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Q13(b):
Find out the role of microbes in the following and discuss it with your teacher.
(b) Soil
Solution :
1. Theoretical Foundation: Microbes as Edaphic Engineers
Soil is a biologically dynamic matrix where microbes function as primary decomposers and nutrient cyclers. Their role is defined by the transformation of complex organic matter into bioavailable inorganic minerals [Per the Law of Conservation of Mass].
2. Key Biological Processes in Soil
| Process | Microbial Agents | Function |
|---|---|---|
| Nitrogen Fixation | Rhizobium, Azotobacter, Clostridium | Conversion of atmospheric $N_2$ to $NH_3$ |
| Nitrification | Nitrosomonas, Nitrobacter | Oxidation of $NH_3$ to $NO_2^-$ and $NO_3^-$ |
| Decomposition | Bacteria, Fungi, Actinomycetes | Breakdown of lignocellulose and proteins |
| Solubilization | Bacillus megaterium | Conversion of insoluble phosphate to $H_2PO_4^-$ |
3. Sequential Analysis of Microbial Roles
Step 1: Nitrogen Cycling and Bioavailability
Microbes bridge the gap between atmospheric nitrogen and plant protein synthesis. Rhizobium forms symbiotic associations with leguminous roots, providing a direct supply of nitrogenous compounds [Symbiotic Mutualism Theory]. Free-living nitrogen fixers like Azotobacter independently enrich the soil nitrogen pool, increasing overall fertility.
Step 2: Humification and Soil Structure
Microbial decomposition of plant and animal residues produces humus—a dark, amorphous colloidal substance.
- Aggregation: Fungal hyphae and bacterial polysaccharides act as biological "glue," binding soil particles into macro-aggregates.
- Porosity: Improved aggregation enhances soil aeration and water retention capacity [By Soil Physics principles].
Step 3: Biocontrol and Soil Health
The microbial community acts as a natural defense system. Saprophytic microbes compete with soil-borne pathogens for resources (space and nutrients), a phenomenon known as competitive exclusion. For example, Trichoderma (a fungus) effectively controls several plant pathogens by producing antifungal enzymes.
4. Summary of Ecological Contribution
Microbes are the fundamental architects of soil health. Without the constant metabolic activity of bacteria and fungi, the recycling of carbon, nitrogen, and phosphorus would cease, leading to the collapse of terrestrial ecosystems [Per the Biogeochemical Cycling Principles]. Their ability to mineralize complex compounds ensures that soil remains a viable medium for primary production.
Final Solution: Microbes facilitate soil fertility through nitrogen fixation, mineral solubilization, humus formation for structural stability, and the biological control of plant pathogens, thereby acting as the primary drivers of edaphic ecosystem sustainability.
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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