Microorganisms: Friend and Foe

Bacteria: single-celled, no nucleus (prokaryote). Found everywhere — soil, water, air, inside us. Both helpful and harmful. Virus: not truly living, needs host cell to reproduce. Smallest — 20-400 nm. Cause flu, COVID, polio. Fungi: mushrooms, yeast, mould. Protozoa: single-celled with nucleus — Amoeba, Plasmodium. Algae: in water, make food by photosynthesis.

Bacteria in curd making (Lactobacillus converts milk→curd). Yeast for bread (CO₂ makes bread rise) and alcohol (fermentation). Bacteria in nitrogen fixation (Rhizobium in roots of legumes converts N₂→ammonia). Decomposers break dead matter into minerals. Antibiotics (Penicillin from Penicillium fungus) fight bacterial infections.

Disease-causing microorganisms are called pathogens. Bacteria cause: TB, cholera, typhoid. Viruses cause: influenza, polio, COVID-19, HIV. Protozoa cause: malaria (Plasmodium via mosquito), amoebic dysentery. Fungi cause: ringworm, athlete's foot. Prevention: vaccines, antibiotics, hygiene, vector control.

Microorganisms spoil food by growing in it. Methods to preserve: 1) Salt — draws out water (dehydrates microbes). 2) Sugar — in jams and jellies. 3) Oil and vinegar — prevent oxygen. 4) Pasteurization — heat to 70°C for 15s (Louis Pasteur). 5) Refrigeration — slows microbial growth. 6) Preservatives — sodium benzoate.