Microbes in Human Welfare

Microbes are present everywhere, and while some cause disease, many are essential to human welfare. In this chapter you will study microbes in household products, such as Lactobacillus and other lactic acid bacteria that convert milk into curd and increase its vitamin B12 content, the bacteria that ferment dosa and idli batter, baker's yeast Saccharomyces cerevisiae used for bread, and Propionibacterium sharmanii, whose carbon dioxide produces the large holes in Swiss cheese. You will then learn about industrial products: alcoholic beverages, antibiotics such as penicillin discovered by Alexander Fleming, organic acids like citric acid from Aspergillus niger, enzymes such as streptokinase, cyclosporin A from Trichoderma polysporum and statins from Monascus purpureus. The chapter also explains sewage treatment, in which primary treatment removes solids and secondary treatment uses aerobic flocs to reduce BOD before anaerobic sludge digesters produce biogas. You will study biogas production by methanogens such as Methanobacterium, biocontrol agents including ladybirds, Bacillus thuringiensis, Trichoderma and baculoviruses, and biofertilisers such as Rhizobium, Azotobacter, cyanobacteria and mycorrhizal fungi like Glomus.

Detailed Worksheet: Microbes in Human Welfare Section A - Definitions (10 marks) 1. What are lactic acid bacteria? State two ways in which they are beneficial to humans. (2 marks) 2. What is BOD? What does a high BOD of a water sample indicate? (2 marks) 3. What are flocs? What is their role in secondary treatment of sewage? (2 marks) 4. Define biofertilisers. Name one bacterial and one fungal biofertiliser. (2 marks) 5. What are methanogens? Name one methanogen and two places where methanogens are found. (2 marks) Section B - Calculations and Applications (15 marks) 6. The BOD of raw sewage entering a treatment plant is 300 mg/L. After primary treatment it falls by 30%, and secondary treatment reduces the remaining BOD by 90%. Calculate the BOD after each stage, and state why the effluent can then be released into a river. (3 marks) 7. A biogas plant produces gas containing 65% methane, 30% carbon dioxide and the rest hydrogen sulphide and other gases by volume. If the plant produces 4 cubic metres of biogas per day, calculate the volume of methane and of carbon dioxide produced daily. Why is cattle dung a good raw material for biogas? (3 marks) 8. Match each product with the microbe that produces it: citric acid, acetic acid, butyric acid, lactic acid, ethanol, statins. (3 marks) 9. A farmer replaces chemical nitrogen fertiliser with Rhizobium inoculation in a legume field and saves Rs 3,600 per acre on urea while spending Rs 400 per acre on the biofertiliser. Calculate his net saving on 5 acres. State two environmental benefits of the change. (3 marks) 10. Identify the biocontrol agent used against each pest or pathogen: (i) aphids (ii) mosquitoes (iii) butterfly caterpillars (iv) plant pathogens in the soil (v) insects and arthropods by species-specific viruses (vi) and name the virus genus used in (v). (3 marks) Section C - Diagrams (10 marks) 11. Draw a labelled diagram of a typical biogas plant showing the dung and water inlet, the digester, the gas holder, the gas outlet and the sludge outlet. (4 marks) 12. Draw a flowchart showing the stages of sewage treatment: primary treatment (filtration and sedimentation), secondary treatment (aeration tanks with flocs, settling tank, activated sludge) and anaerobic sludge digestion. (3 marks) 13. Draw labelled diagrams of the bacteria Lactobacillus and of yeast cells, and of the fungus Penicillium showing conidia. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Explain the discovery of penicillin by Alexander Fleming, including the role of Staphylococci, and the later work of Chain and Florey. Analyse why antibiotics are considered one of the most significant discoveries of the twentieth century, and why their misuse is a concern. (5 marks) 15. Compare the use of chemical pesticides with biocontrol methods in organic farming. Explain the role of Bacillus thuringiensis and baculoviruses, and analyse why an organic farmer prefers to keep some pests in the field rather than eliminate them completely. (5 marks) 16. A city releases untreated sewage into a river. Explain the effects on the aquatic life using the concept of BOD, describe how secondary treatment would solve the problem, and name two government initiatives in India to save major rivers from pollution. (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Draw all diagrams neatly in pencil and label every part. Write the scientific names of microbes correctly.