Summary

Household products: Lactobacillus and other lactic acid bacteria (LAB) convert milk to curd by producing acid that coagulates and partially digests milk proteins. Dough for idli/dosa is fermented by bacteria (the book leaves the species unnamed), producing CO2 that leavens the batter. Bread dough rises due to CO2 from baker’s yeast.

Industrial products: Fermenters (large vessels) are used for large-scale microbial growth. S. cerevisiae (brewer’s yeast) produces ethanol for beverages and fuel. Propionibacterium sharmanii ripens Swiss cheese; Roquefort cheese is ripened by a specific fungus (the NCERT text itself doesn't name the species). Citric acid is produced by Aspergillus niger; acetic acid (vinegar) by Acetobacter aceti.

Antibiotics: Alexander Fleming discovered penicillin from Penicillium notatum. Antibiotics are chemicals produced by microbes that kill or inhibit other microbes. They are selectively toxic — they target bacterial cell walls, ribosomes, or metabolic pathways without harming human cells. Overuse leads to antibiotic resistance.

Sewage treatment: Primary treatment removes solids by sedimentation. Secondary treatment (biological) uses aerobic microbes in an aeration tank to break down organic matter into CO2, water, and settleable flocs. The effluent is then disinfected. The settled sludge is digested anaerobically by methanogens (e.g., Methanobacterium) to produce biogas (CH4, CO2, H2).

Biogas: A mixture of methane (approximately 50-70%), carbon dioxide, and traces of hydrogen sulfide, produced by anaerobic digestion of organic waste. Used as a clean fuel for cooking and lighting. The spent slurry is a rich fertiliser. …