NCERT Solutions for Class 12 Biology Chapter 15 - Biosphere and Conservation

Question 1:

Name the three important components of biodiversity.


(i) Genetic diversity;
(ii) Species diversity and
(iii) Ecological diversity.

Question 2:

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


Due to large number of species yet to be discovered in the tropics, biologists carry out a statistical comparison of temperate-tropical species richness of thoroughly studied group of insects and utilise this ratio to determine the relationship of remaining groups of plants and animals. This gives them the gross estimate of total number of species on earth. This number may range in between 20 to 50 million. However, according to Robert May, for his more better scientific studies, global species diversity is about 7 million.

Question 3:

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


Following three hypotheses explain how tropics show greatest level of species richness 1. Undisturbance in tropics. Speciation is usually a function of time, unlike temperate areas subjected to frequent glaciations in the past. This type of disturbance has not occurred or remained relatively undisturbed in tropical latitudes for millions of years. Tropical regions, thus, got a long evolutionary time for species diversification. 2. Constancy in season. In tropical regions, environment is more constant, less seasonal and predictable. This is not so in temperate regions. Due to this stability and constancy, niche speciation takes place at a faster rate and leads to species richness. 3. Availability of more solar energy. Due to more availability of solar energy in tropics, productivity is higher. This contributes indirectly to greater species diversity.

Question 4:

What is the significance of the slope of regression in a species-area relationship ?


A species relationship derived by Alexander
Von Humboldt for area, it is a straight line on a
logarithmic scale for wide range of taxa.
log S = log C + Z log A
(S = Species richness, A = Area), Z = regression
coefficient (Slope of line) and C = Y – intercept.
If large continents are taken into account, value of
Z differs, it comes between 0.6 to 1.2. Even the slope of line is steeper.

Question 5:

What are major causes of species losses in a geographical area ?


Causes of species losses in a geographic area :
1. Hunting
2. Forest fire
3. Destruction of habitat and fragmentation
4. Introduction of exotic species
5. Increased human population and consumption of resources.

Question 6:

How is biodiversity important for ecosystem functioning ?


Importance of biodiversity to Ecosystem :
1. Ecologists believe that communities with more species tend to be more stable than those with less species.
2. A stable community has the following attributes.
(i) It shall not show too much of variations in the year-to-year productivity.
(ii) It must be either resistant or resilient to seasonal disturbances.
(iii) It must be resistant also to invasion by alien species.
3. David Tilman had shown through his ecology experiments using outdoor plots, the following features.
(i) The plots with more species showed less yearto- year variation in the total biomass.
(ii) Plots with increased diversity showed higher productivity.
4. It is now realised that species richness and diversity are essential for ecosystem health as well as survival of human race on the earth.

Question 7:

What are sacred groves ? What is their role in conservation ?


Sacred Groves are the secret forest patches around places of worship. They are of a great religious value among tribal communities.
In such cases, nature is protected by prevailing religious and cultural traditions. Here tracts of forests are set aside and all plants and animals are venerated and provided with complete protection. Examples of sacred groves are Khasi and Jaintia hills in Meghalaya, Aravali hills in Rajasthan, Western Ghat regions of Karnataka, Maharashtra and Sargiya, Chanda and Bastar areas of M.P. In Sikkim, Khecheopalri lake is declared sacred lake by people, thus protecting the aquatic flora and fauna.
Role in conservation. Many rare and threatened plants have been protected in sacred groves of Meghalaya. Such areas have been found to be most undisturbed and they are usually surrounded by most degraded landscapes.

Question 8:

The species diversity of plants 22% is much less than that of animals. What could be the explanation to how animals achieved greater diversification ?


1. Since plants cannot move from their predators and harsh treatment of environment conditions, thus have become distinct.
2. As the animals can move away from such conditions, their evolution of favourable characters has taken place in them.

Question 9:

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


1. Human effort to eradicate disease causing organisms (Polio virus).
2. This situation may appear when alien species is introduced unintentionally or deliberately into an area. Some of them may become invasive and cause damage to indigenous species.
3. Example Nile pearch introduced into lake Victoria in East Africa led to extinction of 200 species of cichlid fish in the lake. Introduction of African catfish Clarias gariepinus for aquaculture is threatening the indigenous catfishes in rivers of India.