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Q7:
What is sewage? In which way can sewage be harmful to us?
Solution :
1. Definition of Sewage
Sewage refers to the municipal waste-water generated from domestic, commercial, and industrial activities. It consists of a heterogeneous mixture of water and various contaminants. The composition includes:
- Organic Matter: Human excreta, food waste, plant debris, and urea.
- Inorganic Salts: Phosphates, nitrates, and metal ions.
- Pathogens: A diverse population of disease-causing microorganisms including bacteria, viruses, fungi, and protozoa.
- Dissolved and Suspended Solids: Sand, silt, clay, and colloidal matter.
2. Mechanisms of Harm
Sewage poses a significant threat to public health and ecological stability through several specific pathways:
| Mechanism | Biological/Chemical Basis |
|---|---|
| Pathogen Transmission | Sewage serves as a vector for water-borne diseases such as Cholera ($Vibrio \ cholerae$), Typhoid ($Salmonella \ typhi$), and Dysentery ($Shigella$). |
| Eutrophication | The presence of excessive nitrogen and phosphorus leads to algal blooms, which consume oxygen and devastate aquatic biodiversity [Per the Law of Limiting Factors]. |
| Depletion of Dissolved Oxygen (DO) | Aerobic decomposers consume oxygen to break down organic load, leading to a high Biochemical Oxygen Demand (BOD) and causing mortality in fish/aquatic life. |
3. Visual Representation of Pollution Impact
4. Analytical Justification
The harm caused by sewage is scientifically quantified by its Biochemical Oxygen Demand (BOD). BOD is defined as the amount of oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria. [By the principles of microbial metabolism]:
- High organic content induces rapid microbial proliferation.
- The high metabolic rate of these microbes exhausts the dissolved oxygen in the water column.
- This creates an anaerobic environment, resulting in the production of toxic gases such as $H_{2}S$ and $CH_{4}$, rendering the water unsuitable for life and human consumption.
Final Solution: Sewage is the liquid waste of a community containing human excreta, food waste, and pathogens. It is harmful because it facilitates the spread of pathogenic water-borne diseases, causes eutrophication in aquatic ecosystems through nutrient enrichment, and depletes dissolved oxygen (high BOD) in water bodies, leading to the collapse of local aquatic flora and fauna.
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?
- 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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