NCERT Solutions for Class 12 Biology Chapter 14: Ecosystem

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Chapter14. Ecosystem
CategoryNCERT Solutions for Class 12

Our NCERT Solutions for Class 12 Biology is a great resource for students preparing for boards or competitive exams, such as the NEET. These Biology Class 12 Solutions are made by expert faculties, keeping the latest curriculum in mind. Besides helping students with understanding the concepts of Biology, these solutions are also helpful in writing accurate answers that are vital to score full marks in examinations. On this page, we have given the Class 12 Biology Chapter 14: Ecosystem Solutions.

NCERT Solutions for Class 12 Biology Chapter 14

Ecosystem Solutions

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 ………..


(a) Autotrophs
(b) inverted

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
Zooplankton are primary consumers in aquatic food chains that feed upon phytoplankton. Therefore, they are present at the second trophic level in a lake.

Q4) Secondary producers are

(a) Herbivores
(b) Producers
(c) Carnivores
(d) None of the above

Answer) (d) None of the above
Plants are the only producers. Thus, they are called primary producers. There are no other producers in a food chain.

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%
Out of total incident solar radiation, about fifty percent of it forms photosynthetically active radiation (PAR).

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) Differences between Grazing food chain and detritus food chain:

Grazing food chainDetritus food chain
In this food chain, energy is derived from the Sun.In this food chain, energy comes from organic matter (or detritus) generated in trophic levels of the grazing food chain.
It begins with producers, present at the first trophic level.It begins with detritus such as dead bodies of animals or fallen leaves, which are then eaten by decomposers or detritivores.
This food chain is usually large.It is usually smaller as compared to the grazing food chain.

Answer b) Differences between Production and decomposition:

It is the rate of producing organic matter (food) by producers.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 materials.
It depends on the photosynthetic capacity of the producers.It occurs with the help of decomposers.
Sunlight is required by plants for primary production.Sunlight is not required for decomposition by decomposers.

Answer c) Differences between Upright and inverted pyramid:

Upright pyramidInverted pyramid
The pyramid of energy is always upright.The pyramid of biomass and the pyramid of numbers can be inverted.
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.The number and biomass of organisms in the producer level of an ecosystem is the lowest, which keeps on increasing at each tropic level. Light is not required for decomposition by decomposers

Answer d) Differences between Food chain and Food web

Food chainFood web
Food chain is single pathway of energy transfer from upper to lower.Food web is made of several interconnecting pathways.
One individual occupies one trophic level at a time.One individual occupies many trophic level at a time.
It decreases stability of the ecological system and less adaptive.It increases stability of the ecological system and more adaptive.

Answer e) Differences between Litter and detritus

Litter contains all kinds of waste materials above the surface of the earth.Detritus contains dead animals and plants below and above the surface of the earth.
It contains both biodegradable as well as non-biodegradable wastes.It contains only biodegradable wastes.

Answer f) Differences between Primary and secondary productivity:

Primary productivitySecondary productivity
Rate of amount of production of organic matter by producers over a period of time.Rate of amount of production of organic matter by consumers over a period of time.
It is due to photosynthesis.It is due to herbivory and predation.

Q7) Describe the components of an ecosystem.

Answer) Ecosystem is an interacting unit involving both living components and the non-living components of a region. Both of these components interact with each other functioning as a unit which is apparent in the processes of energy flow, nutrient cycling, productivity, decomposition in ecosystems such as grasslands, forest, ponds etc.

Ecosystems have two components, they are:

  1. Abiotic components – These constitute the non-living components of an ecosystem such as temperature, light, water, wind, soil, chemical nutrients etc.
  2. Biotic components – They form the living component of an ecosystem which include biotic factors such as decomposer, consumers, and producers. Plants and some algae form the producers as they contain chlorophyll to synthesize their own food through the process of photosynthesis carried out in the presence of light, hence they are also referred to as transducers or converters. The consumers or heterotrophs are dependent on producers either directly (primary consumers) or indirectly (secondary consumers) while decomposers are constituted by the microbes in the ecosystem, such as fungi and bacteria. They form the largest population in the food chain as they derive their nutrition by disintegrating the residues of dead animals and plants.

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:

  • Pyramid of numbers
  • Pyramid of energy
  • Pyramid of biomass

(i) Pyramid of numbers – it gives the graphical representation of the number of individuals found at each trophic level in a food chain of an ecosystem. This pyramid can be inverted or upright depending on the crowd of producers. Example – In a Grassland ecosystem, this pyramid is upright where in the food chain, the number of producers is followed by the number of herbivores, which in turn is followed by number of secondary and tertiary consumers. Therefore, the number of individuals at the level of producers will be maximum, whereas the number of individuals at the top carnivores will be the least. The pyramid of numbers in a parasitic food chain is inverted, where in the food chain, producers provide food to fruit eating birds which in response support few species of insects

(ii) Pyramid of biomass – it is a graphical representation of the total quantity of living matter found at each trophic level of an ecosystem and can either be inverted or upright. In grasslands and forest ecosystems it is upright as the quantity of biomass at the producer level is higher than at the carnivore level, at the top. This pyramid is inverted in a pond ecosystem as the biomass of fishes far surpass the biomass of zooplankton on which they feed.

(iii) Pyramid of energy – Energy pyramid is a graphical representation indicating flow of energy at each trophic level in an ecosystem. Pyramid of energy is always upright. It cannot be inverted, because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step. In the energy pyramid, each bar shows the amount of energy present at each trophic level in a given time or annually per unit area.

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.

Primary productivity of an ecosystem depends on the variety of environmental factors such as light, temperature, water, precipitation, etc. It also depends on the availability of nutrients and the availability of plants to carry out photosynthesis.

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:

  • 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.
  • Leaching: It is a process where the water soluble nutrients go down into the soil layers and get locked as unavailable salts.
  • Catabolism: It is a process in which bacteria and fungi degrade detritus through various enzymes into smaller pieces.
  • 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.
  • 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) In an ecosystem, energy enters from the ultimate source of energy – the Sun. These solar rays pass through the atmosphere to be absorbed by the surface of the earth, which help plants in performing photosynthesis. Additionally, they also help in maintaining the temperature of the earth so that living entities survive. Some of these incident rays are reflected by the surface of the earth and only close to 2-10% of the solar energy is captured by the producers (green plants) during the photosynthesis process in order to convert it into food.

Gross primary productivity is the rate at which the biomass is generated by plants during the process of photosynthesis. Just 10% of the stored energy is transferred to herbivores from the producers when plants are consumed by herbivores. The rest of 90% of the energy is used for different processes by plants such as growth, respiration and reproduction. Likewise, a mere 10% of the energy of herbivores is conveyed to carnivores. This is referred to as the ten percent law of energy flow.

NCERT Solutions for Class 12 Biology Chapter 14

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.

Sedimentary cycles are very slow. They take a long time to complete their circulation and are considered as less perfect cycles. This is because during recycling, nutrient elements may get locked in the reservoir pool, thereby taking a very long time to come out and continue circulation. Thus, it usually goes out of circulation for a long time.

Q13) Outline salient features of carbon cycling in an ecosystem

Answer) The carbon cycle is an essential gaseous cycle which has its reservoir pool in the atmosphere. All of the living entities consist of carbon as a major constituent of the body. This carbon is a basic element present in all the living forms. Biomolecules such as lipids, carbohydrates, proteins etc that are crucial for life processes are made of carbon. Living forms are incorporated with carbon through the basic process of photosynthesis that is carried out by plants, the primary producers. The process of photosynthesis uses up atmospheric carbon dioxide and sunlight to produce a carbon compound known as ‘glucose’, this in turn is used by other living entities.

Hence, atmospheric carbon gets incorporated into life forms. It now becomes necessary to recycle this absorbed carbon dioxide back to the atmosphere to complete the cycle. For this recycling of carbon back to the atmosphere in the form of carbon dioxide gas, various processes can be carried out. The respiration process disintegrates glucose molecules to produce carbon dioxide gas. The decomposition process gives out carbon dioxide from dead bodies of animals and plants into the atmosphere. Some other sources of carbon dioxide are industrialization, combustion of fuels, deforestation, forest fires, volcanic eruptions and so on.

NCERT Solutions for Class 12 Biology Chapter 14

That’s it. These were the solutions of NCERT Class 12 Biology Chapter 14 – Ecosystem. Our team hopes that you have found these solutions helpful for you. If you have any doubt related to this chapter then feel free to comment your doubts below. Our team will try their best to help you with your doubts.

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