Welcome back to Beyond’s Science Blog! This exciting post focuses on AQA Infection and Response revision. We’ll be looking at everything from Communicable Diseases, How Pathogens are Spread, to Viral Diseases and Vaccinations. Revision is made easy with the key points of the exam topic broken down into easy bite-sized chunks. So, get ready to recap all the important elements you need for the GCSE Biology AQA topic, Infection and Response.
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Communicable Disease
- Pathogens are microorganisms that enter the body and cause communicable disease (infectious). Plants and animals can be infected by them.
- Bacteria are small cells that can reproduce very quickly in the body. They produce toxins that make you feel ill, damaging your cells and tissues.
- Viruses are much smaller than bacteria; they can also reproduce quickly in the body. Viruses live inside your cell where they replicate. They then burst out of the cell, releasing new viruses.
- Protists are eukaryotes (multicellular). Some are parasites which live on or inside other organisms, often carried by a vector.
- Fungi are sometimes single celled, others have hyphae that grow and penetrate human skin and the surface of plants. They can produce spores which can spread to other plants.
How Pathogens Are Spread
Pathogens can be spread in many ways, for example:
- Water – by drinking dirty water, e.g. cholera.
- Air – carried by air and breathed in, e.g. influenza.
- Direct contact – touching contaminated surfaces including the skin, e.g. athlete’s foot.
Viral Diseases
Measles is spread by droplets of liquid from sneezes and coughs etc. Symptoms include a red rash on the skin and a fever. Measles can be serious or even fatal, it can lead to pneumonia. Most people are vaccinated against measles when they are very young.
HIV is spread by sexual contact or exchanging body fluids. HIV can be controlled by antiviral drugs; this stops the viruses replicating. The virus attacks the cells in the immune system. If the immune system is badly damaged, the body cannot cope with other infections. This is the late stage and is called aids.
Tobacco Mosaic Virus affects plants, parts of the leaves become discoloured. This means plants cannot carry out photosynthesis; this will affect the plants growth.
Fungal and Protist Diseases
Fungal
- Rose black spot shows as black spots on the leaves of the plant, this means less photosynthesis occurs. As a result, the plant does not grow as well. It is spread by the wind or the water. They can be treated by using fungicides and taking the leaves off the infected plant.
Protists
- Malaria is caused by a protist, mosquitoes are the vectors. They become infected when they feed on an infected animal. The protist is inserted into the blood vessel. Malaria can cause fever, it can also be fatal.
Bacterial Diseases
- Salmonella bacteria causes food poisoning. Symptoms include fever, stomach cramps, vomiting and diarrhoea. The symptoms are caused by the toxins produced by the bacteria. Food contaminated with salmonella can give you food poisoning. Most poultry in the UK will have had a vaccination against salmonella.
- Gonorrhoea is a sexually transmitted bacterial disease, passed on by sexual contact. Symptoms include pain when urinating and thick yellow/green discharge from the vagina or penis. To prevent the spread, people should be treated with antibiotics and use a condom.
How to prevent the spread:
- Being hygienic – washing hands thoroughly.
- Destroying vectors – killing vectors by using insecticides or destroying their habitat.
- Isolation – isolating an infected person will prevent the spread.
- Vaccination – people cannot develop the infection and then pass it on.
Fighting Diseases
Defence System
- The skin acts as a barrier to pathogens.
- Hairs and mucus in your nose trap particles.
- The trachea and bronchi secrete mucus to trap pathogens. They also have cilia which move backwards and forwards to transport the mucus towards the throat. This traps any pathogens and the mucus is usually swallowed.
- The stomach contains hydrochloric acid to kill any pathogens that enter the body via the mouth.
The Immune System
This kills any pathogens that enter the body.
Phagocytosis is when white blood cells engulf pathogens and then digest them.
They produce antitoxins to neutralise the toxins.
They also produce antibodies. Pathogens have antigens on their surface, antibodies produced by the white blood cells lock on to the antigen on the outside of the pathogen. White blood cells can then destroy the pathogens. Antibodies are specific to one antigen and will only work on that pathogen.
Vaccinations
Vaccinations have been developed to protect us from future infections. A vaccination involves an injection of a dead or weakened version of the pathogen. They carry antigens which cause your body to produce antibodies which will attack the pathogen. If you are infected again, the white blood cells can produce antibodies quickly.
Pros
- Helps to control communicable diseases that used to be very common.
- Epidemics can be prevented.
Cons
- They don’t always work.
- Some people can have a bad reaction to a vaccine – however, that is very rare.
Fighting Disease – Drugs
Painkillers relieve the pain and symptoms, but do not tackle the cause.
Antibiotics kill the bacteria causing the problem, but do not work on viruses. Viruses are very difficult to kill because they live inside the body cells.
Developing Drugs
There are three main stages in drug testing:
Pre-clinical testing:
- Drugs are tested on human cells and tissues.
- Testing carried out on living animals.
Clinical testing:
- Tested on healthy human volunteers in clinical trials. Starts with a very low dose, then tested on people with the illness to find the optimum dose.
- Placebo is a substance that is like the drug, but does not do anything.
- Placebo effect is when the patient thinks the treatment will work even though their treatment isn’t doing anything.
- Blind trial is when the patient does not know whether they are getting the drug or the placebo.
- Double-blind trial is when both the doctor and the patient do not know whether they are getting the drug.
Drugs from Plants
Chemicals produced by plants to defend themselves can be used to treat human diseases or help with symptoms.
| Drug | Plant/Microorganism |
| Aspirin | willow |
| Digitalis | foxglove |
| Penicillin | mould – penicillium |
New drugs are now made by chemists, who work for the pharmaceutical industry, in laboratories.
Infection and Response Key Vocabulary
- Antibodies
- Antigens
- Antitoxins
- Bacteria
- Blind trial
- Double-blind
- Fungus
- Microorganism
- Phagocytosis
- Placebo
- Protist
- Toxins
- Vaccination
- Vector
- Virus
Key terms can be revised using our GCSE Biology: Infection and Response Glossary, below!
Infection and Response Revision from Beyond
AQA Infection and Response Foundation Assessment Pack (Combined)
Infection and Response Foundation Revision Activity Mat
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