Specialisation

Certain cells within an organism are specialised. This means that they have developed to carry out a specific function. See the table below for some examples.

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Dissolved substances

Dissolved substances are able to enter and leave a cell through its cell membrane. One way in which they can achieve this is through a process known as diffusion.

Diffusion can occur in either a liquid or gas. It involves the particles of a substance moving from an area in which there’s a high concentration of it to an area in which there’s a lower concentration. The bigger the difference in concentration, the faster the rate at which diffusion occurs.

There are a number of ways diffusion is used by living organism:

• lungs: oxygen from the alveoli in the lungs is able to move across into the red blood cells so that carbon dioxide can then diffuse into the alveoli and then be expelled out of the body via the lungs.
• photosynthesis: similarly, green plants take in carbon dioxide from the air via chloroplasts by diffusion and release oxygen back into the atmosphere also by diffusion.
• respiration: this process also involves diffusion. In animals, for example, oxygen diffuse from the red blood cells into the tissue cells and then carbon dioxide diffuses in the other direction.

You can apply for entry to universities and colleges online through the UCAS ‘Apply’ system, which is accessible through the UCAS homepage: http://www.ucas.com/

The application is broken down into several stages:

Registration – Filling in your basic details and starting your application.

Personal Details – Making sure UCAS can contact you throughout the application process.

Additional Information – Letting UCAS know a little more about yourself.

Student Finance – Linking your application to the Student Loans Company.

Entering Your Choices – Applying for specific courses.

Education – Entering details of your education.

Employment – Entering any relevant employment you may have undertaken.

The UCAS Personal Statement – Advice on completing a strong UCAS personal statement

Reference – Choosing a referee and what to do next.

Completing Your Application – Paying for your application and sending it off.

Check out this video for a step by step explanation:

In cells respiration can take place in two ways: aerobically or anaerobically. The energy produced is then utilised in a number for different functions. During exercise the human body reacts in a particular way in order to deal with the need for my energy.

By the end of this section you should understand:

• how to interpret data which looks at how the human body is effected by exercise

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Aerobic respiration

Respiration is the process used by cells in order to release energy from glucose. For aerobic respiration oxygen must be present. This can be seen more clearly in the equation below:

glucose + oxygen ? carbon dioxide + water (+ energy)

The reason why energy is shown inside brackets is because it’s not a substance like the other parts of the equation.

The two main points that can be noted are:

• glucose (a sugar) and oxygen are used
• energy is released

Both animals and plants are capable of respiring aerobically and they do so continuously. The majority of the process happens in the mitochondria which can be found in the cytoplasm of cells. This reaction, as with all chemical reactions that occur in cells, is controlled by enzymes.

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Energy uses

The energy released during respiration can be used by an organism in a number of ways:

• to form larger molecules using small one
• to enable muscle contractions in animals
• to ensure that a steady body temperature is maintained when the surroundings are cold in birds and mammals
• to create amino acids from nitrates, sugars and other nutrients which are then used to create proteins in plants

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The effect of exercise

During exercise muscle cells need to respire at a faster rate than when they’re resting. Due to this, changes take place in the body including:

• an increase in heart rate
• an increase in the rate and depth of breathing

Both of these changes work to increase the amount of blood and therefore oxygen and sugar reaching the muscle cells. The heart beating faster means blood can flow around the body quicker. While an increase in breathing rate increases the rate at which gaseous exchange (of oxygen and carbon dioxide) occurs in the lungs. This also helps to increase the rate of removal of the waste product carbon dioxide.

To help increase the amount of sugar available to the cells, the muscle stores glycogen which can be converted back into glucose when required during exercise.

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Anaerobic respiration

The main difference between aerobic and anaerobic respiration is that anaerobic respiration doesn’t require oxygen to be present.

What tends to happen during exercise is that, no matter how fast the heart and breathing rate get, not enough oxygen can reach the muscles. So, they begin to respire anaerobically in order to obtain the energy they need.

Another difference inanaerobic respiration is that glucose isn’t broken down completely. The end result of this is that far less energy is released (only 5% per glucose molecule of what aerobic respiration can achieve) and the waste product lactic acid is produced.

glucose ? lactic acid (+ little energy)

Lactic acid

If muscles are made to exercise for a long period then then become tired or fatigued. This means that they’re unable to contract properly anymore. One of the reasons why this happens is due to a build-up of lactic acid. This is due to the fact that the body simply can’t remove it fast enough. However, once the muscles are at rest, the blood is able to remove the lactic acid from the muscles.

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HIGHER TIER

• Oxygen debt:

The reason why less energy is released during anaerobic respiration compared to aerobic is that the glucose is not broken down completely.

Oxygen debt is caused by anaerobic respiration. It refers to the additional oxygen needed by the body after exercise in order to oxidise the waste product, lactic acid. The lactic acid needs to be broken down into carbon dioxide and water. This explains why, after a lot of exercise, you still need to breathe deeply for a while afterwards.

• Cells can respire either aerobically or anaerobically.
• Aerobic respiration required oxygen as well as glucose and produces carbon dioxide and energy.
• Anaerobic respiration doesn’t require oxygen and produces less energy and lactic acid.
• Cells respire anaerobically in the body during exercise because not enough oxygen can reach the cells fast enough.
• Lactic acid builds up in the muscles because the body can’t remove it fast enough.

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TEST IT!

1. During a work up an athlete respires both aerobically and anaerobically.

a) Write down two differences between these types of respiration.

i. _____________________________________________

ii. _____________________________________________

b) Two athletes work out together. Martin is a beginner while Ferdi is very fit. They both measure their heart ratesand Martin’s is much faster than Ferdi’s.

i. Why is Ferdi’s heart rate slower than Martin’s?

ii. Explain why a change of heart rate is important during exercise.

2. Terry is training for a marathon. He runs every day to build up his muscles.

a) Name two substances that the muscles need in a large amount during exercise.

i. ______________________________

ii. ______________________________

b) At the beginning of his run Terry respires aerobically. However, his body then begins to respire anaerobically. Why is that?

c) What is the waste product of anaerobic respiration?

3. Energy is continuously being made by cells in the body.

a) Name two ways this energy is used by the body.

i. _____________________________________________

ii. ____________________________________________

b) Where does respiration take place? Choose one of the following.

i. the mitochondria

ii. the cytoplasm

iii. the nucleus

c) Respiration is a chemical reaction. What is it controlled by?

ANSWERS

a)

i. Aerobic respiration uses oxygen or anaerobic respiration requires no oxygen.

ii. In aerobic respiration all the glucose is broken down or in anaerobic respiration not all the glucose is broken down.

b)

i. Regular exercise increases the amount of blood and therefor oxygen that can reach the heart per heartbeat. This is why Ferdi’s heart rate is not as high as Martin’s.

ii. Because the muscles in the body are having to work much harder and so oxygen has to reach them at a much higher rate than when the body is resting.

a)

i. Oxygen

ii. Glucose

b) Because not enough oxygen can reach his muscles and aerobic respiration requires oxygen.

c) Lactic acid

a) Choose from:

to form larger molecules using small one

to enable muscle contractions in animals

to ensure that a steady body temperature is maintained when the surroundings are cold in birds and mammals

to create amino acids from nitrates, sugars and other nutrients which are then used to create proteins in plants

b) i. the mitochondria

c) Enzymes

In order to understand cell division it’s important to know first of all how genetic material is composed.

DNA

DNA, short for deoxyribose nucleic acid, is very large molecules which carry the genetic code: this is what determines the characteristics for every organism. Apart from identical twins, every human being has DNA which is unique to them only.

Genes

A gene is the coding for a protein. It’s made up of a small sequence, or segment, of DNA.

Chromosomes

A chromosome is a complete length of DNA molecules. Chromosomes are normally found in pairs within cell nucleus so that each nucleus has two sets.

Nucleus

This is where the genetic information is stored in animals and plants.

Mitosis

All cells in the body divide by a process known as mitosis. When a cell divides in this way:

• the genetic material is replicated
• two genetically identical body cells are formed

There are two main purposes for mitosis:

• growth
• to create replacement cells

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Alleles

Sexual reproduction produces offspring that are different from either parent. This is because the gametes of each parent contain half the genetic material required.

Genetic information is made up of genes and each pair of chromosomes carries the same genes. However, sometimes there are different versions of the same gene available, for example eye and hair colour, and these different versions are called alleles.

Alleles can be either recessive or dominant:

• A recessive allele is only able to show itself as a characteristic if there are two copies of it. In other words, if the allele is present on both chromosomes. For example, blond hair is a recessive allele.
• A dominant gene will always show its characteristic, whether it’s present on one or two chromosomes. Brown hair is a dominant allele.

The variations seen through sexual reproduction is due to the different alleles received from the each parent.

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Differentiation

In animals the cells tend to differentiate at an early stage of development. As an animal matures cell division becomes solely focused on repair and replacement. In many plants, however, the ability to differentiate cells continues throughout its lifetime.

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Stem cells

Stem cells are undifferentiated cells which have the ability to differentiate into specialised cells. They can be found in two main sources:

• adult bone marrow
• embryos

They can be made to differentiate into any kind of human cell, like a nerve cell.

NOTE: You don’t need to know of any stem cell techniques.

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Stem cell treatment

Due to their properties, stem cells can be used to treat a number of conditions, including:

• paralysis
• brain diseases like Alzheimer’s
• skin tissue for burn victims

There are a number of social and ethical concerns regarding the use of embryo stem cells. The main argument is that by destroying an embryo you’re destroying human life.

Each body cell nucleus contains 46 chromosomes which make up 23 pairs. One of these pairs determines whether an individual will be male or female.

• In males the two sex chromosomes are XY.
• In females the two sex chromosomes are XX.

Finger printing

Due to the fact everybody (apart from identical twins) contains DNA unique to themselves, DNA finger printing is a full proof way of identifying people.

Techniques are used to create an image much like a barcode. The small differences between people’s DNA can then be clearly seen. This is particularly useful at crime scenes for matching suspects with samples found.

NOTE: You don’t need to be aware of genetic finger printing techniques.

Genetic diagrams

Gregor Mendel was interested in how pea plants inherited different characteristics. He bred red and white flowered plants with each and noticed interesting results.

• When he bred white and red flowered plants the offspring was red.
• However, when he bred this red flowered offspring with each other most of the offspring was red but some were white.

In Mendel’s era people were unaware of the idea of genetics. Today we’re aware of how genetics works and so can tell from this experiment that the red flower allele must be dominant while the white flower allele is recessive.

A genetic diagram is a visual way of interpreting this. It can show all the possible allele variations for a specific characteristic. Each parent has two alleles. Dominant alleles are written with a capital letter and recessive with a lower case letter. Each allele can then be paired up with each other by drawing lines. The outcome is four possible combinations.

For example, a diagram of Mendel’s first cross would look like this in which all the plants have red flowers.

His second cross would appear like this in which three quarters of the plants have red flowers and a quarter has white flowers.

Chromosomes are large molecules of DNA (deoxyribonucleic acid). This DNA has a double helix structure and is composed of genes.

HIGHER TIER:

• Each gene provides the coding for a specific combination of amino acids which then produces a particular protein.

NOTE: You don’t need to know the names of the four bases or how complementary pairs of bases allow the replication of DNA to occur.

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Genetic disorders

Genetic disorders are diseases that are passed onto the offspring by one or both of parents. They’re caused by gene mutations. There are a number of genetic disorders.

Polydactyl

In this condition an individual is born with additional fingers or toes. It’s caused by the dominant allele of a gene which means that only one parent has to be the carrier for the characteristic to show itself in the offspring.

Cystic Fibrosis

This disorder affects cell membranes mainly in the lungs, liver, pancreas, sinuses, intestines and sex organs. The mucus produced by a sufferer is very thick and sticky and can easily clog up the lungs. It’s caused by a recessive allele which means that both parents need to be carriers. However, neither of them actually has to have the disease because they could both carry a recessive and dominant allele.

Gametes are sex cells which are produced in the reproductive organs.

• females produced eggs in their ovaries
• males produce sperm in their testes

As you’ve already seen, body cells contain two sets of chromosomes. Gametes only have one set. This is because they’re formed by a process called meiosis.

HIGHER TIER:

• When a cell divides by meiosis copies of the genetic information are made.

However, then the cell divides twice thereby creating four gametes each of which contains only one set of chromosomes

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Fertilisation

When a sperm and an egg fuse together this process is known as fertilisation. Each gamete contains half the amount of genetic material required to create an offspring. However, once they’ve fused together the resulting cell, known as a zygote, has the right amount and begins to divide by mitosis. A new individual can now be formed.

Asexual reproduction is very common in plants and very rare in animals. In comparison to sexual reproduction, the cells of the offspring are created by mitosis from the parental cell. This means that their cells contain the same alleles as that of their parents.

NOTE: You don’t have to know all the stages of mitosis or meiosis.

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Embryo screening

Embryo screening can be carried on embryos to see if they have genetic disorder such as polydactyl or cystic fibrosis. However, there are ethical fears over the fact that society could be heading towards ‘designer babies.’

NOTE: You don’t need to be aware of any techniques for embryo screening.

• Mitosis is the process in which genetically identical cells are formed.
• Mitosis is used for growth and to make replacement cells.
• Meiosis creates gametes.
• Gametes only contain one set of chromosomes.
• Fertilisation is the process in which an egg and a sperm fuse together to form a zygote. This then divides by mitosis.
• Alleles are different versions of the same gene.
• An allele can be either recessive or dominant.
• Gender is determined by two alleles: X and Y.
• Due to the fact that everyone (apart from identical twins) has different DNA, DNA finger printing can be used to catch criminals.
• Mendel put forward the idea of separately inherited factors.
• Genetic diagrams show how alleles can create different characteristics.
• Genetics disorders, like cystic fibrosis, are caused by genetic mutations.
• Embryo screening can be used to check for genetic disorders.

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TEST IT!

1. Show dogs are bred for particular characteristics. Complete the sentences choosing from the words below.

characteristic / chromosomes / genes / gamete

a) The colour of dog’s fur is called a ____________________

b) The colour of its fur is controlled by ____________________

c) A pair of ___________________ is found in all cells apart from gametes.

2. In Mendel’s pea plant experiments:

From his experiments Mendel concluded that flower colour was inherited.

a) Which colour is dominant?

b) What are different versions of the same gene called?

c) How does each new generation inherit factors?

3. Sex chromosomes, X and Y, control whether a human is male or female.

a) Complete the Punnett square below which represents sex inheritance.

b) A couple already has two girls. What are the chances that their next child will be a boy?

ANSWERS

1.

a) …characteristic

b) …genes

c) …chromosomes

2.

a) Red

b) Alleles

c) Genetic information is passed on from two parent plants.

a)

b) 50%