XII BIOLOGY BOOK FOR ACADEMIC YEAR 2020-2021

For academic year 2020-2021 from our textbook some points are deleted or non-evaluated due to Covid-19 situation. These points are evaluated for medical entrance or comparative examination purpose

15.Biodiversity, Conservation and Environmental Issues

Biodiversity: It is defined as the part of nature which includes the differences in the genes among the individuals of a species; the variety and richness of all plants and animal species at different scales in a space - local regions, country and the world along with the types of ecosystem.   (Walter Rosen 1982) The diversity is with respect to size (microscopic to macroscopic), shape, colour, form, mode of nutrition, type of habitat, reproduction, motility, duration of life cycle span, etc.

Levels of Biodiversity:

Diversity of living world can be observed at various levels, ranging from molecular to ecosystem level. Major hierarchical and interrelated levels are genetic diversity, species diversity (community), and ecosystem diversity (ecological).

a)    Genetic diversity:

1)      It is the intraspecific diversity.

2)      It is the diversity in the number and types of genes as well as chromosomes present in different species and also the variation in the genes and their alleles in the same species.

3)      It includes variation within a population and diversity between populations that are associated with adaptation to local conditions.

4)      Genetic variations (e.g. allelic genes) lead to individual differences within species which gives evolution.

5)      They also improve chances of continuation of species in the changing environmental conditions or allow the best adapted to survive.

6)      Existence of sub-species races are examples of genetic diversity.

7)      Greater the diversity better would be sustenance of a species. You know about 1000 varieties of mangoes and 50,000 varieties of rice or wheat in India.

8)      Another case of genetic diversity is: a medicinal plant Rauwolfia vomitoria which secretes active component reserpine, is found in different Himalayan ranges. This plant shows variations in terms of potency and concentration of active chemical, from location to location.

9)     Genetic diversity or variability is essential for a healthy breeding population of a species.           

b)   Species diversity:

1)      It is the interspecific diversity.

2)      The number of species of plants and animals that are present in a region, constitutes its species diversity. Some areas or regions are richer in species than in the other regions.

3)      Species diversity deals with variety of species (species richness) as well as number of individuals of different species (species evenness) observed in area under study. E.g. amphibian species diversity is more in western ghats than in eastern ghats.

4)      Natural undisturbed tropical forests have much greater species richness than monoculture plantation of timber plant, developed by forest plantation. India is one among 15 nations that are rich in species diversity. 

14.Ecosystems and Energy flow

1.      An ecosystem is a self-regulatory and self-sustaining structural and functional unit of nature (biosphere).

2.       Ecosystem contains both biotic and abiotic components.

3.      Biotic components interact with each other and also with the surrounding environment.

4.      Ecosystem term is conined by Tansley (1935).

5.      Ecosystems varies  in size from a small pond to large oceans or small farmland to village.

6.       Entire biosphere can be considered as one global ecosystem, made up of many local ecosystems. Since the earth ecosystem is too big and more  complex .

7.      Ecosystem is divided into two basic categories, -

A. terrestrial ecosystems

B. Aquatic ecosystems.

8.      Forest, grassland and desert are the types of terrestrial ecosystems .  

9.      lakes, wetlands, rivers and estuaries are the types of aquatic ecosystems.

10.  The ecosystems can also be classified as-

A. Natural ecosystems

B.  Artificial ecosystems.

11.  Natural ecosystems do not require any human inputs, in other words they are self-sustainable.

12.  Artificial ecosystems e.g. a farm land, a fish tank or even a large pond used for rearing fish, require constant input in terms of energy or materials.

Ecosystem:

Structure and Function:

Biotic and abiotic components differ as the locations vary in space and time. The variation due to space results in spatial pattern. There are two types of spatial patterns. –

1.  Stratification

2.  Zonation.

1.Stratification- Vertical distribution of different species of plants and animals occupying different levels, is known as stratification.

For example, trees occupy top vertical strata or layer of a forest, shrubs the second and herbs and grasses occupy the bottom layer. Similar stratification is also observed in the open seas as epipelagic, meso-pelagic, bathy-pelagic and benthic zones.

2.  Zonation -Horizontal distribution of plants and animals on land or in water, is called zonation.

Zonation is observed in aquatic (wetlands) as well as terrestrial ecosystems, but it is easily seen at the junction of the two. Edges of a large lake or beach show pronounced zonation in the form of Inter-tidal, Littoral, Sub-littoral zones.