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NCERT Solutions Class 12 Biology Chapter 12 Ecosystem

In Chapter 12 of Class 12 Biology - Ecosystem, students learn how living organisms and their physical surroundings work together as a functional unit. It also introduces concepts like nutrient cycles, ecological pyramids, and productivity to help students understand how balance is maintained in nature.

To streamline exam preparation, ALLEN provides high-quality NCERT Solutions with focus on clarifying the distinction between GPP (Gross Primary Productivity) and NPP (Net Primary Productivity), while providing step-by-step breakdowns of the decomposition process. Students can develop a deep, intuitive understanding of ecological balance, ensuring they are fully prepared for descriptive board questions and competitive medical entrance exams.

1.0Key Concepts of Class 12 Biology Chapter 12 Ecosystem

The chapter focuses on understanding how ecosystems are organised and maintained. Some of the key lessons covered in this chapter are given below:

Structure of an Ecosystem: Understand the role of biotic and abiotic components and how they work together to maintain an ecosystem.
Trophic Levels: Learn about producers, consumers, and decomposers and their positions in food chains and food webs.
Energy Flow: Study how energy passes from one trophic level to another and understand the ten percent law of energy transfer.
Ecological Pyramids: Understand pyramids of number, biomass, and energy and how they represent different trophic levels.
Productivity: Learn about primary and secondary productivity and how they indicate the rate of biomass production in an ecosystem.
Nutrient Cycles: Explore the carbon and phosphorus cycles and understand their role in the movement and recycling of nutrients.
Decomposition: Understand how decomposers break down dead organic matter and return nutrients to the ecosystem.

2.0NCERT Class 12 Biology Chapter 12 Ecosystem : Detailed Solutions

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 $____$ .

Ans. (a) Producers

(b) Inverted (c) Light (d) Earthworm, ants and mites (e) Oceans (71% dissolved carbon)

Which one of the following has the largest population in a food chain? (a) Producers (b) Primary consumers (c) Secondary consumers (d) Decomposers Ans. (a) Producers (decomposers can be maximum but they are excluded from the food chain)
The second trophic level in a lake is (a) Phytoplankton (b) Zooplankton (c) Benthos (d) Fishes

Ans. (b) Zooplankton

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

Ans. (a) Herbivores

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%

Distinguish between [IMP.]

(a) Grazing food chain and detritus food chain (b) Production and decomposition (c) Litter and detritus (d) Upright and inverted pyramid (e) Food chain and food web (f) Primary and secondary productivity

Ans. (a) Grazing food chain and detritus food chain -

Grazing food chain	Detritus food chain
It start with green plants called producers as first trophic level.	It begins with dead organic matter and decomposers called saprophytes as first trophic level.
A much less fraction of energy flows through this type of food chain.	A much large fraction of energy flows through this type of food chain.
Energy for food chain comes from sun.	Energy for the food chain comes from organic remains or detrirus

(b) Production and decomposition

Production	Decomposition
It is the process of formation of fresh biomass from inorganic matter by producers using sunlight.	It is the process of degradation of waste biomass into its constituents by decomposers.
It is anabolic process which traps energy.	Its catabolic process and release energy.

(c) Litter and detritus

Litter	Detritus
It is made of dried fallen plant matter.	It is freshly deposited organic matter, i.e. remains of plants and animals.
It is found above the ground.	It is found both above and below the ground.

(d) Upright and inverted pyramid

Upright pyramid	Inverted pyramid
The base bar comprises of producers in large numbers.	The base bar comprises producers in smallest numbers.
The numbers of consumers decrease and become least in top consumer level. e.g. Pyramid of energy is always upright.	The numbers of consumers increase and become largest in top consumers level. e.g. Pyramid of number and biomass may be inverted.

(e) Food chain and food web

Food chain	Food web
The transfer of energy from producers to top consumers through a series of organisms is called as food chain.	The numbers of food chain are inter connected with each other forming a web like pattern is called food web.
One organism hold only one position of trophic level.	One organism can hold more than one position of trophic level.
The flow of energy can be easily calculated.	The flow of energy is very difficult to calculate.
It is always straight and proceed in a progressive straight line.	Instead of straight line it is a series of branching lines.

(f) Primary and secondary productivity

Primary productivity	Secondary productivity
It is the rate at which organic matter is build up by produces.	It is the rate at which organic matter is build up by consumers.
It is the result of synthesis of fresh organic matter from inorganic materials.	It is the result of synthesis of organic matter from plant organic matter.

Describe the components of an ecosystem.

Ans. An ecosystem consists of two types of components, ie., biotic or living and abiotic or non-living. There are three main types of biotic components on the basis of mode of obtaining their food- producers, consumers and decomposers.

(a) Producers (autotrophs): They are photosynthetic or autotrophic plants that synthesise their own organic food from inorganic raw materials with the help of solar radiations. Common producers are algae, plants and photosynthetic bacteria. Phytoplanktons are the producers of aquatic ecosystems. (b) Consumers (heterotrophs): They are animals which feed on other organisms or producers for obtaining their nourishment. Common consumers are deer, goat, etc. (c) Decomposers: They are saprotrophs which obtain nourishment from organic remains. They release digestive enzymes to digest the organic matter. Common decomposers are detritivores, e.g. earthworm.

Abiotic components of ecosystem consists of non-living substances and factors which are as follow: (a) Temperature (b) Light (c) Wind (d) Humidity (e) Precipitation (f) Water

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

Ans. The relationship between producers and consumers at different trophic levels in an ecosystem can be graphically represented in the form of a pyramid called ecological pyramid. Structure: The base always represents the producers or the first trophic level and the apex represents top level consumer or the last trophic level. Ecological pyramids are of three types : (i) Pyramid of number (ii) Pyramid of biomass (iii) Pyramid of Energy

(i) Pyramid of number: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of number of organisms at different trophic levels called pyramid of number. Note: It is inverted, when you count number of insects feeding on a big tree.

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(ii) Pyramid of biomass: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of biomass called pyramid of biomass. It can be

(a) Upright, e.g. in case of grassland ecosystem; (b) Inverted, e.g. in case of pond ecosystem as biomass of fishes for exceeds that of phytoplankton

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What is primary productivity? Give brief description of factors that affect primary productivity. [IMP.]

Ans. Primary productivity is the rate of synthesis of biomass by producers, per unit time, per unit area through the process of photosynthesis. The factors affecting primary productivity are following :-

Plant species inhabiting a particular area.
Environmental factors: (i) Sunlight : The sunlight directly regulates the primary productivity because the plants perform photosynthesis with the help of sunlight. As tropical region receives maximum sunlight so it exhibits higher productivity. (ii) Temperature: Temperature regulates the activity of enzyme. So, optimum temperature is required for proper functioning of enzyme. (iii) Moisture: Rain (humidity) is required for higher primary productivity. Deserts have the lowest primary productivity as the soil is deficient in moisture.

Define decomposition and describe the processes and products of decomposition.

Ans. The process of breaking down complex organic matter into inorganic substances like $CO_{2}$ , water and nutrients is called decomposition. The raw materials for decomposition including dead plant remains like leaves, bark, flowers, and animal remains and their faecal matter are called detritus.

Steps of Decomposition

(1) Fragmentation: The process of breaking down of detritus into smaller particle is called fragmentation, eg., as done by earthworm (farmer's friend). (2) Leaching: The process by which watersoluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts is called leaching. (3) Catabolism: The enzymatic process by which bacterial and fungal enzymes degrade detritus to simpler inorganic substances is called catabolism. (4) Humification: The process of accumulation of a dark coloured amorphous substance, called humus, that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate is called humification. Humus being colloidal is reservoir of nutrients. (5) Mineralisation: The process by which humus is further degraded by some microbes to release inorganic nutrients is called mineralisation.

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Give an account of energy flow in an ecosystem.

Ans. The sun is the only source of energy for all ecosystems on earth. Of the total incident solar radiation, only 50% of it is photosynthetic active radiation (PAR).

Plant capture only 2-10 % of the PAR and this small amount of energy sustains the entire living world. So, there is unidirectional flow of energy from the sun to producers and then to consumers
The energy is transferred in an ecosystem, in the form of food which is degraded and lose major part of food energy as heat during metabolic activities and only a very small fraction becomes stored as biomass
This is correlated to second law of thermodynamics, i.e., ecosystems need a constant supply of energy to synthesize molecules they require, to counteract universal tendency towards increasing disorderliness.
The green plants in the ecosystem which can trap solar energy to convert it into chemical bond energy are called producers.
All the animals that depend for food on plants are called consumers or heterotrophs.
Consumers are divided into the following categories: (i) Primary consumers: Animals which feed directly on plants, i.e., herbivores. (ii) Secondary consumers: Consumers that feed on primary consumers, i.e.. carnivores. (iii) Tertiary consumers: Consumers that feed on secondary consumers
Lindeman's 10 per cent law: At each step of food chain, when food energy is transferred from one trophic level to the next higher trophic level, only about 10 per cent of energy is passed on to the next trophic level. This is known as Lindeman's 10 per cent law given by Lindeman in 1942.

3.0NCERT Solutions for Class 12 Biology | Other Chapter-wise Links

Explore chapter-wise NCERT Solutions for Class 12 Biology with detailed answers, simple explanations, and complete solutions to textbook questions through the links below.

Chapter Number	Chapterwise NCERT Solutions
Chapter 1	Sexual Reproduction in Flowering Plants
Chapter 2	Human Reproduction
Chapter 3	Reproductive Health
Chapter 4	Principles of Inheritance and Variation
Chapter 5	Molecular Basis of Inheritance
Chapter 6	Evolution
Chapter 7	Human Health and Disease
Chapter 8	Microbes in Human Welfare
Chapter 9	Biotechnology: Principles and Processes
Chapter 10	Biotechnology and Its Applications
Chapter 11	Organisms and Populations
Chapter 13	Biodiversity and Conservation

4.0Key Features and Benefits of Class 12 Biology Chapter 12 Ecosystem

Clear Understanding of Energy Flow: Follow the movement of energy from producers to consumers and understand food chains, food webs, and energy transfer.
Diagrams Made Easy: Understand ecological pyramids, nutrient cycles, and other important ecosystem concepts through clear, diagram-focused explanations.
Real-World Ecosystem Examples: Connect textbook concepts with familiar ecosystems such as forests, ponds, grasslands, and other natural environments.
Strong Foundation for NEET: Strengthen your understanding of ecosystem and ecology concepts that are important for NEET Biology.
Quick and Effective Revision: Revise important terms, processes, diagrams, and ecological relationships through simple and well-organised explanations before board examinations.