Ecosystem class 12 NCERT Solution Biology Chapter 14 Explanation Question and Answer

NCERT Solution Ecosystem class 12 taken from NCERT Book biology In this chapter we covered all the Important Topics related to this chapter 14

Ecosystem class 12

Ecosystem class 12 Intoduction

An ecosystem can be visualized as a functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment. Ecosystem varies greatly in size from a small pond to a large forest or a sea.

Many ecologists regard the entire biosphere as a global ecosystem, as a composite of all local ecosystems on Earth. Since this system is too big and complex to be studied at one time, it is convenient to divide it into two basic categories, namely the terrestrial and the aquatic

Forests, grasslands, and deserts are some examples of terrestrial ecosystems; ponds, lakes, wetlands, rivers,s, and estuaries are some examples of aquatic ecosystems. Crop fields and an aquarium may also be considered man-made ecosystems

Ecosystem class 12 Notes

Terrestrial Ecosystems: Includes terrestrial ecosystems such as forests, grasslands, woodlands, and tundra. Each has its own unique organisms and environmental conditions.

Aquatic Ecosystems: Aquatic ecosystems include freshwater environments such as lakes, ponds, rivers, and wetlands, as well as oceans and marine ecosystems. These ecosystems support different forms of aquatic life and are affected by factors such as water depth, temperature, and salinity.

Human-Made Ecosystems: Human activities also create ecosystems, such as farmland, urban parks, gardens, and even aquariums. These ecosystems can have a significant impact on local biodiversity and environmental processes.

Components of Ecosystems: Ecosystems consist of biotic (living) and abiotic (living) components. Biotic factors include plants, animals, fungi, and microorganisms, while abiotic factors include soil, water, air, sunlight, and climate.

Energy flow and nutrient cycling: Ecosystems function through energy flow and nutrient cycling. Energy enters ecosystems through sunlight and is transferred between organisms through food chains and webs. Nutrients such as carbon, nitrogen, and phosphorus are recycled during plant decomposition and nutrient uptake processes.

Ecological Relationships: Organisms within ecosystems interact in a variety of ways, including predation, competition, mutualism, and parasitism. These interactions shape the structure and dynamics of ecosystems.

Health and stability of ecosystems: The health and stability of ecosystems depend on the balance of interactions between organisms and their environment. Human activities such as habitat destruction, pollution, and climate change can disrupt the balance of ecosystems and threaten biodiversity.

Ecosystem class 12 Definition

Ecosystems include all the living organisms in a given area that interact with each other and with their physical environment. They can range from small environments such as lakes to larger ecosystems such as forests and oceans

Ecosystem class 12 Explanation


A constant input of solar energy is the basic requirement for any ecosystem to function and sustain. Primary production is defined as the amount of organic matter produced by photosynthetic organisms in an ecosystem.

It represents the foundation of the food web and supports all higher trophic levels. The rate of primary production varies among ecosystems and depends on factors such as sunlight availability, nutrient availability, and temperature.

Productivity in ecosystems can be classified into two types: gross primary productivity (GPP) and net primary productivity (NPP).

GPP refers to the total amount of organic matter produced by photosynthesis, while NPP is the amount of organic matter available as food for consumers after subtracting the energy used by primary producers for respiration. NPP is a crucial indicator of the energy available to sustain heterotrophic organisms and drive ecosystem processes.


Decomposition is the process by which organic matter is broken down into simpler compounds by decomposers such as bacteria, fungi, and detritivores. It plays a vital role in nutrient cycling by releasing essential nutrients like nitrogen, phosphorus, and carbon back into the soil or water, where they can be taken up by plants for growth.

Decomposition rates vary depending on environmental factors such as temperature, moisture, and the availability of decomposer organisms.


Energy flow in ecosystems follows the laws of thermodynamics, with energy being transferred from one trophic level to another. Primary producers capture solar energy and convert it into chemical energy through photosynthesis.

This energy is then passed on to herbivores, carnivores, and decomposers through consumption and trophic interactions. However, energy transfer between trophic levels is inefficient, with only a fraction of energy being transferred from one level to the next


Nutrient cycling involves the movement and recycling of essential nutrients like carbon, nitrogen, and phosphorus within an ecosystem.

These nutrients are cycled through biotic and abiotic components, including living organisms, soil, water, and the atmosphere. Nutrient cycling is essential for maintaining soil fertility, supporting plant growth, and sustaining ecosystem productivity


Primary productivity refers to the biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It is expressed in terms of weight (g m^-2) or energy (kcal m^-2).

The rate of biomass production is called productivity, and it is expressed in terms of g m^-2 yr^-1 or kcal m^-2 yr^-1 to compare the productivity of different ecosystems.

Primary productivity can be divided into gross primary productivity (GPP) and net primary productivity (NPP). Gross primary productivity is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilized by plants in respiration. Gross primary productivity minus respiration losses (R) equals net primary productivity (NPP).

NPP represents the available biomass for consumption by heterotrophs (herbivores and decomposers). Secondary productivity, on the other hand, is defined as the rate of formation of new organic matter by consumers.

Primary productivity depends on the plant species inhabiting a particular area, as well as a variety of environmental factors such as nutrient availability and photosynthetic capacity. Therefore, it varies in different types of ecosystems.

The annual net primary productivity of the whole biosphere is approximately 170 billion tons (dry weight) of organic matter. Despite oceans occupying about 70 percent of the surface, their productivity is only 55 billion tons, which is much lower compared to land. Discuss the main reasons for the low productivity of the ocean with your teacher.

Ecosystem class 12
Ecosystem class 12


Decomposition is the process by which complex organic matter is broken down into simpler substances by decomposers such as earthworms, bacteria, and fungi. Detritus, which includes dead plant remains and animal matter, serves as the raw material for decomposition.

The process of decomposition involves several steps, including fragmentation, leaching, catabolism, humification, and mineralization.

Detritivores like earthworms break down detritus into smaller particles through fragmentation. Leaching is the process by which water-soluble inorganic nutrients move down into the soil and become unavailable salts.

Bacterial and fungal enzymes degrade detritus into simpler inorganic substances in a process called catabolism. Humification and mineralization occur simultaneously during decomposition in the soil, contributing to the breakdown of organic matter and the release of nutrients back into the ecosystem

to accumulation of a dark-colored amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. Being colloidal in nature it serves as a reservoir of nutrients.

The humus is further degraded by some microbes and the release of inorganic nutrients occurs by the process known as mineralization. Decomposition is largely an oxygen-requiring process. The rate of decomposition is controlled by the chemical composition of detritus and climatic factors.

In a particular climatic condition, the decomposition rate is slower if detritus is rich in lignin and chitin, and quicker if detritus is rich in nitrogen and water-soluble substances like sugars. Temperature and soil moisture are the most important climatic factors that regulate decomposition through their effects on the activities of soil microbes.

Warm and moist environments favour decomposition whereas low temperature and anaerobiosis inhibit decomposition resulting in a build-up of organic materials.


Except for the deep sea hydro-thermal ecosystem, sun is the only source of energy for all ecosystems on Earth. Of the incident solar radiation less than 50 percent of it is photosynthetically active radiation (PAR).

We know that plants and photosynthetic bacteria (autotrophs), fix the sun’s radiant energy to make food from simple inorganic materials. Plants capture only 2-10 percent of the PAR and this small amount of energy sustains the entire living world.

So, it is very important to know how the solar energy captured by plants flows through different organisms of an ecosystem. All organisms are dependent for their food on producers, either directly or indirectly.

So you find the unidirectional flow of energy from the sun to producers and then to consumers. Is this in keeping with the first law of thermodynamics?

Ecosystem class 12

Further, ecosystems are not exempt from the Second Law of thermodynamics. They need a constant supply of energy to synthesize the molecules they require, to counteract the universal tendency toward increasing disorderliness.

The green plants in the ecosystem terminology are called producers. In a terrestrial ecosystem, major producers are herbaceous and woody plants. Likewise, primary producers in an aquatic ecosystem are various species like phytoplankton, algae, and higher plants.

You have read about the food chains and webs that exist in nature. Starting from the plants (or producers) food chains or rather webs are formed such that an animal feeds on a plant or on another animal and in turn is food for another.

The chain or web is formed because of this interdependency. No energy that is trapped in an organism remains in it forever. The energy trapped by the producer, hence, is either passed on to a consumer or the organism dies. Death of an organism is the beginning of the detritus food chain/web.

Ecosystem class 12
Ecosystem class 12

All animals depend on plants (directly or indirectly) for their food needs. They are hence called consumers and also heterotrophs. If they feed on the producers, the plants, they are called primary consumers, and if the animals eat other animals which in turn eat the plants (or their produce) they are called secondary consumers.

Likewise, you could have tertiary consumers too. Obviously, the primary consumers will be herbivores. Some common herbivores are insects, birds and mammals in the terrestrial ecosystem and mollusks in aquatic ecosystems.

The consumers that feed on these herbivores are carnivores, or more correctly primary carnivores (though secondary consumers). Those animals that depend on the primary carnivores for food are labeled secondary carnivores. A simple grazing food chain (GFC) is depicted below:

Grass -> Goat -> Man (Producer) (Primary Consumer) (Secondary consumer)

The detritus food chain (DFC) begins with dead organic matter. It is made up of decomposers which are heterotrophic organisms, mainly fungi and bacteria. They meet their energy and nutrient requirements by degrading dead organic matter or detritus.

These are also known as saprotrophs (sapro: to decompose). Decomposers secrete digestive enzymes that break down dead and waste materials into simple, inorganic materials, which are subsequently absorbed by them.

In an aquatic ecosystem, GFC is the major conduit for energy flow. As against this, in a terrestrial ecosystem, a much larger fraction of energy flows through the detritus food chain than through the GFC.

The Detritus food chain may be connected with the grazing food chain at some levels: some of the organisms of DFC are prey to the GFC animals, and in a natural ecosystem, some animals like cockroaches, crows, etc., are omnivores.

These natural interconnections of food chains make it a food web. How would you classify human beings?

Organisms occupy a place in the natural surroundings or in a community according to their feeding relationship with other organisms.

Based on the source of their nutrition or food, organisms occupy a specific place in the food chain that is known as their trophic level.

Producers belong to the first trophic level, herbivores (primary consumers) to the second, and carnivores (secondary consumers) to the third (Figure 14.2).

The important point to note is that the amount of energy decreases at successive trophic levels. When any organism dies it is converted to detritus or dead biomass that serves as an energy source for decomposers.

Organisms at each trophic level depend on those at the lower trophic level for their energy demands.

Each trophic level has a certain mass of living material at a particular time called the standing crop. The standing crop is measured as the mass of living organisms (biomass) or the number in a unit area.

The biomass of a species is expressed in terms of fresh or dry weight. Measurement of biomass in terms of dry weight is more accurate. Why?

The number of trophic levels in the grazing food chain is restricted as the transfer of energy follows the 10 percent law – only 10 percent of the energy is transferred to each trophic level from the lower trophic level.

In nature, it is possible to have so many levels – producer, herbivore, primary carnivore, and secondary carnivore in the grazing food chain. Do you think there is any such limitation in a detritus food chain?

Any calculations of energy content, biomass, or numbers have to include all organisms at that trophic level. No generalizations we make will be true if we take only a few individuals at any trophic level into account.

Ecosystem class 12
Ecosystem class 12

Also, a given organism may occupy more than one trophic level simultaneously. One must remember that the trophic level represents a functional level, not a species as such.

A given species may occupy more than one trophic level in the same ecosystem at the same time; for example, a sparrow is a primary consumer when it eats seeds, fruits, and peas, and a secondary consumer when it eats insects and worms. Can you work out how many trophic levels human beings function at in a food chain?

In most ecosystems, all the pyramids, of number, of energy, and biomass are upright, i.e., producers are more in number and biomass than the herbivores, and herbivores are more in number and biomass than carnivores. Also, energy at a lower trophic level is always more than at a higher level.

There are exceptions to this generalization: If you were to count the number of insects feeding on a big tree what kind of pyramid would you get? Now add an estimate of the number of small birds depending on the insects, as also the number of larger birds eating the smaller ones. Draw the shape you would get.

The pyramid of biomass in the sea is also generally inverted because the biomass of fishes far exceeds that of phytoplankton. Isn’t that a paradox? How would you explain this?

The pyramid of energy is always upright, can never be inverted, because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step. Each bar in the energy pyramid indicates the amount of energy present at each trophic level in a given time or annually per unit area.

Ecosystem class 12 summary

An ecosystem is a functional unit of nature and comprises abiotic and biotic components. Abiotic components are inorganic materials- air, water, and soil, whereas biotic components are producers, consumers and decomposers.

Each ecosystem has a characteristic physical structure resulting from interaction between abiotic and biotic components. Species composition and stratification are the two main structural features of an ecosystem.

Based on the source of nutrition every organism occupies a place in an ecosystem. Productivity, decomposition, energy flow, and nutrient cycling are the four important components of an ecosystem. Primary productivity is the rate of capture of solar energy or biomass production of the producers.

It is divided into two types: gross primary productivity (GPP) and net primary productivity (NPP). The rate of capture of solar energy or total production of organic matter is called GPP. NPP is the remaining biomass or the energy left after the utilization of producers.

Secondary productivity is the rate of assimilation of food energy by the consumers. In decomposition, complex organic compounds of detritus are converted to carbon dioxide, water, and inorganic nutrients by the decomposers. Decomposition involves three processes, namely fragmentation of detritus, leaching, and catabolism.

Energy flow is unidirectional. First, plants capture solar energy and then, food is transferred from the producers to decomposers. Organisms of different trophic levels in nature are connected to each other for food or energy relationship forming a food chain.

The storage and movement of nutrient elements through the various components of the ecosystem is called nutrient cycling; nutrients are repeatedly used through this process. Nutrient cycling is of two types—gaseous and sedimentary.

The atmosphere or hydrosphere is the reservoir for the gaseous type of cycle (carbon), whereas Earth’s crust is the reservoir for the sedimentary type (phosphorus). Products of ecosystem processes are named as ecosystem services, e.g., purification of air and water by forests.

The biotic community is dynamic and undergoes changes with the passage of time. These changes are sequentially ordered and constitute ecological succession. Succession begins with the invasion of a bare lifeless area by pioneers which later pave way for successors and ultimately a stable climax community is formed. The climax community remains stable as long as the environment remains unchanged.

Ecosystem class 12 Question and Answer

Question:1 What is the unit of nature?

Answer: The unity of nature is called ecosystem. An ecosystem includes all living things (living things) in an area and the non-living parts of their environment (abiotic things), such as air, water, soil, sunlight, and weather.

Simply put, it is like a small, independent community where plants, animals and other living things interact with each other and their environment. Ecosystems can range in size from a small lake to a large forest or even an entire ocean. They are very important to maintain the balance of life on Earth.

Question:2 What is an ecosystem diagram?

Answer :

Relationships include violence, competition, and solidarity

Abiotic component: This includes the non-living components of the environment such as air, water, soil, sunlight, temperature, humidity, and food.

Energy Flow: A diagram of the environment usually shows the energy flow in the environment. It shows that producers (plants) capture the energy of the sun through photosynthesis. Then, it is transferred from the source of food to consumers (plants, carnivores, omnivores) and finally released as energy during the metabolic process.

Nutrient cycle: An ecosystem diagram can show the cycle of nutrients like carbon, nitrogen, phosphorus, etc. Nutrients are recycled in the environment through processes such as decomposition, plant nutrition. animal feed and mineralization

Trophic level: Trophic level indicates the position of organisms in a food or food system based on their nutritional relationship. The manufacturer picks up the first level of food. primary consumers (herbivores), secondary consumers (carnivores), and so on

Question3: What is ecosystem and its function?

Answer :

Primary production: The process by which organisms obtain energy from sunlight or chemical sources and convert it into products through photosynthesis or chemosynthesis. It is the main product of plants and other autotrophs that form the base of the food chain and provide energy for everything in the ecosystem.

Nutrient cycling: Organisms produce carbon, nitrogen, phosphorus, and other nutrients through organic and abiotic components. Nutrients are transported through soil or water, transported through food for herbivores, and transported through the food chain for carnivores. Decomposers break down nutrients, returning them to the soil or water for use by plants.

Habitat and shelter: Ecosystems provide habitat and shelter for various species. Different species have adapted to specific ecosystems based on factors such as temperature, humidity, soil type and resource availability. The diversity of habitats and ecosystems supports a wide variety of species.

Weather and climate regulation: Environmental processes play a role in controlling weather patterns and weather events. For example, forests can affect local and regional climate by absorbing carbon dioxide, releasing oxygen, influencing temperature and influencing precipitation patterns.

Water Purification: In ecosystems, lakes, streams and ponds act as natural filters, purifying water by trapping sediment and absorbing some decaying nutrients. Healthy aquatic ecosystems contribute to the production of clean water for drinking, irrigation and other human needs.

Pollination and seed dispersal: Ecosystems support pollination by providing habitats for pollinators such as bees, butterflies, birds, and bats. Pollinators increase the production of flowering plants by transferring pollen between flowers, which produces seeds and fruits. Likewise, animals help by eating the seeds and spreading them to new areas.

Question:4 What are the 7 main ecosystems?


  1. Forests
  2. Grasslands
  3. Deserts
  4. Tundra
  5. Freshwater ecosystems (lakes, rivers, streams)
  6. Marine ecosystems (oceans, coral reefs, estuaries)
  7. Wetlands

Question:5 What are the main components of an ecosystem?


  1. Abiotic factors: These include non-living components such as air, water, soil, sunlight, temperature, and nutrients.
  2. Biotic factors: These are the living organisms within the ecosystem, including producers (plants), consumers (animals), decomposers (fungi, bacteria), and other microorganisms

Read also

  1. Reproduction in Organisms class 12
  2. Sexual Reproduction in Flowering Plants Class 12
  3. Human Reproduction Class 12
  4. Reproductive Health class 12
  5. Principles of Inheritance and Variation Class 12