NCERT Solutions for Class 12 Biology Chapter 12 - Ecosystem - Free PDF
Chapter 12, Ecosystems is one of the most important and scoring topics covered in the Class 12 Biology syllabus. The NCERT Solutions for Class 12 Biology Chapter 12 are prepared in a simple manner by our subject-matter experts to help you learn the topics covered in this chapter easily. These solutions are available in the PDF format on Vedantu. You can download the PDF file for free. By referring to these NCERT Solutions, you can revise chapter 12 of Class 12 Biology thoroughly and secure good marks in the exams.
Table of Content
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Ecosystem Chapter at a Glance - Class 12 NCERT Solutions
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:
Grazing food chain | Detritus food chain | ||
1. | Energy is derived from the Sun in the grazing food chain. | 1. | Energy comes from organic matter which is generated in trophic levels of the grazing food chain. |
2. | It starts with the producers,available at the first trophic level. The plant biomass is then eaten by herbivores, which successively are consumed by a spread of carnivores. | 2. | It starts with detritus like dead bodies of animals or fallen leaves, which are then consumed by decomposers or detritivores. These detritivores are in turn eaten by their predators. |
3. | This food chain is a large one. | 3. | Detritus food chain is smaller as compared to the grazing food chain. |
The difference between Production and decomposition are:
Production | Decomposition | ||
1. | It is the rate of organic matter produced by producers. | 1. | Breaking down of complex organic matter with the help of decomposers from the body of dead plants and animals and converting into organic raw materials like CO2, H2O, and other nutrients. |
2. | It is dependent on the photosynthetic capacity of the producers. | 2. | It occurs with the help of decomposers. |
3. | The requirement of sunlight is necessary by plants for primary production. | 3. | No sunlight requirement is there in the process of decomposition. |
The difference between the upright and inverted pyramid are:
Upright pyramid | Inverted pyramid | ||
1. | The pyramid of energy is always upright. | 1. | The pyramid of biomass and the a pyramid of numbers can be inverted. |
2. | The number and biomass of organisms in the producer level of an ecosystem are the highest in an upright pyramid, which further keeps on decreasing at each trophic level in a food chain. | 2. | The number and biomass of organisms in the producer level of an ecosystem is the lowest in an inverted pyramid, which further keeps on increasing at each trophic level. |
The difference between the Food chain and the Foodweb is:
Food chain | Food Web | ||
1. | It is a single linear sequence of organisms. | 1. | It is a network formed by interconnecting food chains. |
2. | In this chain, members are present at higher trophic levels which sustain single types of organisms. | 2. | Alternate food sources are present in one organism. |
Difference between Litter and detritus are:
Litter | Detritus | ||
1. | Litter is all the wastes that are produced above the ground. | 1. | Detritus is the remains of dead plants and animals in an ecosystem. |
2. | Litter consists of both biodegradable and non-biodegradable matter. | 2. | Detritus consists of only biodegradable matter. |
The difference between Primary and secondary productivity are:
Primary Productivity | Secondary productivity | ||
1. | It is defined as the rate at which organic energy is stored as organic matter produced by producers per unit the area over a period of time. | 1. | It is defined as the rate of production of organic matter by consumers over a period of time. |
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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Conclusion
The Ecosystem chapter teaches us about the way different living things in our world connect and depend on each other. It looks at the parts of ecosystems, how energy moves through them, and how new life takes over from old life. We also learn how things like carbon and water move around the planet, and how we can affect these processes. The chapter reminds us that everything in nature is linked, and we need to take care of it for ourselves and the future. It asks us to make good choices and protect the variety of life and the Earth’s materials that keep us alive. Learning about ecosystems helps us deal with environmental problems and live in harmony with nature.
FAQs on NCERT Solutions for Class 12 Biology Chapter 12 Ecosystem
1. How do Vedantu’s NCERT Solutions for Class 12 Biology Chapter 12 help in board exam preparation?
These solutions are designed to align perfectly with the CBSE 2025–26 syllabus and marking scheme. They provide a clear, step-by-step methodology for solving every question in the textbook exercise, which helps you understand the expected answer format and include all necessary keywords and diagrams to secure full marks.
2. What is the correct method to answer questions about the components of an ecosystem from the NCERT exercise?
Start by defining an ecosystem. Then, use a structured format to explain its two main components as per the NCERT guidelines:
- Abiotic Components: List non-living factors such as light, temperature, water, and soil.
- Biotic Components: Detail the living organisms by their trophic levels—Producers (autotrophs), Consumers (heterotrophs), and Decomposers (saprotrophs).
3. How should I draw and explain ecological pyramids for questions in Chapter 12 to score well?
To correctly present an ecological pyramid answer:
- First, draw a neat, labelled diagram representing the specific pyramid (e.g., Pyramid of Numbers or Biomass).
- Clearly label each trophic level, from producers at the base to top carnivores at the apex.
- State whether the pyramid is upright or inverted and briefly explain why, using examples from the NCERT textbook, such as a grassland ecosystem for an upright pyramid or a single tree ecosystem for an inverted one.
4. What is the best way to structure an answer for "distinguish between" questions, like comparing the grazing and detritus food chains?
For distinction questions, a tabular format is the most effective method as shown in NCERT Solutions. Create two columns, one for each concept (e.g., Grazing Food Chain and Detritus Food Chain). List the differences point-by-point based on key criteria such as:
- The starting point or primary energy source.
- The organisms involved at the first trophic level.
- The relative size and speed of energy flow.
5. How do the NCERT Solutions explain the complex process of decomposition step-by-step?
The solutions break down decomposition into five distinct, sequential steps to make it easy to remember and explain:
- Fragmentation: The breakdown of detritus into smaller particles by detritivores.
- Leaching: The process where water-soluble inorganic nutrients go down into the soil horizon.
- Catabolism: The enzymatic degradation of detritus into simpler inorganic substances.
- Humification: The formation of a dark-coloured, amorphous substance called humus.
- Mineralisation: The final release of inorganic nutrients from the humus.
6. Why is the flow of energy in an ecosystem always unidirectional, as explained in the NCERT Solutions?
The NCERT Solutions explain that energy flow is unidirectional because it follows the laws of thermodynamics. Energy enters the ecosystem from the sun and is captured by producers. At each successive trophic level, a significant amount of energy (about 90%) is lost as heat during metabolic activities. This lost energy cannot be reused by organisms at a lower trophic level, so it flows in one direction only and does not cycle back.
7. How can I use the NCERT Solutions to master the concept of the "ten percent law" of energy transfer?
The solutions demonstrate the ten percent law by explaining that only about 10% of the energy from one trophic level is transferred and stored as biomass in the next. They advise using simple examples, like a food chain from a producer to a tertiary consumer, to show the drastic reduction in available energy at each step. This explanation helps clarify why food chains are typically limited to 4-5 trophic levels.
8. What is the recommended approach for answering application-based questions on nutrient cycles like the carbon cycle?
According to the CBSE pattern, you should first define the nutrient cycle. Then, systematically outline the key processes involved, such as photosynthesis, respiration, decomposition, and combustion for the carbon cycle. It is highly recommended to support your explanation with a simple, labelled diagram showing the reservoirs (e.g., atmosphere, oceans) and the flow of the nutrient between biotic and abiotic components.
9. What are common mistakes to avoid when solving problems from the Ecosystem chapter using NCERT Solutions?
A common mistake is simply memorising the solutions without understanding the underlying concepts. For example, students often confuse the inverted pyramid of biomass (seen in aquatic ecosystems) with the pyramid of numbers. Another frequent error is neglecting to draw labelled diagrams where required, such as for ecological pyramids or nutrient cycles, which can result in losing marks. Always focus on understanding the 'why' behind each step in the solution.
10. How do NCERT Solutions help in tackling Higher Order Thinking Skills (HOTS) questions related to this chapter?
NCERT Solutions provide a strong foundational understanding of core concepts like productivity, decomposition, and energy flow. For HOTS questions, which often require applying these concepts to new scenarios (e.g., "What would happen to an ecosystem if all decomposers were removed?"), the solutions equip you with the correct terminology and logical framework. By mastering the standard answers, you can better analyse, synthesise, and formulate responses for complex, application-based problems.
