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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 :
Selection of Biological Specimen: Curd (Lactobacillus)
To demonstrate the presence of microbes under a light microscope, the most efficient and readily available sample is a small quantity of curd (or yogurt). This sample serves as a rich medium for the observation of lactic acid bacteria (LAB), specifically species belonging to the genus Lactobacillus.
Step 1: Justification of Specimen Selection
- High Population Density: During the process of fermentation, Lactobacillus bacteria multiply exponentially, utilizing lactose sugar in milk to produce lactic acid [Per the process of biochemical fermentation]. This results in a sample containing millions of cells per milliliter, ensuring a high probability of observation within a single field of view.
- Ease of Preparation: Curd is a semi-solid matrix. A minute amount diluted with a drop of water provides an ideal smear density for light microscopy.
- Morphological Distinction: Lactobacillus organisms are typically rod-shaped (bacilli). Their uniform morphology makes them easily distinguishable from cell debris or milk proteins under a $40\times$ or $100\times$ objective lens.
Step 2: Microscopic Preparation Procedure
To ensure visibility, the sample must be prepared using standard microbiological techniques:
- Sampling: Take a small drop of curd using a sterile inoculating loop or a clean toothpick.
- Smear Preparation: Place the sample on a clean glass slide and add a single drop of distilled water. Spread into a thin, uniform film [Technique: Smear preparation for air-drying].
- Fixation: Pass the slide briefly over a flame to heat-fix the bacteria, ensuring they adhere to the glass surface and retain structural integrity.
- Staining: Apply a simple stain such as Methylene Blue or Crystal Violet for 1–2 minutes. Bacteria are transparent; staining provides the necessary contrast to distinguish the organisms from the background [Justification: Differential absorption of light by stained cytoplasm].
- Rinsing and Blotting: Gently rinse with water to remove excess stain and blot dry using absorbent paper.
Step 3: Schematic Representation of Microscopic Observation
Analytical Conclusion
The sample of curd is selected because it represents a controlled biological culture. The conversion of milk to curd is a metabolic activity performed by Lactobacillus. By observing this sample, one not only confirms the existence of microbes that are invisible to the naked eye but also visualizes the agents responsible for the primary industrial and domestic fermentation processes [Reference: Bioprocessing of dairy products].
Final Solution: The recommended sample is curd, as it provides a concentrated, easily stained culture of rod-shaped Lactobacillus bacteria, ideal for demonstration under a compound light microscope.
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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