4.1 Communicable Diseases

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