing reduce the spread of coronavirus.
5. In the case of highly infectious diseases such as Coronavirus and Ebola, patients may be quarantined or isolated. This prevents the pathogen from spreading to other people.
6. We can also reduce the spread of pathogens by vaccination and we’re going to look at that in more detail in lesson eight.
Lesson 2 : Measles and HIV
Learning Objectives I
By the end of this lesson, learners should be able to :
• Describe the causes and the symptoms of the viral diseases measles and HIV
Viruses
Recap
Remember that viruses are an example of a pathogen. As we said before, pathogens are microorganisms that cause infectious disease. One key fact about viruses is that viruses cannot be killed by antibiotics and it really important you learn that. In this lesson, we’re going to be exploring specific viral diseases and these include measles and HIV.
Measles
Description
Measles is a highly infectious disease and the first symptom of measles is often a fever. In other words a very high temperature. Usually after three days, the patient develops a red skin rash like the one I’m showing you here.
The measles virus is spread in droplets when an infected person coughs or sneezes. The virus then passes into a different person when these droplets are inhaled. In some cases, complications can develop. These can cause damage to the breathing system and the brain and in severe cases, measles can be fatal. Most children are vaccinated against measles when they are very young.
HIV
The first symptom of HIV is often a flu-like illness but this usually disappear after one or two weeks. At this point, the virus is attacking the cells of the patient’s immune system. Over time, the immune system becomes severely damaged.
At some point, the patient’s immune system becomes so badly damage that it cannot fight other infections that other healthy people could easily deal with. The damaged immune system is also unable to fight off cancer cells.
When the immune system reaches this highly damaged stage, the patient can now easily contract other infections such as tuberculosis (TB). The patient may also
develop cancer. At this point, the patient is described as having late – stage HIV or AIDS. Frequently at this stage , the disease is fatal.
How HIV is Spread
HIV is transmitted through the exchange of fluids between humans. HIV can be spread by unprotected sexual intercourse. It can also be spread when drug users share infected needles. That’s because blood containing HIV can pass in the needle from one person to another. HIV can equally spread by infected mother to fetus. It can as well be spread through blood transfusion.
Prevention
People who are infected with HIV can be treated with antiretroviral drugs like the one shown. These drugs stop the virus from multiplying inside the patient so the virus does not damage the patient’s immune system.
Patients who take antiretroviral drugs do not go on to develop AIDS and they can leave a normal life expectancy. Remember that antiretroviral drugs are not a cure for HIV or AIDS. The patient must take these drugs for the rest of their life.
Lesson 3 : Salmonella and Gonorrhea
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe the causes and the symptoms of the bacterial diseases salmonella food poisoning and gonorrhoea.
Bacterial Diseases
Salmonella food poisoning and gonorrhea are communicable diseases. In other words they are passed from person to person by a pathogen. Remember that a pathogen is a microorganism that causes infectious disease.
One key fact that you need to learn is that unlike viruses, bacteria can be killed using antibiotics.
Salmonella Food poisoning
Description
This shows you the bacteria that cause food poisoning. The bacteria that cause salmonella food poisoning are spread by ingesting infectious food. The word ingested means eating. This is the kind of food that is prepared in unhygienic conditions. For example if raw chicken is prepared on a chopping board and then the same chopping board is not cleaned before it is used to prepare other foods example salad. Any salmonella bacteria in the chicken will be killed when it is cook. However, the salmonella bacteria which have contaminated the salad will not be killed and can cause salmonella food poisoning. When salmonella bacteria enter the human body, they secrete harmful chemicals called toxins. Toxins are chemical which can damage cells. These toxin cause the symptoms of salmonella food poisoning. These symptoms include a fever, abdominal cramps, vomiting and diarrhoea.
Salmonella bacteria are sometimes found in poultry such as chicken. In Nigeria, chicken are vaccinated against salmonella. This controls the spread of the disease.
Gonorrhoea
Gonorrhoea is a sexually transmitted disease (STD). In other words it’s transmitted by sexual intercourse. Symptoms include a thick yellow /green discharge from the penis or vagina. Gonorrhoea can also cause pain when urinating.
In the passed, gonorrhea was easily treated using the antibiotic penicillin. Now gonorrhoea is treated with different antibiotics. This is because the bacteria have become resistant to penicillin. What this means is that the bacteria have changed so they are no longer killed by penicillin. However, antibiotic resistant strains of bacteria are now common.
Stopping the Spread of Gonorrhoea
We can stop the spread of gonorrhoea in two main ways :
• Using a condom during sexual intercourse stops the bacterium passing from person to person.
• People who have unprotected sex should be tested for gonorrhoea. They can be treated with antibiotic to kill the bacteria before they pass it on to another person.
Lesson 4 : Malaria
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe the cause and symptoms of malaria.
• Describe the life – cycle of the malaria pathogen.
• Describe how we can reduce the spread of malaria.
Malaria
Description
Malaria is a very common disease in certain parts of the world and it causes over 400,000 deaths every year.
Malaria is a communicable disease. In other words it is spread by a pathogen and I’m showing you the picture of the malaria pathogen here in a sample of human blood. The key fact that you need to learn is that the malaria pathogen is an example of a protists. Malaria is a very serious disease. People with malaria experience repeated bouts of fever.
The Life Cycle of Malaria Pathogen
As we said earlier, the malaria pathogen is a protists. This cannot pass directly from one person to another. This shows a person infected with malaria.
First, the infected person is bitten by a mosquito. The malaria pathogen then passes into the mosquito. The mosquito now bites a different person and passes the malaria pathogen to them. Scientists call the mosquito a vector because it carries the pathogen from one person to another . Remember the causative agent of malaria is plasmodium.
Stopping the Spread of Malaria
There are two main ways to prevent the spread of malaria.
Firstly, we need to stop the vector (the mosquito) from breeding. Mosquitoes breed in still water like the picture shown. To stop mosquitoes from breeding, we need to find areas of still water and drain them. We can also spray areas of still water with insecticide which kills mosquitoes.
The second thing we can do to reduce the spread of malaria is to prevent the mosquitoes from biting humans. One of the best ways to do this is to sleep under a mosquito net like this.
The mosquitoes cannot get through the net so they cannot bite anyone sleeping in the net. If we spray the mosquito net with insecticide then any mosquitoes that land on it are also killed.
So by preventing the mosquitoes from breeding and by preventing them from biting humans, we can reduce the spread of malaria.
Lesson 5 : Non-Specific Defense System
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe the non – specific defense systems of the human body.
Recap
We’ve already seen that a lot of human diseases are caused by pathogens for example salmonella food poisoning, HIV, measles, chicken pox, coronavirus and a lot more.
The body has two main defense systems against pathogens and these include non – specific defense system and the immune system. In this lesson, we’re looking at the non – specific defense system.
Non-Specific Defense System
The job of the non – specific defense system is to prevent pathogens from entering the human body.
Components of the Non - specific Defense System
There are four main parts of the non - specific defense system. These are :
The Skin : The skin forms a protective layer covering the body. The outer layer of the skin consists of dead cells and is difficult for pathogens to penetrate. The skin also produces an oily substance called sebum which kill bacteria. Sometimes, the skin is damaged and that could allow pathogens to enter the body. To stop this, the skin scabs over. Now, there are some parts in the body which are not covered by the skin example nostrils and the mouth. These are openings where pathogens can enter the body. So the body has defense systems in place to protect us.
The Nose : The nose contains hair and mucus. These can trap pathogens before they enter the breathing system. Sometimes pathogens pass through the nose and then make their way down towards our lungs. To stop this, the trachea and bronchi are covered with tiny hairs called cilia. Cilia are covered in mucus which can trap pathogens. The cilia then waft the mucus upwards towards the throat where it is swallowed into the stomach.
Stomach : There’re lots of different pathogens that can be present on food. A good example of a disease caused by a pathogen is salmonella food poisoning. To prevent us from disease, the stomach contains hydrochloric acids. Hydrochloric acids kills pathogens before they can make their way further down into the digestive system. Also, I should point out that even with all these non-specific defense systems, pathogens can still get into the human body and cause serious disease. To protect us, we also have the immune system and we’re going to look at that in our next lesson.
Lesson 6 : The Immune System
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how the Immune system protects us against pathogens.
Recap
In the last lesson, we saw that the job of the non - specific defense system is to stop pathogens from entering the human body. However, sometimes this doesn’t work.
When the skin is damaged like this, pathogens can invade the body and enter the bloodstream. Once inside the body, pathogens can multiply and damage the healthy tissue. For example bacteria can release chemical called toxins which make us feel unwell.. To protect us in case it happens, the body also have the immune system and we’re looking at that in this lesson.
The Immune System
The immune system has two main functions.
The immune system destroys pathogens and any toxins they produce.
The immune system protects us in case the same type of pathogen invades us again in the future.
How the Immune System Work
The key fact that you need to understand is that the immune system involves the white blood cells and these have three functions :
Phagocytosis
The white blood cells can ingest and destroy pathogens and I’m showing you the picture here.
The white blood cell detects chemicals released from the pathogen and moves towards it.
The white blood cell then ingests the pathogens like the picture shown below. The word ingest means take in. In your exam make sure you say ingest and not eat.
The white blood cell uses enzymes to destroy the pathogens. This whole process is called phagocytosis
The second way that white blood cells can destroy pathogens is by making antibodies. It’s really important that you learn the details of how antibodies work.
Antibodies
Antibodies are protein molecules produced by white blood cells. As you can see this white blood cell is releasing antibodies and the antibodies stick to the pathogen and this triggers the pathogens to be destroyed. There are two key factors about antibodies.
Firstly, antibodies are extremely specific. For example, if a person catches measles, they will develop antibodies against the measles virus.
However, those antibodies will only protect against the measles virus. They will not protect against any other pathogen.
Secondly, antibodies can remain in the blood for a long time. This means they can protect us in case we ever get infected again with the same pathogen.
Certain types of bacteria can release toxins. Toxins are chemicals that harm cells and can make us feel very unwell.
White blood cells can produce chemicals called antitoxins. Antitoxins are proteins which stick to toxins molecules and prevent them from damaging cells.
Lesson 7 : Infectious Diseases in Plants
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe the causes the symptoms of infectious diseases in plants :
• The viral disease tobacco mosaic virus
• The fungal disease rose black spot.
Tobacco Mosaic Virus (TMV)
Tobacco mosaic virus is a very widespread plant infection. TMV infects a number of different plant species including tomatoes. It causes the leaves to discolour in a mosaic pattern. Because of this discolouration, the rate of photosynthesis is reduced. This means that the growth of the plant is also reduced
Rose Black Spot
Rose black spot is caused by a fungus. This causes the leaves to develop purple or black spots. The leaves then often turn yellow and fall off. Rose black spot causes the rate of photosynthesis to fall and this reduces the rate of growth. Rose black spots are caused by a fungus and can be spread by water or by wind.
Ways to Treat Rose Black Spot
• We can spray the plants with chemicals which kill fungi (fungicides)
• We can also remove the infected leaves and destroy them eg by burning. .
Lesson 8 : Vaccination
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how vaccination can prevent illness in an individual.
• Describe how vaccination can prevent the spread of pathogens in a population.
Recap
In the last lesson, we looked at the immune system. We saw that one of the roles of the white blood cell is to produce antibodies against pathogens which entered the body. Remember that the antibodies stick to pathogens and this triggers the pathogens to be destroyed. In this lesson, we’re looking at how vaccination can prevent illness.
How Vaccination can Prevent Illness in an Individual
Vaccination involves introducing small quantities of dead or inactive form of a pathogen into the body. Here I’m showing you a white blood cell and the dead or inactive form of the pathogen in the vaccination. Because the pathogen is dead or inactive, it cannot lead to the disease in the patient. The white blood cells are now stimulated to produce antibodies against the dead or inactive pathogen.
Remember that inactive or inactivated means that the pathogen has been treated with chemicals so that it cannot cause the actual disease.
At the same time, the white blood cell divides by mitosis to produce lots of copies of itself like this.
These copies of the white blood cell can stay in the body for decades (10 years).
If the same pathogen then enters the body, even years later, the white blood cells can produce the correct antibodies quickly and this prevents infection. So as you can see, vaccines directly protect us from infection by pathogens.
This graph shows you the level of the antibody after vaccination and after the body is invaded by the live pathogen.
As you can see, when the live pathogen invades the body , the antibodies number rises very quickly onto a very high level. This is because after vaccination, the white blood cells undergo mitosis. This means that there is a large number of white blood cells producing antibodies after the live pathogen has invaded the body.
Again, remember that antibodies are specific. This means that vaccination against one pathogen does not protect us against a different pathogen. For example vaccination against coronavirus cannot protect us against HIV
Herd Immunity
It is really important that a very large number of people are vaccinated against pathogens like in the case of coronavirus. The reason for this is that ; there are always some people who did not get vaccinated. For example people who may be new to a country or people who missed the vaccination appointment.
If enough people are vaccinated, this also protects unvaccinated people. The unvaccinated person cannot catch the disease because no one around them can pass the pathogen on. Scientists call this herd Immunity.
Lesson 9 : Antibiotics
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how certain disease can be treated using antibiotics.
• Describe what is meant by antibiotic resistance and why that is a problem.
Recap
In the previous lesson, we saw that many diseases are caused by bacteria (e.g. salmonella food poisoning and gonorrhoea). In many cases, bacterial diseases are extremely unpleasant and they can be fatal.
In 1940s, many people died from bacterial diseases. However, around that time scientists discovered the first antibiotic which is called penicillin. These days, the use of antibiotics means that most bacterial diseases are treatable.
Antibiotics kill infective bacteria inside the human body without harming body cells.
Antibiotic Resistance
Several years ago, doctors discovered that certain antibiotics were no longer effective against certain bacteria. That’s because antibiotics had been overused. The bacteria had evolved so that they were no longer killed by the antibiotic. Scientists call it antibiotic resistance. Antibiotic resistance is a serious problem. It’s possible that in the future bacteria diseases will become very difficult to treat.
There’re couple of point about antibiotic that you need to learn:
Firstly, doctors always use specific antibiotics to treat specific bacteria.
Secondly, antibiotics cannot kill viruses. That’s why doctors will not prescribe antibiotic for conditions that may be caused by a virus for example certain types of sore throat. One type of drug that doctors will prescribe is painkillers. Pain killers treat the symptoms of a disease by relieving pain.
However, medicines such as painkillers do not kill pathogens. In other words they do not treat the disease itself. As we said before, antibiotic cannot kill viruses. Remember that viruses live and reproduce inside human cells. Because of this, it is difficult to develop drugs that kill viruses without also damaging the body’s tissues.
Lesson 10 : Testing Medicine
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how new medicines are discovered and then tested.
Recap
In the previous lesson, we looked at medicines such as antibiotics and painkillers. Now medicines are being developed all the time and all of them have to be extensively tested.
In the past, medicines were often extracted from plants. The plant foxglove as shown above was used to extract the heart drug digitalis.
The painkiller aspirin was extracted from willow trees.
Drug were also extracted from microorganisms. The scientists Alexander Fleming discovered penicillin in the mould penicillium.
These days, most new drugs are synthesized by chemists working for pharmaceutical companies. But the starting point is still often a chemical extracted from a plant. Now, all new drugs no matter where they come from have to be tested on trialed.
Firstly, we need to check the toxicity of the drug. In other words whether it is safe or toxic to humans . We then need to check that the drug is effective. In other words it treats the disease that we’re looking at. Lastly, We need to check the dosage. In other words we need to investigate the best dose to treat the disease with the minimum amount of unwanted side effects.
The first stage of drug testing is called preclinical testing. Remember that preclinical testing is not carried out on humans. That’s because the drug could be extremely toxic. Instead preclinical testing is carried out on cells, tissues and on live animals.
Clinical Testing
Clinical testing is carried out on humans. In the first stage of clinical testing, very low doses of the drug are given to healthy volunteers. That is to check that the drug is safe in humans. If the drug is found to be safe, then clinical testing continues to find the optimal dose. This is the best dose to treat the disease with the fewest side effects. There is one clear idea about drug testing that you need to understand and that’s the idea of a placebo.
Placebo
A placebo looks like the treatment but contains no active drug. A lot of placebo are tablets or injections. These are designed to look exactly like the tablets containing the active drug. Some patients will get better if you give them a placebo. That’s because they think they are being treated so they believe that they’re going to get better.
Double – blind Trial
In a double – blind trial, one group receives the active drug and another group receives the placebo or control group receive a dummy drug which looks exactly like the test drug but has no active ingredient . In a double – blind trial, neither the patients nor the doctors know which people are receiving the active drug and which are receiving the placebo. That is to stop bias in case the doctors pay closer attention to people receiving the active drug.
Lesson 11 :Monoclonal Antibodies
Learning Objective
By the end of this lesson, learners should be able to :
• Describe what is meant by a monoclonal antibody.
• Describe how monoclonal antibodies are produced.
• Describe the uses of monoclonal antibodies
Monoclonal antibodies
Recap
We’ve already looked at the immune system and we saw that white blood cells can produce antibodies. Antibodies are protein molecules which stick to pathogens like this. There are some key ideas about antibodies that you need to learn.
Antibodies
Antibodies are produced by white blood cells called lymphocytes.
Lymphocytes produce antibodies against anything that the body detects as foreign and scientists call foreign objects antigens.
Scientists can trigger lymphocytes to produce antibodies and that can be really useful. For example antibodies are used in pregnancy testing kits… and in certain cancer treatments.
If we inject a mouse with an antigen, then lymphocytes will produce antibodies against the antigen.
We can then collect the lymphocytes from the mouse.
The problem is that lymphocytes like this will not divide by mitosis. So in the stage, we fuse (join) our lymphocytes with a tumour cell.
Tumour cells are very good at dividing by mitosis. The cell produced is called hybridoma. Hybridoma cells can produce antibodies and divide by mitosis.
In the next stage, we select a single hybridoma cell producing the antibody that we want.
We then allow this hybridoma cell to divide by mitosis to form a clone of identical hybridoma cells like this
So the antibodies produced from this clone of hybridoma cells are all identical. We call these monoclonal antibodies because they all come from a single hybridoma clone.
A large amount of monoclonal antibody can then be collected and purified.
The Key facts about Monoclonal Antibodies
Monoclonal antibodies are produced from a single clone of hybridoma cells.
That means that monoclonal antibodies are specific to one binding site on one protein antigen.
The benefit of this is that monoclonal antibodies can target a specific chemical or specific cells in the body and that means that monoclonal antibodies have a large number of uses.
Uses of Monoclonal Antibodies
Monoclonal antibodies are produced from a single clone of identical hybridoma cells. This means that monoclonal antibodies are specific to a single binding site on one protein. We can produce monoclonal antibodies against any antigen that we want. This makes them extremely useful in medicine. Some of these uses include :
1. Monoclonal Antibodies in Diagnosis .
Firstly, monoclonal antibodies are used for diagnosis and a good example is in pregnancy testing.
In pregnancy testing, monoclonal antibodies are used to detect a specific hormones This hormone is produced by the placenta of the developing fetus.
Pregnancy test kits based on monoclonal antibodies are cheap and easy to use. If you’re woman, simply urinate on the test strip and looks for a reaction. The test is also highly accurate if it is used correctly.
2. Monoclonal Antibodies in Lab Testing
We can use monoclonal antibodies to measure the levels of hormones in blood. For example the person is tired a lot and lack energy, then that is caused by low levels of certain hormones. A blood sample is taken and sent off for analysis. The test of these hormones used monoclonal antibodies.
We can also use monoclonal antibodies to detect pathogens in the blood for example virus. The advantage of using monoclonal antibodies in these cases is that they are completely specific to what we are looking for.
3. Monoclonal Antibodies for Location
Another use of monoclonal antibodies is to locate or identify specific molecules in a cell or tissue. For example in this cell, monoclonal antibodies have been attached to fluorescent dyes. The antibodies then stick to specific molecules within the cell and allow us to see their locations.
4. Monoclonal Antibodies for Treating Diseases
Cancer cells undergo uncontrolled mitosis and they spread around the body. Scientists can make antibodies specific to cancer cells.
When the antibody is injected into the blood, it attaches to the cancer cells. The radioactive or toxic drug stops the cancer cells from growing and dividing. The advantage here is that the antibody delivers the substance specifically to the cancer cells without harming other cells in the body.
Clinical trials using monoclonal antibodies have produced some very severe side effects. This is why there are not many drugs based on monoclonal antibodies at this time.
Remember that in conventional chemotherapy, a cancer patient is given a toxic drug which is designed to kill cancer cells. However, chemotherapy drugs are also toxic to normal body cells. This means that conventional chemotherapy can be very damaging to the patient’s body (for eg they may feel extremely sick or lose their hair ). However, if we attach the toxic drug to a monoclonal antibodies, then this drug is delivered exactly to the cells that we are trying to kill. This makes it much less toxic to the rest of the body.
In conventional radiotherapy, the patient is given a powerful dose of radiation. This will kill cancer cells but also damage normal body cells, producing unwanted side effects. However, with monoclonal antibodies, the radiation is delivered specifically to the cancer cells. Again, this reduces the damaging effects on the rest of the body.
Lesson 12 : Plant Disease
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how we can diagnose diseases in plants.
• Describe plant ion deficiency diseases
Plant Disease
Recap
We’ve already looked at plant pathogens in our previous lesson. For example Tobacco mosaic virus is a viral plant disease and Rose blackspot is caused by a fungus plant disease. Plant can also be attacked by bacterial pathogens.
There are many example of plants being attacked by insects such as aphid which I’m showing you here.
Aphids extract nutrients such as sugars from the plant. When a plant is covered with hundreds of aphids, then a very large amount of the sugars produced by photosynthesis are taken by the aphids. This means that the ability of the plant to release energy by respiration is reduced so the growth of the plant is slow. . Remember that aphids are not a pathogen as they do not cause any infectious disease. Aphids can carry pathogens from one plant to another. This means that aphids are vectors for pathogens. (in a similar way to mosquito acting as a vector for malaria which we saw earlier ). There are several ways we can diagnose plant diseases.
Symptoms of Diseases in Plants
To diagnosis plant diseases we can look for the following symptoms
• Discolouration ( for example leaves changing colour ).
• Spots on leaves
• Stunted growth
• Decay/rot
• Growth and
• Malformed stems or leaves ( I.e stems or leaves which have not developed in the expected ways ). All of these are potential symptoms of plant disease.
How to Identify Plant Diseases
Once a gardener has noticed symptoms of a disease in a plant, they can identify the disease by using a garden manual or a website.
If they think that the disease is caused by a pathogen, then they can send a sample of the plant to a laboratory to identify it .
The laboratory could use a testing kit based on monoclonal antibodies to identify the pathogen .
There is another category of plant diseases and these are not caused by pathogens. These are called plant ion deficiency diseases.
Plant Ion deficiencies
• A lack of the nitrate ion causes stunted growth in plant . That’s because nitrate is needed for protein synthesis and also for growth.
• A Lack of the magnesium ion causes the condition chlorosis, because magnesium is required to make chlorophyll. In chlorosis, the leaves lose their green colouration like this.
Lesson 13 : Plant Defense Response
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how plants defend themselves against attack
• Physical response
• Chemical response
• Mechanical response
How Plants Defend Themselves against Attack
Plants have three main defense systems against attack. These are :
1. Physical response
• All plant cells have a cellulose cell wall. This is difficult for microorganisms such as bacteria to penetrate.
• Leaves are covered with a thin oily layer called the waxy cuticle. The waxy cuticle is difficult for microorganisms to penetrate which protects the plant from attack.
• Bark is a barrier to entry by microorganisms. As bark ages, it eventually falls off and is replace with fresh bark underneath.
2. Chemical response
o Plant can also release chemicals to protect themselves and this is called the chemical response. For example plants can release antibacterial chemicals which kill bacteria and prevent them from attacking the plant.
o Plants can also release poisons to deter herbivores from grazing on the plant.
3. Mechanical defense system :
o The first example of mechanical defense are thorns or hairs.
o Sharp thorns directly protect a plant from being eaten by a herbivores. Other plants have hairs which irritate the mouth of herbivores, making the plant difficult to eat.
Sometimes, we find plants which have special leaves like this which droop or curl when touched. This might scare herbivores as they are not used to plants that move like that.
o Finally, the white dead nettle looks very similar to a stinging nettle but it has no sting. Herbivores are less likely to eat white dead nettle as they can easily mistake it for a stinging nettle.
Lesson 14 : Plant Hormones
Learning Objectives
By the end of this lesson, learners should be to :
• Describe how plants use hormones to respond to light and gravity.
• Describe the roles of gibberellins and ethene.
• Describe the uses of plant hormones.
How Plants use Hormones to Respond to Light and Gravity .
This shows plant shoots growing towards the light. This is called phototropism and that’s a word that you need to learn. Scientists carried out a number of experiments to find out how phototropism works. It is possible that you could be shown these experiments in an exam question.
This shows some shoots and we are shining light from one side only. As we have seen, the shoots grow towards the light and scientists wondered whether this is controlled by hormones.
First, scientists removed the very tips of the shoots. They found that now the shoots did not grow towards the light. Scientists suggested that shoot tips produce plant hormones. This hormones is called auxin and again, you should learn that word.
Scientists then covered the tips shoots with foil to block out the light. Again , the shoots did not grow towards the light… so this tells us that the tips are sensitive to light.
Scientists then used foil to cover the lower parts of the shoots. In this case, the shoots grew towards the light as normal. This tells us that the lower parts of shoots are not sensitive to light.
How Shoots use the Hormones Auxin to Grow towards the Light
Auxin is produced at the very tip of the shoot and the shoots triggers cell growth. Light causes auxin to concentrate on the darker side of the shoot tip. Auxin now spreads down the shoot. Cells on the darker side grow faster than cells on the lighter side. This causes the shoot to grow towards the light.
Plant roots grow towards the force of gravity and I’m showing you that here. This is called is called gravitropism or geotropism and this also involves auxin.
Auxin is produced in two root … but gravity causes the auxin to concentrate on the lower side. The key fact is that in roots, auxin inhibit cell growth. So the lower side now grows more slowly than the upper side and this causes the roots to grow towards the force of gravity. As well as auxin, plants use other chemicals like gibberellins and ethene to regulate their behaviour.
Roles of Gibberellins and Ethene
Gibberellins are important in starting the germination of seeds. The chemical ethene controls the cell division and the ripening of fruits.
Uses of Auxin
Auxin have three main uses:
1. Auxins are used as weed killers for example in gardens.
2. They are used as rooting powders.
3. They are used for promoting growth in tissue culture.
Uses of Gibberellins
Gibberellins are another group of plant hormone. These have lots of different uses.
1.It can be used to end seed dormancy. In other words, they can force a seed to germinate earlier than it normally would.
2. Gibberellins can also be used to encourage plants to flower
3. Finally, gibberellins can be used to make fruit grow larger
Uses of Ethene
1.The chemical ethene is used a lot in the food industry. For example fruits like bananas are usually harvested before they are ripe. These are then transported long
distances and can be stored before they are needed. Ethene is then used to trigger the bananas to ripen just before they are sold in Nigeria.
Required Practical : Plant Responses
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how to investigate the effect of light or gravity on the growth of newly germinated seedlings.
Recap
In the last lesson, we looked at how plants use the hormone auxin to control their growth. In this lesson, we’re looking how to investigate this.
Investigating the Effect of Light on the Height of Seedlings.
In this case, the independent variable is the light intensity… and the dependent variable is the height of the seedlings.
Procedure
1.First, we place cotton wool in three petri dishes and soak them with equal volume of water. The volume of water is a control variable.
2.We then place ten mustard seeds in each dish and again another control variable of the type of seed.
3. We leave the dishes in a warm place and allow the seeds to germinate.
4. We need to water the seeds every day with the same volume of water.
5.After few days, the seeds will germinate like this. At this point, we need to make sure that the three dishes have the same number of Seedlings and that’s because the number of seedlings is another control variable. For example imagine that only eight seeds germinate in one of the dishes… but ten seeds germinate in both of the other dishes.
In this case, we would need to remove seedlings from two of the dishes… so that all three dishes now contain eight seedlings.
6.We use a ruler to measure the height of each seedling and we need to the stems to make sure that they are straight. However, we need to be careful not to damage the seedlings.
Now, we place the three dishes in different conditions.
One dish is placed in full sunlight for example on a very bright windowsill.
One dish is placed in partial light for example at the back of a lamb.
Finally, the last dish is placed in darkness for example in a cupboard.
7.We then measure the height of each seedling every day for at least five consecutive days… and record the results in a table such as the one I am showing you here. When the experiments is finished, we calculate a mean seedling height for each day. We should also draw diagrams to show the effects of different light intensities on the seedlings.
I am showing you some typical results for this experiment. As you can see, the height of the seedlings is similar for both full light and partial light and that’s because chlorophyll is very efficient at absorbing light energy. So plant do not need full light to grow.
However, you will notice that the seedlings have grown towards the light source. This is due to photosynthesis and we’ll be looking at that in chapter four. Remember that auxin concentrates on the side of the seedling furthest from the light and causes this side to grow faster.
If we look at the seedling in the dark, we can see that these have grown the longest and that’s because seeds usually germinate underground and they grow rapidly to reach the light. If we keep seedlings in the dark, then they continue to grow rapidly, trying to reach light. You will also notice that the leaves are small and yellow. That is because once the seedlings have used all their energy stores… they cannot carry out photosynthesis in the dark.
Effects of Gravity on Seedlings
We can also investigate the effect of gravity on seedlings and I am showing that here. In this case, a dish of Seedlings is placed on its side in the dark. As you can see, the shoots have grown upwards, against the direction of gravity… and the roots grown downward towards the direction of gravity. As we saw in the previous lesson, auxin inhibits cell growth in roots.
Gravity causes auxin to build up on the lower side of the root. This now grows more slowly than the upper side and this makes the root grow in the direction of gravity.
Lesson 15 : Cloning Plants
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how plants are cloned by cutting and by tissue culture.
Cloning Plants
Cloning plants has one big advantage. Because the clone is genetically identical to the original plant … we know exactly what the clone’s characteristics will be (example the colour of flowers).
If we used seeds, which are produced by sexual reproduction… then all of the offspring would be different.
A really simple way to clone a plant is to take cuttings and gardeners have been using this method for a very long time. In this case, a small piece of the plant is removed and the end is dipped in rooting powder. Rooting powder contains plant hormones and this encourages the plant to develop roots.
By taking cuttings, we produce a genetically - identical clone of the starter plant. Taking cuttings works really well if we just want a few clones from a plant.
However, what if we need hundreds of clones? To do this, we use tissue culture.
In tissue culture, we take a plant that we want to clone and we divide the plant into hundreds of tiny pieces. Each of these pieces contains a small number of cells. This shows a scientists splitting a plant into lots of small pieces. These small groups of cells are then incubated with plant hormones. The plant hormone stimulate the plants to grow and develop into fully grown clones.
The conditions that we use for tissue culture must be sterile and that’s because we do not want to introduce any microorganisms such as bacteria or fungi.
Tissue culture is extremely useful in commercial plant nurseries. It allows growers to produce thousands of genetically – identical plants quickly and cheaply.
Again, because all the plants are clones… gardeners can be certain that they will get the characteristics they want example flower colour. Tissue culture is also used to preserve rare species of plants.
Lesson 16 : Cloning Animals
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how animals can be cloned by embryo transplants and by adult cell cloning and this is for tertiary students only.
Cloning Animals
Recap
In the last lesson, we looked at how plants can be cloned. In this lesson, we’re looking at cloning animals. This is much more complicated and it is really important that you learn the stages as it is a common exam question. We are going to start by looking at cloning by embryo transplants and we are going to look at cloning horses but this could be used for any mammal.
We start with sperm and an egg cell from horses with characteristics that we want. Fertilization produces a fertilized egg.
We then allow the fertilized egg to develop into an early stage embryo. It is very important that the cells in this embryo must not have started to specialize. In other words, none of these cells must have started to change into any specific cell type.
Next, we now use a glass rod to split this embryos into two.
Finally, we transplant the two embryos into host mothers. The embryos will then grow and develop and when these animals are born, we will get two identical offspring ( clones) as shown.
There is one big problem with embryo transplants. Because we start with sperm and an egg… we cannot be certain that the offspring will have the characteristics that we want. We can overcome this problem by using adult – cell cloning.
Adult cell cloning can seem tricky but it is worth learning the stages. The key benefit of adult cell cloning is that we are cloning from an adult. This means that we know the characteristics that the clone will have. We are going to use sheep as an egg.
Diagram
We start by removing a cell from the animal that we want to clone for example skin cells.
We then remove the nucleus from this cell. This nucleus contains the genetic information from the animal that we are cloning.
Next we take an unfertilized egg cell from the same species. In this case, it would be from any female sheep.
We then remove the nucleus from the unfertilized egg and throw it away. The unfertilized egg now contains no genetic material at all.
We now insert the nucleus from the original adult body cell. Remember that this egg cell now contains only genetic information from the animal that we are cloning.
Diagram
We then give the egg cell an electric shock and this makes the egg cell divide to form an embryo. These embryo cells contain the same genetic information as the adult skin cell that we started with.
Finally, when the embryo has developed into a ball of cells … it is inserted into the womb of an adult female to continue its development. The host mother then gives birth to the clone.
One key point is that the clone looks nothing like the host mother and that’s because the clone contains none of her genetic information.
The benefit of adult cell cloning is that because we are cloning from an adult… we already know the characteristics that the clone will have.
Chapter Four : Bioenergetics
Lesson 1 : Photosynthesis
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe what is happens in photosynthesis.
• Describe the factors that affect the rate of photosynthesis.
• Describe how the glucose produced in photosynthesis is used.
What Happen in Photosynthesis
The word photosynthesis can be broken down as ‘photo’ – meaning ’ light’ and ‘synthesis’ – meaning ‘ to make ‘. Photosynthesis is a chemical reaction that takes place inside a plant, producing food for the plant to survive. Carbon dioxide, water and light are all ingredient needed for photosynthesis to take place.
Plant use light for their source of energy. This brings us to the first key fact about plants. The reaction that plants use to trap this light energy is called photosynthesis. Because photosynthesis takes in energy, it is an example of an endothermic reaction.
Photosynthesis happens in the leaves of a plant and leaves contain the green chemical called chlorophyll. Chlorophyll can absorb light energy.
Carbon dioxide + water Light glucose + oxygen
Chlorophyll
CO2 + H2O C6H12O6 + O2
In the first stage of photosynthesis, plant takes carbon dioxide and water into the leaf. Light energy is then absorbed by chlorophyll. This light energy is then used to convert the carbon dioxide and water into the sugar glucose.
In this reaction, oxygen is also produced. The reaction shown is called word equation for photosynthesis and you are expected to know this. You’re also expected to recognize the chemical formulas for the molecules in this reaction. The formula for carbon dioxide is CO2 and the formula for water is H2O, the formula for glucose is C6H12O6 and the formula for oxygen is O2. I should point out that this equation isn’t balanced.
Limiting Factors of Photosynthesis
As we saw before, in other for photosynthesis to take place, we need carbon dioxide, water and light. The question is what happen if there’s not enough of these?
Imagine that I take a plant and I increase the light intensity. I keep everything else constant. I then measure the rate of photosynthesis at each level.
Diagram
When the light intensity is zero, the rate of photosynthesis is zero. Plants need light to carry out photosynthesis.
As we increase the light intensity, the rate of photosynthesis increases and that’s because the plant now has more light energy to carry out the photosynthesis reaction, so the reaction get faster. There’s key point here that you need to get, if we increase the light intensity, the rate of photosynthesis also increases. That tells us that the light intensity was limiting. In other words, photosynthesis was not as fast as it could have been, because there was not enough light.
At this point, light intensity is a limiting factor. If we keep increasing the light intensity, there comes a point where the rate of photosynthesis no longer increases and it levels off like this.
At this point, light intensity is no longer the limiting factor. Something else is now in short supply example the level of carbon dioxide in the air. We can now do the same experiment but this time increasing the level of carbon dioxide. Again, keeping everything else constant we get a graph like this
Diagram
You can see the shape of the graph is exactly the same as the one for light intensity. As we increase the carbon dioxide level, the rate of photosynthesis increases. This tells us that carbon dioxide is the limiting factor. At a certain point, the rate of photosynthesis no longer increases, telling us that the carbon dioxide is no longer the limiting factor.
Now, there are two other factors that can affect the rate of photosynthesis. The first is the amount of chlorophyll in the leaf.
Diagram for leaves
I’m showing you here a leaf and because these leaves can trap less light energy than normal leaves, they will have a lower rate of photosynthesis
Graph Diagram for temperature
As we increase the temperature, the enzymes involved in photosynthesis work faster so the rate increases. However, if we keep increasing the temperature, the enzymes will be denatured and the rate of photosynthesis falls.
Uses of Glucose Produced in Photosynthesis
Diagram of plant
The first used for the glucose is to release energy in respiration. Remember that respiration takes place in the mitochondria and I’m showing you that here. Photosynthesis only produces glucose during the day, when there is light. But plant cells respire all the time including at night.
The second use of the glucose produced by photosynthesis is to produce the insoluble storage molecules starch. The starch can be converted back to glucose by the plant when it is needed.
In many plant, the glucose produced in photosynthesis is converted to fats and oils. Fats and oils are used by the plant as a storage form of energy.
In the previous lesson, we saw that the plant cell is enclosed in a cell wall. The cell wall contains the molecule cellulose, which gives it strengths. This cellulose is made from glucose produced by photosynthesis.
The glucose produce in photosynthesis is used to produced amino acids. Amino acids are used by the plant to synthesize proteins. To make amino acids from glucose, plants need to absorb nitrate ions from the soil.
Lesson 2 : Limiting Factors
Learning Objectives
By the end of this lesson, learners should be able to :
• Interpret graphs to determine the limiting factor in photosynthesis.
• Explain how greenhouses are used to increase the rate of photosynthesis.
Recap
Carbon dioxide + water Light glucose + oxygen
Chlorophyll
In the last lesson, we looked at equation for photosynthesis. We saw that light energy is absorbed by chlorophyll and used to react carbon dioxide with water to make the sugar glucose, oxygen is also produced in this reaction. We then saw that if we increase the light intensity and measure the rate of photosynthesis, we get a graph like this
Initially, the rate of photosynthesis increases as we increase the light intensity. This tells us that light intensity is the limiting factor at this point. In other words, the rate of photosynthesis is limited by the light intensity.
However, at a certain point, the rate of photosynthesis stops increasing, now light intensity is no longer the limiting factor. Something else must be limiting.
How to Determine the Limiting Factor in Photosynthesis
As we saw in the last lesson, there are three factors that limit photosynthesis. These are the carbon dioxide concentration, the temperature and the amount of chlorophyll in the leaves. We can’t do much to change the amount of chlorophyll but we can change the temperature and the concentration of carbon dioxide.
This shows the same experiment, but with a higher concentration of carbon dioxide. As you can see, when the concentration of carbon dioxide is increased, the rate of photosynthesis increases. This tells us that the concentration of carbon dioxide was the limiting factor.
What is the limiting factor this time?
Well, if we increase the concentration of carbon dioxide one more time, we get this graph
As you can see, the rate of photosynthesis hasn’t changed so carbon dioxide concentration was no longer the limiting factor in this case. That’s because at the higher concentration, there was plenty of carbon dioxide available.
What happen if we now increases the temperature?
Well, here’s a graph and as you can see, at the higher temperature, the rate of photosynthesis has increased. That tells us that temperature was the limiting factor.
However, as we said in the last lesson, if we increase the temperature too much then the enzymes in the leaf will start to denature and the rate of photosynthesis will fall.
As we’ve seen, light intensity, carbon dioxide concentration and temperature can all act as limiting factors.
How Greenhouses are used to Increase the Rate of Photosynthesis .
The idea of limiting factor can be exploited to increase the rate of photosynthesis and to do that we use a greenhouse like this one
Farmers want to increase the rate of photosynthesis as this increases the yield of crops they produce. To do this, farmers light and heat their greenhouses. They also add extra carbon dioxide. The extra cost has to be justified by the increase in yield. Some gardeners use oil burners as these release heat and carbon dioxide at the same time.
Lesson 3 : Respiration
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe what happens in aerobic and anaerobic respiration.
Respiration
Energy is really important in Biology for example we need energy for movement.
Humans and other mammals need energy to keep warm.
We need energy for chemical reactions to build larger molecules for example, proteins are made by chemically joining amino acids.
Cellular Respiration
The energy we need is supplied by a process called cellular respiration, but we normally just call this respiration for short. Respiration is an exothermic reaction because it releases energy and this takes place continually in all living cells.
Types of Respiration
There are two different types of respiration and you need to be able to compare them.
Aerobic Respiration
glucose + oxygen carbon dioxide + water
energy
C6H12O6 + O2 CO2 + H2O
In aerobic respiration, the sugar glucose is reacted with oxygen gas. This produces carbon dioxide and water and releases energy. This shows the word equation and chemical equation for aerobic respiration and its essential that you learn this for your exam.
Now, one key fact is that aerobic respiration releases a great deal of energy and that’s because the glucose molecule has been fully oxidized and you’ll find out more about oxidation in my capstone learning chemistry book. In the exam you could be asked for the chemical symbols for the molecules in this equation. The symbol for glucose is C6H12O6 and the symbol for oxygen is O2. The symbol for carbon dioxide is CO2 and the symbol for water is H2O. So as we’ve seen, if oxygen is present then cells carry out aerobic respiration. But what if there’s not enough oxygen?
Well, the cells carry out anaerobic respiration. We’re going to look at anaerobic respiration in two different situations and the first is in muscles.
Anaerobic Respiration in Muscles
Muscle cells need a great deal of energy for contraction. Under certain conditions, the amount of oxygen is limited. We’d be looking at those conditions in more detail in the next lesson on exercise.
When there is a shortage of oxygen, muscle cells respire anaerobically and I’m showing you the equation for that here .
Glucose lactic acid
energy
During anaerobic respiration in muscles, glucose is converted to lactic acid and as you can see, anaerobic respiration does not require any oxygen.
Now, one key fact is that anaerobic respiration releases much less energy than aerobic respiration. That’s because in anaerobic respiration, the oxidation of glucose is incomplete and again, it’s important to learn that now. Anaerobic respiration can also take place in plant cells and in yeast cells and I’m showing you that here
Anaerobic Respiration in Plant and Yeast Cells
glucose ethanol + carbon dioxide
energy
As you can see in this reaction, the glucose is converted to ethanol and carbon dioxide and again, no oxygen is needed for this reaction.
In the case of yeast, this reaction is really useful. Anaerobic respiration in yeast cells is called fermentation and we use this reaction to make alcoholic drink such as beer.
The alcohol in these drink is ethanol and that is produced by fermentation. We also use yeast to make bread. In the case of bread, the carbon dioxide produced by fermentation is useful. This creates bubbles in the dough, causing the bread to rise.
Lesson 4 : Exercise
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe what happens in the body during exercise.
• Describe what is meant by oxygen debt
Recap
As we saw in the last lesson, humans need energy for movement, to keep warm and for chemical reaction to build large molecules. All of the energy we need is provided by respiration. As we saw, there were two types of respiration : These are aerobic and anaerobic respiration. When we’re relaxing like the man in this picture, we do not need a great deal of energy and that’s because we are not moving.
During exercise like this, the body needs a great deal of energy for muscle contraction and the body has to react to the increased demand for the energy. Because the body needs more energy, aerobic respiration increases. This means that the body cells require more oxygen.
To provide this extra oxygen, both the breathing rate and the breathing volume increase. In other words, we breathe more frequently and we take deeper breaths. This gets more oxygen into the bloodstream.
The heart rate also increases to pump this oxygenated blood around the body. There’s a big problem here. Sometimes not enough oxygen can be supplied to the muscles, especially if we are exercising hard.
At this point, anaerobic respiration now takes place in the muscles.
Glucose lactic acid
energy
As we saw in the last lesson during anaerobic respiration, the oxidation of glucose is incomplete. This leads to a build – up of the chemical lactic acid. Remember that lactic acid is a waste product produced during anaerobic respiration.
During long period of vigorous activity, the lactic acid causes the muscles to become fatigue. In other words, running fast can lead to a build – up of lactic acid in your muscles, causing cramp. This causes the muscles to stop contracting efficiently.
At this point, the body has to remove the lactic acid from the muscles and this creates a conditions called the oxygen debt.
As we’ve seen during vigorous exercise, anaerobic respiration produces lactic acid in the muscles. The lactic acid is transported out of the muscles by the blood. The lactic acid is then taken to the liver and converted back to glucose in a series of chemical reactions. Reacting with the accumulated lactic acid and removing it from the cells require oxygen.
What is Meant by Oxygen Debt?
The oxygen debt is the amount of extra oxygen the body needs after exercise to deal with the accumulated lactic acid. That is why people continue breathing rapidly for some time after finishing exercise.
Lesson 5 : Metabolism
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe what is meant by metabolism
• Describe how metabolism converts between different molecules.
Recap
In the previous lesson, we saw that respiration is a chemical reaction which releases energy from glucose. The energy released by respiration is used by enzymes to synthesize new molecules in the cell.
Meaning of Metabolism
Metabolism is the sum of all the chemical reactions in a cell or the body.
How Metabolism Molecules Convert Between Different Molecules
Glucose is really important chemical in metabolism. As we’ve seen, energy is released from glucose in respiration. Glucose is also the starting point for many new chemicals for example in the plant cell.
Glucose in Plant
In the plant cell, glucose is converted into cellulose, which strengthen the plant cells wall. Also in plant cells, glucose is converted into starch which is a storage form of glucose and finally again in plant cells, glucose is reacted with nitrate ions to make amino acids and these are then used to synthesize proteins.
In humans and other mammals, glucose is converted to the molecule glycogen. Glycogen is a storage form of glucose.
There are two final reactions in metabolism that we need to look at.
Firstly, one molecule of glycerol is reacted with three molecules of fatty acids to form lipid. We find lipids in the cell membrane. It’s really important that you learn the details of lipid synthesis as it could come up in your exam.
The final reaction of metabolism involves proteins.
Humans do not need to eat a large amount of protein. Excess proteins are broken down into the chemical urea and the urea is then excreted by the Kidneys.
Required Practical 7 : Photosynthesis
Learning Objectives
By the end of this lesson, you should be able to :
• Describe how to investigate the effect of light intensity on the rate of photosynthesis.
• Explain how the results of this are affected by the inverse – square law
How to Investigate the Effect of Light Intensity on the Rate of Photosynthesis
Start by taking a boiling tube and placing it 10cm away from an LED light source. An LED light is used as these do not release very much heat.
Too much heat would change the temperature of the experiment. If we have to use a normal light bulb then we need to place a beaker of water between the light and the boiling tube. This absorbs the heat produced by the bulb.
Now, fill the boiling tube with sodium hydrogen carbonate solution. Sodium hydrogen carbonate solution releases carbon dioxide, which is needed for photosynthesis
Put a piece of pondweed into the boiling tube with the cut end at the top.
Leave this for 5 minutes to acclimatize to the conditions in the boiling tube.
We should see bubbles of gas being produced from the cut end of the pondweed. This gas is oxygen and that is produced by photosynthesis.
Start a stopwatch and count the number of bubbles produced in one minute.
Repeat this two more times and calculate the mean number of bubbles produced in one minute.
Next, we do the whole experiment again from the start but this time at 20c, then we do to 30cm and finally at 40cm.
There are two main problems with this practical.
Firstly, the number of bubbles can be too fast to count accurately.
Secondly, the bubbles are not always the same size so for example large bubble would count the same as a small bubble.
We can solve these problems by measuring the volume of oxygen produced instead of counting bubbles and we use this equipment.
Place the pondweed under a funnel and catch the bubbles in a measuring cylinder.
Then use the measuring cylinder to measure the volume of the oxygen gas produced.
If we plot the mean number bubbles per minute or the volume of oxygen per minute against the distance from the lamp to the pondweed, then we get this graph.
The key point about this is that if we double the distance, then the number of bubbles per minute falls by factor of four. Going from a distance of 10cm to a distance of 20cm causes the number of bubbles per minute to fall by four times and going from 20cm to 40cm the number of bubbles per minute again falls by four times. Scientists call this inverse – square law. The reason for this is that if we double the distance, the light intensity falls by four times. Because we need light for photosynthesis, that also causes the number of oxygen bubbles to fall by four times.
Lesson 6 : Monosaccharides
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe what is meant by a monosaccharides and give examples.
• Describe the structure of glucose.
Biological Molecules (carbohydrates)
In this lesson, we’re going to start looking at a group of biological molecules called carbohydrates.
Carbohydrates are extremely important in Biology. In fact carbohydrates are a major part of the human diet. For example we find sugars such as sucrose in cakes and biscuits … and we find starch in foods such as pasta and rice. Both sugars and starch are examples of carbohydrates.
I’m showing you here the structure of the sugar glucose and as you can see, glucose has a ring shape. The formula of glucose is C6H12O6. All carbohydrates, including glucose contain only the elements carbon, hydrogen and oxygen. Glucose contains six carbon atoms and we can see these here. Sugars with six carbon atoms are called hexose sugars and you need to learn that word.
As you can see, the structure of glucose is fairly complicated.
So scientists usually draw in a simpler form which I’m showing you here. In this diagram we’re not showing the carbon atoms or most of the oxygen and hydrogen atoms. In the exam, you could be asked to draw this structure of glucose so you do need to learn it.
Glucose is a single sugar molecule and scientists call single sugar molecules monosaccharides. Mono means “ one “… and saccharide means “ sugar “
There are a number of different monosaccharides … for example glucose, galactose and fructose and you needs to learn these examples.
Coming up, we’re going to look at a key property of monosaccharides… and what is meant by a pentose monosaccharide.
Properties of Monosaccharides
Okay one key feature of monosaccharides is that they are soluble in water and if we look again at the full structure of glucose we can see why.
Monosaccharide including glucose have a large number of OH groups and scientists call OH groups hydroxyl groups. Hydroxyl groups can form hydrogen bond with water molecules and because of this, monosaccharides are soluble in water. Scientists call molecules like this hydrophilic. Hydrophilic means water loving and hydrophilic molecules all dissolves in water.
We’ve already seen that glucose is a hexose monosaccharides as it contains six carbon atoms.
However, some monosaccharides contain five carbon atoms… and these are called pentose monosaccharide. A good example is ribose.
I’m showing you the simplified structure of ribose here. If you’re following the OCR or Edexcell specs, then you need to learn the structure of ribose. Monosaccharides can be chemically joined to form larger carbohydrates and scientists call these disaccharides and polysaccharides and we’ll be starting to look at those in the next lesson.
Lesson 7 : Disaccharides
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how disaccharides are formed from monosaccharides.
Recap
In the last lesson, we looked at the structure of the monosaccharides glucose and we saw that there are two forms or isomers of glucose and these differ in the position of the hydroxyl group on carbon 1.
In alpha glucose, the carbon 1 hydroxyl points below the plane of the ring whereas in the beta glucose, the carbon 1 hydroxyl points above the plane of the ring. So in this lesson, we’re going to look at disaccharides.
Disaccharides
I’m showing you here two molecules alpha glucose. Now these glucose molecules can react together… and when they do, they form a disaccharides and I’m showing you that here
Disaccharides form when two monosaccharides chemically react together. There are a couple of really important points about this reaction.
Firstly, when we react together two alpha glucose molecules… the disaccharides we make is called maltose and you need to learn that.
Secondly, when we make a disaccharides we also produce a molecule of water. The water molecule is formed from a hydrogen atom from one of the monosaccharides… and a hydroxyl group form the other and we can see that here.
When a reaction forms a water molecule like this… scientists call that a condensation reaction.
Coming up, we’re going to look at what is meant by a glycosidic… and a hydrolysis reaction.
The Glycosidic Bond
We’ve already seen that two molecules of alpha glucose can react to form the disaccharide maltose. As you can see in this reaction, we’ve formed a new chemical bond between the two molecules of alpha glucose. This type of bond is called a glycosidic bond and I’m showing you that here. If I number the carbon atom… we can see that this glycosidic bond is between carbon 1 on one alpha glucose… and carbon 4 on the other. So we call this a 1,4,glycosidic bond. I would recommend that you learn this whole diagram as you could be asked to draw it in your exam.
So as we’ve seen, disaccharides are formed in a condensation reaction… and a molecule of water is produced. Now if we add water to a disaccharide we can break the glycosidic bond. This converts the disaccharides back to the original monosaccharides and this is called a hydrolysis reaction. In cells this reaction is normally carried out by enzymes.
Sucrose = glucose + fructose
Lactose = glucose + galactose
As well as maltose, there are two other disaccharides that you need to learn.
The disaccharide sucrose is formed from monosaccharides glucose and fructose and the disaccharide lactose is formed from the monosaccharides glucose and galactose.
Lesson 8 : Testing for Reducing and Non – Reducing sugars
Learning Objectives
By the end of this lesson, learners should be able to :
• Describe how to test for the presence of reducing sugars and non reducing sugars.
Recap
In previous lessons, we looked at monosaccharides and disaccharides. Remember that monosaccharides consists of a single sugar molecule and a good example is glucose. Disaccharides consists of two sugar molecules… joined by a glycosidic bond. Examples of disaccharides include maltose, lactose and sucrose.
One key idea that you need to understand is that we can divide all sugars into two categories. These are reducing sugars and non - reducing sugars.
Reducing sugars can donate an electron to another molecules and you need to learn this definition. All monosaccharides are reducing sugars. Some disaccharides are also reducing sugars… for example maltose and fructose.
However, some disaccharides are non- reducing sugars… for example sucrose.
In this lesson, we’re looking at how to test for reducing and non reducing sugars and we’re going start to look at testing for reducing sugars first. Remember that safety goggles should be worn throughout this experiment. We are going to assume that we are testing different foods.
Just like the other food tests that we saw in the last lesson… we start by grinding up the food with distilled water… and
filtering away the solid food particles..
Testing for Reducing Sugars
We then place 3cm3 of our food solution into a boiling tube… and add 3cm3 of Benedict’s solution like this
Benedict’s solution contains the copper ion Cu2+ … which makes the solution blue.
We then place the boiling tube into a beaker of boiling water… and leaves this for five minutes. If the solution remains blue then there’s no reducing sugar present.
However, if a reducing sugar is present… then this adds an electron to the copper 2+ ion… and this forms a red precipitate. This now form the copper 1+ ion… and this forms a red precipitate.
If there is only a very small amount of reducing sugar… then only a very small amount of red precipitate forms and this causes the Benedict’s solution to appear green.
If more reducing sugar is present then the colour turns yellow.
A high level of reducing sugar produces an orange colour. If a lot of reducing sugar is present, then we see a brick-red colour like this .
One thing that you need to remember is that the Benedict’s test… only gives us a very approximate idea of the amount of reducing sugar. That’s because the Benedict’s test only shows a narrow range of colour changes… and all humans perceive colours slightly differently.
Scientists say that the Benedict’s test is semi quantitative.
Coming up, we’ll look at the test for non reducing sugars.
Testing for Non-reducing Sugars
In the last section we saw that all monosaccharides are reducing sugars… but some disaccharides are non – reducing for example sucrose.
Remember that sucrose contains the monosaccharides glucose and fructose… joined by glycosidic bond.
How do we test for non – reducing sugars like sucrose?
The first thing you need to understand… is that we cannot test for non – reducing sugar directly. Instead, we need to break the glycosidic bond… releasing the monosaccharides. Because all monosaccharides are reducing sugars… we can now test for them using Benedict’s solution.
Imagine we have a solution… and we want to see if it contains a non – reducing sugar such as sucrose. The first thing we need to do is check to see if the solution also contains any reducing sugar. If it does, we will need to take that into account later.
First, we take a small amount of our unknown solution and carry out the Benedict’s test. We need to note down any colour change that takes place
Next we take a fresh boiling tube and add 3cm3 of our unknown solution.
We then add 3cm3 of dilute hydrochloric acids… and gently boil the solution in a water bath for five minutes.
If a non – reducing sugar is present, then the acid hydrolyses the glycosidic bond… releasing the monosaccharides.
Next we add 3cm3 of a dilute alkali… such as sodium hydroxide solution. Then use pH paper to check that our solution is alkaline. That’s because the Benedict’s test cannot work under acidic conditions.
Finally, we add 3cm3 of Benedict’s solution… and then heat in boiling water for five minutes. Again note down the colour change.
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Sample Results
Let look at some sample results and work out what they mean.
Our first Benedict’s test is negative. In other words the colour remains blue.
This tells us that solution does not contain a reducing sugar.
The second Benedict’s test produced an orange colour. This tells us that the solution contains a non – reducing sugar.
Here’s a different solution. The first Benedict’s test produced a green colour. This tells us that a very small amount of reducing sugar is present.
The second Benedict’s test produced a red colour. This tells us that a non – reducing sugar is also present.
Here’s our final solution. In this case, the first Benedict’s test produced a red colour. This tells us that the solution contains a large amount of reducing sugar. In this case, we cannot test for a non – reducing sugar and that’s because even if non – reducing sugar was present… we would not be able to see a colour change beyond red.
So as you can see, we can only test for a non – reducing sugar… if there is either no reducing sugar present or only a very small amount.
Hopefully now you can describe how to test for a reducing sugar and a non – reducing sugar.
Remember you’ll find plenty of questions on all the lessons in my capstone Learning Biology workbook and you can get that by placing order (capstonelearning9@gmail.com or call 08071228071, 08039542966, 08030534776).
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