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Everything you need to know about soil microbiology. Some of the most frequently asked exam questions are as follows:-
Q.1. Name the bacterium that prey on other bacteria.
Ans: Bdellovibrio.
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Q.2. Give some examples of mutualism (symbiosis) in which both organisms are benefitted.
Ans: (1) Association of fungus and alga in lichens.
(2) Protozoa serving as host to single celled algae which live inside the cytoplasm of protozoan. The protozoa give space and protection while the algae provide additional nutrients for the host.
Q.3. What is commensalism?
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Ans: In commensalism, one organism benefits from the relationship without affecting the other, e.g., some bacteria can degrade polymers such as cellulose into simpler component glucose which is utilized readily by the neighbouring scavengers.
Q.4. What is co-metabolism?
Ans: Some organisms cannot break down the resistant chemicals like pesticides but they can do so if given a primary source of energy such as glucose.
Q.5. Why is soil regarded as “biologic fire”.
Ans: The leaf shed by a tree is consumed easily by the soil converting its organic matter into carbon, nitrogen and other chemical compounds.
Q.6. What is the percentage of organic matter in soil?
Ans: It is 2-10% in agricultural soils and up-to 95% in peat bog soils.
Q.7. What is humus?
Ans: The dark coloured material in soil which consists of partially decomposed organic matter is called humus.
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Q.8. Why do soil gases generally have a high proportion of carbon dioxide and a low proportion of oxygen?
Ans: Due to respiration of soil organisms.
Q.9. Where do soil gases exist?
Ans: Soil gases exist in pores and spaces between soil particles or are dissolved in the water contained by it.
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Q.10. Name the animals that occur in fertile soil.
Ans: They range from nematodes (minute worms) to large forms as insects, millipedes, centipedes, spiders, slugs, snails, earthworms, mice, moles, gophers (burrowing rodents) and reptiles.
Q.11. At which depth in a garden soil does the maximum number of microorganisms per gram occur?
Ans: At a depth of 3-8 cm.
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Q.12. What is geosmin?
Ans: The gaseous material produced by the actinomycetes which provides soil with the characteristic of musty odour is called geosmin.
Q.13. What is biomass?
Ans: The total mass of living organisms in a given volume is biomass. The biomass of actinomycetes is about equal to the biomass of all bacteria present in the soil.
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Q.14. The number of protozoa tends to rise or fall with the bacterial populations. Why?
Ans: Because of the predatory habit of many of them.
Q.15. Name the common microbial pathogens of soil.
Ans: The endospore forming bacteria are common survivors in soil, e.g., Bacillus anthracis causative agent of anthrax in animals, Clostridium tetani which causes tetanus, Clostridium botulinum the causal organisms of botulism and Clostridium perfringens the causal organisms of gas gangrene.
Q.16. Name the soil bacterium which is a pathogen of insects.
Ans: Bacillus thuringiensis.
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Q.17. What elements are dependent on biogeochemical cycles?
Ans: These are carbon, nitrogen, sulphur and phosphorus.
Q.18. Where from comes the inorganic carbon used in synthesis of organic compounds.
Ans: From CO2.
Q.19. What is greenhouse effect?
Ans: It is the increase of carbon dioxide in the atmosphere due to excessive use of fossil fuels universally resulting in the warming of the earth.
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Q.20. How does ammonia released from decomposition of proteins in the soil behave?
Ans: In dry soil the ammonia passes out while in moist soil it solubilizes.
The ammonium ions so formed are used by bacteria and plants for the synthesis of amino acids.
Q.21. What is nitrification? Name the two bacterial species associated with nitrification.
Ans: The process of oxidation of ammonium ion to nitrate is called nitrification. The autotrophic nitrifying bacteria living in the soil are Nitrosomonas and Nitrobacter. Nitrification takes place in the two steps given below:
Q.22. What is denitrification? Name the bacterial species causing it.
Ans: The breaking down of nitrates into atmospheric nitrogen is denitrification, e.g.,
Common denitrifying bacteria are Pseudomonas. Some other genera include Paracoccus, Thiobacillus and Bacillus.
Q.23. Name the non-symbiotic nitrogen fixing bacteria.
Ans: They are Azotobacter and some cyanobacteria. The other species are Clostridum, Klebsiella, Enterobacter (anaerobic) and Rhodospirillum and Chlorobium (aerobic photoautotrophic).
Q.24. What is rhizophere?
Ans: The region where soil and roots make contact particularly in grasslands. This region is rich in microbial population.
Q.25. Name the symbiotic nitrogen fixers.
Ans: Rhizobium and Bradyrhizobium which form nodules in the roots of leguminous plants.
Q.26. Give an example of nitrogen economics in a forest involving alga and fungus.
Ans: Lichen.
Q.27. Name three symbionts of cyanobacteria.
Ans: (1) Anthoceros a bryophyte
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(2) Azolla a small floating-fern and
(3) Cycas a gymnosperm.
Q.28. Give example of symbiotic nitrogen fixing root nodule formed by a member of actinomycetes.
Ans: Frankia.
Q.29. Give steps in the formation of root nodules.
Ans: (1) Attachment of Rhizobium on the root hair.
(2) Formation of infection thread through which bacteria enter.
(3) The bacterial cells change into pleomorphic bactericide and the packed root cells enlarge in size.
(4) The enlarged root cells form a nodule.
Q.30. What is recalcitrance? Give an example?
Ans: It is resistance to degradation, e.g., DDT as a recalcitrant.
Q.31. What is one of the major causes of elimination of eagles and other predatory birds that enjoyed abundance of food two decades back in the plains of North India.
Ans: Accumulation of DDT from contaminated food resulting in impairing of their reproductive system.
Q.32. Define amensalism.
Ans: It is an interactive association between two populations which is detrimental to one and does not adversely affect the other. In it one microbial population produces a sub lance which is inhibitory to other populations. Such inter population relationship is called amensalism. The terms antibiosis and allelopathy are also used to describe the cases of chemical inhibition. The first population may not be affected by the inhibitory substance or may gain competitive edge i.e., beneficial.
