NCERT Solutions for Class 12 Biology Chapter 12 - 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 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

The pyramid of numbers illustrates the relationship between producers, herbivores, and carnivores in an ecosystem. It can be either upright or inverted based on the number of producers. In a grassland ecosystem, grasses act as producers, making the pyramid upright. In this food chain, the number of individuals is highest at the producer level and decreases as we move up to tertiary carnivores like eagles.

Pyramid of Numbers

On the flip side, in a parasitic food chain, the pyramid of numbers is upside-down. In this setup, a single tree (the producer) supports various fruit-eating birds, and these birds, in turn, sustain multiple insect species.

Biomass pyramid depicts the total living matter at each trophic level in an ecosystem, whether it's higher or lower. In grasslands and forests, it's upright, indicating more biomass at the producer level than the top carnivore level. Conversely, in pond ecosystems, it's inverted, showcasing fishes' biomass surpassing that of zooplankton they consume.

9. What is primary productivity, and what factors influence it?

Ans: Primary productivity refers to the organic matter produced by producers per unit area over time. Environmental factors like light, temperature, water, and precipitation, along with nutrient availability and plant access for photosynthesis, determine an ecosystem's primary productivity.

10. Q: What is decomposition, and what does it involve?

Ans: Decomposition is when decomposers break down complex organic matter from dead plants and animals into inorganic substances like carbon dioxide, water, and 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: is the creation of a dark, finely divided substance known as humus. This acts like a nutrient reservoir for plants.

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 from the soil.

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

Ans. In ecosystems, energy follows a one-way path, entering living things from the physical world, passing between organisms, and eventually returning to the environment in a less useful form. Solar energy enters through the Sun, absorbed by Earth's surface for photosynthesis and maintaining temperatures. Green plants capture a small portion (2-10%) of solar energy for photosynthesis. This energy, called gross primary productivity, is used for plant respiration. When herbivores consume plants, only 10% of the stored energy is transferred, with 90% used for various processes. Similarly, only 10% of herbivores' energy is transferred to carnivores. This pattern, known as the ten percent law of energy flow, highlights the gradual loss of energy as it moves through different trophic levels in an ecosystem.

Flow of Energy

12. Write the 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 the salient features of carbon cycling in an ecosystem.

Ans. An essential cycle in nature is the carbon cycle, with the atmosphere as its main reservoir. Carbon is a crucial element in all living organisms, forming the backbone of organic components like carbohydrates, lipids, and proteins. Through photosynthesis, sunlight and carbon dioxide create glucose, a carbon compound, entering living organisms. Recycling is vital, and processes like respiration and decomposition release carbon dioxide back into the atmosphere. In respiration, glucose is broken down, producing carbon dioxide. Decomposition releases carbon dioxide from dead plants and animals. Additionally, human activities like industrialization, fuel combustion, deforestation, volcanic eruptions, and forest fires contribute significantly to carbon dioxide levels in the atmosphere. Understanding the carbon cycle helps us comprehend how this essential element moves through living organisms and the environment, emphasizing the interconnectedness of all living things and their dependence on natural processes.

Carbon Cycle

NCERT Solutions for Biology Class 12 Chapter 12 - Ecosystem

Class 12's Ecosystem chapter delves into vital ecology topics, a key part of the Biology syllabus. Covered in NCERT Ch 12, it explores Ecosystem Structure and Function, Productivity, Decomposition, Energy Flow, Ecological Pyramids, Ecological Succession, Nutrient Cycling, and Ecosystem Services. These subjects enable students to grasp the complexities of Earth's ecosystems, offering insights into their structures and functions.

Ecosystem Class 12 NCERT PDF Explanation

This summary covers the Class 12 NCERT Chapter 12, "Ecosystem." It breaks down the ecosystem's structure and functions, distinguishing between terrestrial and aquatic ecosystems. The PDF elaborates on different types of productivity and the intricate process of decomposition. Exploring Energy Flow, the chapter delves into food chains, detailing producers and consumers, culminating in an Ecological Pyramid. Ecological Successions are explained, particularly in plant contexts, followed by insights into Nutrient Cycles—specifically, the Nitrogen and Phosphorus Cycles. Finally, Ecosystem Services are discussed in the NCERT Solution for Chapter 12, offering a comprehensive understanding of these essential elements in the study of ecosystems on Earth.

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

• The NCERT Solutions for Biology Class 12 Chapter 12 (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 Chapter 12; Ecosystems, make an excellent resource for self-study and revision purposes. Therefore saving a lot of time during the exams.

• Since these solutions are available in a PDF format, you can consult them even when you are not connected to the internet.

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