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NCERT Class 12 Biology Textbook Chapter 14 With Answer PDF Free Download
Chapter 14: Ecosystem
14.1 Ecosystem – Structure And Function
In chapter 13, you have looked at the various components of the environment- abiotic and biotic. You studied how the individual biotic and abiotic factors affected each other and their surrounding.
Let us look at these components in a more integrated manner and see how the flow of energy takes place within these components of the ecosystem.
The interaction of biotic and abiotic components results in a physical structure that is characteristic of each type of ecosystem.
Identification and enumeration of plant and animal species of an ecosystem give its species composition.
The vertical distribution of different species occupying different levels is called stratification. For example, trees occupy the top vertical strata or layers of a forest shrubs the second, and herbs and grasses occupy the bottom layers.
The components of the ecosystem are seen to function as a unit when you consider the following aspects:
(i) Productivity;
(ii) Decomposition;
(iii) Energy flow; and
(iv) Nutrient cycling.
To understand the ethos of an aquatic ecosystem let us take a small pond as an example.
This is fairly a self-sustainable unit and rather a simple example that explain even the complex interactions that exist in an aquatic ecosystem.
A pond is a shallow water body in which all the above-mentioned four basic components of an ecosystem are well exhibited.
The abiotic component is the water with all the dissolved inorganic and organic substances and the rich soil deposit at the bottom of the pond.
The solar input, the cycle of temperature, day-length, and other climatic conditions regulate the rate of function of the entire pond.
The autotrophic components include the phytoplankton, some algae, and the floating, submerged, and marginal plants found at the edges. The consumers are represented by the zooplankton, the free-swimming, and bottom-dwelling forms.
The decomposers are the fungi, bacteria, and flagellates especially abundant in the bottom of the pond.
This system performs all the functions of any ecosystem and of the biosphere as a whole, i.e., conversion of inorganic into organic material with the help of the radiant energy of the sun by the autotrophs; consumption of the autotrophs by heterotrophs;
decomposition and mineralization of the dead matter to release them back for reuse by the autotrophs, these events are repeated over and over again.
There is the unidirectional movement of energy towards the higher trophic levels and its dissipation and loss as heat to the environment.
| Author | NCERT |
| Language | English |
| No. of Pages | 17 |
| PDF Size | 4.2 MB |
| Category | Biology |
| Source/Credits | ncert.nic.in |
NCERT Solutions Class 12 Biology Chapter 14 Ecosystem
1. Fill in the blanks.
(a) Plants are called as_________ because they fix carbon dioxide.
(b) In an ecosystem dominated by trees, the pyramid (of numbers) is_________ type.
(c) In aquatic ecosystems, the limiting factor for the productivity is_________.
(d) Common detritivores in our ecosystem are_________.
(e) The major reservoir of carbon on earth is_________.
Solution:
(a) Autotrophs
Plants are called as autotrophs because they fix carbon dioxide
(b) inverted
In an ecosystem dominated by trees, the pyramid (of numbers) is inverted type.
(c) Light
In aquatic ecosystems, the limiting factor for productivity is light.
(d) earthworms
Common detritivores in our ecosystem are earthworms.
(e) Oceans
The major reservoir of carbon on earth is oceans.
2. Which one of the following has the largest population in a food chain?
(a) Producers
(b) Primary consumers
(c) Secondary consumers
(d) Decomposers
Solution:
(d) Decomposers
Decomposers form the largest population in food chain. They include microbes such as bacteria and fungi, that derive their nutrition by disintegrating the remains of animals and dead plants.
3. The second trophic level in a lake is
(a) Phytoplankton
(b) Zooplankton
(c) Benthos
(d) Fishes
Solution:
(b) Zooplankton
Zooplankton forms the second trophic level in a lake as they are the primary consumers in food chain that is aquatic, feeding upon phytoplankton. Hence, they hold the second level.
4. Secondary producers are
(a) Herbivores
(b) Producers
(c) Carnivores
(d) None of the above
Solution:
(d) None of the above
There are no secondary producers. Plants are the only producers. They are autotrophs and synthesize their own food through the process of photosynthesis.
5. What is the percentage of photosynthetically active radiation (PAR) in the incident solar radiation?
(a) 100%
(b) 50 %
(c) 1-5%
(d) 2-10%
Solution:
(b) 50 %
Photosynthetically active radiation or PAR constitutes about 50% of the total incident solar radiation.
Ecosystem NCERT Textbook With Solutions PDF Free Download