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Summary Module 4.1: Disease and the immune system
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OCR biology A level A summary of key concepts ranging from communicable diseases and defence, to the immune system and antibiotics
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COMMUNICABLE DISEASESPathogen
Bacteria
- Produce toxins – break down membranes, inactivate
enzymes, genetic material = not divide
- TB, meningitis, ring rot (food)
Viruses
- Invade living cells, take over cell metabolism
- Attack bacteria – bacteriophages (replication)
- HIV, influenza, tobacco mosaic virus (plants)
Protoctista Non-specific animal defences
- Parasitic, use vector, use cell contents (not DNA) - Skin – healthy microorganisms, sebum
- Potato blight, malaria - Mucous mem – trap microorg, phagosome
- Lysosomes in tears and urine
Fungi - Acid in the stomach
- Produce spores, digest living cells - Expulsive reflexes (cough, sneeze)
- Mitochondria near growing hyphae tips
- Black sigatoka (bananas), ringworm, athletes foot Blood clotting
- Platelets = collagen
Transmission - Release Thromboplastin
Direct transmission (animals) (enzyme triggering cascade)
1) Direct contact – body fluids, skin, faeces - Serotonin (sm, restrict blood)
2) Inoculation – break in the skin, bite, wound - Stem cells differentiate
3) Ingestion – contaminated food below scab (epidermal)
- New vessels grow to
Indirect transmission (animals) provide O2 + nutrients
1) Fomites – inanimate objects - Collagen deposited (scar), tissue contracts edges
2) Inhalation (saliva droplet), water
3) Vectors – animals, insects, humans Inflammatory response
- Mast cells activated by damaged tissue, release chem
Factors affecting animal transmission - Histamines = blood vessels dilate, localised heat to ↓
- Overcrowded, trained health workers reproduction, vessel walls leaky = tissue fluid
- Poor nutrition + waste disposal - Cytokines = attract WBC to site + phagocytosis
- Climate change – wider spread
Specific animal defences
Plant transmission Phagocytosis
1) Direct contact between plants - Neutrophils (lobed), macrophage (bean) = pus
2) Soil contamination – infect next crop - Macrophage + surface pathogen antigens = APC
3) Vectors (wind, water, animals, humans) - Cytokines from phagocytes, cell signalling, ↑ temp
- Opsonins bind to pathogen = phagocyte recognises it
Factors affecting plant transmission
- Crop varieties that are susceptible
- Over crowding, poor mineral nutrition
- Damp, warm conditions (climate change)
Plant defences
Physical defence
- Receptors recognise, cell signalling, genes on/off
- Waxy cuticle – barrier + stops water collecting
- Callose in wall, blocks sieve plates + plasmodesmata
Chemical defence
- Insecticide, antibacterial, antifungal compounds
- General toxins (cyanide kills living things)
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