NCERT Solutions Class 12 Biology Chapter 14 - Free PDF

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 productivity is _________. 

(d) Common detritivores in our ecosystem are_________.

(e) The major reservoir of carbon on earth is_________.
Ans.

(a) Plants are called autotrophs because they fix carbon dioxide. 

(b) In an ecosystem dominated by trees, the pyramid (of numbers) is of inverted type. 

(c) In aquatic ecosystems, the limiting factor for productivity is light.

(d) Common detritivores in our ecosystem are earthworms. 

(e) A major reservoir of carbon on Earth is the 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 

Ans.

(d) Decomposers 

Decomposers include microorganisms like bacteria and fungi. The largest population is formed by them in a food chain and they obtain nutrients by breaking down the remains of dead plants and animals.

3. The second trophic level in a lake is

(a) Phytoplankton

(b) Zooplankton

(c) Benthos

(d) Fishes

Ans.

(b) Zooplankton

Primary consumers are at the level of Second trophic. These are the organisms that eat the primary producers. Zooplankton is also one of them. They are the primary consumers in aquatic food chains that feed upon phytoplankton and efficiently digest plant matter for energy. 

4.  Secondary producers are 

(a) Herbivores

(b) Producers

(c) Carnivores

(d) None of the above 

Ans.

(d) None of the above.

Plants are the only producers and they lie at the lowest trophic level. Thus, they are called primary producers. There are no other producers in the food chain. 

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%

Ans.

(b) 50% 

About fifty percent of total incident solar radiation forms photosynthetically active radiation of PAR. 

6.  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

Ans. The difference between the grazing food chain and the detritus food chain are: 

The difference between Production and decomposition are: 

The difference between the upright and inverted pyramid are: 

The difference between the Food chain and the Foodweb is: 

Difference between Litter and detritus are: 

The difference between Primary and secondary productivity are: 

7. Describe the components of an ecosystem.

Ans. An ecosystem creates a link that has both the biological community as well as the non-living components of an area. The ecosystem was defined as the living world and its habitat by A.G. Tansley. It meant that any habitat on the earth which includes plants, animals, and non-living substances interact to produce materials that can be exchanged between living and nonliving components of the habitat in an ecosystem. Thus, they perform as a unit, which gets conspicuous during the processes of nutrient cycling, energy flow, decomposition, and productivity. Many ecosystems like ponds, forests, grasslands, etc are there. 

The two components of an ecosystem are:

• Biotic Component: The living component of an ecosystem is the biotic component. Which includes biotic factors such as producers, consumers, decomposers, etc. It is divided into major groups:

(a) Producers are green plants that include plants and algae. The presence of chlorophyll pigment, helps them carry out the process of photosynthesis in the presence of light. Thus, they are also referred to as converters or transducers. 

(b) Consumers or heterotrophs are organisms that cannot manufacture food and are, therefore, directly (primary consumers) or indirectly (secondary and tertiary consumers) dependent on producers for their food.

(c) Decomposers are the microorganisms like bacteria and fungi. The largest population is contributed by them in a food chain by breaking down the remains of dead plants and animals, and nutrients are obtained. 

• Abiotic component: These are the nonliving components within an ecosystem such as light, temperature, water, soil, air, inorganic nutrients, etc.

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

Ans. An ecological pyramid is a graphical representation of the number, biomass, and energy of the successive trophic levels of an ecosystem. In an ecological pyramid, the lowermost trophic level is formed by the producers and the topmost level is that of carnivores. 

There are three types of pyramids:

• Pyramid of numbers

• Pyramid of energy

• Pyramid of biomass

Pyramid of numbers: It shows the association between the number of producers, herbivores, and carnivores. Depending on the number of producers, it can be upright or inverted. In a grassland ecosystem, grasses are the producers. The pyramid of numbers is often upright. In this type of 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, At the producer level the number of individuals will be greatest, while at the top carnivores,  the number of individuals present will be least.

Pyramid of Numbers

Whereas on the other hand, in a parasitic food chain, the pyramid of numbers is inverted. In this type of food chain, several fruit-eating birds are provided with food by a single tree (producer), which in turn supports several insect species.

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

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

Ans. It is defined as the amount of organic matter or biomass produced by producers per unit area over a period of time. The primary productivity of an ecosystem depends on a 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.

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

Ans. Decomposition is the process that involves the breakdown of complex organic matter or biomass with the help of decomposers from the body of dead plants and animals into inorganic raw materials like carbon dioxide, water, and other nutrients. The processes involved in decomposition are as follows:

Fragmentation: The first step in the process of decomposition is fragmentation. By the action of detritivores, there is a breakdown of detritus into smaller pieces like in earthworms is called fragmentation.

Leaching: Several water-soluble inorganic substances percolate into the deeper layers of soil along with rain or irrigation water, it is known as leaching.  

Catabolism: Bacteria and fungi degrade detritus through various enzymes into smaller pieces is called catabolism.

Humification: The formation of a finely divided, amorphous dark-colored colloidal substance called humus, which acts as a reservoir of nutrients for plants is called humification.

Mineralization: By the action of microbes, humus is further degraded which finally results in the release of inorganic nutrients into the soil. 

A dark-colored, nutrient-rich substance called humus is produced by the process of decomposition. Humus thus degrades and releases inorganic raw materials such as CO2, water, and other nutrients in the soil.

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

Ans. In ecosystems, useful energy flows in a one way path. It enters the living things from the physical world, passes from one organism to a different and eventually escapes back to the physical environment in a less useful form. Energy enters an ecosystem from the Sun. Solar radiations are absorbed by the Earth’s surface through the atmosphere. The process of photosynthesis is carried out by these radiations. Also, they help to maintain the Earth’s temperature for the survival of living organisms. Few of the solar radiations are reflected by the Earth’s surface. However, a very little 2-10 percent of solar energy is captured by green plants (producers) during photosynthesis to be converted into food. The total rate of photosynthesis, including the organic matter that is almost immediately used up in plant respiration, 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. For various processes such as respiration, growth, and reproduction, the remaining 90% of the energy is used.  Similarly, only 10% of the energy of herbivores is transferred to carnivores. Therefore, this is called the ten percent law of energy flow.

Flow of Energy

12. Write important features of a sedimentary cycle in an ecosystem?

Ans. Sedimentary cycles have their reservoir pool in deep sediments or in the earth’s crust or rocks. Nutrient elements that are found in the sediments of the Earth are Sulphur, phosphorus, potassium, and calcium. There is absence of a gaseous phase in this cycle.

This cycle is very slow.  A  longer period of time is taken to complete their circulation and is considered a less perfect cycle. Since, In the process of recycling, nutrient elements get locked in the reservoir pool, which thereby takes a long time to come out and continue circulation. Thus, it always goes out of circulation for an extended time.

13. Outline salient features of carbon cycling in an ecosystem.

Ans. An important gaseous cycle is the carbon cycle which has its reservoir pool in the atmosphere. Organic components of all organisms always have a carbon major body constituent. It is considered to be a fundamental element found in all living forms. All molecules like carbohydrates, lipids, and proteins required for life processes are made of carbon. Carbon is present in combined form in all living forms by a fundamental process called ‘photosynthesis. Sunlight and atmospheric carbon dioxide are used to produce a carbon compound called ‘glucose’ in the process of photosynthesis. Other living organisms also utilize this glucose molecule. Thus, atmospheric carbon gets inside in living forms. Now, it becomes important to recycle this absorbed carbon dioxide back into the atmosphere to complete the cycle. There are several processes by which carbon is recycled back into the atmosphere in the form of carbon dioxide gas. First is the process of respiration in which glucose molecules are broken to produce carbon dioxide gas. Second is the process of decomposition which also releases carbon dioxide from dead bodies of plants and animals into the atmosphere. Industrialization, Combustion of fuels deforestation, volcanic eruptions, and forest fires act as other paramount sources of carbon dioxide.

Carbon Cycle

NCERT Solutions for Class 12 Biology Chapter 14 - Ecosystem

The Ecosystem chapter of Class 12 covers various topics about ecology, which is an important part of the Biology syllabus. The topics covered in NCERT Ch 14 of Class 12 Bio are Ecosystem- Structure and Function, Productivity, Decomposition, Energy Flow, Ecological Pyramids, Ecological Succession, Nutrient Cycling, and lastly, Ecosystem Services. All of these topics help students to understand the various nuances and intricacies of the existing Ecosystems on Earth.

Ecosystem Class 12 NCERT PDF Explanation

The various topics of the Class 12 NCERT chapter 14, Ecosystem, have been discussed here. The structure and functions of an ecosystem are explained by classifying it into terrestrial and aquatic ecosystems for convenience of understanding. Various different kinds of productivity of ecosystems are explained in the Ecosystem Class 12 NCERT PDF, as have the various facets and processes that accompany the scientific process of decomposition. Under the topic of Energy Flow, Ecosystem chapter for Class 12 discusses the food chain, producers, and consumers in detail, and then going on to put these into an Ecological Pyramid. Ecological Successions are discussed next, in terms of how it works in plants, then Nutrient Cycles, and its types, the Nitrogen Cycle and Phosphorus Cycle. Lastly, the Ecosystem Services are discussed in the NCERT Solution for chapter 14.

NCERT Solutions for Class 12 Biology Chapter 14 Weightage

The chapter Ecosystem is part of Unit X of the class 12 NCERT Biology textbook, Ecology and Environment. Unit X of the book has a total of 4 chapters and Ecosystem is the second chapter of the unit. Unit X carries a total of 14 marks, split into four chapters including Ecosystem itself. The weightage of chapter 14 is 3.5 marks for the Class 12 final examination of Biology, if questions are asked from all the chapters in this unit. The marks allotment may vary depending on the question format of the examination.

Important Topics in NCERT Solutions Class 12 Biology Chapter Ecosystem

In Class 12 Biology Chapter 14 Ecosystem, students will get a detailed explanation of the following topics:

• Structure and Function of Ecosystem

• Decomposition

• Energy Flow

• Ecological Succession

• Productivity

• Ecological Pyramids

• Nutrient Cycling

• Ecosystem Services

All of these topics are important for the Class 12 Biology exam; therefore, one must go through these topics in detail and clear their doubts beforehand.

NCERT Solutions of Ecosystem Class 12 Benefits

NCERT Biology's chapter 14 for class 12 is very scoring from the examination point-of-view. The benefits of the NCERT Solutions for Class 12 Biology's Chapter 14 (Ecosystem) are as follows. 

• The NCERT Solutions for Class 12 Biology Chapter 14 (Ecosystem) facilitates a holistic understanding of the topics covered in the chapter.  

• By referring to the NCERT Solutions for Ecosystem you will be able to learn the appropriate answer pattern for the Class 12 Biology exam.

• The NCERT Solutions for Class 12 Biology Chapter 14; Ecosystems, make an excellent resource for self-study and revision purposes. Hence, it will save a lot of time during the exams.

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