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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?
Solution :
Initial Biological Hypothesis & Sample Selection
To demonstrate the presence of microorganisms, specifically bacteria, a sample containing a high concentration of active, culturable cells is required. The most accessible and scientifically viable sample to transport from a home environment to a laboratory is curd (yogurt).
Step 1: Rationale for Sample Selection
- Microbial Content: Curd contains millions of Lactic Acid Bacteria (LAB), primarily species of Lactobacillus [Per biological classification: Kingdom Bacteria, Phylum Bacillota].
- Visibility: Under a compound light microscope, the rod-shaped (bacilli) morphology of Lactobacillus is readily observable once stained, typically appearing as distinct, elongated structures.
- Safety and Stability: Curd is a non-pathogenic, stable medium that maintains bacterial viability at room temperature for the duration of transport, unlike samples collected from environmental surfaces which may contain low densities of diverse, unknown, and potentially pathogenic organisms.
Step 2: Microscopic Preparation Methodology
To visualize these bacteria, the following standard protocol is required to transition from a macroscopic sample to a microscopic image:
- Smear Preparation: Take a small dilution of the curd in distilled water and spread a thin film on a clean glass slide [Principle: Uniform distribution prevents cellular overlapping].
- Heat Fixation: Pass the air-dried slide through a flame 2–3 times to denature surface proteins, ensuring the bacteria adhere to the glass [Principle: Immobilization].
- Staining: Apply Methylene Blue or Crystal Violet stain for 1–2 minutes, then rinse. This increases the refractive index contrast between the bacterial cell wall and the background [Principle: Selective absorption of chromophores].
Step 3: Schematic Visualization of Lactobacillus
Analytical Summary of the Biological Interaction
| Feature | Description |
|---|---|
| Taxonomy | Lactobacillus acidophilus |
| Metabolic Action | Converts lactose to lactic acid [Biochemical pathway: Fermentation]. |
| Morphology | Rod-shaped (Bacillus) |
Final Solution: The recommended sample is curd because it serves as a concentrated, safe, and easily observable culture of Lactobacillus bacteria, which are essential in the conversion of milk into curd and provide a clear demonstration of bacterial morphology under standard laboratory light microscopy.
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?
- 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
- 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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