NCERT Solutions for Class 12 Biology Chapter 14
Ecosystem Class 12
Chapter 14 Ecosystem Exercise Solutions
Exercise : Solutions of Questions on Page Number : 256
Q1 :
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 .
Answer :
(a) Plants are called as because they fix carbon dioxide.
(b) In an ecosystem dominated by trees, the pyramid (of numbers) is of type.
(c) In aquatic ecosystems, the limiting factor for productivity is .
(d) Common detritivores in our ecosystem are .
(e)
Q2 :
Which one of the following has the largest population in a food chain?
(a) Producers
(b) Primary consumers
(c) Secondary consumers
(d) Decomposers
Answer :
(d) Decomposers
Decomposers include micro-organisms such as bacteria and fungi. They form the largest population in a food chain and obtain nutrients by breaking down the remains of dead plants and animals.
Q3 :
The second trophic level in a lake is-
(a) Phytoplankton
(b) Zooplankton
(c) Benthos
(d) Fishes
Answer :
(b) Zooplankton
Q4 :
Secondary producers are
(a) Herbivores
(b) Producers
(c) Carnivores
(d) None of the above
Answer :
(d) None of the above
Q5 :
What is the percentage of photosynthetically active radiation (PAR), in the incident solar radiation. (a) 100%
(b) 50 % (c) 1-5% (d) 2-10%
Answer :
(b) 50%
Q6 :
Distinguish between
(a) Grazing food chain and detritus food chain
(b) Production and decomposition
(c) Upright and inverted pyramid
(d) Food chain and Food web
(e) Litter and detritus
(f) Primary and secondary productivity
Answer :
(a) Grazing food chain and detritus food chain
|
Grazing food chain |
|
Detritus food chain |
1. |
In this food chain, energy is derived from the Sun. |
1. |
In this food chain, energy comes from organic matter (or detritus) generated in trophic levels of the grazing food chain. |
2. |
It begins with producers, present at the first trophic level. The plant biomass is then eaten by herbivores, which in turn are consumed by a variety of carnivores. |
2. |
It begins with detritus such as dead bodies of animals or fallen leaves, which are then eaten by decomposers or detritivores. These detritivores are in turn consumed by their predators. |
3. |
This food chain is usually large. |
3. |
It is usually smaller as compared to the grazing food chain. |
(b) Production and decomposition
|
Production |
|
Decomposition |
1. |
It is the rate of producing organic matter (food) by producers. |
2. |
It is the process of breaking down of complex organic matter or biomass from the body of dead plants and animals with the help of decomposers into organic raw material such as CO2, H2O, and other nutrients. |
2. |
It depends on the photosynthetic capacity of the producers. |
2. |
It occurs with the help of decomposers. |
3 |
Sunlight is required by plants for primary production. |
3. |
Sunlight is not required for decomposition by decomposers |
(c) Upright and inverted pyramid
|
Upright pyramid |
|
Inverted pyramid |
1. |
The pyramid of energy is always upright. |
1. |
The pyramid of biomass and the pyramid of numbers can be inverted. |
2. |
In the upright pyramid, the number and biomass of organisms in the producer level of an ecosystem is the highest, which keeps on decreasing at each trophic level in a food chain. |
2. |
In an inverted pyramid, the number and biomass of organisms in the producer level of an ecosystem is the lowest, which keeps on increasing at each tropic level. |
(d)
Q7 :
Describe the components of an ecosystem.
Answer :
An ecosystem is defined as an interacting unit that includes both the biological community as well as the non-living components of an area. The living and the non-living components of an ecosystem interact amongst themselves and function as a unit, which gets evident during the processes of nutrient cycling, energy flow, decomposition, and productivity. There are many ecosystems such as ponds, forests, grasslands, etc.
The two components of an ecosystem are:
(a) Biotic component: It is the living component of an ecosystem that includes biotic factors such as producers, consumers, decomposers, etc. Producers include plants and algae. They contain chlorophyll pigment, which helps them carry out the process of photosynthesis in the presence of light. Thus, they are also called converters or transducers. Consumers or heterotrophs are organisms that are directly (primary consumers) or indirectly (secondary and tertiary consumers) dependent on producers for their food.
Decomposers include micro-organisms such as bacteria and fungi. They form the largest population in a food chain and obtain nutrients by breaking down the remains of dead plants and animals.
(b)
Q8 :
Define ecological pyramids and describe with examples, pyramids of number and biomass.
Answer :
An ecological pyramid is a graphical representation of various ecological parameters such as the number of individuals present at each trophic level, the amount of energy, or the biomass present at each trophic level.
Ecological pyramids represent producers at the base, while the apex represents the top level consumers present in the ecosystem. There are three types of pyramids:
(a) Pyramid of numbers
(b) Pyramid of energy
(c) Pyramid of biomass
On the other hand, in a parasitic food chain, the pyramid of numbers is inverted. In this type of a food chain, a single tree (producer) provides food to several fruit eating birds, which in turn support several insect species.
Pyramid of biomass
Q9 :
What is primary productivity? Give brief description of factors that affect primary productivity.
Answer :
It is defined as the amount of organic matter or biomass produced by producers per unit area over a period of time.
Q10 :
Define decomposition and describe the processes and products of decomposition.
Answer :
Decomposition is the process that involves the breakdown of complex organic matter or biomass from the body of dead plants and animals with the help of decomposers into inorganic raw materials such as carbon dioxide, water, and other nutrients. The various processes involved in decomposition are as follows:
(1) Fragmentation: It is the first step in the process of decomposition. It involves the breakdown of detritus into smaller pieces by the action of detritivores such as earthworms.
(2) Leaching: It is a process where the water soluble nutrients go down into the soil layers and get locked as unavailable salts.
(3) Catabolism: It is a process in which bacteria and fungi degrade detritus through various enzymes into smaller pieces.
(4) Humification: The next step is humification which leads to the formation of a dark-coloured colloidal substance called humus, which acts as reservoir of nutrients for plants.
(5) Mineralization: The humus is further degraded by the action of microbes, which finally leads to the release of inorganic nutrients into the soil. This process of releasing inorganic nutrients from the humus is known as mineralization.
Decomposition produces a dark coloured, nutrient-rich substance called humus. Humus finally degrades and releases inorganic raw materials such as CO2, water, and other nutrient in the soil.
Q11 :
Give an account of energy flow in an ecosystem.
Answer :
Q12 :
Write important features of a sedimentary cycle in an ecosystem.
Answer :
Sedimentary cycles have their reservoirs in the Earth's crust or rocks. Nutrient elements are found in the sediments of the Earth. Elements such as sulphur, phosphorus, potassium, and calcium have sedimentary cycles.
Q13 :
Outline salient features of carbon cycling in an ecosystem
Answer :