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GRADE 9 NOTES AQA Biology GCSE Topic 3 Infection & Response

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These are in-depth notes for topic 3 infection and response in the AQA Biology GCSE. It covers everything you need to know for your GCSE exam for topic 3, highlighting the important parts of the specification to help you get those top GRADE 9s.

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Topic 3: Infection & Response o Spread by sexual contact/exchange of body
Communicable adaptations: fluids – like blood when drug users share
 A infectious disease that can be spread between needles
animals and plants directly or indirectly  TMW
 Viral o Widespread plant pathogen affecting many
o Very small species of plants
o Move into cells, live and reproduce and o Like tomatoes
make copies of themselves until cell bursts - o Mosaic pattern – discoloration of leaves 
LYSIS affect leaf growth as can’t photosynthesise
o Damage and destroys cells o Prevent with good field hygiene & pest
 Bacterial control
o Produce toxins Bacterial Diseases:
o Directly damage the cells  Salmonella
o Multiply very quickly in body through binary o Food poisoning
fission o Bacteria ingested in food
 Protist o Food prepared in unhygienic conditions
o Use animals and humans as their hosts o UK – poultry vaccinated against salmonella
(parasitic) to control spread
o Live on the inside and cause damage o Fever, abdominal cramps, vomiting &
 Fungi diarrhoea – caused by bacteria & its toxins
o Produce spores that can be spread to other  Gonorrhoea
organisms o STD
o Can be single celled or have a hyphae body o Thick/yellow green discharge
(thread like structure) o Pain on urinating
 Pathogen: Micro-organisms that cause infectious o Treated with penicillium until restraint
diseases strains
 Diseases can be transmitted by: o Spread by sexual contract
o Direct contact – Kissing, infected plant o Spread controlled by antibiotics or barrier
material, Skin to skin method of contraception
o Air - Droplets Fungal Diseases:
o Water – Contaminated water  Rose Black Spot
drinking/contact  Purple/black spots on leaves
 Preventing disease  Leaves turn yellow & drop early  reduce
o Good hygiene – hand washing, disinfectants photosynthesises & growing
o Reducing contact with infected individuals  Spread in environment by water/wind
o Removing vectors – using pesticides, etc  Treated with fungicides/removing or destroying
o Vaccination – Injecting small amounts of affected leaves
dead or inactive pathogen into someone’s Protist Diseases:
body to stimulate the immune system to  E.g. Pathogens that cause malaria
create antibodies  Malaria protest has a life cycle that includes the
Viral Diseases mosquito
 Measles:  Recurrent episodes of (possibly fatal) fevers
o Fever  Control spread by preventing vectors, mosquitos
o Red Skin Rash from breeding
o Fatal if complications arise  Using mosquito nets to avoid being bitten
o Young chidren are vaccinated against  Vaccine to prevent
measles Human Defence Systems:
o Spread by ihalations of droplets – sneezes &  Non-Specific Defence systems ↓
 Skin
coughs
1. Physical barrier
 HIV
2. Produced antimicrobial secretions to kill
o Flu-like illness
pathogens
o Attacks body’s immune cells unless
 Nose
controlled by antiretroviral drugs
1. Hair to trap dust
o Late-stage HIV/AIDS – body’s immune
2. Mucus to trap dust to stop particles from
system badly damaged & can’t deal with
entering your lungs
other infections/ cancers
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