Topics and Subtopics in NCERT Solutions for Class 12 Biology Chapter 15 Biodiversity and Conservation:

QUESTIONS FROM TEXTBOOK SOLVED

1. Name the three important components of  biodiversity.
Ans: Three components of biodiversity are:
(a) Genetic diversity
(b) Species diversity
(c) Ecological diversity

2. How do ecologists estimate the total number of species present in the world?
Ans: Ecologists estimate the total number of species present in the world by comparing species richness of some exhaustively studied groups between any two regions (tropics, temperate or polar regions). Species richness, as a measure of diversity, has been used by many ecologists. Species density or the number of species per m² is most commonly used to measure species richness. Species abundance and species proportional abundance based indices are some other alternative approaches to the measurement of diversity.

3. Give three hypothesis for explaining why tropics ’”show greatest levels of species richness.
Ans: (1) The tropical area have a more stable climate than temperate zones. Local species continues to live in absence of natural disturbances.
(2) Warm temperature and high humidity in most tropical areas provide favourable conditions for growth and survival of diverse species.
(3) Tropical areas receive more solar energy over year and thus tropical communities are more productive and can support a wide range of species.

4. What is the significance of the slope of regression in a species-area relationship?
Ans: Slope of regression or regression coefficient makes it easier to measure species richness along an area. For a limited area like, a country, it gives a constant value of 0.1 to 0.2 irrespective of the taxonomic group or region. It remains amazingly similar for all those small regions. On the contrary, for measuring species-area relationship over large areas like the entire continents, the slope of regression values in the range of 0.6 to 1.2.

5. What are the major causes of species losses in a geographical region?
Ans: Species are lost in a geographical region due to natural disturbances like forest fires; famine, drought and also due to human disturbance with over replantation, habitat destruction, habitat displacement, over specialization, intensive agriculture and pollution.

6. How is biodiversity important for ecosystem functioning?
Ans: Biodiversity is important for ecosystem functioning because,
(1) It contributes to productivity.
(2) It cause more efficient recycling of energy and matter.
(3) It has many alternative pathways for survival under diverse conditions.
(4) Rich biodiversity provides alternatives available at each trophic level. All organisms are linked in food chains and interact with their abiotic environment in such a way so as to keep the natural cycles going and make the ecosystems self – sustaining units. Disappearance of any link in a food chain will not affect the ecosystem as other alternatives are there.

7. What are sacred groves? What is their role in conservation?
Ans: Sacred forests or sacred groves are forest patches around places of worship which are held in high esteem by tribal communities. They are the most undisturbed forest patches which are often surrounded by highly degraded landscapes. They are found in several parts of India, e.g., Karnataka, Maharashtra, Rajasthan (Aravalli), Madhya Pradesh (Sarguja, Bastar), Kerala, Meghalaya. Temples built by tribals are found surrounded by deodar forests in Kumaon region, Jaintias and Khasjas in Meghalaya. Not a single branch is allowed to be cut from these forests. As a result many endemic species which are rare or have become extinct elsewhere can be seen to flourish here. Bishnois of Rajasthan protect Prosopis cineraria and Black Buck religiously. Some water bodies are also held sacred in certain places, e.g., Khecheopalri in Sikkim. Their aquatic flora and fauna are naturally preserved.

8. Among the ecosystem services are control of floods and soil erosion. How is this achieved by the biotic components of the ecosystem?
Ans: Ecosystem services are products or benefits given by ecosystem processes to the environment for its purification, beauty, biodiversity, protection of natural resources, habitat to wild life and tribals, protection of soils, CO₂ – O₂ balance, retention of water against floods, drought and pollution. Plants play a vital role in the control of floods and soil erosion. Their roots bind the soil 10. particles firmly and in this way they do not allow the top soil to be drifted away by winds or moving water. Roots of plants also make the soil porous and allow water to go into the soil.

9. The species diversity of plants (22 per cent) is much less than that of animals (72 per cent). What could be the explanations to how animals achieved greater diversification?
Ans: Species diversity refers to the variety of species within a region which is less in plants as compared to animals. It is due to greater dispersal/more number of surviving individuals. Most animals possess simple or complex nervous system to control and coordinate various activities. They possess receptors to receive against them. Most of their responses are adaptive and ensure their survival in changing environmental conditions. They, therefore, have evolved to reveal much higher species diversity than plants who do not possess nervous system and respond differently against environment stimuli.

10. Can you think of a situation where we deliberately want to make a species extinct? How would you justify it?
Ans: Humans can cause extinction of species through various means. We are trying to eradicate disease causing organisms (e.g., poliovirus) from this world to make this world disease free. Since such micro-organisms are harmful to the human society, such attempt is justified. Further, such micro-organisms are not essential components (producers or decomposers) of any ecosystem, and losing one or few such organisms would not affect the functioning of ecosystem.