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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?
Solution :
Step 1: Theoretical Basis of BOD (Biochemical Oxygen Demand)
Biochemical Oxygen Demand (BOD) refers to the amount of dissolved oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria. [Per the principles of Environmental Microbiology, BOD is a direct quantitative measure of the organic pollutant load in an aqueous ecosystem].
The fundamental inverse relationship is expressed as:
$BOD \propto \text{Organic Pollution Load}$
Higher levels of organic matter (pollutants) necessitate increased microbial activity for decomposition, which in turn consumes more dissolved oxygen, resulting in a higher BOD value.
Step 2: Quantitative Analysis of Provided Samples
The given data points are:
- Sample (A): $20\text{ mg/L}$
- Sample (B): $8\text{ mg/L}$
- Sample (C): $400\text{ mg/L}$
| Sample | BOD Value (mg/L) | Pollution Severity |
|---|---|---|
| (A) | 20 | Moderate (Secondary Effluent) |
| (B) | 8 | Low (River Water) |
| (C) | 400 | High (Untreated Sewage) |
Step 3: Logical Assignment of Samples
Assignment Rationale:
- Sample (C) - $400\text{ mg/L}$: This represents the highest BOD value. Untreated sewage contains significant amounts of raw organic waste, leading to maximum microbial oxygen demand. Therefore, this is the most polluted sample.
- Sample (A) - $20\text{ mg/L}$: Secondary effluent from a sewage treatment plant has undergone aerobic digestion. While significantly cleaner than raw sewage due to the reduction of organic matter, it remains higher in BOD than natural, unpolluted water.
- Sample (B) - $8\text{ mg/L}$: This represents the lowest BOD value. Given the premise that river water is relatively clean, this value reflects the minimal organic load expected in a natural water body compared to sewage-affected samples.
Visual Representation of Pollution Load vs. BOD
Final Solution: The most polluted water sample is (C). The labels are assigned as follows: Sample (B) is River Water, Sample (A) is Secondary Effluent, and Sample (C) is Untreated Sewage Water.
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?
- 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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