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Q11(a):
Discuss briefly the following:
(a) Greenhouse gases
Solution :
1. Theoretical Foundation: The Greenhouse Effect
The Earth’s atmosphere acts as a thermal blanket that regulates global temperatures. The Greenhouse Effect is a naturally occurring phenomenon responsible for heating the Earth’s surface and atmosphere. Without this process, the average temperature at the surface of the Earth would be $-18^{\circ}\text{C}$ rather than the present average of $15^{\circ}\text{C}$. [Per the principles of radiative forcing and atmospheric physics].
2. Classification of Primary Greenhouse Gases (GHGs)
Greenhouse gases are atmospheric constituents that absorb and emit radiant energy within the thermal infrared range. The primary contributors are listed below in terms of their relative impact and origin:
| Gas | Chemical Formula | Primary Anthropogenic Source |
|---|---|---|
| Carbon Dioxide | $CO_2$ | Fossil fuel combustion, deforestation |
| Methane | $CH_4$ | Rice paddies, cattle enteric fermentation, landfills |
| Chlorofluorocarbons | $CFCs$ | Refrigerants, industrial solvents |
| Nitrous Oxide | $N_2O$ | Synthetic fertilizers, industrial processes |
3. Mechanism of Action
The process follows a specific sequence of energy transfer:
- Step 1: Short-wave solar radiation ($UV$ and visible light) penetrates the atmosphere and reaches the Earth's surface.
- Step 2: Surface Absorption: The Earth’s surface absorbs this energy and re-emits it as long-wave infrared radiation (heat). [Per Stefan-Boltzmann Law].
- Step 3: Trapping: Greenhouse gases present in the troposphere absorb these long-wave infrared photons, preventing them from escaping into space.
- Step 4: Re-radiation: These molecules re-radiate the heat in all directions, including back toward the surface, causing an increase in global mean temperatures—a process termed Global Warming.
4. Visualizing Atmospheric Thermal Trapping
5. Environmental Implications
The escalation of these gases due to anthropogenic activities has led to a deleterious rise in global mean temperatures, termed Enhanced Greenhouse Effect. Consequences include:
- Cryosphere degradation: Accelerated melting of polar ice caps and glaciers, leading to sea-level rise. [Per the thermodynamics of phase transition].
- Climate instability: Increased frequency of extreme weather events such as hurricanes, prolonged droughts, and erratic precipitation patterns.
- Ecosystem shifts: Forced migration of species and loss of biodiversity due to inability to adapt to rapidly changing microclimates.
Final Solution: Greenhouse gases (such as $CO_2$, $CH_4$, $N_2O$, and $CFCs$) act as heat-trapping agents in the atmosphere by absorbing long-wave infrared radiation reflected from the Earth's surface, thereby driving the phenomenon of global warming and climate change.
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(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(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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