AQA Biology GCSE
Topic 3: Infection and Response Notes
Content in bold is for higher tier only.
Content is for both separate science and double award students unless
indicated in heading.
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Communicable Diseases (3.1)
Communicable (Infectious) Diseases (3.1.1)
Pathogens, which include viruses, bacteria, protists and fungi, are microorganisms
that cause infectious disease. They can infect plants or animals, spreading through
either direct contact, by water or by air.
1. Viruses
● Very small
● They move into cells and use the biochemistry of it to make many copies of
itself
● This leads to the cell bursting and releasing all of the copies into the
bloodstream
, ● The damage and the destruction of the cells makes the individual feel ill
2. Bacteria
● Small
● They multiply very quickly through dividing by a process called binary
fission
● They produce toxins that can damage cells
3. Protists
● Some are parasitic, meaning they use humans and animals as their hosts
(live on and inside, causing damage)
4. Fungi
● They can either be single celled or have a body made of hyphae (thread-like
structures)
● They can produce spores which can be spread to other organisms
The ways they are spread:
● Direct contact- touching contaminated surfaces
Examples: kissing, contact with bodily fluids, direct skin to skin, microorganisms
from faeces, infected plant material left in field
● By water- drinking or coming into contact with dirty water
● By air- pathogens can be carried in the air and then breathed in (a common
example is the droplet infection, which is when sneezing, coughing or talking
expels pathogens in droplets which can be breathed in)
The damage that disease causes to populations can be reduced by limiting the spread of
the pathogens.
● Improving hygiene: Hand washing, using disinfectants, isolating raw meat, using
tissues and handkerchiefs when sneezing
● Reducing contact with infected individuals
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● Removing vectors: Using pesticides or insecticides and removing their habitat ●
Vaccination: By injecting a small amount of a harmless pathogen into an individual’s
body, they can become immune to it so it will not infect them. This means they cannot
pass it on.
Viral Diseases (3.1.2)
Viruses are particularly dangerous as they can enter all types of cells, and scientists are
yet to develop medicines to cure them.
Measles
Symptoms: Fever and red skin rash, can lead to other problems such as pneumonia (lung
infection), encephalitis (brain infection) and blindness.
How it is spread: Droplet infection
, How it is being prevented: Vaccinations for young children to reduce transmission
HIV
Symptoms: Initially flu-like symptoms, then the virus attacks the immune system and leads
to AIDS (a state in which the body is susceptible to many different diseases)
How it is spread: By sexual contact or exchange of bodily fluids such as blood
How it is being prevented:
● The spread- Using condoms, not sharing needles, screening blood when it is used
in transfusions, mothers with HIV bottle-feeding their children instead of
breastfeeding
● The development to AIDS- Use of antiretroviral drugs (stop the virus replicating in
the body)
Tobacco mosaic virus (a plant pathogen affecting many species of plants including
tomatoes)
Symptoms: Discolouration of the leaves, the affected part of the leaf
cannot photosynthesise resulting in the reduction of the yield.
How it is spread: Contact between diseased plants and healthy plants, insects act as
vectors.
How it is being prevented: Good field hygiene and pest control, growing TMV-resistant
strains.
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Bacterial Diseases (3.1.3)
Bacterial diseases are on the rise as they are becoming resistant to antibiotics.
Salmonella food poisoning (bacteria that live in the gut of different animals, which we
ingest when we eat the meat)
Symptoms: Fever, stomach cramps, vomiting, diarrhoea (all caused by the toxins they
secrete).
How it is spread: These bacteria can be found in raw meat and eggs, unhygienic
conditions.
How it is being prevented: Poultry are vaccinated against Salmonella, keeping raw meat
away from cooked food, avoid washing it, wash hands and surfaces when handling it, cook
food thoroughly.
Gonorrhoea
Topic 3: Infection and Response Notes
Content in bold is for higher tier only.
Content is for both separate science and double award students unless
indicated in heading.
https://bit.ly/pmt-edu-cc https://bit.ly/pmt-cc
This work by PMT Education is licensed under CC BY-NC-ND 4.0https://bit.ly/pmt-edu
https://bit.ly/pmt-cc https://bit.ly/pmt-cc
Communicable Diseases (3.1)
Communicable (Infectious) Diseases (3.1.1)
Pathogens, which include viruses, bacteria, protists and fungi, are microorganisms
that cause infectious disease. They can infect plants or animals, spreading through
either direct contact, by water or by air.
1. Viruses
● Very small
● They move into cells and use the biochemistry of it to make many copies of
itself
● This leads to the cell bursting and releasing all of the copies into the
bloodstream
, ● The damage and the destruction of the cells makes the individual feel ill
2. Bacteria
● Small
● They multiply very quickly through dividing by a process called binary
fission
● They produce toxins that can damage cells
3. Protists
● Some are parasitic, meaning they use humans and animals as their hosts
(live on and inside, causing damage)
4. Fungi
● They can either be single celled or have a body made of hyphae (thread-like
structures)
● They can produce spores which can be spread to other organisms
The ways they are spread:
● Direct contact- touching contaminated surfaces
Examples: kissing, contact with bodily fluids, direct skin to skin, microorganisms
from faeces, infected plant material left in field
● By water- drinking or coming into contact with dirty water
● By air- pathogens can be carried in the air and then breathed in (a common
example is the droplet infection, which is when sneezing, coughing or talking
expels pathogens in droplets which can be breathed in)
The damage that disease causes to populations can be reduced by limiting the spread of
the pathogens.
● Improving hygiene: Hand washing, using disinfectants, isolating raw meat, using
tissues and handkerchiefs when sneezing
● Reducing contact with infected individuals
https://bit.ly/pmt-cc https://bit.ly/pmt-cc
https://bit.ly/pmt-edu
● Removing vectors: Using pesticides or insecticides and removing their habitat ●
Vaccination: By injecting a small amount of a harmless pathogen into an individual’s
body, they can become immune to it so it will not infect them. This means they cannot
pass it on.
Viral Diseases (3.1.2)
Viruses are particularly dangerous as they can enter all types of cells, and scientists are
yet to develop medicines to cure them.
Measles
Symptoms: Fever and red skin rash, can lead to other problems such as pneumonia (lung
infection), encephalitis (brain infection) and blindness.
How it is spread: Droplet infection
, How it is being prevented: Vaccinations for young children to reduce transmission
HIV
Symptoms: Initially flu-like symptoms, then the virus attacks the immune system and leads
to AIDS (a state in which the body is susceptible to many different diseases)
How it is spread: By sexual contact or exchange of bodily fluids such as blood
How it is being prevented:
● The spread- Using condoms, not sharing needles, screening blood when it is used
in transfusions, mothers with HIV bottle-feeding their children instead of
breastfeeding
● The development to AIDS- Use of antiretroviral drugs (stop the virus replicating in
the body)
Tobacco mosaic virus (a plant pathogen affecting many species of plants including
tomatoes)
Symptoms: Discolouration of the leaves, the affected part of the leaf
cannot photosynthesise resulting in the reduction of the yield.
How it is spread: Contact between diseased plants and healthy plants, insects act as
vectors.
How it is being prevented: Good field hygiene and pest control, growing TMV-resistant
strains.
https://bit.ly/pmt-cc https://bit.ly/pmt-cc
https://bit.ly/pmt-edu
Bacterial Diseases (3.1.3)
Bacterial diseases are on the rise as they are becoming resistant to antibiotics.
Salmonella food poisoning (bacteria that live in the gut of different animals, which we
ingest when we eat the meat)
Symptoms: Fever, stomach cramps, vomiting, diarrhoea (all caused by the toxins they
secrete).
How it is spread: These bacteria can be found in raw meat and eggs, unhygienic
conditions.
How it is being prevented: Poultry are vaccinated against Salmonella, keeping raw meat
away from cooked food, avoid washing it, wash hands and surfaces when handling it, cook
food thoroughly.
Gonorrhoea
