An Overview of Ncert Solutions Class 3 Physical Education And Well Being Chapter 3
FAQs on Ncert Solutions Class 3 Physical Education And Well Being Chapter 3
1. Which topics from Chapter 16, Environmental Issues, are considered most important for the CBSE Class 12 Board Exam 2025-26?
For the CBSE Class 12 Biology exam, several topics from Environmental Issues are frequently asked and carry high importance. Students should focus on:
Eutrophication and Biomagnification: Understand the process, causes, and consequences of both.
Control of Air Pollution: The working of an electrostatic precipitator, a scrubber, and a catalytic converter are very important 3-mark questions.
Ozone Depletion: The mechanism of ozone degradation by CFCs and the significance of the Montreal Protocol.
Greenhouse Effect and Global Warming: The gases involved and the potential impacts.
Case Studies: The case study of organic farming by Ramesh Chandra Dagar and the remedy for plastic waste by Ahmed Khan are often asked as 5-mark questions.
2. What kind of 5-mark questions can be expected from the water pollution section of Environmental Issues?
A common 5-mark question from this section asks you to explain the impact of discharging untreated sewage into a river. To score full marks, your answer must cover:
An initial increase in Biochemical Oxygen Demand (BOD) as microorganisms decompose organic matter.
A sharp decline in Dissolved Oxygen (DO), leading to the death of fish and other aquatic life.
The eventual recovery of the river, where DO increases and BOD decreases downstream.
A well-labelled graph showing the relationship between BOD and DO levels along the river's course is crucial for securing full marks.
3. Why is using unleaded petrol a mandatory requirement for vehicles fitted with catalytic converters?
This is a critical Higher Order Thinking Skills (HOTS) question. The catalytic converter uses expensive metals like platinum, palladium, and rhodium as catalysts to convert harmful pollutants into less harmful substances. Unleaded petrol must be used because the lead in leaded petrol inactivates these catalysts. This renders the catalytic converter ineffective, and the vehicle will release toxic gases like carbon monoxide and nitrogen oxides without any treatment.
4. How does biomagnification explain the high concentration of toxins like DDT in top carnivores?
Biomagnification is the increase in the concentration of a toxicant at successive trophic levels in an aquatic food chain. This happens because a toxic substance, like DDT, cannot be metabolised or excreted by an organism. When an organism is consumed by another, the toxin gets transferred to the next trophic level. For example:
DDT concentration might be very low in water (e.g., 0.003 ppb).
Zooplankton accumulate it to a higher level (e.g., 0.04 ppm).
Small fish feeding on zooplankton concentrate it further (e.g., 0.5 ppm).
Large fish concentrate it more (e.g., 2 ppm).
Finally, fish-eating birds (top carnivores) accumulate the highest concentration (e.g., 25 ppm), which can cause serious health issues like thinning of eggshells.
This shows how a substance present in low amounts in the environment can become highly concentrated and dangerous at the top of the food chain.
5. What are the key differences between the greenhouse effect and ozone layer depletion?
While both are major environmental issues, students often confuse them. The key differences important for the exam are:
Atmospheric Layer: The greenhouse effect is a phenomenon of the troposphere (lower atmosphere), while ozone depletion occurs in the stratosphere (upper atmosphere).
Causative Agents: The greenhouse effect is caused by gases like CO₂, CH₄, and N₂O that trap heat. Ozone depletion is primarily caused by chlorofluorocarbons (CFCs).
Mechanism: Greenhouse gases prevent the escape of long-wave infrared radiation from the Earth, causing global warming. CFCs release chlorine atoms that catalytically break down ozone (O₃) molecules, creating an 'ozone hole'.
Consequences: The primary consequence of the enhanced greenhouse effect is global warming. The main consequence of ozone depletion is the increased penetration of harmful UV-B radiation to the Earth's surface.
6. Explain the working principle of an electrostatic precipitator as an important question on air pollution control.
An electrostatic precipitator is a highly efficient device for removing particulate matter from industrial exhaust. Its working principle is a frequently asked 3-mark question:
The device has electrode wires maintained at several thousand volts, which produce a corona that releases electrons.
These electrons attach to the dust particles in the exhaust, giving them a net negative charge.
The charged dust particles are then attracted to grounded collecting plates.
The velocity of air between the plates is kept low to allow the dust to fall. This way, nearly 99% of particulate matter can be removed, and clean air is released.
7. Why is integrated organic farming, as practised by Ramesh Chandra Dagar, considered a zero-waste and sustainable procedure?
This is a significant application-based question. Integrated organic farming is considered a zero-waste procedure because the waste products from one process are used as nutrients for another. Ramesh Chandra Dagar’s model included:
Agriculture: Main crop cultivation without chemical fertilisers or pesticides.
Dairy Management: Cattle were used for milk and their dung was used to create slurry for biogas production.
Biogas Plant: The slurry from the dung was used to produce biogas for energy needs, and the remaining slurry was used as a natural fertiliser for the crops.
Water Harvesting: Creating a system to capture and use rainwater efficiently.
This cyclical, resource-efficient approach makes it highly sustainable and economically viable, eliminating the need for costly and harmful agro-chemicals.
