Biology, Paper 1- Infection and Response



Pathogens are microorganisims which cause communicable diseases (infections). 

These can spread by:

- Direct contact

- Food

- Sex 

- Water or air

- Vectors, organisms who pass on the desise without actually having it

The spread of disease can be limited by; giving vaccinations; simple hygiene (washing hands), destroying vectors, isolating people who are infected so they cannot pass the infection on. 

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Viral Pathogens

Viral pathogens reproduce rapidly in body cells, causing damage and spreading the disease

Measles- Can be spread by breathing in droplets from sneezes, or touching infected fluids. It has many symptoms such as fever and a red skin rash with a cough. It can be treated with fever medicine or goes within two weeks. It can be prevented by having the vaccination when young. 

HIVCan be spread by sex or contact with bodily fluids, eg when drug users share needles.  It has many symptoms such as flu like illnesses. It cann't be treated but can be prevented with antiviral drugs, as it effects lymph nodes and attacts immune system, when this is fully damaged it means that other disesease cannot be fought off. It can be prevented by using condom and not touching body fluids.

TMV- A plant disese, can be spread by touch eg. a healthy leaf touching an infected on or using contaminated tools.  It has many symptoms such as leaf curling, mosaic and mottling. It can be prevented by killing infected plants once sympoms are seen to prevent spread. 

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Bacterial Pathogens

Bacteria can damage cells directly or produce toxins which damage tissues. 

SalmonellaCan be spread by eating food containing the disease.  It has many symptoms such as sickness, fever, headaches or cramps.  It can be treated with antibiotics, or will just go away with a healthy immune sytem. It can be prevented by cooking food thourghly to kill bacteria or wash down surfaces to prevent cross contamination. 

Gonorrhoea- An STD can be spread by sex or in pregnant mothers onto babies. It has symptoms such as pain urinating or a thick yellow or green discharge.  It can be treated with penicillin- but resistant strains have appeared. It can be prevented by wearing condoms, and having just on sexual partner. 

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Protists are single celled organisms, and are usually eukaryotic (have a nucleus).

MalariaCan be spread by the vector of a particular mosquito who passes the disease when biting people. It has many symptoms such as drowsiness, chills, fever and the repetition of symptoms at diferent intervals which can be fatal. It can be treated once tested. It can be prevented by stopping people being bitten, eg by killing mosquitos or using mosquito nets. 

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Fungal Disease

Rose Black SpotCan be spread when spores from an infected plant is carried by water or wind to another non-infected plant.  It has many symptoms such as black patches forming on the upper leaf and leaves turning yellow and dropping early- this stunts plant growth as photosythesis is reduced. It can be treated by spraying fungicides. It can be prevented by remoning and destroying effected leaves so it doesnt spread as fast. 

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Human defences

There are many non-specific defences in the body against pathogens to stop them entering the body. Such as:

- Skin- provides a barrier to anything entering the body. 

- Hair, eg. nose + ear wax, catches pathogens before they can enter the body. 

- Lysozymes enzymes in tears and saliva destroy microorganisims. 

- Glands in stomach wall produce hydrochloric acid which kills bacteria in food. 

- Platelets (scabs) stop pathogens entering the body whilst it is wounded.

Cilliated cells line the airways, these have small hairs with mucas on them. The bacteria on its way to the lungs become trapped in the mucas, and at night the small hairs beat in unison so the mucas with the bacteria travels up the airways where it is swallowed and nutralised by the hydrochloric acid in the stomach. 

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White Blood Cells

If a pathogen enter the body the white blood cells destroy it. They do this by having two different types of cell:

Phagocytes- find microorganisms and englulf and ingest them. This means the microorganism has been ingested and destroyed. 

Lymphycytes- produce protiens called antibodies which attatch onto specific antigens on the pathogens suface. Once the specific antibodies have locked onto the pathogens surface they then clump together so the phagosytes can digest them. 

Lymphycytes can also produce anti toxins which when locked onto anti gens neutralises the poison of toxins. 

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When a pathogen reenters the body for the second time white blood cells can respond more quickly to find the correct antibodies- from the immuno memory. This stops the person from getting ill as the disease doesn't have time to develop- and the person has immunity. 

The same effect can be found with vaccinations where dead or weakened forms of the pathogen are ingected into the body, to stimulate the production of antibodies and develop immunity. 

This was first discovered by Edward Jenner who found the vaccination for the fatal smallpox by injecting a weaker strain of the disease- cowpox to patients. 

In a large population this can help to eradiacate some diseases, as if most people are vaccinated and are immune from the diseases it is harder for the disease survive between people suseptable to it.  

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Antibiotics are medicines which kill bacteria in the body, not viruses. These can be prescribed specificly for certian diseases. This helps reduce illness as a whole and death. 

However antibiotic resistance is increasing meaning antibiotics don't effect the spread of pathogens eg. MRSA. This is because of evolution and natural selection meaning that because of a mutation in the bacteria a resistant dtrain develops. This is the most successfull in the new environment with drugs and so all the weak bacteria is killed and the strong ones exist to reproduce, and so the whole population becomes resistant to disease. 

To try and limit antibiotic resistance doctors only prescribe anti-biotics when nessecary. They also ensure all corses are finished to ensure all bacteria is killed, and so none survive to form resistant strains. They can also release drugs in circuits to mean pathogens don't become used to one antibiotic. 

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New Drugs

A drug is any chemical which changes how the body works. Painkillers relieve symptoms of a illness but do not kill the pathogens, by reducing nevous impulses so pain is not felt. Antibiotics and antiviral drugs kill pathogens. In antibiotics this is by interfering with the metabolism of a bacterium cell. Antiviral drugs are needed to ensure they don't damage body tissue.

Traditionally many drugs are extracted from plants, such as Digitalis a heart drug from floxgloves, aspirin a painkiller from willow, Penicillin from the pencillin mould discovered from Alexander Femming. However now most drugs are synthesised by chemists in pharmacies. But the starting point may still be the chemical from the plant. Drugs have to undergo rigouruos testing to ensure they do not have any adverse side effects (Thalidomide drug):

1) Preclinical trials, new drugs found before being developed into a possible treatement.

2) Medicine is treated on tissue cultures, cells and whole organs to ensure they do not have any adverse side effects, and see if they perform their function. 


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Drug Testing

Drugs have to undergo rigouruos testing to ensure they do not have any adverse side effects (Eg. like the Thalidomide drug):

1) Preclinical trials, new drugs found before being developed into a possible treatement.

2) Medicine is treated on tissue cultures, cells and whole organs to ensure they do not have any adverse side effects, and see if they perform their function. 

3) Drugs are tested on animals although not ethically correct, it shows how the drug reacts on a whole organisims, as it is more ethical than testing on humans before it is fully safe. 

4) Clinical testing begins on healthy people, so if the drug reacts they have a higher chance of surving. It is also easy to see if it has any side effects, and targets the area intended. 

5) Testing begins on those suffering from the disease. This is to find if it still works or in what dosage. This is done in double blind trials, where some patients are given a placebo but the doctors do not know who, this is to see if the drug has a worthwhile effect. It is also double blind to ensure the test is fair. 

6) Drug is given a license but is still monitered to ensure it doesnt have effects in conditions not tested. 

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Monoclonal Antibodies

To produce: Faccinate an amimal to stimulate the production of lympocytes which produce antibodies but don't divide. Merge these with tumor cells which divide. This forms a hybridoma cell which makes the specific antibody and divides. Grow these in a tissue culture to clone the cells and collect many antibodies ready to use.

These can be used for: Pregnancy tests to bind to the hormone HCG found in eary pregnancy.

In labs to measure the level of hormones or pathogens in blood.

In research to locate specific molecules in a cell by binding to them with a flurecent dye.

To treat some diseases eg. cancer by delivering a substance which stops cells dividing. 

Although the development of these brings many benefits, they have created more side effects that expected- and so are not widely used. 

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Plant Disease

Signs a plant is diseased:

- Stunted growth (nitrated deficiency)

- Spots on leaves 

- Areas of decay

- Growth 

- Malformed stems of leaves 

- Discoloration (Chlorosis in magnesium deficiency)

- Pests (aphids)

To identify a particular disease you could; consult a gardening manual or website, using testing kits including monoclonial antiodies. tskeing infected plats to a lab to identify the pathogen. 

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Plant Disease (2)

Aphids are tiny insects which such the sap (sugar) from plants- hence this reduces the plants rate of growth and make leaves wilt and discolour. They are eaten by ladybugs. 

Plants can also have non-communcable diseases caughts by a lack of minerals in the soil. Eg. stunted growth is caused by a nitrate defficency- because nitrate is needed for protien synthesis. Chlorosis is caused by magnesium deficiency, because magnesum is needed to make chlorophyl. 

Plants have many defences physically like; thick cellulose cell walls to act as a barrier to pathogens, tough waxy cuticule on leaves, layers of dead cells (bark) which fall off and take pathogens with them. 

Some plants have chemical defences, like mint and witch hazel have antibacterial chemicals which stop infections. Some plants also have poisonous chemicals to deter prey Eg. tobacco, foxgloves, poison ivy. 

Other plants have adapted to include machanical defences like; thorns and spikes so they are not eaten, leaves which droop and curl when touched, or mimicry. 

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