Biology and Human Welfare: Health, Disease and Microbes in Human Welfare
This domain links pathogen biology and immunity with the industrial and agricultural uses of microbes. Questions typically ask you to match a microbe to a product, identify a lymphoid organ, or explain BOD and biocontrol logically.
Human health and disease
- Pathogens to know: Salmonella typhi (typhoid), Plasmodium (malaria), Entamoeba histolytica (amoebiasis), Ascaris, Wuchereria (filariasis) and HIV, a retrovirus carrying reverse transcriptase.
- Innate immunity includes barriers, phagocytes and interferons; acquired immunity is antibody-mediated or cell-mediated. Active immunity follows infection or vaccination; passive immunity comes from colostrum or antivenom.
- An antibody is H2L2, made by plasma cells.
- Primary lymphoid organs are bone marrow and thymus; secondary ones are spleen, lymph nodes, tonsils, Peyer's patches and appendix.
- Cancer arises when proto-oncogenes become oncogenes; cells lose contact inhibition and may metastasise.
Microbes in human welfare
- Lactobacillus curdles milk and adds vitamin B12; Aspergillus niger gives citric acid; Penicillium notatum gives penicillin; Trichoderma polysporum gives cyclosporin A, an immunosuppressant; Monascus purpureus gives statins.
- Saccharomyces cerevisiae is used for bread and ethanol; methanogens such as Methanobacterium produce biogas in anaerobic sludge.
- Sewage treatment: primary physical removal, then secondary activated sludge with aerobic flocs; BOD measures the organic load.
- Biocontrol: Bacillus thuringiensis against caterpillars, Trichoderma against root pathogens, baculovirus against insects. Biofertilisers include Rhizobium, Azotobacter, Azospirillum, Azolla and the mycorrhizal Glomus.
Worked example
A plant receives sewage with BOD 300 mg per litre and discharges effluent at 30 mg per litre. Reduction = (300 - 30)/300 x 100 = 90 per cent. Because high BOD means bacteria strip dissolved oxygen from the river, the effluent must reach a low BOD before release.
Traps that cost marks
- Interferon is a cytokine, not an antibody.
- Colostrum confers passive, not active, immunity.
- Cyclosporin A is an immunosuppressant from a fungus; statins lower cholesterol.
- BOD measures oxygen demanded by microbes, not oxygen produced.