NCERT Solutions for class 12th Biology Chapter 15 Biodiversity and Conservation


Question 1. Name the three important components of biodiversity.

Sol. Biodiversity refers to heterogeneity existing at all levels of biological organisation ranging from macromolecules within cells to biomes.

Three components of biodiversity are:

  1. Genetic diversity– It refers to total genetic information contained in the individuals of plants, animals and microorganisms.
  2. Species diversity– It comprises of the number of different species that are present in a region.
  3. Ecological diversity– It refers to variety of habitats, biotic communities and ecological processes in an area.

Question 2. How do ecologists estimate the total number of species present in the world?

Sol. The ecologists estimate the total number of species present in the world using the statistical methods because the number of species is too large. They make a significant comparison of species richness of exhaustively studied groups of insects of the temperate and tropical regions and extrapolate this ratio to other groups of animals and plants to calculate gross estimate of the total number of species existing on the earth.

Question 3. Give three hypotheses for explaining why tropics show greatest levels of species richness.

Sol. Tropics harbour more species than temperate or polar areas. The three hypotheses explaining the reason for greatest species richness in tropics are as follows:

  • Constant environment : Tropical environments, unlike temperate ones, are less seasonal, relatively more constant and predictable. Such constant environments promote niche specialisation and lead to a greater species diversity.
  • Prolonged evolutionary time : Temperate regions are subjected to frequent glaciations in the past and resulted in extinction of the species. In contrast, tropical regions have remained relatively undisturbed for millions of years and thus, had a long evolutionary time for species diversification.
  • Higher productivity : Tropics receive more solar energy which contributes to higher productivity which, in turn, contributes indirectly to greater diversity.

Question 4. What is the significance of the slope of regression in a species area relationship?

Sol. The species-area relationship describes the relationship between the part of a habitat and the number of species found within that area. On a logarithmic scale, the relationship between species richness and area for a wide variety of taxa (angiosperm plants, birds, bats, freshwater fishes) is a straight line described by the following equation:

log S = log C + Z log A


  • S = Species richness A=Area
  • Z = slope of the line (regression coefficient)
  • C = Y-intercept

In this equation, the slope of a regression line (Z) represents the rate of change in species richness as area changes. It is very important for determining species-area relationship. On analysing species-area relationship, regardless of the taxonomic group or the region, the value of Z lies in the range of 0.1 to 0.2 for smaller area whereas Z ranges from 0.6 to 1.2 for large areas. It signifies that species richness increases with increasing area of observation. In larger areas, the slope of regression coefficient becomes steeper.

Note: Steeper slopes signifies that number of species found increases faster than the area explored in very large areas like the entire continents.

Question 5. What are the major causes of species losses in a geographical region?

Sol. Loss of biodiversity means extinction of species. Species are lost in a geographical region due to the following reasons:

(i) Habitat loss and fragmentation: Habitats of various organisms are altered or destroyed by uncontrolled and unsustainable human activities (such as deforestation, slash and burn agriculture, mining, and urbanisation). This will lead to breaking up of the habitat into small pieces, which effect the movement of migratory animals and also, decrease the genetic exchange between populations leading to a declination of species.

(ii) Over-exploitation: Overexploitation can lead to the destruction of the resource. Due to over-hunting and over-exploitation of various plants and animals many species have become endangered or extinct. For example: Tiger and Steller’s sea cow, the passenger pigeon).

(iii) Alien species invasions: Accidental or intentional introduction of non­ native species into a habitat has led to the declination or extinction of indigenous species. For example, the Nile perch introduced in Lake Victoria in Kenya led to the extinction of more than two hundred species of native fish in the lake.

(iv) Co-extinction: In a native habitat, one species is connected to the other in an intricate network. The extinction of one species causes the extinction of other species, which is associated with it in an obligatory way. Co-extinction is especially common when a keystone species goes extinct. For example, the extinction of the host will cause the extinction of its parasites.

Question 6. How is biodiversity important for ecosystem functioning?

Sol. Biodiversity is important for ecosystem functioning because,

  • It contributes to productivity. High biodiversity makes the ecosystem more stable in productivity and more resistant towards disturbances such as alien species invasions and floods.
  • It cause more efficient recycling of energy and matter.
  • It has many alternative pathways for survival under diverse conditions.
  • If an ecosystem is rich in biodiversity, then the ecological balance should be maintained and would not get affected. 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. Therefore, it can be concluded that if an ecosystem is rich in species, then there will be other food alternatives at each trophic level which would not allow any organism to die due to the absence of their food resource.

Question 7. What are sacred groves? What is their role in conservation?

Sol. •  Sacred groves are areas of forest or trees which are regenerated around places of worship. These areas are dedicated to local deities or ancestral spirits and are protected by local communities through social traditions and taboos that incorporate spiritual and ecological values. These groves are found in Rajasthan, Western Ghats of Karnataka, and Maharashtra, Meghalaya, and Madhya Pradesh. Deforestation is strictly prohibited in this region by tribals.

Role in conservation: Sacred groves give much ecological and genetically significance and help in the protection of many rare, threatened, and endemic species of plants and animals found in that area. It also provides vital ecosystem services to local people.

Question 8. Among the ecosystem services are control of floods and soil erosion. How is this achieved by the biotic components of the ecosystem?

Sol. 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 – 02 balance, retention of water against floods, drought and pollution.

The biotic components of an ecosystem include the living organisms such as plants, animals, fungi and microorganisms that make up ecological communities. Plants play a vital role in the control of floods and soil erosion. Their roots bind the soil 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. They also increase the soil fertility and biodiversity.

Question 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?

Sol. Species diversity refers to the variety of species within a region which is less in plants as compared to animals.

  • More than 70 percent of species recorded on the Earth are animals and only 22 percent species are plants. There is quiet a large difference in their percentage. This is because animals have adapted themselves to ensure their survival in changing environments in comparison to plants.
  • Animals achieved such greater diversification due to the following reasons:
    • 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.
    • Similarly, repeated body segments with paired appendages and external cuticles have made insects versatile and given them the ability to survive in various environments as compared to other lifeforms.

Question 10. Can you think of a situation where we deliberately want to make a species extinct? How would you justify it?


  • Yes, there are different types of parasites and disease-causing microbes that we deliberately want to eradicate from the Earth. Since these micro­ organisms are harmful to human beings, scientists are working hard to fight against them.
  • Scientists have been able to eliminate small pox virus from the world with the help of vaccinations. This shows that humans want to make these species extinct and make this world disease free. Several other eradication programmes such as polio and Hepatitis B vaccinations are aimed to eliminate these disease-causing microbes. Since, such micro-organisms are harmful to the human society, these 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.

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