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NCERT Solutions for Class 12 Biology
Page No. 268
Exercises
Q1. Name the three important components of biodiversity.
Answer: Biodiversity includes variability among life forms from all sources including land, air, and water. Three important components of biodiversity are:
(a) Genetic diversity
(b) Species diversity
(c) Ecosystem diversity
Q2. How do ecologists estimate the total number of species present in the world?
Answer: Living entities exhibit a vast diversity on Earth. Researchers estimate it to be close to seven million. Ecologists can estimate the total number of species on Earth through a statistical comparison between species richness of a well-studied group of insects of tropical and temperate regions. Later these ratios are extrapolated with groups of other plants and animals to estimate the net species richness found on Earth.
Q3. Give three hypotheses for explaining why tropics show greatest levels of species richness.
Answer: (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.
Q4. What is the significance of the slope of regression in a species-area relationship?
Answer: To find a species-area relationship, the slope of regression (z) has great significance. Thus, it provides an estimation of the species richness of the area. It is independent of taxonomic category or sort of area studied. In smaller areas, it has been found that where the species-area relationship is analyzed, the slope of regression is analogous no matter the taxonomic category or the region. However, when in larger areas, a similar analysis is completed, then the slope of regression is far steeper.
Q5. What are the major causes of species losses in a geographical region?
Answer: Biodiversity is the variety of living forms present in various ecosystems. It includes variability among life forms from all sources including land, air, and water. Biodiversity around the world is declining at a very fast pace. The following are the major causes for the loss of biodiversity around the world.
(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 urbanization. This results in the breaking up of the habitat into small pieces, which effects the movement of migratory animals and also, decreases the genetic exchange between populations leading to a declination of species.
(ii) Over-exploitation: Due to over-hunting and over-exploitation of various plants and animals by humans, many species have become endangered or extinct (such as the tiger and the passenger pigeon).
(iii) Alien species Invasions: Accidental or intentional introduction of non-native species into a habitat has also 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 i
Q6. How is biodiversity important for ecosystem functioning?
Answer: An ecosystem with high species diversity is much more stable than an ecosystem with low species diversity. Also, high biodiversity makes the ecosystem more stable in productivity and more resistant towards disturbances such as alien species invasions and floods.
If an ecosystem is rich in biodiversity, then the ecological balance would not get affected. As we all know, various trophic levels are connected through food chains. If any one organism or all organisms of any one trophic level is killed, then it will disrupt the entire food chain. For example, in a food chain, if all plants are killed, then all deer’s will die due to the lack of food. If all deer’s are dead, soon the tigers will also die. 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.
Hence, biodiversity plays an important role in maintaining the health and ecological balance of an ecosystem.
Q7. What are sacred groves? What is their role in conservation?
Answer: Sacred groves are forest patches around places of work. These are held in high esteem by tribal communities/state or central government. Tribals do not allow to cut even a single branch of trees in these sacred groves. Preserved over the course of many generations, sacred groves represent native vegetation in a natural or near-natural state & thus is rich in biodiversity & harbour many rare species of plants & animals. This is the reason why many endemic species flourish in these regions.
Q8. Among the ecosystem services are control of floods and soil erosion. How is this achieved by the biotic components of the ecosystem?
Answer: Ecosystem has two types of components, the abiotic and the biotic components. While the abiotic components are air, light, water, temperature, soil etc, biotic components are constituted by the animals, plant, humans. The role of plants is crucial in controlling soil erosion and floods. Plant roots secure and bind the soil particles together, thus inhibiting the top layer of the soil to get eroded by running water or wind. Plant roots cause the soil to be porous enabling ground water infiltration and averting floods. This is how, plants are able to prevent erosion of soil and other natural calamities such as droughts and floods. Also, they are critical in enhancing biodiversity and increasing the fertility of soi
Q9. 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?
Answer: 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.
For example, insects and other animals have developed a complex nervous system to control and coordinate their body structure. Also, repeated body segments with paired appendages and external cuticles have made insects versatile and have given them the ability to survive in various habitats as compared to other life forms.
Q10. Can you think of a situation where we deliberately want to make a species extinct? How would you justify it?
Answer: Yes, there has been such a situation where different types of parasites and disease-causing micro-organisms would want to be eradicated from the planet. Scientists are working extensively to fight and wipe them out completely as these microbes are harmful to human existence and have been successful in eliminating smallpox from the Earth through the successful use of vaccination. This shows how humans deliberately want to make these species extinct. Some other programmes aiming at eradication are for Hepatitis B, polio vaccinations etc to eliminate those microbes that cause diseases.
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