CBSE Important Questions Class 12 Biology Chapter 13 – Biodiversity and Conservation

Class 12 Biology Chapter 13 Biodiversity and Conservation is the last chapter of the NCERT Class 12 Biology textbook. It explains the three levels of biodiversity (genetic, species and ecological), how many species exist on earth and why insects are so many, the patterns of biodiversity such as the latitudinal gradient and the species-area relationship, why biodiversity matters (the rivet popper hypothesis), the causes of biodiversity loss (the Evil Quartet), and in situ and ex situ methods of conservation.

These CBSE important questions for Class 12 Biology Chapter 13 cover plant tissue culture, the effect of habitat fragmentation on a food web, the species-area relationship calculation, species diversity versus ecological diversity (Western Ghats and Norway), the two components of an ecosystem, a pie chart of plants, insects and other animals, why insects are so diverse, and the rivet popper hypothesis. The set has multiple-choice, data-based and case-based questions with answers for board exam revision.

Q1. A particular plant variety was propagated using two methods, X and Y. In method X, seeds were used for propagation, while in method Y, explants from leaves were used under aseptic and controlled environmental conditions for propagation.
a. Identify the method that can be used to produce a large number of clones in less time. Is there any specific name for this method?
b. If the plant variety that has to be propagated is affected with a disease, can we use method X for propagation in that case?

Answer: a. Method Y, in which explants are used for propagation, can be used to produce a large number of clones in less time. This method is commonly known as plant tissue culture or micropropagation.
b. If the plant variety is affected with a disease, method X cannot be used, as the seeds will also be diseased and will carry the infection to the next generation. In this case, method Y, i.e. propagation using explants from leaves, can be used. The disease can be eliminated by carefully selecting a healthy stock plant (mother plant) for the explants, which are then propagated under aseptic and controlled conditions to give healthy clones.

Q2. In a city, the fragmentation of forest for road development resulted in the separation of animals. This affects the food chain in the forest habitat. If the population of deer is present in region A and its natural predators are present in region B, what will be the outcome of the situation?
I. The population of both deer and its predators will decline over time.
II. The population of deer will thrive compared to its natural predators.
III. Grasses will thrive in region B and vanish from region A.
IV. The food web will be disturbed.
(a) I only
(b) II only
(c) I, II and III
(d) I, III and IV

Answer: (d) I, III and IV
Fragmentation divides the habitat into regions A and B, separating the deer from their predators. In region A, the deer first increase because there are no predators, but overgrazing then uses up the food and the deer population crashes. In region B, the predators starve without deer and decline. So both populations decline over time (I). Heavy grazing makes the grasses vanish from region A, while in region B the grasses thrive without herbivores (III). The separation of deer and predators disturbs the food web (IV). Statement II is wrong because the deer do not thrive in the long run.

Q3. A conservation biologist studying species richness on islands of different sizes collected the following data. The species-area relationship follows log S = log C + Z log A, where Z = 0.15 for these islands.

Island Area (km²) Recorded Plant Species
Island A 10 42
Island B 100 75
Island C 1,000 133
Island D 10,000 237

If 90% of Island C is converted, reducing its area to 100 km², use the data to predict the expected species richness after the reduction. Estimate the proportion of species likely to be lost and justify your reasoning.

Answer: If Island C is reduced by 90%, its area falls from 1,000 km² to 100 km². From the table, an island of 100 km² (Island B) supports about 75 plant species. So the reduced Island C is expected to support about 75 species.
Current species on Island C = 133
Expected remaining species = 75
Potential species loss = 133 − 75 = 58 species
Percentage loss = (58 ÷ 133) × 100 ≈ 43.6%
So about 44% of the plant species may be lost. This happens because species richness decreases with area according to the species-area relationship (S = CAZ), so a major reduction in habitat area causes a substantial loss of biodiversity.

Q4. A group of ecology students conducted a biodiversity survey in two regions – the Western Ghats of India and a Scandinavian country (Norway). They observed that the Western Ghats had a much greater number of amphibian species and a wider range of ecosystems, including rainforests, wetlands and mangroves. In contrast, Norway had fewer species and less variation in habitats due to its uniform climatic conditions.
4.1. Based on the case, differentiate between species diversity and ecological diversity, and explain how both contribute to the stability and productivity of an ecosystem.
4.2. Using the example from the case, analyse two major factors that could explain why India shows higher biodiversity and ecosystem variety than Norway.

Answer: 4.1. Species diversity measures the variety of species in a region and their relative abundance. Example: the Western Ghats have more amphibian species than the Eastern Ghats. Ecological diversity refers to the variety of ecosystems or habitats in a region. Example: India has deserts, rainforests, mangroves, coral reefs, wetlands, estuaries and alpine meadows.
Contribution to stability and productivity: Greater species diversity ensures ecosystem functions like pollination, nutrient cycling and food web stability (alternative prey reduce the risk of collapse). Ecological diversity provides resilience against environmental changes by offering many habitat types and supports many ecological processes, such as water purification in wetlands and soil formation in forests, which together increase overall productivity.
4.2. Two factors explain why India has higher biodiversity and ecosystem variety than Norway:
1. Climatic diversity: India has tropical, temperate, alpine and coastal climates, which support a wide range of species and ecosystems (rainforests, wetlands, mangroves). Norway's cold temperate climate limits habitat variety and species richness.
2. Geographical variation: India has mountains, plateaus, plains, rivers, coasts and islands, offering many habitats and niches for species. Norway's relatively uniform terrain provides fewer habitat types and so lower species diversity.

Q5. The two main components that make up an ecosystem are:
(a) Producers and consumers
(b) Living organisms and non-living factors
(c) Plants, animals and humans
(d) Energy flow and nutrient cycling

Answer: (b) Living organisms and non-living factors
An ecosystem is made up of two main components: biotic components, the living parts such as plants, animals and micro-organisms, and abiotic components, the non-living parts such as sunlight, water, air, soil and minerals. These two components interact to maintain the balance of the ecosystem.

Q6. A biodiversity survey revealed the following pattern on earth: More than 70% of all recorded species are animals, while plants make up only 22%. Out of the total animals, 70% are insects (i.e. out of every 10 animals, 7 are insects).
6.1. Represent the given data visually by drawing a pie chart showing the proportion of plants, insects and other animals.
6.2. Explain what the pie chart indicates about species dominance on earth.
6.3. Why do insects constitute such a large proportion of animal species? Give two ecological reasons.
6.4. Suggest one practical implication of the high insect diversity for humans and ecosystems.

Answer: 6.1. Plants = 22%, Animals = 78% of the total. Insects = 70% of the animals = 0.7 × 78% ≈ 54.6%. Other animals = 78% − 54.6% = 23.4%.
Central angles for the pie chart: Plants = 22/100 × 360° = 79.2°; Insects = 54.6/100 × 360° = 196.56°; Other animals = 23.4/100 × 360° = 84.24°. Draw a circle and mark each sector with its central angle.

Pie chart showing the proportion of plants, insects and other animals among recorded species

6.2. The chart indicates that animals dominate global biodiversity, and insects are the most abundant group among animals, whereas plants, although essential, make up a smaller proportion of recorded species.
6.3. Reasons for high insect diversity:
1. High reproductive rate: Insects reproduce quickly and have short generation times, producing large populations and more opportunities for speciation.
2. Ecological adaptability: Insects occupy diverse habitats (soil, water, air, plants), feed on a wide variety of resources and can survive in extreme conditions.
6.4. High insect diversity is crucial for ecosystem services such as the pollination of crops, decomposition and recycling of nutrients, and food for other animals. It supports both natural ecosystems and human agriculture.

Q7. Ecologist Paul Ehrlich proposed the Rivet Popper Hypothesis to explain the relationship between biodiversity and ecosystem stability. He gave the example of an aeroplane, where rivets hold the structure together. When a few rivets are removed, the aeroplane may still function, but continuous removal weakens it, and eventually it may collapse. The loss of rivets on the wings poses a much greater threat to the plane's safety.
7.1. Identify the main idea of the Rivet Popper Hypothesis.
7.2. In this analogy, what does the aeroplane represent, and what do the rivets symbolise?

Answer: 7.1. The Rivet Popper Hypothesis states that each species plays an important role in maintaining the stability and functioning of an ecosystem. Removing a few species may not immediately collapse the ecosystem, but continuous species loss weakens it and may ultimately lead to its collapse.
7.2. The aeroplane represents the ecosystem. The rivets represent the species that keep the ecosystem stable and functional. The rivets on the wings represent the key species (keystone species) whose loss is a much greater threat to the ecosystem than the loss of other species.

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