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OCR A A-Level Biology
Pathogen
microorganism that causes disease
Bacteria (reproduction, method of infection, plant infection)
can reproduce every 20 minutes, can damage cells or release waste products/toxins, in plants can cause blackening and death in vascular tissues
Examples of Bacterial diseases
Tuberculosis, Ring rot, Bacterial meningitis
Fungi (method of infection)
fungus lives in skin of animal, mycelium grows under skin surface, specialised reproductive hyphae grow to the surface of the skin and release spores
Hyphae
fine white filaments branching from the fungus
Mycelium
vegetative part of fungus made from network of hyphae
Fungus (plant infection)
in vascular tissue, hyphae release extracellular enzymes that digest surrounding tissues, decays vascular tissue; leaves become mottled, curl up and shrivel; fruit/tubers turn black and decay
Examples of Fungal diseases
Black sigatoka (bananas), Ringworm, Athlete’s foot
Viruses (method of infection)
invades cells and takes over genetic machinery/organelles to produce many copies of the virus, host cell bursts to release new viruses
Examples of Viral Diseases
HIV/AIDS, Influenza, Tobacco Mosaic Virus
Protoctista (method of infection)
enters host cell and feeds on cell contents
Examples of Protist Diseases
Malaria caused by Plasmodium (feeds on haemoglobin in red blood cells), Potato/Tomato late blight
Note 
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