GCSE BIOLOGY REVISION: INFECTION AND RESPONSE
Please note: Text in bold is what the AQA GCSE biology specification requires an understanding of.
Measles is a viral disease showing symptoms of fever and a red skin rash. Measles is a serious illness that can be fatal if complications arise. For this reason most young children are vaccinated against measles. The measles virus is spread by inhalation of droplets from sneezes and coughs. HIV initially causes a flu-like illness. Unless successfully controlled with antiretroviral drugs the virus attacks the body’s immune cells. Late stage HIV infection, or AIDS, occurs when the body’s immune system becomes so badly damaged it can no longer deal with other infections or cancers. HIV is spread by sexual contact or exchange of body fluids such as blood which occurs when drug users share needles. Tobacco mosaic virus (TMV) is a widespread plant pathogen affecting many species of plants including tomatoes. It gives a distinctive ‘mosaic’ pattern of discolouration on the leaves which affects the growth of the plant due to lack of photosynthesis.
What is HIV?
Human immunodeficiency virus
What is AIDS?
Acquired immune deficiency syndrome
Transmission of HIV occurs through body fluids, particularly occurring during unprotected sex. Infection can also happen through cuts, and injecting people with shared needles. Immediate symptoms consist of mild flu-like feelings which do pass. Because of this, it is easy to not realise that one is infected. After months or years after HIV infection, the virus becomes active and begins attacking the immune system cells. HIV has now become AIDS. Scientists are doing ongoing research but to this date there is no cure. The most effective treatment is antiviral drugs, these can slow the development of AIDS.
Measles viral disease is highly infectious and caught by young children. An infected person can transmit the virus when sneezing as they leave tiny droplets in the air. The infection results in a rash on the skin and fever. In developed countries, most children are given the MMR vaccine (measles, mumps and rubella), providing them with immunity. Unfortunately, this is not the case for a lot of developing countries. If an adult did not catch the disease a child, infection can be more severe, they may face effects such as infertility.
Salmonella food poisoning is spread by bacteria ingested in food, or on food prepared in unhygienic conditions. In the UK, poultry are vaccinated against Salmonella to control the spread. Fever, abdominal cramps, vomiting and diarrhoea are caused by the bacteria and the toxins they secrete. Gonorrhoea is a sexually transmitted disease (STD) with symptoms of a thick yellow or green discharge from the vagina or penis and pain on urinating. It is caused by a bacterium and was easily treated with the antibiotic penicillin until many resistant strains appeared. Gonorrhoea is spread by sexual contact. The spread can be controlled by treatment with antibiotics or the use of a barrier method of contraception such as a condom.
Pathogens are microbes which cause disease. Not all bacteria are pathogens. Inside our bodies we have plenty of what we consider ‘healthy bacteria,’ we actually need this bacteria in our bodies. Bacteria are prokaryotes and therefore do not have a nucleus. They are cells, unlike viruses, and are therefore bigger. We still need a microscope to be able to see them however.