NCERT Solutions for Class 12 Biology Chapter 8 Microbes in Human Welfare

Short Note:

• Microbes such as Lactobacillus are used to convert milk into curd, and yeast (Saccharomyces cerevisiae) is used in the fermentation process for making bread and alcoholic beverages.

• In large-scale industrial processes, microbes are used to produce various products, including antibiotics (e.g. Penicillium notatum for penicillin), organic acids (e.g. Aspergillus niger for citric acid), and enzymes used in detergents and the food industry.

Short Note:

• In sewage treatment, microbes play a key role in the secondary (biological) treatment stage, where heterotrophic bacteria and other microbes break down organic matter present in sewage, significantly reducing the biochemical oxygen demand (BOD) of the water.

• Biogas, primarily composed of methane, is produced through the anaerobic breakdown of organic waste (cattle dung, plant material) by a consortium of bacteria called methanogens, such as Methanobacterium, and serves as a renewable source of energy for cooking and lighting.

Short Note:

• Biocontrol agents use natural predators, parasites, or pathogens to control pests and diseases without harmful chemical pesticides; examples include the bacterium Bacillus thuringiensis (Bt), used to control butterfly caterpillars, and the fungus Trichoderma, used against plant pathogens.

• Biofertilisers are organisms that enrich soil fertility through processes like nitrogen fixation; examples include the bacterium Rhizobium (in symbiosis with leguminous plant roots), the cyanobacterium Nostoc, and mycorrhizal fungi that improve phosphorus absorption in plants.