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Biology Notes Essay

Chromosomes: They are found inside the nucleus of cells. They are X Shaped Objects that Contain DNA. Each Chromosome is made from two Chromatids. Chromosomes are held together by a disc called a centromere. Chromosomes are always found in Pairs.

A| T|
G| C|
C| G|
DNA: It Stands for Deoxyribonucleic acid. DNA is Made from Nucleic acids of ten (referred to as bases). The four bases are Adenine (A) which always pairs with Thymine (T) and Cytosine (C) which always pairs with Guanine (G).

T| C|
A| G|
T| G|

Genes: A gene is the short length of the chromosome which is a molecule of a DNA. Genes can exist in Different Versions. Different Versions of the same gene are known as ALLELES. Each gene codes for a specific Protein. Some proteins are Structural, meaning they can form skin, hair, blood and cytoplasm. Others are Functional (enzymes) controlling chemical reactions such as respiration or digestion. Genetic Information is stored by Genes who are arranged on Chromosomes. Variation: This is the Difference between humans. There are two types of variation. The First is Genetic Variation (Caused by your Genes and can’t be changed e.g. your natural hair colour, eye colour).

The Second is Environmental Variation (Caused by your surrounding and can be changed e.g. Dying your Hair, Ear Piercings). Genetic Variation: Caused by the DNA in the cells in your body. We Can’t Change this. Environmental Variation: Caused by your Surroundings, Family and Friends. We can Change this. Determining Your Gender: A Sperm Cell has an X chromosome and a Y chromosome. An Egg Cell has two X Chromosomes. If the fertilised egg has a X Chromosome from the sperm the Foetus will be a Girl if it has a Y Chromosome (the Chromosome carrying Testosterone) the Foetus will Be a Boy. There is a 50:50 Chance of Having a Boy or a Girl. Further Gender Determination

Chromosome pair 23 is known as the Sex Chromosomes. There are two Different types of of Chromosome 23 – The X and Y chromosome. The only Difference is that the Y chromosome carries the gene for testosterone, X does not. All Cells carry at least one X Chromosome. Sperm Cells carry either a Y or X chromosome. Allele – A different version of the same gene.

Heterozygous – When There are two types of an allele in the genotype e.g. Bb – Brown. Homozygous – When there is only one type of Allele in the genotype e.g. BB(-Brown) or bb(-Blonde). B = Dominant – Always Expressed, b = Recessive – only expressed in a Homozygous genotype. Natural Cloning

* The Hydra (Plant) Shows Budding * Asexual Reproduction – The Spider Plant and Strawberries often reproduce this way. Twins: They are formed by the fertilised egg splitting in half and the two halves turn into to two identical babies. Artificial Cloning

For many years, mammals have been cloned by splitting embryos – Artificial Cloning. There are two types of Artificial Cloning Cloning Way 1
1. They take an egg cell from one mammal.
2. A Body Cell is taken from a second mammal (the same mammal as the first)
3. The egg cell nucleus is removed from the cell
4. The body cell nucleus is also removed
5. The Nucleus from the body cell is inserted into the egg cell to make a clone of the Second Mammal. 6. The egg cell divides and is put into the uterus of the first Mammal. The Clone grows into a mature mammal. Cloning Way 2

It isn’t just Reproductive Cloning (Cloning People/mammals) we could use this technology for. Cloning human cells may be useful in treating humans.

Reproductive Cloning – When a baby is born from cloning

Stem Cells

A stem cell is an undifferentiated cell which means they can turn into any type of cell required. They can therefore be used to make organs. They Can be used to replace damaged cells.

Inherited diseases

Cystic Fibrosis
* 1 in 200 Children are affected by Cystic Fibrosis.
* Is an Inherited disease
* They produce thick sticky mucus. This can block the air passages and the tubes that carry digestive juices to the gut.
* The Child has trouble breathing and absorbing food.
* Patients are treated by chest physio-therapy.
* The Mucus is a good breeding ground for germs.
* Sufferers often get infections and have to be treated with strong antibiotics. At the moment there is no cure. * Cystic fibrosis is caused by a recessive Allele(c) – So to contract the disease a person must have two recessive alleles (cc). * Heterozygous people (Cc) do not get the disease but can act as carriers and pass it on to their children. * The disease is shown from Birth.

* It affects the lungs and gut.
Huntington’s Disease
* This is a rare inherited disease.
* It affects about 1 in 20,000
* It shows up when the patient is about 30 – 40 years old.
* The cells of the brain degenerate and the patient makes clumsy and jerky movements.
* The sufferers become moody and depressed.

* The memory is affected and they eventually become totally disabled. * Huntington’s disease is caused by a dominant gene – so only one allele is needed to give the disease. * So all heterozygous people are sufferers because the onset of the disease occurs so late many people have produced a family before they find out they have the condition. * The Organ Effected is the Brain.

Bacteria cell

Bacteria are known as micro-organisms. Many of these cause disease. Those that cause disease are called Pathogens. Other micro-organisms include Protozoans, Fungi and Viruses. Micro Organisms reproduce quickly in warm, damp places. Once inside a host of Pathogens reproduce and cause Infection.

How Pathogens can enter our Body

* Nat Bites/ Being Bitten
* Eating
* Touch
* Sexually Transmitted
* Bugs
* Dogs/ Animals
* Breathing it in
* Birds
* Injections
* Cuts
* Natural Openings
* Blood Transplants
* Organ Transplants
Things that protect our Body from Pathogens
* Eyebrows/ Eyelashes
* Cilia
* Acid
* Mucus
* Tears
* Skin
* White Blood Cells
* Healing over cuts
Gaining Immunity

1) James is Infected by some bacteria that causes a disease 2) The bacteria reproduce and James gets ill. 3) One of James’ white blood cells detect the bacteria. It makes anti bodies to destroy the bacteria. 4) The white blood cells reproduce. Now there are lots of them making Anti-bodies. 5) The bacteria are all killed. James gets better.

6) Most of the white blood cells that make the antibodies die, but a few of them stay in the blood. 7) James is infected with the same bacteria again. 8) The white blood cells to make the antibody are still in James’ Blood. So this time they are ready to kill the bacteria very quickly. 9) The bacteria are killed before they can make James ill. He is Immune to this disease. Anti-body = A Chemical made by White blood cells which binds to Antigen. Antigen = A marker on the surface of a Pathogen that identifies it as foreign. Pathogen = A micro-organism which causes Disease.

White Blood Cells:
* Produce Anti-bodies to neutralise the Microbe
* They eat the microbe
* They produce anti-toxins to neutralise the poisons produced by microbes.

Producing Anti-bodies
1. A White Blood cell detects a pathogen.
2. A White Blood cell produces Anti-bodies.
3. The anti-bodies bind with Antigens.
4. The Pathogen is engulfed by the White Blood Cell.

Natural Immunity
This is when Anti-bodies are produced by a Person when needed or they are passed on by a mother during Pregnancy.

Artificial Immunity

A Vaccine with dead Microbes is injected – the body is ‘tricked’ into producing anti-bodies ready for the real thing. This is called Passive Immunisation. We should use the new influenza vaccines every year because influenza reproduces very quickly. Also it has a high mutation rate, which means that it changes so you need to continually be protected by Influenza. Especially if you suffer from other illnesses, because you would be at risk the most. Also the antigens would have changed shape.

Vaccinations Policy

Benefits – Wont spread through a large population is a benefit. Also if a woman has a vaccination then falls pregnant she passes the antibodies onto the child. A vaccine Policy is a decision made by the government to vaccinate a large amount of people. This usually only works if the majority of people agree to it.


Immunity/ Immune: When your body has already met a Pathogen once and therefore cannot make you ill again Antibody: These attach to pathogens and Stick the together. Vaccine/ Vaccination: An inactive or dead version of a pathogen is introduced into the body. Antigen: The marker on a Pathogen that a White Blood Cell can recognise. White Blood cells: a Cell that produces Antibodies.

* You take them and they kill the bacteria and it makes you better
* You have to take them continually
* They take a while to settle in
* They kill infections
* They are produced by Bacteria and Fungi
* Are Drugs that are effective at killing Bacteria and Fungi
* Antibiotics do not seriously damage body cells
* Antibiotics are derived from micro-organisms
* Penicillin comes from bread mould and was the first antibiotic discovered.
* However they have limited use and have no effect on viruses.

Antibiotics and Superbugs

Antibiotics are used to kill Bacteria and Fungi in an infection in the body. The chemicals are made from Fungi and Bacteria. Antibiotics are Drugs that kill Bacteria and Fungi without harming body cells. These drugs do not affect viruses. A Superbug Bacteria is a Mutation to a Normal Bacteria. It is resistant to normal Antibiotics.

How could we help Reduce Superbugs?

Hospitals can make sure that they treat people with the Superbug properly to
stop it from spreading. Keep the Hospital Clean. Inject staff to Stop it Spreading, and to make them Immune. GP
Inject people more Often and Give out Leaflets.
Drug Companies
Make a more effective drug and make a vaccine.
The Public
Allow people to inject them and make them immune.
Antibiotic Resistance


1. The cell starts to replicate the DNA
2. The cell has had the DNA Replicate. So therefore the cell has elongated.
3. The Cell has started budding.
4. Binary Fission has taken place and the cell has cloned itself.

A Mutation is a change in the bases that make up DNA. These changes can cause a change in a gene. This can change a Protein and thus affect the Characteristics of an Organism.

Drug Trials

It is important to do strict test on drugs to check that they are safe for use, do what they are supposed to do and to check the side effects. Drugs are tested on human cells that have been developed in a laboratory (The drug is tested on different body cells), then it is tested on animals (to see whether it works as well on whole animals as on the cells) before it is used on human patients(these are tested on volunteers).The three drug trials are Double blind(both doctor and patient do not know the drug is new), Blind trial(only the patient does not know the drug is true but the doctor does), and Open trial(both doctor and patient know the drug is new). A placebo is when a doctor gives a patient something that does not contain Drugs. A Placebo is used in blind trials.

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