NCERT Solutions for class 12 Biology chapter 14-Ecosystem

NCERT Solutions for class-12 Biology Chapter 14 Ecosystem is prepared by Physics Wallah senior teacher team, primary focus while solving these questions of class-12 in NCERT textbook, Do read theory of this Chapter while going before solving the NCERT questions. You can download and share NCERT Solutions of Class 12 Biology from Physics Wallah.

Chapter 14 Ecosystem

 

Answer the following Questions.

Question1. 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
(b) inverted
(c)Light
(d)Earthworm
(e)Ocean

Question2. 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 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

Question3. The second trophic level in a lake is
(a) Phytoplankton
(b) Zooplankton
(c) Benthos
(d) Fishes

Solution :
(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.

Question4. Secondary producers are
(a) Herbivores
(b) Producers
(c) Carnivores
(d) None of the above

Solution :
(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.

Question5. 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%
Out of total incident solar radiation, about fifty percent of it forms photosynthetically active radiation (PAR).

Question6. 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

(a) Grazing food chain and detritus food chain

Grazing food chain

Detritus 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.

(b) Production and decomposition

Production

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.

(c) Upright and inverted pyramid

Upright pyramid

Inverted 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


(d) Food chain and Food web

Food chain

Food 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.


(e) Litter and detritus

Litter

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.

(f) Primary and secondary productivity

Primary productivity

Secondary 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.

Question7. Describe the components of an ecosystem.

Solution :
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:

  • 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. 
  • Abiotic component: They are the non-living component of an ecosystem such as light, temperature, water, soil, air, inorganic nutrients, etc.

Question8. Define ecological pyramids and describe with examples, pyramids of number and biomass.

Solution :
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

Pyramid of numbers:It is a graphical representation of the number of individuals present at each trophic level in a food chain of an ecosystem. The pyramid of numbers can be upright or inverted depending on the number of producers. For example, in a grassland ecosystem, the pyramid of numbers is upright. In this type of a food chain, the number of producers (plants) is followed by the number of herbivores (mice), which in turn is followed by the number of secondary consumers (snakes) and tertiary carnivores (eagles). Hence, the number of individuals at the producer level will be the maximum, while the number of individuals present at top carnivores will be least. 

NCERT Solutions for Class 12  Biology Chapter 14 - Ecosystem

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 : A pyramid of biomass is a graphical representation of the total amount of living matter present at each trophic level of an ecosystem. It can be upright or inverted. It is upright in grasslands and forest ecosystems as the amount of biomass present at the producer level is higher than at the top carnivore level. The pyramid of biomass is inverted in a pond ecosystem as the biomass of fishes far exceeds the biomass of zooplankton (upon which they feed). 

NCERT Solutions for Class 12  Biology Chapter 14 - Ecosystem

Question9. What is primary productivity? Give brief description of factors that affect primary productivity.

Solution :
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. 

Question10. Define decomposition and describe the processes and products of decomposition.

Solution :
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. 

Question11. Give an account of energy flow in an ecosystem.

Solution :
Energy enters an ecosystem from the Sun. Solar radiations pass through the atmosphere and are absorbed by the Earth’s surface. These radiations help plants in carrying out the process of photosynthesis. Also, they help maintain the Earth’s temperature for the survival of living organisms. Some solar radiations are reflected by the Earth’s surface. Only 2-10 percent of solar energy is captured by green plants (producers) during photosynthesis to be converted into food. The rate at which the biomass is produced by plants during photosynthesis is termed as ‘gross primary productivity’. When these green plants are consumed by herbivores, only 10% of the stored energy from producers is transferred to herbivores. The remaining 90 % of this energy is used by plants for various processes such as respiration, growth, and reproduction. Similarly, only 10% of the energy of herbivores is transferred to carnivores. This is known as ten percent law of energy flow. 

Chapter 14 - Ecosystem

Question12. Write important features of a sedimentary cycle in an ecosystem.

Solution :
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.

Question13. Outline salient features of carbon cycling in an ecosystem

Solution :
The carbon cycle is an important gaseous cycle which has its reservoir pool in the atmosphere. All living organisms contain carbon as a major body constituent. Carbon is a fundamental element found in all living forms. All biomolecules such as carbohydrates, lipids, and proteins required for life processes are made of carbon. Carbon is incorporated into living forms through a fundamental process called ‘photosynthesis’. Photosynthesis uses sunlight and atmospheric carbon dioxide to produce a carbon compound called ‘glucose’. This glucose molecule is utilized by other living organisms. Thus, atmospheric carbon is incorporated in living forms. Now, it is necessary to recycle this absorbed carbon dioxide back into the atmosphere to complete the cycle. There are various processes by which carbon is recycled back into the atmosphere in the form of carbon dioxide gas. The process of respiration breaks down glucose molecules to produce carbon dioxide gas. The process of decomposition also releases carbon dioxide from dead bodies of plants and animals into the atmosphere. Combustion of fuels, industrialization, deforestation, volcanic eruptions, and forest fires act as other major sources of carbon dioxide. 

Chapter 14 - Ecosystem

NCERT Solutions For Class 12 Biology Chapter Wise.

  1. Chapter 1 Reproduction in Organisms

  2. Chapter 2 Sexual Reproduction In Flowering Plants

  3. Chapter 3 Human Reproduction

  4. Chapter 4 Reproductive Health

  5. Chapter 5 Principles of Inheritance And Variation

  6. Chapter 6 Molecular Basis of Inheritance

  7. Chapter 7 Evolution

  8. Chapter 8 Human Health And Disease

  9. Chapter 9 Strategies For Enhancement In Food Production

  10. Chapter 10 Microbes In Human Welfare

  11. Chapter 11 Biotechnology And Processes

  12. Chapter 12 Biotechnology And Its Applications

  13. Chapter 13 Organisms And Populations

  14. Chapter 14 Ecosystem

  15. Chapter 15 Biodiversity And Conservation

  16. Chapter 16 Environmental Issues

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