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GCSE AQA Biology Topic 3: Infection and Response
This is a draft cheat sheet. It is a work in progress and is not finished yet.
Viruses
Viruses are not cells |
They are very small (about 1/100th the size of a bacterium) |
They move into cells and replicate themselves using the cell's systems |
This causes the cells to burst making you feel ill, releasing all of the copies into the bloodstream |
Bacteria
Small prokaryotic cells |
Multiply rapidly by binary fission in your body |
Toxins are produced which causes you to feel unwell |
Fungi
Can be single celled or have a body made of hyphae |
Can produce spores which can be spread to other organisms |
Protists
Some are parasitic meaning they use humans and snimals as their hosts |
All eukaryotic and most are single celled |
Reducing Spread of Disease
Improving Hygiene |
Using simple hygiene measures can prevent the spread of disease. For example, doing thinhs like washing your hands thoroughly |
Destroying Vectors |
By taking precautions to remove vectors, you can prevent the disease from being passed on |
Isolation |
If you isolate someone with a communicable disease, it prevents them from passing it on to anyone else |
Vaccination |
Vaccinating people and animals from communicable disease prevents them from developing the disease and passing it on |
Spread of Pathogens
Direct Contact |
touching contaminated surfaces |
By Water |
drinking or coming into contact with dirty water |
By Air |
pathogens can be carried in the air and then breathed in (droplet infection happened when sneeze droplets are inhaled) |
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HIV
Human Immunodeficiency Virus (HIV) can eventually lead to Acquired Immunodeficiency Syndrome (AIDS) |
Symptoms
- starts with flu-like illness and symptoms |
- if untreated, can travel to lymph nodes and attack immune system cells |
- can stay hidden for many years which is called AIDS |
Spread
- direct sexual contact (eg unprotected sex) |
- exchange of bodily fluids (eg blood through drug users sharing needles) |
- mother to child during pregnancy, birth or breast feeding |
Treatment and Prevention
- no cure but antiretroviral drugs used early can slow or halt the progress to AIDS |
- using barrier methods of contraception to prevent spread |
- not sharing needles or mixing blood |
Gonorrohoea
Introduction: |
- It's a sexually transmitted disease
- In 2018, it was the cause of 13% of diagnosed STDs - Bacterial infection and had the largest increase in the UK |
Symptoms: |
- Thick yellow/green discharge from genitals
- Can be asymptomatic
- Can cause infertility, pelvic pain, ectopic pregnancies, blind babies |
Spread: |
- Unprotected sex |
Treatment and Prevention: |
- Barrier methods of contraception
- can be treated with antibiotics but many strains are now becoming resistant to penicillin
- tracing of all sexual partners in essential so all individuals can be treated and/or treated |
Measles
- Measles is a highly contagious and potentialyl fatal viral infection. |
- Most often seen in children so the majority of young children are vaccinated |
Symptoms
- fever |
- red skin and a rash |
- can lead to blindness and brain damage in extremely severe cases |
Spread
- inhalation of droplets from coughs and sneezes |
- very infectious as these droplets can linger in the air/on surfaces |
Treatment and Prevention
- no treatment so infected people must be isolated to stop spread |
- greatly reduced in the UK due to improved living conditions and a vaccination programme for young children in place |
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Salmonella
- Salmonella food poisoning is spread by bacteria ingested in food or food which has been prepared in unhygienic conditions |
- found in the gut of many different animals |
Symptoms
- symptoms start between 8-72 hours after eating food |
- generally doesn't last for more than a few days |
- more serious in young children and the eldery due to dehydration |
- fever |
- vomiting |
- diarrhoea |
- abdominal cramps |
Spread
- uncooked, contaminated food, including eggs and chicken |
- bacteria can remain on surfaces for some time after so other foods can also get infected |
Treatment and Prevention
- chickens in the UK are vaccinated for salmonella |
- food should be cooked thoroughly |
- hands should be washed before and after handling raw meat and other foods |
- raw meat shouldn't be washed |
Tobacco Mosaic Virus
Introduction: |
- Tobacco Mosaic Virus (TMV) was the first virus to be isolated
- Widespread plant pathogen which affects ~150 species of plant |
Symptoms: |
- Mosaic pattern leaf discolouration
- Stunted growth due to lack of photosynthesis taking place |
Spread: |
- Plants in direct contact with an infected plant can also get the disease
- This particular virus can remain in the soil for ~50 years |
Treatment and Prevention: |
- No treatment currently
- Good field hygiene is the best method of control of TMV (this includes destroying any infected plants as soon as possible)
- Gentically-modified TMV-resistant crops could be grown |
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