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Lecture notes Module 4: Biodiversity, evolution and disease $20.23   Add to cart

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Lecture notes Module 4: Biodiversity, evolution and disease

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Want an A* in A-level biology? This document contains detailed yet easy-to-digest A-level notes for OCR Biology A. It contains several images and diagrams as well as bullet pointed, summarised typed information which will save you HOURS of making your own notes. These notes are uncomplicated to rea...

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  • November 19, 2022
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  • 2018/2019
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Module 4
Communicable diseases
• Communicable disease- disease that’s passed from one organism to another (within and possibly
between species).
• Caused by infective organisms- pathogens.
- E.g. bacteria, viruses, fungi and protoctista.
• Vectors carry pathogens from one organism to another e.g. water and insects.
• Cause of 23% of deaths world-wide.
• Major problem in domestic and wild animals and plants e.g. pets and farm animals- cows, goats
and sheep etc.

Bacteria
• Classified in 2 main ways:
1. Basic shape:
- Rod (bacilli).
- Spherical (cocci).
- Comma shaped (vibrios).
- Spiral (spirilla).
- Corkscrew (spirochaete).
2. Cell wall:
- Gram +ve = purple under light
microscopeà thick cell wall e.g.
staphylococcus aureus.
- Gram –ve= red- safranin counterstain.
Important to identify bacteria so we know what medication to prescribe etc.

Viruses:
• Non-living and are all pathogenic.
• 0.02- 0.3 micrometers.
• Structure- DNA/RNA surrounded by protein.
• Invade living cell, take over its biochemistry to make more copies of
virus rapidly- ultimate parasites (only active when inside host cell,
have little structure but take over whole host cell).
- Bacteriophage= viruses that attack bacteria.

Protoctista/ protista:
• Eukaryotic organism.
• Unicellular.
• Parasitic- use people or animals as their host e.g. malaria/ sleeping sickness or enter through
polluted water e.g. amoebic dysentery/ Giardia.
• Take over host e.g. plasmodium and Hb.

Fungi:
• Eukaryotic.
• Can be multicellular or unicellular.
• Can cause diseases in plants and animals.
• Reproduce- make millions of spores which spread huge distances.
Pathogens- mode of action:
- Damaging host tissues directly.


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, 1. Viruses- get into host cell’s DNA and takes over cells metabolism to make new viruses which burst
out of the cell and spread to infect other cells.
2. Protoctista- takes over cell and feed on cell contents as they reproduce e.g. plasmodium.
3. Fungi- digest living cells and destroy them.

Pathogens- mode of action:
- Producing toxins which damage host tissues- indirect.
1. Bacteria- produce toxins/poison as a by-product of their normal function, which damages host cells
e.g. by breaking down cell membranes/ inactivating enzymes/interfering with genetic material to
prevent cell division.
2. Some fungi- produce toxins to cause disease.

Plant diseases:
Plant disease Caused by Host Description
Ring rot - Gram positive - Potatoes. - Damages leaves, tubers, fruits.
bacterium. - Tomatoes. - No cure.
- Clavibacter - Aubergines. - If ring rot infects a field, potatoes can’t grow
michiganenesis. on that field for 2 years.
Tobacco - Virus. - Tobacco plants. - Damages leaves, flowers, fruit and stops
mosaic virus - Tomatoes. growth and reduces yield.
(TMV) - Peppers. - No cure.
- Cucumbers. - Resistant crop strains available.
- 150 other plant
species.
Potato blight - Fungus like - Potatoes. - Destroys leaves, tubers and fruit.
protoctist. - No cure.
- Phytophthora - Resistant strains.
infestans. - Careful management and chemical
treatments can reduce infection risk.


Black sigatoka - Fungus. - Bananas. - Hyphae penetrates and digests leaves,
- Mycosphaerella - Plantains. turning them black.
fijiensis. - Resistant strains being developed.
- No cure.
- Good husbandry and fungicide can control
speed.


PLANT DISEASES CANNOT BE TREATED/ CURED.




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,Animal diseases:
Animal disease Caused by Host Description
TB - Bacteria. - Humans. - Destroys lung tissue.
- Mycobacterium - Cows. - Suppresses immune system.
tuberculosis. - Pigs. - Curable by antibiotics.
- M.bovis. - Badgers. - Preventable by improving living conditions +
- Deers. vaccinations.
Meningitis - Bacteria. - Humans- - Causes septicaemia- purple/red rash when
- Streptococcus young glass is pressed.
pneumoniae. children and - 10% of infected ppl die.
- Neisseria teenagers. - 25% recover but still have permanent
meningitidis. damage.
- Antibiotics cure it if treated early.
- Vaccines can protect against it in some
forms.
HIV - Virus. - Humans. - Destroys T cells so you are susceptible to
- Non- human other infections.
primates. - No vaccine/ cure.
- Anti-retroviral drug to slow down
progression.
Flu - Virus. - Mammals- - Destroys ciliated epithelial cells, leaving
- Orthomyxoviridae humans, airways open to secondary infections- can
spp. pigs, birds be fatal to young/old.
and - 3 main strains- A, B, C (A- most virulent).
chickens. - Classified by surface proteins e.g. A (H1N1).
- Mutate regularly.
- No cure.
Malaria - Protoctista. - Mosquitoes. - Reproduce in female mosquito- after 2
- Plasmodium. - Humans. blood meals, she lays eggs and is passed on.
- Spread by bites of - Invades erythrocytes, liver and brain-
anopheles increases vulnerability to other infections.
(female) - No vaccines/ limited cures.
mosquito. - Preventative measures (insecticides,
mosquito nets/ door screens).
Ring worm - Different fungi - Cattle. - Causes grey- white, crusty infectious,
affect different - Dogs. circular areas of skin- itchy.
species. - Cats. - Anti- fungal cream is effective cure.
- Trichophyton - Humans.
verrucosum.
Athletes foot - Fungus. - Humans. - Grows on and digests the warm, moist skin
- Tinia pedia. between toes- causes cracking and scaling-
itchy and sore.
- Anti-fungal cream is an effective cure.

Direct transmission:
- Pathogen directly transferred from one individual to another.
1. Direct contact (contagious diseases):
- Exchange bodily fluids e.g. STD.
2. Inoculation:
- Skin-to-skin contact. E.g. ringworm/athletes foot.

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, 3. Ingestion:
- Microorganisms from faeces transmitted on hands e.g. diarrhoeal diseases.

Indirect transmission:
- Pathogen indirectly transferred from one individual to another through another medium e.g. air/
H2O.
1. Tomites:
- Sharing inanimate objects such as bedding, socks or cosmetics e.g. athletes foot, gas gangrene.
2. Droplet infection (inhalation):
- Inhaling droplets of saliva/ mucus containing pathogens from someone sneezing e.g. flu/ TB.
3. Vectors:
- Often, but not always animal carrying pathogen e.g. dogs transmit rabies, mosquitoes transmit malaria.

Transmission between animals and humans:
• Bird flu strain H1N1 and bucellosis passed from sheep to humans.
• We can minimise contact and wash hands to reduce infection rates.
• People can act as vectors of some animals’ diseases e.g. foot and mouth disease.

Factors affecting transmission of communicable diseases in animals:
1. Overcrowded conditions.
2. Poor nutrition.
3. Compromised immune system system e.g. people with HIV/ babies/ old people.
4. Poor waste disposal provides breeding site for vectors.
5. Climate change introducing new vectors e.g. higher temps= optimum for mosquitoes. If it gets hot
here, we could get malaria etc.
6. Culture and infrastructure.
7. Socioeconomic factors.

Preventing spread of communicable diseases:
- Keep clean/ shower everyday/ wash hands.
- Have probiotics- yogurt etc.
- Multivitamins- nutrition.
- Hand sanitiser.
- Dispose of waste properly.

Transmission of pathogens between plants:
• Plant pollen and seeds move widely.
• Less well developed immune system than humans.
- Direct transmission:
• Direct contact of a healthy plant with any part of a diseased plant.
- Indirect transmission:
1. Soil contamination:
- Pathogens and reproductive spores from protoctista and fungi spread to crops.
- Some survive composting process and infection cycle is completed when contaminated compost is
used.
2. Vectors:
- Wind-spores carried to other plants.
- Water-spores swim on the surface water of leaves and spread by raindrop splashes.
- Animals- insects/ birds carry spores. Aphids inoculate pathogens directly into plant tissues.
- Humans- transmitted by hands, clothing, formites, farm machinery.

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