A-Level Biology OCR A - Module 4 – Chapter 12 – Communicable diseases
Disclaimer: These notes are for the OCR spec (but can be used for any spec). My notes do not cover
everything but it’s a pretty decent summary. Use at your own risk, there may be errors, but there shouldn’t
be. Also, some words are abbreviated.
Youtubers I recommend: BioRach, Free Science Lessons, Clare Biology, Miss Estruch.
12.1 - Animal and plant pathogens
o Communicable diseases are caused by infective organisms known as pathogens and can be
passed from one organism to another.
o What do vectors do? → Carry pathogens from one organism to another. E.g. water, insects
o Which pathogen is not alive? → Viruses. They are non-living.
o How do bacteria damage host tissues? → Produce toxins to break down the cell's membrane,
inactivate enzymes, or interfere w HC's genetic material so cells cannot divide.
o How do viruses damage host tissues? → Their genetic material is inserted into host DNA.
Virus reproduce + burst out of cell. Cell is destroyed and virus spreads.
o How do protists damage host tissues? → Digest and use the cell's contents as they reproduce.
Then break open cell. (Do not take over genetic material)
o What do some protists need to be transferred to their hosts? → A vector. E.g. malaria,
amoebic dysentery.
o How do fungi damage host tissues → Digest living cells and destroy them. Some fungi
produce toxins to damage host cells.
12.2 - Animal and plant diseases
o How do plant diseases threaten people? → Starvation, economies struggle, jobs lost
o What pathogen causes ring rot and how does it affect a plant? → Bacteria. Affects potatoes,
tomatoes etc. Damages leaves + fruit.
o What pathogen causes tobacco mosaic virus and how does it affect a plant? → Virus.
Infects tobacco plants, tomatoes etc. Damages leaves, fruit and stunts growth.
o What pathogen causes potato blight and how does it affect a plant? → Protist. Penetrates
host cells, destroys leaves, fruit.
o What pathogen causes black sigatoka and how does it affect a plant? → Fungi. Affects
bananas. Penetrates and digests cells. Leaves turn black.
o Despite there being no cure for these plant diseases, how can the spread be controlled? →
Careful management, chemical treatments, resistant crop strains.
o What pathogen causes TB and what is the effect it has? → Bacteria called Mycobacterium
tuberculosis or M. bovis (cattle). Affects humans, cows, pigs, badgers. Destroys lung tissue,
suppresses immune system.
o What pathogen causes bacterial meningitis and what is the effect it has? → Bacteria.
Mainly affects children + teenagers. Infects meninges (membrane) of brain and can spread
into rest of body causing septicaemia (blood poisoning).
, o What pathogen causes HIV/AIDS, how does it happen, and what effect does it have? →
Human immunodeficiency virus. Passed from one person to another in bodily fluids:
Unprotected intercourse, shared needles, breast feeding. HIV targets T helper cells + destroys
the immune system.
o What pathogen causes influenza and what does it do? → Virus. Affects humans, pigs, birds.
Kills ciliated epithelial cells in gas exchange system, leaving airways open to secondary
infection.
o What pathogen causes malaria, effect, prevention? → Protist Plasmodium. Vector: female
Anopheles mosquito. Invades RBCs, liver, brain. Prevent with insecticides, nets, door
screens.
o What pathogen causes ringworm? → Fungi. Affects humans, cattle, dogs. Prevent w
antifungal cream.
o What pathogen causes athlete's foot? → Fungi Tinia pedia. Affects humans. Causes
cracking and scaling between toes, digests skin. Prevent w antifungal cream.
12.3 - The transmission of communicable diseases
o ANIMALS
What are some examples of direct contact? → Holding hands (ring worm)
What are some examples of inoculation? → Breaking skin (HIV), animal bite
(rabies), sharing needles (septicaemia)
What ingestion can cause a disease? → Consuming contaminated food/water.
What are fomites? → Objects like bedding, socks, makeup, which can transfer
pathogens (athlete's foot)
What is droplet infection? → Breathing in droplets of saliva/mucus containing
pathogens (tuberculosis, influenza)
What is another way a disease can be transmitted indirectly? → Vectors: mosquitoes,
fleas, dogs, water.
Factors affecting transmission of diseases in animals? → Overcrowded living, Poor
nutrition, Weak immune system, Poor waste disposal, Climate change, Social factors
(insufficient public warning, lack of trained health workers)
How to prevent the spread of communicable diseases in humans? → Reduce
overcrowding, wear masks, immediate quarantine for ppl w symptoms, improve
ventilation, kill the diseased rats, train untrained workers in hospitals, educate
population about risk of X, dispose waste effectively, quarantine, travel ban, hand
washing gels.
