CBSE Class 12 Biology Biodiversity and Conservation Assignment Set 03

Very Short Answer Type Questions

Question. What is meant by alien species?
Answer: Non-native powerful species which invade a new area are known as alien species.

Question. Define biodiversity.
Answer: The occurrence of different types of genes, gene pools, species, habitats and ecosystems in a particular place and various parts of earth is called biodiversity.

Question. According to David Tilman, greater the diversity greater is the primary productivity. Can you think of a very low diversity man-made ecosystem that has high productivity. 
Answer: Agricultural fields like wheat field or paddy field which are also examples of monoculture practices.

Question. “Stability of a community depends on its species richness.” Write how did David Tilman show this experimentally. 
Answer: David Tilman found that plots with more species showed less year-to-year variation in total biomass. He also showed that in his experiments, increased diversity contributed to higher productivity.

Question. Lantana and Eichhornia are examples of two weeds. How do they affect the ecosystem?
Answer: These are examples of Alien species invasions. They threaten the indigenous species and lead to their extinction.

Question. What are the major causes of species losses in a geographical region?
Answer: There are four major causes (The Evil Quartet):
(i) Habitat loss and fragmentation (ii) Over-exploitation
(iii) Alien species invasions (iv) Co-extinctions

Question. Name the type of biodiversity represented by the following:
(i) 1000 varieties of mangoes in India.
(ii) Variations in terms of potency and concentration of reserpine in Rauwolfia vomitoria growing in different regions of Himalayas. 
Answer: (i) Genetic diversity
(ii) Genetic diversity

Question. Why are sacred groves highly protected? 
Answer: Sacred groves are highly protected because of religious and cultural traditions. These are refuges for large number of rare and threatened plants. They are ecologically unique and biodiversity rich regions.

Question. How is the presently occurring species extinction different from the earlier mass extinctions?
Answer: Species extinction occurring at present is due to anthropogenic or man-made causes whereas the earlier extinction was due to natural causes. Present extinction is occurring at 100 – 1000 times fast rate.

Short Answer Type Questions

Question. What are sacred groves? What is their role in conservation?
Answer: Sacred groves are forest patches for worship in several parts of India. All the trees and wildlife in them are venerated and given total protection. They are found in Khasi and Jaintia Hills in Meghalaya, Western Ghat regions of Karnataka and Maharashtra, etc. Tribals do not allow anyone to cut even a single branch of tree in these sacred groves, thus sacred groves have been free from all types of exploitations.

Question. Explain, giving one example, how co-extinction is one of the causes of loss of biodiversity. List the three other causes also (without description). 
Answer: When a species becomes extinct, the plant and animal species associated with it in an obligatory may also become extinct. This is called co-extinction. For example, when a host fish species becomes extinct, its unique assemblage of parasites also becomes extinct.
The three other causes are:
(i) Habitat loss and fragmentation, (ii) Over-exploitation, (iii) Alien species invasion.

Question. How do ecologists estimate the total number of species present in the world?
Answer: There are two methods to estimate the number of species in the world:
(i) By estimating the rate of discovery of new species.
(ii) By statistical comparison of the temperate–tropical species richness of an exhaustively studied group of insects and extrapolate this ratio to other groups of animals and plants to come up with a gross estimate of the number of species on earth.

Question. Mention the kind of biodiversity of more than a thousand varieties of mangoes in India represent. How is it possible? 
Answer: Thousand varieties of mangoes represent genetic diversity.
This is possible because:
(i) Single species show high diversity at genetic level over its distributional range.
(ii) Different varieties grow in different geographical areas.
(iii) Mutations.

Question. What does the term genetic diversity refer to? What is the significance of large genetic diversity in a population?
Answer: Genetic diversity is the measure of variety in genetic information contained in the organisms.
Significance of large genetic diversity are as follows:
(i) Larger genetic diversity provides adaptability at the time of environmental changes and helps the species in surviving.
(ii) Larger genetic diversity is also useful in the evolution of species.

Question. Biodiversity must be conserved as it plays an important role in many ecosystem services that nature provides. Explain any two services of the ecosystem. 
Answer: The two ecosystem services are:
(i) Forest ecosystem purify air, mitigate droughts and floods.
(ii) The cycling nutrients generate fertile soil and maintains biodiversity.

Question. Co-extinction and introduction of alien species too are responsible for the loss of biodiversity. Explain how. 
Answer: There are four major causes of biodiversity loss. These are also known as ‘The Evil Quartet’.
(i) Habitat loss and fragmentation
• Destruction of habitat is the primary cause of extinction of species.
• The tropical rainforests initially covered 14 per cent of the land surface of earth, but now cover only 6 per cent of land area.
• The Amazon rainforest (called the “lungs of the planet”) is being cut and cleared for cultivation of soya beans and for conversion into grasslands for raising beef cattle.
• When large-sized habitats are broken or fragmented due to human settlements, building of roads,digging of canals, etc., the population of animals requiring large territories and some animals with migratory habitats declines.
Over-exploitation
• When biological system is over-exploited by man for the natural resources, it results in degradation and extinction of the resources.
• For example, Stellar’s sea cow, passenger pigeon and many marine fishes have become extinct due to over-exploitation by man.

Question. Explain ‘rivet popper’ hypothesis. Name the ecologist who proposed it.
Answer: Paul Ehrlich proposed the rivet popper hypothesis. This hypothesis states that in an airplane (ecosystem) all parts are joined together using thousands of rivet (species). If every passenger travelling in it starts popping a rivet to take home (causing a species to become extinct), it may not affect flight safety (proper functioning of the ecosystem) initially but as more and more rivets are removed, the plane becomes dangerously weak over a period of time. Also, which rivet is removed may also be critical like loss of rivets on the wings (key species) is more serious threat to flight safety than loss of few rivets on the seats or windows inside the plane.

Question. ‘In situ’ conservation can help endangered/threatened species. Justify the statement.
Answer: In ‘in situ’ conservation threatened organisms are conserved in their natural habitat or ecosystem,and such regions are legally protected. This has been carried out by identifying certain regions as hotspots, biosphere reserves, national parks, sanctuaries, sacred groves and Ramsar sites. For details, Refer to Basic Concepts Point 8(i).

Question. (a) “India has greater ecosystem diversity than Norway.” Do you agree with the statement?
Give reasons in support of your answer. 
(b) Write the difference between genetic biodiversity and species biodiversity that exists at all the levels of biological organisation.
Answer: (a) Yes, India has greater ecosystem diversity than Norway because of following reasons. (table 542)
(b) Genetic diversity refers to the variation within a species over its distributional range.Species diversity refers to the variation at a species level.