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.

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.

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.

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:

Important Dates You Need To Know

UCAS has three separate application deadlines, all applicable to specific courses or institutions. Make sure that you find out exactly when you need to apply and have your application form completed in plenty of time.

15^th October

The 15^th of October is the deadline for applications for Medicine, Dentistry, Veterinary Medicine and Veterinary Science courses, and for applications to Oxford and Cambridge.

15^th January

The 15^th of January is the deadline for application to all other courses, except for art and design.

24^th March

The 24^th of March is the deadline for all art and design applications, except for those which have specifically listed earlier deadlines.

30th June

Applications received between any of the three deadlines above and the 30^th of June are NOT GUARANTEED to be considered by universities. It could be worth applying late, however, as some universities will consider later applications if they have places to fill.

If you apply after the 30^th of June your application will not be considered and you will automatically be entered into clearing.

You also can apply for courses with earlier deadlines and then add further choices on subsequent deadlines through the Track system. You still only get five choices maximum, however, so be sure to think carefully whether you want to apply for art and design courses before you leave a space on your application.

This video will give you a bit more information on applying after the deadline:

Course Start Dates

Not all courses start at the same time. Be sure to check with your chosen institution to find out the correct start of the course you are interested in. A course’s start date may effect when you need to have the application completed so it is essential that you get this information straight right from the start.

International Applications

Many universities will accept international applications right up until the 30^th of June. The exceptions to this rule are courses and institutions which insist on the 15^th of October deadline, which must also be adhered to by international applicants. As with UK students, universities will not guarantee to consider your application after the 15^th of January, so it is always best to apply within this deadline if you possibly can.

It is also a good idea to look into the practicalities of moving to another country to study before you apply. Do you need to think about a student visa? If so, make sure you have plenty of time to apply as it can be harder to get one in the busy summer months.

If you are an international student, why not check out this video for a few more pointers:

Deferred Entry

If you want to apply for deferred entry, if you are taking a year out to travel or work, you must also apply within the above deadlines for the year before you wish to take up your place. Remember to check with universities that they will accept deferred entry before applying.

If you have accepted a deferred place for one year, 2012 for example, you may not apply for another place within the same year unless you cancel this confirmed place first.