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Q13(b):
Find out the role of microbes in the following and discuss it with your teacher.
(b) Soil
Solution :
Step 1: Theoretical Foundation of Soil Microbiology
Soil is not merely a mineral substrate but a complex, biologically active ecosystem (the rhizosphere and bulk soil) where microbes act as the primary catalysts for biogeochemical cycling. Microbes, including Bacteria, Fungi, Actinomycetes, Protozoa, and Algae, maintain soil fertility and structure [Per the principles of Soil Ecology].
Step 2: Key Roles of Microbes in Soil Maintenance
The roles of microbes in soil can be categorized into distinct functional groups:
- Biogeochemical Cycling: Microbes drive the transformation of essential elements ($N, P, K, S, C$). For instance, in the Nitrogen cycle, Rhizobium (symbiotic) and Azotobacter (free-living) facilitate Nitrogen fixation [Biological Nitrogen Fixation].
- Organic Matter Decomposition: Saprophytic fungi and bacteria break down complex plant polymers (cellulose, lignin, hemicellulose) into simpler inorganic nutrients, a process known as mineralization, which regenerates soil fertility [Per the Second Law of Thermodynamics regarding entropy and nutrient recycling].
- Humification: Microbes synthesize humic substances from decomposed organic residues, which are critical for maintaining soil aggregation and water-holding capacity.
- Plant Growth Promotion: Certain microbes, termed Plant Growth-Promoting Rhizobacteria (PGPR), produce phytohormones like Indole-3-acetic acid (IAA) or siderophores, which chelate iron for plant uptake.
Step 3: Visual Representation of the Microbial Soil Food Web
Step 4: Comparative Analysis of Microbial Contributions
| Microbial Group | Primary Biological Role | Significance to Soil |
|---|---|---|
| Nitrogen-fixers | Atmospheric $N_2$ conversion to $NH_3$ | Enrichment of Nitrogen-depleted soil |
| Mycorrhizal Fungi | Symbiotic phosphorus uptake | Enhanced mineral absorption for roots |
| Decomposers | Hydrolysis of complex organics | Release of $CO_2$ and mineral ions |
Step 5: Synthesized Conclusion
Microbes act as the "engine" of the soil ecosystem. Without their metabolic activities, dead organic matter would accumulate indefinitely, and plants would be deprived of the essential mineral ions ($NO_3^-$, $PO_4^{3-}$, $K^+$) required for survival. Their role is central to sustainable agriculture, soil structure formation, and the prevention of environmental degradation [Per the Law of Conservation of Mass].
Final Solution: Microbes are essential to soil health as they mediate biogeochemical cycling, decompose organic matter into humus, provide bio-fertilization through nitrogen fixation, and facilitate nutrient uptake for plant roots, thereby maintaining the fundamental ecological balance of the pedosphere.
More Questions from Class 12 Biology Microbes in Human Welfare EXERCISES
- Q1: Bacteria cannot be seen with the naked eyes, but these can be seen with the help of a microscope. If you have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbes with the help of a microscope, which sample would you carry and why?
- Q1: Bacteria cannot be seen with the naked eyes, but these can be seen with the help of a microscope. If you have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbes with the help of a microscope, which sample would you carry and why?
- Q2: Give examples to prove that microbes release gases during metabolism.
- Q2: Give examples to prove that microbes release gases during metabolism.
- Q3: In which food would you find lactic acid bacteria? Mention some of their useful applications.
- Q3: In which food would you find lactic acid bacteria? Mention some of their useful applications.
- Q4: Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.
- Q4: Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.
- Q5: In which way have microbes played a major role in controlling diseases caused by harmful bacteria?
- Q5: In which way have microbes played a major role in controlling diseases caused by harmful bacteria?
- Q6: Name any two species of fungus, which are used in the production of the antibiotics.
- Q6: Name any two species of fungus, which are used in the production of the antibiotics.
- Q7: What is sewage? In which way can sewage be harmful to us?
- Q7: What is sewage? In which way can sewage be harmful to us?
- Q8: What is the key difference between primary and secondary sewage treatment?
- Q8: What is the key difference between primary and secondary sewage treatment?
- Q9: Do you think microbes can also be used as source of energy? If yes, how?
- Q9: Do you think microbes can also be used as source of energy? If yes, how?
- Q10: Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.
- Q10: Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.
- Q11: Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled \(A\), \(B\) and \(C\); but the laboratory attendant did not note which was which. The BOD values of the three samples \(A\), \(B\) and \(C\) were recorded as 20mg/L, 8mg/L and 400mg/L, respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?
- Q11: Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled (A), (B) and (C); but the laboratory attendant did not note which was which. The BOD values of the three samples (A), (B) and (C) were recorded as (20mg/L), (8mg/L) and (400mg/L), respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?
- Q12: Find out the name of the microbes from which Cyclosporin \(A\) (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained.
- Q12: Find out the name of the microbes from which Cyclosporin (A) (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained.
- Q13(a): Find out the role of microbes in the following and discuss it with your teacher. (a) Single cell protein (SCP)
- Q13(a): Find out the role of microbes in the following and discuss it with your teacher. (a) Single cell protein (SCP)
- Q13(b): Find out the role of microbes in the following and discuss it with your teacher. (b) Soil
- Q14: Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answer. Biogas, Citric acid, Penicillin and Curd
- Q14: Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answer. Biogas, Citric acid, Penicillin and Curd
- Q15: How do biofertilisers enrich the fertility of the soil?
- Q15: How do biofertilisers enrich the fertility of the soil?
CBSE Solutions for Class 12 Biology Microbes in Human Welfare
Chapters in CBSE - Class 12 Biology
- Reproduction in Organisms
- Human Reproduction
- Reproductive Health
- Principles of Inheritance and Variation
- Molecular Basis of Inheritance
- Evolution
- Human Health and Disease
- Strategies for Enhancement in Food Production
- Biotechnology: Principles and Processes
- Biotechnology and Its Applications
- Organisms and Populations
- Ecosystem
- Biodiversity and Conservation
- Environmental Issues
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