Previous year questions: Biodiversity and Conservation

Board pattern for this chapter

This chapter supplies one-mark assertions and MCQs, two-mark definitions, and three-mark answers on extinction causes or conservation. All ten items below are rewritten from official CBSE papers between 2022 and 2024. Marks are printed in each heading, and the year tells you which paper to open for the original.

Q1 (CBSE Board 2022, 3 marks)

What are the consequences of the loss of biodiversity in a region? Explain.

Answer: Loss of biodiversity leads to three broad consequences. Plant production declines, because fewer species are available to occupy the different roles and the total photosynthetic output falls. A community with fewer species also resists drought and similar shocks less well. Plant output, water use and pest cycles then wobble from one season to the next.

Q2 (CBSE Board 2022, 3 marks)

Explain the rivet popper hypothesis as an argument for conserving biodiversity.

Answer: The hypothesis, proposed by Paul Ehrlich, compares an ecosystem to an aeroplane held together by thousands of rivets, each representing a species. Passengers who pull out rivets to take home represent the human habit of causing extinctions. Removing a few rivets may not affect flight at first, just as losing a few species may not visibly change the ecosystem. The more rivets are pulled, the weaker the aircraft becomes, and losing wing rivets, the key species, is far worse than losing a few from the seats. The argument for conservation is that we cannot predict which rivet is critical, so removing species carelessly risks the whole system. The analogy is deliberately mechanical, and that is what makes it memorable in an answer.

Q3 (CBSE Board 2023, 3 marks)

State the observations made about species diversity as one moves from the equator towards the poles, and give two reasons for the pattern.

Answer: Species diversity is highest in the tropics and falls as one moves towards the poles. Colombia near the equator has nearly 1,400 bird species, New York at 41 degrees north has 105 and Greenland at 71 degrees north has only 56. Two reasons: the tropics stayed relatively undisturbed for millions of years, giving speciation a long run, while temperate regions were glaciated again and again; and tropical environments are less seasonal and more predictable, which promotes niche specialisation and therefore more species.

Q4 (CBSE Board 2023, 1 mark)

Name the region in the world that records the greatest biodiversity, and mention why.

Answer: The greatest biodiversity on earth is in the Amazon rain forest of South America: over 40,000 plant species, 3,000 fishes, 1,300 birds, 427 mammals, 427 amphibians, 378 reptiles and more than 1,25,000 invertebrates, with at least two million insects still unnamed. Its position in the tropics gives it a long evolutionary history, a stable climate and high solar energy input, all of which favour species richness.

Q5 (CBSE Board 2023, 2 marks)

Illustrate with an example how the introduction of an alien species turns invasive and causes the decline of an indigenous species.

Answer: The Nile perch was introduced into Lake Victoria in east Africa and eventually wiped out an ecologically unique set of more than 200 cichlid fish species in that lake. The perch arrived as a predator in a lake whose native fish had never met one, so the cichlids declined and eventually disappeared. In India, invasive weeds such as carrot grass (Parthenium), Lantana and water hyacinth similarly crowd out native species.

Q6 (CBSE Board 2024, 3 marks)

The world faces accelerated rates of species extinction largely because of human activities. Explain any three human activities responsible for this.

Answer: First, habitat loss and fragmentation: tropical rain forests that once covered more than 14 per cent of the land now cover no more than 6 per cent, and fragmentation leaves populations too small to survive. Second, over-exploitation: species such as Steller's sea cow and the passenger pigeon were hunted to extinction, and many marine fish populations are over-harvested today. Third, alien species invasions: introduced species such as the Nile perch in Lake Victoria and Parthenium in India become invasive and drive native species to decline or extinction.

Q7 (CBSE Board 2024, 1 mark)

Assertion (A): A biodiversity hotspot has unusually high species richness and a high degree of endemism. Reason (R): The world has 22 biodiversity hotspots, two of them in India.

Answer: Assertion A is true, but Reason R is false. Biodiversity hotspots do have high species richness and high endemism, but the current total is 34 after nine additions to the original 25, and India's share comes from the Western Ghats with Sri Lanka, Indo-Burma, and the Himalaya.

Q8 (CBSE Board 2024, 2 marks)

Why is there no estimated number of prokaryote species when plants and animals have such estimates?

Answer: Conventional taxonomic methods are not suited to identifying microbial species, and many prokaryotes cannot be cultured under laboratory conditions, so they cannot be counted the way plants and animals are. If biochemical and molecular criteria are used to define species in this group, prokaryote diversity alone might run into millions.

Q9 (CBSE Additional PQ 2023-24, 3 marks)

Which conservation strategy is used when endangered species are removed from an unsafe or threatened habitat and placed under human care? How is it different from the other strategy of conservation?

Answer: That is ex situ conservation, where threatened animals and plants are taken out of their habitat and kept in zoological parks, botanical gardens or safari parks, and increasingly in cryopreserved gametes, seed banks and tissue culture. It differs from in situ conservation, where the whole ecosystem is protected on site so that biodiversity at all levels survives together. In situ keeps the species in its ecological interactions; ex situ gives urgent protection to a species whose habitat is no longer safe.

Q10 (CBSE Additional PQ 2021-22, 2 marks)

(a) Mention one condition when ex situ conservation is more viable. (b) What are the two most important parameters that help in naming an area as a biodiversity hotspot?

Answer: (a) Ex situ conservation is more viable when a species is endangered and its natural habitat is unsafe or under immediate threat, so it needs urgent care outside the habitat. (b) The two parameters are very high species richness and a high degree of endemism, meaning many of its species are found nowhere else.

Common mistakes in this chapter

Three errors recur. Students give the latitudinal gradient without an example, when the marks are in Colombia, New York and Greenland. They list the evil quartet without an example for each cause. And they treat hotspots as simply rich places, missing the endemism condition that makes a hotspot a hotspot. Each of these is a one-line fix during revision.

What the board rewards

This chapter rewards named examples and figures. Keep the region examples for the latitudinal gradient, the four causes with one example each, and the three Indian hotspots. For conservation questions, separate in situ from ex situ in the first sentence, then give examples. A table with two columns is faster than two paragraphs and easier for the examiner to mark. Numbers carry marks here, so learn the IUCN extinction count, the 34 hotspots and India's 2.4 per cent land share against 8.1 per cent species share. When a question asks for reasons, give each reason a separate example; a single example repeated twice earns no extra mark.

A last note on examples

Every cause, every pattern and every conservation approach in this chapter has at least one named example in the textbook. Answers that stay at the level of definition lose marks that an example would have saved. Before the exam, write one line for each of these: Rauwolfia for genetic diversity, Western Ghats for amphibian richness, the Amazon for the latitudinal gradient, the Nile perch for alien invasion, the Western Ghats with Sri Lanka for hotspots, and Meghalaya's sacred groves for in situ protection. If those six examples come to mind without effort, the chapter is ready. Read them once more on the morning of the exam and leave the rest to the writing.