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Q7:
What is sewage? In which way can sewage be harmful to us?
Solution :
Definition and Composition of Sewage
Sewage, often termed municipal wastewater, is defined as a complex mixture of liquid waste and water-borne contaminants originating from domestic, commercial, and industrial activities. It is primarily composed of:
- Organic Matter: Human excreta, food waste, plant residues, and biodegradable kitchen waste. [Per biological decomposition principles].
- Inorganic Salts: Nitrates, phosphates, and metal ions originating from detergents and cleaning agents.
- Pathogenic Microorganisms: Viruses, bacteria, protozoa, and helminthic eggs capable of inducing disease. [By epidemiological classification].
- Synthetic Chemicals: Pesticides, herbicides, and other non-biodegradable pollutants.
Mechanisms of Harm and Environmental Impact
Sewage poses severe threats to human health and ecological stability through the following pathways:
| Path of Harm | Mechanism of Action |
|---|---|
| Pathogen Transmission | Direct contact or ingestion of water contaminated with fecal matter leads to water-borne diseases such as Cholera ($Vibrio \ cholerae$), Typhoid ($Salmonella \ typhi$), and Dysentery. |
| Eutrophication | Excessive discharge of nitrates and phosphates triggers algal blooms in water bodies, causing oxygen depletion. [Per Limnological laws]. |
| BOD Increase | High organic content forces aerobic microorganisms to consume dissolved oxygen, leading to a high Biochemical Oxygen Demand (BOD), resulting in the death of aquatic flora and fauna. |
Visual Representation of Sewage Pollution Dynamics
Biological & Public Health Consequences
The accumulation of sewage in water bodies disrupts the aquatic ecosystem by causing hypoxia. When the organic load is excessive, the aerobic decomposition processes are exhausted, shifting the environment toward anaerobic conditions. This leads to the release of toxic gases like hydrogen sulfide ($H_{2}S$) and methane ($CH_{4}$), which are harmful to human respiratory health and environmental air quality.
Final Solution: Sewage is a heterogeneous mixture of water and organic/inorganic waste containing human excreta and pathogens. It is harmful because it serves as a vector for water-borne pathogenic diseases and causes ecological degradation via increased Biological Oxygen Demand (BOD) and subsequent eutrophication of aquatic ecosystems.
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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