• Improve Tuition
  • Improve Tuition
  • Improve Tuition
  • Improve Tuition
  • Improve Tuition


Fill in your details and we
will get back to you shortly

 Book a trial session enquiry

BIOLOGY – 14 to 16 years

Diet and exercise                                                                                                                                       3

Nerves and Hormones                                                                                                                           5

Defense against infection                                                                                                             11

Drugs                                                                                                                                                                  13

Carbon cycle                                                                                                                                               16

Energy and biomass in food chains                                                                                       18

Interdependence and Adaptation                                                                                        23

Evolution                                                                                                                                                       26

DNA and Genetics                                                                                                                                    28

Cells                                                                                                                                                                    33

Enzymes                                                                                                                                                            38

Respiration                                                                                                                                                  43

Photosynthesis                                                                                                                                        45

Genetic diagrams                                                                                                                                   50

Cell division                                                                                                                                                 52

Stem cells                                                                                                                                                      56

Fossils and extinction                                                                                                                       57

Osmosis                                                                                                                                                              59

Gas and solute exchange                                                                                                                61

The human gas exchange system                                                                                            63

The circulatory system                                                                                                                  65

Homeostasis                                                                                                                                                68

Blood glucose                                                                                                                                            70

Humans and the Environment                                                                                                   71

Climate change                                                                                                                                        73

Biofuels                                                                                                                                                            74

Food production                                                                                                                                     76

Diet and exercise

Our diet consists of many different components. These components have different functions within the body and an unbalced diet can lead to a lack of on component, which can lead to a disease

This table provides information about the different nutrients the body requires

Nutrients Use in the body Source
Carbohydrates To provide energy for the body, acts as a short term energy supply Bread, pasta and potatoes
Proteins Helps build muscle for growth and repair Meat, eggs and dairy products
Lipids (fats and oils) Provides energy and also a long term energy supply Butter and oil
Minerals Needed to maintain health Milk provides calcium and meat provides iron
Vitamins Needed to maintain health Fruit and vegetable
Dietary Fibre To help move food through the gut Whole wheat products, fruit and vegetables
Water Needed for cells Water

In our diet we require different vitamins as they all have different functions within our body.

Vitamin C  – this vitamin is required help heal injuries on the outside or on the inside of the body. Vitamin C is found in fruits such as oranges and lemons. It can also be found in green vegetables such as spinach and broccoli.

A lack of vitamin C can lead to a disease called scurvy, first noticed when sailors went to sea and did not have fruit or vegetable. This causes a loss of teeth, swelling and bleeding in the gums and joint pains.

Vitamin D  –   This vitamin is required to help the bones grow. It is mainly sourced from sunlight but can also be found in foods such as fish and eggs. A lack of vitamin D will lead to sore bones and a disease called rickets

Vitamin A  – This is required to help maintain good vision. A good source of vitamin A is eggs are other dairy products. A lack of vitamin A can lead to night blindness ,which is an inability to see in dim light.

In our diet we also require minerals, which also come from a variety of sources.

Calcium  – calcium is very important in the formation of bones and teeth. Calcium can be found in eggs and dairy products such as cheese and milk. A lack of calcium will lead to weak bones and teeth

Iron – iron is required to help form hemoglobin, which is a key component within our blood. Hemoglobin is required to carry oxygen from our lungs to the rest of the body.

A lack of iron will lead to a disease called anemia, of which symptoms include tiredness and feeling weak.

Iron can be found in red meats and green leafy vegetables

Balanced diet

When we eat we have to make sure we get the correct amounts of each component. The government recommends a carbohydrate, fruit and vegetable all make two thirds of our diets.  The last thirds is made up of protein dairy and fats.

The energy requirements of a person differ depending on these three factors

Daily activity

When trying to assess how many calories you should be consuming, you should always look at the side of food packets, as all the nutritional information will be displayed

For example, a man should be aiming for approximately 2600kcal per day and a women 2200kcal per day

However complications can occur when you consume to may calories than you burn or you consume less calories than you burn. This can lead to either an overweight or underweight body.

The calories you consume must be consumed from all the nutrients mentioned above, thus leading to a balanced diet.

Food additives

Some foods may contain additives. These additives have a number of functions.

They may be used for :

Colouring – to make the food a different colour
Flavoring – to enhance the flavor of the food
Sweetener – to make the food sweeter
Preservative – to make the food last longer
Antioxidant – prevents reactions going on in the food that may make it go off.

Nerves and Hormones

Nervous system

The human nervous system consists of two parts

The central nervous system is the main control centers like the brain and the spinal chord

The peripheral nervous system consists of nerves, which reach the rest of the body which is also known as the periphery

Nerve cell

Nerve cells can also be called neurons and carry messages known as impulses

Nerves carry the impulse through the body and then the nerve is sent to the rest of the body through the dendrites which have many other nerves attached to it.

There are two types of neurons sensory and motor neurons

Sensory neurons are involved in relaying the impulses from the point of impact or otherwise known as the receptors to the central nervous system

The central nervous system then decides what action to take, and it then send another set of impulses through a set of motor neurons to the effector


Receptors are a group of cells, which help to detect a change in the environment for example, your skin will detect if the temperature change around you.

Your skin can also detect pain and it will be send an impulse to the CNS  which will then respond to move you body part away from pain.

Your eyes will respond to the light by either dilating or constricting


Effectors are parts of the body that respond to what the receptor has felt. This can come in the form of a muscle contracting or a gland releasing a hormone or saliva.

The effector will then stimulate a response.

Reflex actions

A reflex action is the way the body quickly reacts to dangerous situations. It follows a sequence which does not involve the brain

This nerve action is called the reflex arc

The reflex arc process –

The receptor detects the stimulus
Sensory neurons send the impulse to the spinal chord
The spinal chord sends an impulse via the motor neurone
The effector then responds

The synapse

Where two neurons join together, there is usually a tiny gap called a synapse. the impulse crosses this gap in the for of chemical messengers called neurotransmitters. These diffuse across the gap and continue the synapse


The conditions in our body are carefully controlled by hormones, to ensure that everything is constant and our body functions efficiently.

There are several aspects of our body that need to be controlled. Body temperature needs to be controlled to ensure that the enzymes can work efficiently

Blood sugar levels need to be controlled to ensure the brain has the correct levels of glucose

Water content also needs to controlled to ensure our cells have the correct amount of water. Too much water can cause cells to burst and too little will cause cells to shrink.

Hormones use a system called negative feedback, which allows them to maintain the conditions at just the right level.

One of the main hormones in the body is insulin. Glucose levels are regulated in the body by insulin which ensures that the levels do  not get too high or too low. Insulin is produced by the pancreas.

Action of insulin

Low glucose High glucose
Insulin level low high
Effect on liver Does not convert glucose into glycogen
Converts glucose into glycogen

Effect on blood glucose level increases decreases

Insulin in the presence of high glucose causes the liver to convert glucose into a molecule called glycogen, which is used for storage

When there is no insulin, and there are low levels of glucose in the blood, molecule called glycogen is converted into glucose.

When insulin does not work properly this can cause diabetes. Diabetes is a condition where the blood glucose level remains high..There are two types of diabetes

Type 1 diabetes is when there is a complete lack of insulin. The insulin is not produced in the body, this is usually due to a genetic defect from birth

Type 2 diabetes is when there is plenty of insulin but it is not working properly, as the person has become resistant to it.

The menstrual cycle

The menstrual cycle is a cycle of approximately 28 days. It is process in which the uterus lining builds up in anticipation of the arrival of an egg. If the egg is not fertilized, the uterus is shed and released in blood through the vagina.

Hormones play a key part within the menstrual cycle.

FSH  –   it is produced in the pituitary gland and it causes the egg to mature and causes the ovaries to release oestrogen

Oestrogen- it stops FSH from being releases and causes the uterus lining to thicken. Also stimulates the pituitary gland to release LH

LH – causes the egg to be releases on day 14

Progesterone – it helps to maintain the lining of the uterus for the rest of the menstrual cycle, if fertilization occurs then progesterone levels remain high, if not then the progesterone levels fall and the uterus lining breaks down.

Control in plants

Plants are sensitive to light, moisture and gravity. Therefore when a plant grows it will try to grow towards the light, and towards water. Sometimes gravity can help the plant achieve this.

Plants growing with the light are known as phototropism, whereas a plant growing with gravity is called geotropism.

Different part of the plant will respond to different things. The stem will respond to light but will not respond to gravity. Therefore this is knows as positive phototropism and negative geotropism

The root of the plant is the opposite of the stem. It responds to gravity but does not respond to light, as it is underground.  Therefore it is knows as a positive geotropism and negative geotropism


Auxins are a group of hormones that are only present in plants. They are mostly present in the tips of the stems and roots. The auxins help certain grow more and faster.

The auxins present in the stems help it grow faster, the auxins present in the roots causes a decrease in growth rate.

If a plant was growing the side that is not facing the sun will have more auxin and therefore grow more causing it to bend towards the sun. This is highlighted in the picture

In roots the auxins causes less growth upwards and causes it to bend down in the direction of gravity therefore the roots can get further into the ground.

Defense against infection

Bacteria and viruses cause infections and diseases. When they enter your body they can damage cells and can also cause death of cells.


Bacteria are microorganisms that cause disease when they enter the body, they are very small organisms and cause a variety of illnesses such as food poising, cholera and whooping cough


Viruses are smaller than bacteria, but are potentially more harmful. Once viruses enter the body they cannot survive by themselves, therefore they invade cells and reproduce within the cell. Once they make thousands of copies the cell will burst releasing the copies of the virus into the blood stream and around the body.

The most common illnesses causes by viruses are influenza (the common flu), chicken pox and HIV

Defending against infection

Our body have several ways of protecting us from diseases, one of the first barriers to disease is our skin. This is the external barrier. This is why when we cut our skin we are at risk to developing more infections

Our internal protection are cells known as white blood cells.

White blood cells engulf the bacteria and viruses and destroy. They can produce antibodies and antitoxins which help to destroy the bacteria and viruses.

White blood cells

White blood cells can be divided into different groups as they have different functions

Phagocytes are the initial molecule released into the blood stream to tackle the pathogens. The phagocytes ingest the bacteria or virus and then destroy it, or the release antibodies specific to the bacteria.

Once the phagocyte has identified the bacteria, it send a chemical message to release an army of lymphocytes which have developed specific antibodies to fight the bacteria.

The lymphocytes works in different ways

They bind to the pathogens and will destroy them
They cause the pathogens to stick together so they can be easily destroyed by the phagocytes
They bind to the pathogen and release chemical signals to call the phagocytes


A vaccination is a kind of medication given to people to ensure that certain diseases do not affect people.

Vaccinations work by injecting a small amount of a bacteria into your body, so pathogens can produce lymphocytes, which are specific to that pathogen.  Therefore the next time that pathogen enters the body, we are already prepared to fight the infection.


A bacteria strain can develop a resistance to a certain antibiotic. Resistance occurs when the bacteria undergoes a random mutation which allows it to survive against the antibiotic. Because it has a random mutation not only does it survive it can also reproduce.


a drug is a chemical substance that alters the working of the human body, this can come in the form of medication which alters the body in a positive way, or a recreational drug which will alter the body in a negative way

there are many different types of drugs

Type of drug Effect on body Example
Painkiller It blocks nervous impulses sent from the brain to stop pain being felt paracetamol
Performance enhancer Helps you perform better in sport by improving your muscle strength Anabolic steroids
Depressant Slows down brain activity alcohol
Stimulant Activates nervous impulses and increases brain activity Caffeine
Hallucinogenic  Alters you brain activity and makes you things that aren’t really there LSD

Stimulants and depressants work on the chemical messengers known as the neurotransmitters, which travel between the neurons in the space called synapses.

By altering the neurotransmitters it affects how fast the impulse can travel around the body

Stimulants will increase the amount of neurotransmitters present where as depressants stop neurotransmitters from binding to the next neurone

Classification of drugs

There are certain drugs which are legal and other drugs which are illegal. Most drugs used for medication purposes are legal but have to be prescribed from the doctor to prevent misuse.

Illegal drugs are classed from A to C. Class A drugs are the most dangerous and come with the highest penalty in the face of the law.

Before drugs can be releases on the maket they have to be tested to ensure there are no side effects and to make sure that they work.

There are three stages of testing

First they are tested in lab and tests are completed on a computer to ensure they can move onto the next stage

The next stage of testing is moving onto animals. They test on animals to ensure that there are no side effects and to ensure the drug actually works on a small scale

The final stage is testing on human volunteers. This stage is usually called clinical trials. They initially test on healthy volunteers then move on to those affected by the disease

Clinical trials

In clinical trials the tests are usually carried out in two groups. The first group is given the new drug and the second group is either given the old drug or a placebo. The placebo is a something that looks like a drug but is not. They are split into two groups to ensure that they can compare the results

Sometimes these trials are carried out in different ways.

Blind trials – these are trials where the volunteers do not know whether they are receiving the drug or not.

Double bind trials – these trials are when both the volunteers and the scientist do not know who is receiving the drug or the placebo


Antibiotics are a form of drug which work by slowing down the growth of bacteria

A scientist called alexander Fleming who accidently discovered it when he left bacteria in a petri dish first discovered antibiotics in 1928.

There have been many different antibiotics been developed since as many bacteria have developed a resistance towards a certain bacteria


Cigarettes have a substance called tobacco, which is very harmful to our health. Smoking can cause many different diseases due to the substances it contains. It contains a substance called nicotine which makes cigarettes very addictive.

It also contains carbon monoxide which combines with heamoglobin and prevents oxygen entering red blood cells, this places extra pressure on the heart to pump more blood around the body which can cause heart attacks and stroke

It also contains tar which can cause many different kinds of cancer


Alcohol is also a drug as it alters with the function of the body. However alcohol is deemed to be socially acceptable in regulated amount. Alcohol is a depressant as it slows down and stops signals in the brain and neurons.

The liver is a key organ is removing alcohol from the bloodstream, consuming too much alcohol can have several short term effect such as:

A lack of judgement
Loss of balance
Slurred speech
Blurred vision

There are also many long term effects such as damage to the liver and the brain. Consuming too much alcohol for long periods of time can lead to liver damage and thus preventing alcohol from being removed from the blood stream

Carbon cycle

The carbon cycle highlights how carbon moves from one organism in different forms

1 – Carbon is present in the atmosphere in the form of carbon dioxide. Carbon dioxide enters the atmosphere when organisms respire and release carbon dioxide

2 – Producers take up carbon in the form of carbon dioxide through the process of photosynthesis. The carbon is then stored in the plant in the form of glucose or other carbon based molecules such as protein or fats

3- Once the produces are eaten by the consumers the carbon stored in the producers in the form of glucose

4 – The consumers will die and are then decomposed by decomposers. This process is known as decay, which will occur faster in warmer and moist conditions and slower in cooler dry conditions

5 – Thedecomposers then respire and release carbon in the form of carbon dioxide back into the atmosphere


Decay is the process of recycling the elements back to the start of the food chain. As all living things are made of materials such as carbon, oxygen, nitrogen. These molecules are then converted into other molecules for storage

Before the organisms die, these materials are then returned through waste products, which are broken down by microorganisms.

Microorganism also breaks down organisms, when they die therefore ensuring all the molecules return back either into the soil or into the air

Microorganisms also work best when the conditions are warm and moist, as the enzymes work quicker in hotter conditions and the moist environment provides the organisms with the nutrients to survive.

All the important elements such as carbon are recycled so they can be put back into the soil and be used by plants and enter the food chain again

Energy and biomass in food chains

Food chains show how energy is transferred from one organism to the next.  The food chain starts with a producer usually a plant who can produce its own energy using the light from the sun

The producer is then eaten by the primary consumer, then the secondary consumer and so on.

The arrows in a food chain show in which direction the energy is moving

Producers in this case, the grass can make the energy through the process of photosynthesis.  The primary consumer usually only eats plants and can also be referred to as a herbivore

The secondary consumer will eat the primary consumer, so because it eats other animals it can be referred to as a carnivore.

Food webs

Food webs are a series of interconnected food chains, they can be complicated to look at but if you break them down they can be very simple.

An example of a food web can be seen below

The food web can be split up into five simple food chains

From the food web we can deduce that the grass is the producer.

The mouse, grasshoppers and rabbits are the primary consumer

The snake and lizards are secondary consumer and the hawk is the tertiary consumer (it is also a secondary consumer)


Food webs also demonstrate his level of competition within organisms. For example the mouse, grasshopper and the rabbit are all competing for the grass, if one organism eats more then there is less for the others.

Animals and plants also compete for water, space and habitats in order to survive

In a food web, changes in a population of certain organisms can impact the rest of the food web.  A major example is if the population of grass dramatically decreased, that would mean less food for the primary consumers and thus the population of the primary consumers will decrease and this will affect the secondary consumers and the tertiary consumers also. This process is known as interdependence

Pyramids of number

The pyramid of numbers highlights how many organisms are present at each level. Each level is called a trophic level. As we move up each trophic level the energy is lost. Energy is lost to the surroundings in a number of ways. The most common way of energy loss is through movement. As organisms move they consume energy and therefore less is passed on. Also as organisms respire energy is lost to the environment in the form of heat.

The pyramid illustrates how there is a lot of grass and it is eaten by many grasshoppers. There are less snakes but they eat more grasshoppers and the same applies to the eagles.

However all pyramids are not symmetrical and can come in other shapes

This pyramid highlights how there is only one tree but there are many insects feeding off it. The insect is the primary consumer. The bird is the secondary consumer; there are less birds however they eat more insects.

Pyramids of biomass

Pyramids of biomass highlight how much dry massthere is at each trophic level. The dry mass of an organisms is the mass present when all the water has been removed.

Even in pyramids of biomass energy is lost as you move up each trophic level

Energy is lost in a number of ways

It is lost as heat energy through movement
In certain animals, energy is used to maintain body temperature
It is also lost in processes such as respiration and photosynthesis
It is also lost in feces

Interdependence and Adaptation

Above are some key terms, which will help you understand this topic


Each organism is adapted to its environment. A key example of this, is how a polar bear is adapted to the cold environment it lives in

They have thick layers of fat and fur to help them keep warm in the old months. The fat and fur act as layers of insulation

Adapting to hot climates is completely different, if we have a look at a camel as an example.

Plants also adapt to the extremely warm conditions. Plants like cacti have spines instead of leaves, which reduce surface area, so reduce water loss. The also have very large roots which help them get as much water as possible.

The stems in cacti have adapted in such a way that they can store water for long periods of time



Evolution is the theory that organisms change over time. They change to adapt to their surroundings and ultimately they change to survive. This is where the term “Survival of the fittest” come in. Survival of the fittest is the process of natural selection where the ones that were the most adapted to a particular environment survived and those that were not, died.

Charles Darwin created the theory of evolution. Darwin studied plants and animals for nearly 30 years. He then wrote his ideas in his book, origin of species.

The theory of evolution also highlighted that in some way shape or form all organisms are related.

It illustrated that species with similar characteristics are often related for example chimpanzees and humans. These characteristics mean the two organisms often look alike and behave in similar ways.

Sometimes tow organisms may look alike but may be from completely different ancestors. An example for this is sharks and dolphins, which look alike but are not related.  Evolutionary trees highlight this

Dolphins have a similar ancestor to the whale but only have a far ancestor to the shark

Natural selection

Natural selection occurs due to a series of steps

Organisms show a wide range of variation due to the genes they possess
These genes allow them to survive in particular environments, because they survive they are able to pass on their genes
The genes passed on to the offspring also allows them to survive
Those without the genes are not able to compete for food or shelter and will soon die
Over time only certain individuals within a species will exist as they evolve and out compete others

Not everyone agreed with Darwin and many scientists had different views. A key viewpoint was that of Lamarck’s. Lamarck argued that the characteristics used a lot by the organisms would then be developed and passed on to the next generation.


Extinction occurs when there are no more individuals left in a particular species

This can occur due to a number of reasons

Disease – a disease which wipes out a whole species
Predator – a new predator which eats all the prey before they can reproduce
A change in the environment – a change in temperature or climate, may reduce the chances of a particular species of surviving
Competition – competition form another species for food and habitats will cause the other species to die out


Biodiversity is having as many species in a particular environment as possible. This ensures that food chains survive and ensures that we protect the variety of living organisms on this earth

Conservation methods are ways of ensuring that levels of certain species remain high. If they become lower than a certain threshold that species is considered endangered.

There are many ways to protect a species, the simplest way is through education, educating the public about a particular species will increase the awareness and help reduce the aspect, which is causing the decline in numbers

Another way is to start breeding programs, which encourage organism to breed, and thus increasing the population of that particular species

DNA and Genetics


Organisms of the same species will have many differences.  This is known as variation. Variation simply occurs due to the different genes we possess. There are two different types of variation, environmental and genetic.

Genetic variation

Genetic variation occurs due to the different genes we get from our parents.  The genes we get from parents are due to random chance so no two offspring will be the same, unless you are a twin!!!

In humans we get half of our genetic information for our mother and half from our father, which is why we look like our parents

The characteristics that are determined by genetics are characteristics such as eye colour, height, blood group

Environmental variation

Environmental variation occurs due to the differences in the environment we live in.  The characteristics influenced by the environment are weight or sometimes even height.

Both determine the majority of your characteristics. A prime example of this is height as this can be determined by your nutrition but also can be determined by genes.

Genes, chromosomes and DNA

In the majority of cells we have a nucleus, within this nucleus we have chromosomes are contain our DNA

In humans we have 23 pairs of chromosomes, one chromosome from each parent. And these chromosomes contain the genetic information on the DNA

The DNA double helix is coiled up to form the arms of the chromosome. A gene is small part of a chromosome, and therefore a small amount of DNA.

There can be different versions of the same gene, these are called alleles. For example for the eye colour gene you can have two different versions, consisting of two different colours.

Sexual reproduction

In sexual reproduction you will always produce genetically different cells.

Sexual reproduction combines a sex cell from the mother and the father. These sex cells are referred to as gametes.

Each gamete only contains 23 chromosomes, which is half a set within humans when these gametes fuse together they will from a full set of 23 pairs of chromosome.

Asexual reproduction

Asexual reproduction produces genetically identical cells. This is because is only involves one parent cell. There is no joining or mixing from two parents.

Within the parent cell there are chromosomes, which are made up of two identical halves. The parent cell will split into to two cells and in each cell will have one half of each chromosome.

Those chromosomes will then replicate to form full pairs and thus creating identical cells to the parent cell.

This method of reproduction is how all plant and animal cells replace lost or dead cells. Whereas bacteria will use this method of reproduction to produce offspring which is why they can reproduce at a quicker rate.


Cloning has been used in animals and plants.

In plants it is a more common method to regrow and reproduce many plants. One of the methods is called cuttings.

Cuttings involve taking a cut piece from a plant and replanting it elsewhere which will genetically reproduce the parent plant.

Another method is tissue culture; this involves taking a few plant cellsand allowing them to grow in a growth medium with hormones. This allows them to grow very quickly in a short space.

Animals can also be cloned using a variety of methods. Farmers use the method of getting a sperm cell from the prized bull and an egg cell from the cow. Once these two cells fuse together from a cluster of cells, they are then separated forming clone cells. These cells are then implanted in other cows until they are ready to give birth. This method is known as embryo transplants.

Another method is adult cell cloning in which an adult egg cell is taken and the nucleus is removed. The nucleus from another adult cell is then taken and added to that egg cell. The egg cell complete with a new set of DNA is then given an electric shock to allow it to divide.

Once the embryo has reached a ball of cells it is then implanted into a female until it gives birth to an identical copy of the adult cell.

This diagram illustrates this

Problems with cloning

Cloning, although it is a quicker way of producing offspring I will reduce the gene pool, making that set of offspring susceptible to disease
Studies of cloning done in the past has shown that especially in adult cell cloning the new born clone often has an old set of genes and will therefore show signs of ageing very quickly
Many people are worried human may be cloned which bring about many issues

Genetic engineering

Genetic engineering is the concept of being able to use enzymes to “cut and paste” genes from one organism to the next.

A key example of this is the use of insulin. In type 1 diabetes some people cannot produce effective insulin. So therefore insulin can be taken from a healthy insulin cells.

They can then be transferred to bacteria, which reproduce quickly and can be used to form drugs.

Genes can also be transferred into plants. In plants it is also very important as it can be used to make plants resistant to certain pests or viruses to ensure that farmers have a  higher yield.

Advantages and disadvantages of genetic engineering


GM crops will help to increase the yield as more plants are likely to survive
People in developing nations will be able to get more food as plants can be engineered to have more nutrients


GM crops will reduce the biodiversity as it will reduce the number of weeds growing
Some people are worried that GM crops may not be safe
There are concerns that the genes for resistance that are in the plants may get transferred to other pests and weeds


All living organisms are made up of cells. Cells are the building blocks of life. Because there are a vast number of cells, some cells are specialized to ensure they provide a specific function.

Specialized cells

Type of Cell Function Special Features
Red Blood cell To carry oxygen in the blood.
Has hemoglobin which carries the oxygen

Has a concave, donut like shape

Does not have a nucleus so it can carry more oxygen

Has a large surface area to allow to carry more oxygen

Nerve Cell Carries nerve impulses (messages) from the body to the brain and back again.
They are long, have many connections so can reach every corner of the body

They carry electrical signals so the impulse is relayed quickly

Egg cell To join with the sperm cell and provide nutrition for the zygote (new cell) when formed. It is large and contains lots of cytoplasm for reaction to take place.
Sperm Cell To reach the egg cell and join.
Has a tail, which allows it to move.

Also has a head to carry genetic information and penetrate the egg cell.

Root Hair Cell To absorb water and minerals. Has a large surface area, which allows it to absorb as much as possible.
Palisade cell (Leaf cell) To absorb sunlight to allow the plant to photosynthesize. Has a large surface area and many chloroplasts, which allow it to absorb as much sunlight as possible.

Animal cells and plant cells

Animal cells have a very irregular shape and often look uneven and unequal however plant cells have a very regular shape. Plant cells and animal cells differ in function due to the different parts they have.

This is highlighted in the diagram below

Cell membrane Outer part of cell, which acts as a barrier controlling what goes in and out Animal and plant cells
Cytoplasm This is where all the reactions occur Animal and plant cells
Nucleus Controls the cell and carries all the genetic information Animal and plant cells
Chloroplast This is where photosynthesis occurs as it contains chloroplasts Plant cells
Vacuole Keeps the cell firm as it contains a liquid call cell sap Plant cells
Cell wall Outer wall which supports the cell ensuring its structure Plant cells
Unicellular organisms

A unicellular organism is one that only has one cell for example bacteria, protozoa and fungi .


Bacteria are very small cells, they differ from normal animal cells as they do not contain a nucleus so the DNA is either floating free or kept in small containers called plasmids they also may have a tail like structure usually called a Flagellumallowing the cell to move.


Protozoa are also unicellular organisms however it has certain characteristics that are similar to animal cells.

It has feet like projections that allow it to move and take food into the cell.


Yeast is commonly used in bread making and making alcohol as it converts sugar into alcohol.

Yeast is similar to plant cells in that, they have cells walls, which means they can absorb sugars.

Cells, tissues, organs and systems

Tissues are a group of cells working together to perform a specific function e.g. muscle, lining the intestines or lungs.

Organs are a group of tissues which work together to perform a larger task e.g. heart, lungs, stomach.

Organ systems are a group of organs working together to perform a task in the body e.g.

Cardiovascular system or the reproductive system.


Diffusion is the movement of particles from one place to another.  Diffusion usually occurs in both gases and liquids, as those particles are free to move around. A common type of diffusion occurs in gases, as one set of gas particles will move from one area to another. The gas particles move from an area of high concentration to an area of low concentration.

This explained in the diagram below.

Cell membranes help with the diffusion process. Cell membranes not only help keep the structure of the cells, but also control what moves in and out. The cell membranes have tiny holes, which allow small particles such as oxygen to pass through, but they do not large particles such as protein to pass through. That is why proteins have to be broken down into smaller articles such as amino acids


A catalyst is a substance that helps to speed up processes without being used up or changed in the reaction

Enzymes have a particular shape which allows them to bind to certain molecules. Each enzyme is unique and only fits the substrate that it is designed to fit.

Enzymes have an active site, which binds to the substrate; the substrate is the molecule being broken down by the enzymes.

This illustration highlights how an enzyme works

Rates of reactions


To make use of food, the food has to be broken down in our gut. Digestion is the process of breaking down large molecules in to smaller molecules, this process is usually aided by enzymes

Digestive enzymes help to break down big molecules into smaller ones. The main digestive enzymes are amylase, protease and lipase.

Amylase helps to convert starch, which is a long chain of glucose into simple sugars. These simple sugars can then be easily absorbed. Amylase is found in three places within the body. It is found in the saliva, the pancreas and the small intestine
Protease helps to convert proteins, which are very large molecules into smaller molecules called amino acids. These protease enzymes are found in the pancreas, small intestine and the stomach
Lipase helps to convert lipids into two molecules called glycerol and fatty acids. Lipase is only found in two places the pancreas and the small intestine.

The body also has another way of dealing with the lipids that enter the body. Bile is produced by the liver and stored in the gall bladder. Bile is a substance which helps to break down fat into tiny droplets. This process is called emulsification. This gives the fat droplets a larger surface area and therefore easier for the lipase enzyme to break them down.

Uses of enzymes

Enzymes also have other uses. Enzymes are used in the washing up process. Enzymes can be used as biological detergents.  They are used to break down any lipids or fats present in the stains on the clothes and thus help to clean the clothes.

They can also be used to change foods. In baby foods protease enzymes are used to break down some proteins so it is pre-digested and easier for the bay to digest

Enzymes can also be used in industry to help speed up certain reactions. There are many advantages to using them in industry but also many disadvantages.

The advantages are that the enzymes are very specific and help to lower cost and save energy.
However the disadvantages are that a small change in conditions can cause the enzymes to denature and enzymes are very expensive to produce


All living cells need energy to stay alive.  Respiration is a chemical reaction that occurs in all living cells to produce energy.

There are two types of respiration:

Aerobic respiration

Aerobic respiration can only occur in the presence of oxygen.

Oxygen taken in from the air combines with the glucose take from food. The two combined produce carbon dioxide, water and energy is released as well.

Respiration occurs in a part of the cell called the mitochondria

There are many uses for the energy released from respiration.

It is used to build larger molecules from smaller molecules. An example of this is making protein from amino acids
In animals the energy used from respiration can be used for movement. For the muscles to contract energy is required
In mammals and birds, those animals who are considered to be warm blooded, require the energy produced from respiration to maintain a constant body temperature
In plants, the energy is required to build larger molecules such as starch, proteins and nitrates

Anaerobic respiration

Anaerobic respiration occurs when there is not enough oxygen.  In humans a common situation is during exercise when the oxygen supply is less than the demand from the cells. Therefore the cells have to use anaerobic respiration to get the energy.  However you do not get the same products. Anaerobic respiration produces a substance called lactic acid.

Anaerobic respiration can also be used to make alcohol.  This reaction occurs in microorganisms such as bacteria and yeast, which use glucose to form carbon dioxide and ethanol.  This process is known as fermentation

Oxygen debt

The process of anaerobic respiration can lead to oxygen debt. Oxygen debt is when the amount of oxygen entering the body is less than required by the muscles. Therefore your heart, lungs, and blood cannot keep up with the demand.

Therefore after you stop doing the exercise you will keep breathing heavily to ensure that enough oxygen enters the system to enter the muscles and to ensure all the harmful lactate and carbon dioxide.


Photosynthesis is the process required by plants to produce energy. The process involves absorbing the sunlight and making energy.

Photosynthesis is a very important process in maintaining the levels of oxygen and carbon dioxide

Photosynthesis takes place in plants cells in small subunits called chloroplasts which contain a small green pigment called chlorophyll

These green pigments help to absorb light and convert light into energy which can be used by the plant

Adaptations of a leaf

Leaves are made of different components

The leaf has a mesophyll layer where most of the photosynthesis occurs
It has xylem and phloem which help to transport the substances around the plant
It also contains epidermal tissue which covers the whole leaf

Taking these graphs into account, you can artificially control the environments for plants.  This can be done in a number of ways:

A greenhouse can be used to trap the suns heat in order to make sure that the temperature is no longer the limiting factor
To make sure light is not the limiting factor, artificial lights can used to ensure photosynthesis occurs
Carbon dioxide can also be an issue, however this can be slved using a paraffin heater which provides carbon dioxide


A leaf has many parts. The top of the leaf is known as the waxy cuticle, which protects the leaf and prevents water loss.

The upper part of the leaf is where the sunlight hits. Therefore the upper part of the leaf has many palisade cells (for photosynthesis). These palisade cells have many chloroplasts and look like the plant cell drawn above.

Carbon Dioxide

Carbon dioxide enters the plant through small pores in the leaves called stomata. Guard cells control these pores and help maintain the conditions within the plant and help it adapt to the conditions outside for example weather.

The lower part of the leaf cell is called the spongy layer. It has many gaps, which allows the carbon dioxide to move around and reach other cells.


Water is absorbed from the ground. The roots have root hair cells, which are adapted to getting the maximum amount of water from the ground. There are long and thin , which allows them to reach the maximum area, also they have very thin walls thus reducing the diffusion distance for water.

The rate of photosynthesis

The rate that photosynthesis occurs is dependent on a variety of conditions. By looking at the equation you would guess that a plant would need a large amount of water and carbon dioxide for the highest rate of photosynthesis to occur.

There are also other variables to take into account such as temperature and sunlight.  If any of these are lacking then it is called a limiting factor

The limiting factor also depends on the environmental conditions:

At night the obvious limiting factor is sunlight
In the winter months it is temperature
And in the summer months, when it is warm and bright, carbon dioxide can be the limiting factor

Rate limiting graphs

Taking these graphs into account, you can artificially control the environments for plants.  This can be done in a number of ways:

A greenhouse can be used to trap the suns heat in order to make sure that the temperature is no longer the limiting factor
To make sure light is not the limiting factor, artificial lights can used to ensure photosynthesis occurs
Carbon dioxide can also be an issue, however this can be slved using a paraffin heater which provides carbon dioxide

How do plants use the glucose

Once photosynthesis is complete plants use glucose in a number of ways

Respiration – it is used in respiration to produce energy
Cell walls – glucose can also be used in making cell walls in a plant, especially one that has a fast growth rate
Protein – glucose can be turned into protein.
Seeds – glucose can be turned into fatty substances called lipids which are then stored in seeds
Starch – the glucose if not used can be stored as starch, and can be used when
the rate of photosynthesis is low. Starch is insoluble which makes it better for storage

Genetic diagrams

Genetic diagrams can be used to show the several possibilities that may occur within the genes of the offspring.

The initial pioneer of genetic experiments was a scientist called Gregor Mendel who performed experiments on pea plants in the 19th century.

He investigated the height of pea plants. The first experiment included tall pea plants and dwarfed pea plants. He crossed the two types and observed the offspring. He found that all the offspring were tall pea plants.

This is illustrated in the genetic diagram below

A capital T highlights the tall pea plant and a lower case t highlights a dwarfed pea plant

He then crossed the offspring and found that the results were slightly different

When looking at the genetic diagrams and when answering exam questions it is important to know the correct terminology when describing the offspring genetic information.

Allele is a term used to describe different versions of the same genes. For example for the eye colour gene, different colours would be alleles as they all determine the same characteristic.

If an organism has two alleles, which are the same, then it is known as homozygous, if there are different then it is heterozygous

When considering the diagram, if the dominant allele is present once, then it is heterozygous dominant, it is present twice, it is called homozygous dominant. This is also true of the recessive allele.

Genetic diagrams are particularly useful in determining the possibility of the child getting a disease from the parent. The parent can either be infected by the disease or can be a carrier.

A carrier is someone who is heterozygous, meaning they have both alleles; lucky for them the one that causes the disease is a recessive one so they are not affected.

Cell division

For organisms to survive, cell division has to occur, to ensure that the organism can grow and replace any lost cells.

There are two types of cell division, mitosis and meiosis.


Mitosis is performed when a cell is required to produce two identical offspring.  Cells usually have two copies of chromosomes within the nucleus.

Mitosis is the process of splitting one cells to produce two identical copies

Mitosis is primarily used in a sexual reproduction, this type of reproduction has no variation and is mainly used in plants and bacteria.


Meiosis produce cells which have half the number of chromosomes and are not exactly the same.

Meiosis only occurs in reproductive organs where the products have to be genetically different

X and Y chromosomes

In the human body we have 23 pairs of chromosomes, however the 23rd pair is responsible for our gender. It either comes in the form of XX or XY. XY determines a male and XX determines a female

Genetic diagrams show the possibility of what gender the gamete will be. As the sperm will be carrying an X and a Y, and the female egg cell will be carrying a X and a X.

When the sperm and egg fuse together there is a 50% chance of either combination forming as shown below

Shown above is a genetic diagram. The first set of genes are the parents and then they are split up in the next row to highlight the possible combinations, and in the final set those are the possible combinations of gametes. Note that only one of these combinations will actually happen.

Stem cells

Stem cells are cells that can turn into cells. The scientific term for this is undifferentiated.  Differentiated cells have already become specialized and will now carry out a certain job within the body.

In animals the ability to stay undifferentiated is lost at an early stage therefore it is very difficult to gain stem cells as they specialize very early in the process.

The majority of stem cells are found in embryos, they are of much use in the medical context as they can be used to cure many diseases and organ defects as the stem cells have the possibility to form any other cell.

Adults also have stem cells, they are only found in the bone marrow, and however they are not as useful as the stem cells found in the embryos as they do not have the ability to form any cell on certain ones

Stem cell research

As we have started stem cells can be used to cure many diseases, this is due to its ability to form other cells in the human body. These cells that may have been affected or destroyed by diseases.

Scientists can extracts stem cells from embryos and then use them in replacing faulty cells in those with diseases such as sickle cell anemia or diabetes.

There is a lot of debate around the use of stem cell research; many people feel embryos should not be used for research as each one is human life.

Other believe that helping and curing people is the most important thing, and as embryos cannot consent either way, and would be discarded anyway, it is okay to use them as part of the research

Due to this debate in many countries stem cell research is banned, in the UK it is allowed to a certain extent

Fossils and extinction

How are fossils formed

Fossils are the remains of animals and plants from many centuries ago, when animals and plants die, and soil and rocks from on top of them, some of the animal carcasses many leave an indentation on one of the rocks, due to the pressure build up over the years.

Fossils can form on rocks in one of three ways

1 – When an animal dies the carcass which consists of bones, teeth, shells etc, which don’t decay and they are eventually replaced by minerals which eventually form a rock like substance. The surrounding areas will also turn to rock, however the fossil will form a distinct shape within the rock

2 – Sometimes fossils are formed when plants and animals are buried in soft substances such as clay which will then form a cast around the organism and therefore preserving the shape

3 – Sometimes fossils are formed when the whole animal or plant is preserved due to the environmental conditions, such as the lack of oxygen in tar pits, or due to the temperature, for example in extreme cold where the animal may get frozen in ice.


Why does extinction happen – this can be due a number of reasons

The environment changes – the living conditions can change causing the habitat to be destroyed and therefore an organism can die out
Predation – the introduction of a new predator can lead to an organism can be becoming extinct
Disease – a new disease can wipe out a species, if the species fails to recover quickly
Competition – if a species cannot compete then it will soon start dying and become extinct
A natural event – events such as volcanic eruptions or earthquakes can wipe out a whole population


Speciation is the development of a new species, which occur due to populations of the new species becoming separated to such an extent that they develop new characteristics until they become totally different species

The process of speciation

Isolation occurs which separates a population, the isolation occurs due to a physical barrier
Conditions on either side of the barrier will be different and therefore the organism will develop different characteristics due t natural selection
Each population will show variation and therefore will have a wider range of alleles, in each population the ones with the preferred characteristics will survive and pass on those characteristics to the offspring
Eventually the two populations will be so different to such an extent that if they were to breed together they would not be able to produce fertile offspring

The image illustrates this process


Definition – the above definition may need some explaining. A partially permeable membrane is like a cell membrane which only allows certain molecules pass. For example it will let water pass but it may not let other large molecules like starch or protein pass.

High water concentration is simply an area that has a lot of water molecules in it, the volume as such does not matter, and it is the concentration.  So for example one container may have 500ml of water but it is 100% water, whereas the other container may have 600ml of water but there are some starch and protein molecules in there so the total percentage or concentration of water is at 80%. Therefore container A has a high concentration of water.

This diagram will help to explain

In the above diagram, the orange molecules are too big to pass through the partially permeable membrane, however the concentration of water is higher in the left compartment than the right compartment therefore the water moves.

Uses for osmosis

Osmosis is used in the body, it is used as a means of transporting liquid in and out of cells. The main liquid substance in the body is tissue fluid, which is usually transported in the blood and transferred across to cells

If a cell is short of water then the cell will begin to shrink, therefore water will move into the cell

If the cell has to much water, it will expand, therefore eater will move out of the cell

Gas and solute exchange

All organism need to exchange substance, this is done via a number of method; diffusion, osmosis or active transport.

In order for life process, such as respiration or photosynthesis to occur, certain molecules need to enter organisms, such as water, oxygen or carbon dioxide. These substances all enter or leave via the processes mentioned above

As mentioned previously osmosis is the movement of water from an area of high water concentration to an area of low water concentration across a partially permeable membrane.

Diffusion is the passive movement of particles from an area of high concentration to an area of low concentration; therefore in many ways osmosis and diffusion are very similar.

However active transport is completely different. Active transport uses energy to transport molecules from an area of low concentration to an area of high concentration, therefore going in the opposite direction to diffusion and osmosis.

Exchange surfaces

Exchange surfaces are adapted in the following ways to make the process as efficient as possible

They are thin – this reduces the diffusion distance and ensures the substance diffuses across very quickly
A large surface area – this ensures that many substances can diffuse across at the same time
Large blood supple – this maintains the diffusion gradient

Illustration of leaf cell

The under side of the leaf is the exchange surface, this part of the leaf has many holes and pores called stomata which allow substances to pass through the cell

Water and oxygen diffuses out of the cell and carbon dioxide will diffuse into cell

The stomata are controlled by guard cells which control when substance enter and leave the cell

The flattened shape of the leaf increases the area of exchange, which makes it more efficient

There are air spaces within the leaf which allow the substances to exchange

The water is evaporate as soon as it leaves the cell which keeps the concentration gradient high, this is best in hot dry windy conditions where more water can be evaporated quickly.

Active transport

In plants root hair cells use the process of active transport to take in minerals.  Root hair cells are very long and have a very large total surface area which allows it to absorb as much water as possible

When it comes to absorbing minerals there is usually more minerals in the root hair cell than in the soil surrounding it, therefore the cell uses active transport to absorb as much minerals as possible.

Water flow through plants

Xylem tubes take water up through the plant; it is made of dead cells. The process of transpiration carries the water.

Transpiration is caused by evaporation and diffusion, so as water leaves the plant through the leaves it will leave a gap which will then be filled by the water below, therefore creating a running transpiration stream, so as water is lost ist is constantly replaced.

Phloem tubes carry food through the plant. They transport food substances such as sugars and proteins. The food can travel in both directions

The human gas exchange system

Respiration requires oxygen as a substrate and produces carbon dioxide. That means we need to get oxygen into the body and carbon dioxide out.

The main part of the human gas exchange system is the lungs, which moves air in and of the body

Air enters the lungs via the trachea (wind pipe), which then divide into bronchus and further divide into bronchioles in the lungs. At the end of the bronchioles are alveoli, which are small air sacs where the gas exchange occurs


During inhalation air moves in. For this to occur the pressure inside the lungs needs to be lower than outside

To ensure the pressure in the lungs is lower, the diaphragm contracts and flattens and therefore increases the volume in the lungs. Also the intercostal muscles, the muscles that surround the rib cage contract, this move the ribs up and out, therefore allowing the lungs to increase in volume even more

During exhalation air moves out of the body. For this to occur the pressure inside the lungs has to be greater than outside

To ensure the pressure in the lungs is lower, the diaphragm relaxes and moves upwards back into its original shape, the intercostal muscles also relax letting the ribs move down. Overall this makes the volume in lungs decrease and therefore the pressure increases so air moves out

Inhaling Exhaling
Diaphragm Contracts causing it to flatten Relaxes causing it to move back to its original shape
Intercostal Muscles Contract causing the ribs to move up and out Relaxes causing the ribs to move down and in
Volume of ribcage increases decreases
Pressure inside the chest decreases increases
Movement of air Air move in to the lungs Air moves out of the lungs

Gas exchange in the lungs

The lungs are optimized to ensure that exchange happens efficiently as possible.  In the lungs the two main gases that are exchanged are oxygen and carbon dioxide.  Ths gas exchange across the alveoli

Features of the alveoli

The alveoli are small structures within the lungs, which resemble a hollow bunch of grapes. They help to increase surface area, they have very thin walls and have a very large blood supply. All these factors help to increase the rate of diffusion

Active transport in the human body

Active transport is used in the gut when there is a low concentration of nutrient in the gut, but a high concentration in the blood.

When there is a lower concentration in the gut and the nutrients need to enter the blood then active transport allows the nutrients to travel against the concentration gradient

The circulatory system

The human body has a double circulatory system; the first pumps deoxygenated blood to the lungs then the second pumps oxygenated blood to the rest of the body.

this illustration will show that in a very simplified manner.

The heart

The heart contracts to pump blood around the body

The heart consists of a right side and a left side. Both sides have an atria and a ventricle

Blood flows into the atria and then enters the ventricle. When the heart contracts the blood flows out of the atria and enters the ventricles and the second contraction allows blood to go from the ventricles to the destination. The blood from the right ventricle goes to the lungs to get oxygenated and the blood from the left ventricle goes to the rest of the body.

Inside the heart

The heart is an organ, which is made up of muscle. The muscles allow the heart to contract and pump the blood around the body.

Within the heart as described there are four chambers; two atria and two ventricles. Between the atria and the ventricles there are valves, which prevent blood moving in the wrong direction

As the image illustrates deoxygenated enters the right atrium and oxygenated blood enters the left atrium
When the ventricle contract the blood enters either the pulmonary artery ( the only artery which has deoxygenated blood) or the aorta, a large blood vessel, which takes the blood to the rest of the body.
Between the atrium and ventricle are valves, which prevent backflow back into the atrium.
Between the ventricles and the major blood vessels are valves which help to maintain the pressure and prevent backflow
The left ventricle in the heart has thicker walls compared to the right ventricles because it has to pump blood much further

Blood vessels

There are three types of blood vessels, which have different functions

Arteries – they carry blood away from the heart and usually carry oxygenated blood ( except from the pulmonary artery)
Veins – they carry blood to the heart and usually carry oxygenated blood (except from the pulmonary vein)
Capillaries – they are involved in the exchange process between cells

When the heart pumps blood out, is leaves the heart at very high pressure, therefore to withstand this pressure the walls of the arteries are very elastic to ensure they can expand and deal with the extreme pressure without bursting.

The walls are made of thick muscle and elastic fibers which allows it to recoil back into position and help maintain that pressure around the body.


Veins take blood back to the heart, because after the blood has travelled around the body, it looses the pressure it gained from the initial contraction. Therefore the walls of the veins do not have to have thick walls as it does not need to deal with the pressure.

The veins do have a unique mechanism, which allows the blood to flow in the right direction. The veins have valves to make the sure the blood travels towards the heart.


Arteries branch into capillaries, which then divide into even more capillaries. The capillaries are really close to the cells and are extremely thin. They also have a very high total surface area. All these aspects help to increase the diffusion rate into the cells.


The blood contains many components. The main component of blood is red blood cells, they help carry oxygen. They have a very large surface area and contain hemoglobin, which binds to the oxygen and also makes the blood cell appear red.

The blood also has white blood cells. They are used for defense against disease; they roam the body and ingest or engulf any foreign microorganisms.

Platelets in the blood help to clot the blood when there is an injury, which prevents large blood loss

The liquid that carries everything in the blood is called plasma.  Plasma is a pale straw-colored liquid and can contain molecules such as glucose, carbon dioxide, urea, hormones etc.

When problem occur in the body and blood is lost, blood can be given to the person through a blood transfusion to keep them alive. If the arteries become blocked, then stents can be places within the arteries to keep them open and prevent the artery becoming blocked.

If an artery becomes blocked, then blood will stop flowing to the heart and therefore a heart attack will occur.


Within the human body three are many aspects that need to be controlled :

Body temperature – need to ensure the body does not get too hot or cold
Water – the cells should not shrink or increase in size
Blood sugar level – the blood sugar level needs to be maintained to prevent disease
Carbon dioxide and oxygen – the levels of both need to be maintained and can be altered through breathing
Urea – it is a waste product of amino acids

Body temperature

The body temperature needs to be maintained around 37 degrees Celsius, if the body gets too hot then there are several mechanisms to help the body cool down and if the body gets too cold then there are mechanisms to help the body get warmer.

If the body gets too warm:

Hairs on the body lie flat
Sweat is produced from sweat glands, which then evaporates and removes heat from the skin surface
The blood vessels dilate and therefore blood flows near to the surface and therefore more heat is lost from the body

When the body gets too cold

Hairs stand up, trapping heat and insulating the skin
No sweat is produced
Blood vessels near the skin constrict therefore minimizing heat loss
Your muscles contract quickly and create heat in a process more commonly known as shivering


Kidneys act as filters and help to clean the blood of all the waste materials.

One of the key substances the kidney filters is urea. Urea is a waste product from the break down of amino acids. Proteins cannot be stored in the body, so any excess is either converted into carbohydrates or fats.  This occurs in the liver and as a bi product the liver produces urea.

If urea remains in the body then it can be poisonous and therefore has to be filtered out of the body.

The kidneys also have a key role in controlling the ion levels in the body.  The levels of ions aer very important as they essentially control the level of water. The ions determine how much water the cell holds and therefore if the ion levels are not correct the water levels can also be disturbed.

Therefore if the ion level is too high then, some of the ions are filtered then removed, if the level of water is too low then ions are retained in order to retain water as well.

The ultimate role of the kidneys is to control the levels of water in the body, if there is too much water in the body then more is lost in urine, if there is less water in the water then the urine is more concentrated with waste materials and less water is present.

Kidney filtration

The process of kidneys filtering occurs in three steps. The kidney has smaller units called nephrons, which help to filtrate the blood.

The first step is ultrafiltration

A high pressure is built up which squeezes water and all the other materials from the blood into the nephrons.
The membrane between the blood and the nephron is known as the bowman’s capsule which helps to filter all the small molecules and keep the large molecules in the blood.

The second step is reabsorption

As the filtrate flows along the nephrons, certain substances are reabsorbed like glucose, water, ions etc. the volumes at which each is reabsorbed depends on the body conditions at that moment

The third step is release of waste

As you get to the end of the nephron, whatever is not reabsorbed is then taken to the bladder and releases from the body via urine.

If the kidney fails, then the body will struggle to remove waste products and therefore lead to disease and can also lead to death

However if the kidney does not work properly, then a machine called the dialysis machine can perform the same function, by drawing blood of the body and removing the waste products and essentially cleaning the blood. Thereafter returning the blood back to the body.

Blood glucose

When you consume carbohydrates, the body breaks it down into simple sugars such as glucose.  Therefore the body releases hormones to control the levels. When the body is in-between meals and the glucose levels get too low, then the body can also release hormones to increase the blood glucose levels

When you eat:

The blood glucose level increases, this is sensed in the body causes a hormone called insulin to be released
The hormone insulin stimulates the liver to take up the glucose and convert into a molecule called glycogen, which is a storage molecule
Insulin is secreted by the pancreas and ensures the blood glucose level does not get too high

When you are not eating:

The blood glucose levels decrease and therefore a hormone called glucagon is released.
Glucagon causes the liver to break down glycogen molecules back into glucose and is released back into the blood
Glucagon is secreted by the pancreas and ensures the blood glucose level does not get too low

Controlling blood glucose

If the blood glucose levels cannot be controlled, they either have type one diabetes or type 2 Diabetes.

Type 1 Diabetes

Type 1 Diabetes is caused by a lack of insulin. The cells that produce insulin are no longer present and therefore the blood glucose levels cannot be controlled and they continue to rise.

So in this case, diet has to be strictly controlled and insulin has to be administered either via an injection or in medication

Type 2 diabetes

This type of diabetes is when there is plenty of inulin but it has become ineffective, due to the diet of the person or lifestyle.

Humans and the Environment

The population of humans is ever growing and has currently reached to around 7 billion and it is still growing at a fast rate

This graph illustrates how the human population has grown rapidly

The human population has grown rapidly due to the growth of modern medicine and increasing the levels of sanitation and food.

One of the main negatives to the human population increasing is the levels of waste we produce.  This affects water, air and land.

Water  – sewage and toxic chemicals from industry can pollute rivers, lakes and oceans which affect animals and plants. Also chemicals, which are used in agriculture, also drains into rivers and lakes which affect the animals and plants

Land – we bury a lot of household water and nuclear waste underground, which can affect habitats of animals

Air  – smoke and gasses released from industry can affect the atmosphere and pollute the air

The greenhouse effect

As the human population increases the amount of carbon dioxide being released into the atmosphere is also increasing. Oceans, plants and peat bogs can take some of the carbon dioxide up again.

The greenhouse effect – when carbon dioxide is released into the atmosphere is causes the heat released from the sun to become trapped around the earth and prevents is being released back into space. Therefore all this trapped heat causes the earth to warm up.


Deforestation is the cutting down of trees in forests. This causes many problems. One of the main issues is that trees absorb the carbon dioxide released by humans to use for photosynthesis; therefore if more trees are being chopped down then less carbon dioxide is being chopped down.

Also the trees may be burned for fuel, which will release more carbon dioxide, or the land cleared through deforestation may be used for agriculture, such as breeding cattle who release methane which is also a greenhouse gas.

Another issue is that once the trees are chopped down, many animals will lose there habitats and plants will be removed and therefore this process reduces biodiversity within the environment

Peat bogs

Peat bogs are areas of land, which are very acidic and waterlogged. Therefore the plants that live in that environment do not fully decay so they trap the carbon within the peat bog.

Therefore the plant does not release any carbon into the atmosphere and it is locked within the peat instead.

However due to the population increasing, there is an increased demand for food, therefore more land is needed for agriculture.  When farmers come across peat bogs, the eat bogs are drained and the plants begin to decay. This adds to the compost fro farmers but now the carbon is released into the atmosphere, which adds to the greenhouse effect.

Climate change

The greenhouse effect can heat up the earth, which can have many serious effects:

The sea will get warmer which will cause ice caps to melt and thus expanding the oceans, this will cause the sea levels to rise which will risk flooding to low – lying countries.
Global warming has changed weather patterns. This means that certain parts of the world will suffer more extreme weather for example, extreme hot weather, causing droughts or very windy, tropical weather creating hurricanes etc
The change of weather can also affect plants and animals. Some species, which cannot survive in extreme weather, may die out where as those which can may thrive and population may increase.
Biodiversity may be reduced as more plants and animals become extinct t
There may be change in migration patterns in animals due to the weather changes.

There are a lot of debates as to whether the climate change theory is true or not.

Scientist collects their data through a number of methods.

Satellites can be used to monitor snow and ice levels; they can also be used to measure temperature of the sea

The temperature and speed of ocean currents are also measured

Automatic weather stations record atmospheric temperatures.


With fossils fuels running out, the human race is looking at alternative ways to make fuel. One of the ways is using microorganisms to make biofuels.


The process of fermentation can make fuels. This involves the use of bacteria or yeast to break down sugars by anaerobic respiration


Ethanol can be made when yeast is used to break down glucose. This produces ethanol.

The glucose is derived form sugar cane or maize starch and the ethanol produced is distilled to separate it from the yeast


Biogas is a fuel, which consists of methane and carbon dioxide on scale of approximately 70:30

Biogas is produced from animal and plant waste which is placed in a generator with microorganisms, which are kept at a constant temperature to produce biogas.

There are two types of biogas generators

Batch generators  – they make biogas in small batches, they are manually loaded with waste and it is left to digest.

Continuous generators – they make biogas all the time, the waste is continuously fed into this generator and it used for a more large-scale production of biogas

This diagram below helps to illustrate a biogas generator

There are many advantages of using biofuels

Food production

As you move up the food chain as explain earlier, energy is lost to the environment.  Therefore it is more efficient to use land to grow crops than to breed animals as growing crops involves less stages in the food chain so more energy reaches the consumer.

One way in which famers make the process of breeding animals efficient, is by restricting energy lost by farm animals. Chicken and pigs are often kept in small cages, indoors, to prevent them wasting energy on movement or maintaining body temperature.

Therefore the farmers can make the animals grow faster, which means cheaper meat for the consumer in the supermarket

This way of producing efficient food has many disadvantages