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BIOLOGY SUMMARY

Biodiversity, Evolution & Disease

MODULE 4

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MODULE 4Biodiversity, Evolution & Disease

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TOPIC 1Pathogens in Plants and Animals • Pathogen = disease-causing microorganism

○ Bacteria – Produce harmful toxins – E.g. tuberculosis, meningitis, ring rot

○ Viruses – Invade host cells + infect with DNA – New copies of virus secreted by host cell – E.g. HIV/AIDS, influenza

○ Fungi – Release hyphae which cause irritation – E.g. ringworm, athlete’s foot

○ Protoctista – Feed on cell contents for growth – E.g. Malaria, potato blight

• Tuberculosis – Caused by M. tuberculosis bacterium – Survives 6 months outside host – Droplet transmission – 1% global population newly infected/year

• HIV/AIDS – Human immunodeficiency virus – Attacks + weakens immune system – Secondary pathogen/opportunistic infection

causes death – Sexually transmitted/ vertical transmission/

shared needles – 5 million new infections/year worldwide

• Malaria ○ Caused by P. falciparum ○ Parasite lives in RBCs ○ Enters mosquito vector during feeding ○ Enters next host upon next mosquito feeding

• Means of transmission ○ Direct transmission

– Droplet (sneezing) – Physical contact – Faecal-oral – Transmission by spores

○ Indirect transmission – Vector

• Climate and the spread of disease ○ Some pathogens only exist in warm climates (e.g. malaria — where mosquitoes are)

○ Very cold climates can kill some pathogens • Environment and the spread of disease

○ Cramped conditions = increased droplet and physical contact transmission

○ Dirty environments = increased faecal-oral transmission

• Passive plant defences against pathogens ○ Cellulose wall with lignin ○ Waxy cuticles ○ Bark ○ Closed stomata ○ Callose ○ Tylose ○ Chemical production

• Active plant defences against pathogens ○ Leaf sensation of pathogens ○ Increase cellulose/chemical production ○ Oxidative bursts

• Primary defences = stop pathogens entering body • Secondary defences = prevent pathogens harming body

once it has entered host • Non-specific defences = occur in the same way no matter

the pathogen • Specific defences = specifically target the pathogen • Primary, non-specific defences in animals:

○ Epidermis ○ Dermis ○ Cell division in deep skin layers ○ Replace cells lost from surface ○ Sebaceous glands ○ Mucous membranes with lysosomes ○ Blood clots stop blood loss and create barrier to infection

○ Clotting cascade ○ Histamine in inflammation = increase phagocyte supply

○ Phagocytes phagocytose ○ Coughing and sneezing reflexes

• Neutrophils are a type of phagocyte ○ Multilobed nucleus ○ Produced in bone marrow ○ Short lived but present in large numbers

• Macrophages are a type of phagocyte ○ Larger than neutrophils ○ Produced in bone marrow ○ Present in organs, esp. Lymph nodes

• Phagocyte action ○ Phagocyte envelopes and engulfs pathogen ○ Membrane folds inwards: phagocytosis ○ Pathogen in phagosome in cell ○ Lysosomes + phagosome = phagolysosome ○ Lysins digest pathogen ○ Final products are harmless and exocytosed

• T cells are a type of lymphocyte ○ T helper cells

– Release cytokines that promote phagocytosis ○ T killer cells

– Kill infected host cells ○ T memory cells

– Long-term immunity ○ T regulator cells

– Ends the immune response • B cells are a type of lymphocyte

○ Plasma cells – Circulate in blood + produce antibodies

○ B memory cells

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