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Q10:
Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.
Solution :
1. Theoretical Foundation: The Shift toward Bio-fertilizers and Biopesticides
The reliance on synthetic chemical fertilizers and pesticides leads to soil degradation, groundwater contamination, and the biomagnification of toxins in the food chain. Microbes provide a sustainable alternative by cycling nutrients and acting as natural biological control agents. This transformation is achieved through two primary pathways: Bio-fertilization and Biopesticidal Management.
2. Mechanisms of Bio-fertilizers
Bio-fertilizers are organisms that enrich the nutrient quality of the soil through biological processes. The following table summarizes the key microbial agents:
| Microbe Type | Mechanism | Example |
|---|---|---|
| Nitrogen-fixing Bacteria | Converts atmospheric $N_2$ into ammonia ($NH_3$) | Rhizobium, Azospirillum |
| Cyanobacteria | Autotrophic nitrogen fixation in paddy fields | Anabaena, Nostoc |
| Fungal Symbionts | Forms mycorrhizal associations to absorb $P$ from soil | Glomus species |
Step-by-Step Nitrogen Fixation Process:
- Symbiosis: Bacteria such as Rhizobium colonize the root hairs of leguminous plants, forming nodules [Per the principle of mutualism].
- Enzymatic Action: The nitrogenase enzyme complex catalyzes the reduction of $N_2$ to $NH_3$ [$N_2 + 8H^+ + 8e^- + 16ATP \rightarrow 2NH_3 + H_2 + 16ADP + 16P_i$].
- Nutrient Availability: By providing nitrogen directly in a plant-assimilable form, the dependence on synthetic urea is eliminated.
3. Mechanisms of Biopesticides
Biopesticides utilize the natural predators or pathogens of pests to maintain crop health, preventing the need for broad-spectrum chemical insecticides.
- Bacillus thuringiensis ($Bt$): This bacterium produces a protein crystal containing an insecticidal $Cry$ protein. When ingested by a caterpillar, the alkaline gut pH of the insect solubilizes the toxin, causing perforation of the midgut epithelium and subsequent death [By pore-forming toxin mechanism].
- Trichoderma species: These are free-living fungi very common in root ecosystems. They act as effective biocontrol agents against several plant pathogens via mycoparasitism and antibiosis.
- Baculoviruses: Specifically of the genus Nucleopolyhedrovirus. These are excellent candidates for species-specific, narrow-spectrum insecticidal applications. They have no negative impact on plants, mammals, birds, or non-target insects [Ecological preservation principle].
4. Summary of Integrated Pest and Nutrient Management
By leveraging these microbial pathways, farmers can execute Integrated Pest Management (IPM), which prioritizes biological balance over chemical interference. This approach preserves the soil's organic matter, improves plant resistance to environmental stress, and protects biodiversity.
Final Solution: Microbes decrease the need for chemical inputs through two primary methods: 1) Bio-fertilizers, such as Rhizobium and Glomus, which biologically fix nitrogen and enhance phosphorus absorption, and 2) Biopesticides, such as Bacillus thuringiensis and Trichoderma, which provide target-specific pest control through natural pathogen interaction, thereby maintaining ecological 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.
- 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
- 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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