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Q5(a):
Write critical notes on the following:
(a) Eutrophication
Solution :
1. Definition and Thermodynamic Basis
Eutrophication is the ecosystem response to the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system [Per the Law of Limiting Factors (Liebig’s Law)]. In aquatic environments, phosphorus is frequently the limiting nutrient; its sudden abundance triggers a shift in the trophic state of the body of water from oligotrophic (nutrient-poor) to eutrophic (nutrient-rich).
2. Sequential Process of Cultural Eutrophication
The progression of eutrophication involves a cascading biological failure:
- Nutrient Loading: Effluents rich in $N$ and $P$ enter the water body, acting as a fertilizer for aquatic flora.
- Algal Bloom: Rapid proliferation of planktonic algae, specifically cyanobacteria (blue-green algae), occurs, forming a dense surface mat [Biological Productivity Axiom].
- Light Attenuation: The surface mat restricts light penetration to submerged macrophytes, leading to their death and decomposition.
- Microbial Respiration: Aerobic decomposers flourish, utilizing massive amounts of dissolved oxygen ($DO$) to break down organic matter.
- Hypoxia and Anoxia: The $DO$ levels drop below the threshold required for aerobic life, leading to the asphyxiation of fish and other invertebrates.
3. Visual Representation of Nutrient Cycling
4. Quantitative Impact Analysis
| Parameter | Oligotrophic State | Eutrophic State |
|---|---|---|
| Nutrient Concentration ($N, P$) | Low | Extremely High |
| Dissolved Oxygen ($DO$) | High ($8-12 \text{ mg/L}$) | Very Low ($< 2 \text{ mg/L}$) |
| Biological Diversity | High (Complex food web) | Low (Monoculture of algae) |
5. Ecological Consequences
The reduction in biodiversity is not merely aesthetic; it involves the loss of niche-specific species. The decay process often releases toxic gases like Hydrogen Sulfide ($H_2S$) and Ammonia ($NH_3$) into the water column [By Le Chatelier’s Principle in biological equilibrium]. Furthermore, certain cyanobacteria produce hepatotoxins and neurotoxins that pose significant public health risks to terrestrial animals that consume the contaminated water.
Final Solution: Eutrophication is the process of accelerated nutrient enrichment leading to excessive plant growth, subsequent microbial decomposition, and drastic reduction in dissolved oxygen, ultimately resulting in the degradation of aquatic biodiversity and ecosystem collapse.
More Questions from Class 12 Biology Environmental Issues EXERCISES
- Q1: What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
- Q1: What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
- Q2: List all the wastes that you generate, at home, school or during your trips to other places. Could you very easily reduce the generation of these wastes? Which would be difficult or rather impossible to reduce?
- Q2: List all the wastes that you generate, at home, school or during your trips to other places. Could you very easily reduce the generation of these wastes? Which would be difficult or rather impossible to reduce?
- Q3: Discuss the causes and effects of global warming. What measures need to be taken to control global warming?
- Q3: Discuss the causes and effects of global warming. What measures need to be taken to control global warming?
- Q4: Match the items given in column A and B:
- Q4: Match the items given in column A and B: Column A Column B (a) Catalytic converter (i) Particulate matter (b) Electrostatic precipitator (ii) Carbon monoxide and nitrogen oxides (c) Earmuffs (iii) High noise level (d) Landfills (iv) Solid wastes
- Q5(a): Write critical notes on the following: (a) Eutrophication
- Q5(b): Write critical notes on the following: (b) Biological magnification
- Q5(b): Write critical notes on the following: (b) Biological magnification
- Q5(c): Write critical notes on the following: (c) Groundwater depletion and ways for its replenishment
- Q5(c): Write critical notes on the following: (c) Groundwater depletion and ways for its replenishment
- Q6: Why does ozone hole form over Antarctica? How will enhanced ultraviolet radiation affect us?
- Q6: Why does ozone hole form over Antarctica? How will enhanced ultraviolet radiation affect us?
- Q7: Discuss the role of women and communities in protection and conservation of forests.
- Q7: Discuss the role of women and communities in protection and conservation of forests.
- Q8: What measures, as an individual, would you take to reduce environmental pollution?
- Q8: What measures, as an individual, would you take to reduce environmental pollution?
- Q9(a): Discuss briefly the following: (a) Radioactive wastes
- Q9(a): Discuss briefly the following: (a) Radioactive wastes
- Q9(b): Discuss briefly the following: (b) Defunct ships and e-wastes
- Q9(b): Discuss briefly the following: (b) Defunct ships and e-wastes
- Q9(c): Discuss briefly the following: (c) Municipal solid wastes
- Q9(c): Discuss briefly the following: (c) Municipal solid wastes
- Q10: What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?
- Q10: What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?
- Q11(a): Discuss briefly the following: (a) Greenhouse gases
- Q11(a): Discuss briefly the following: (a) Greenhouse gases
- Q11(b): Discuss briefly the following: (b) Catalytic converter
- Q11(b): Discuss briefly the following: (b) Catalytic converter
- Q11(c): Discuss briefly the following: (c) Ultraviolet B
- Q11(c): Discuss briefly the following: (c) Ultraviolet B
CBSE Solutions for Class 12 Biology Environmental Issues
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
- Microbes in Human Welfare
- Biotechnology: Principles and Processes
- Biotechnology and Its Applications
- Organisms and Populations
- Ecosystem
- Biodiversity and Conservation
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