CBSE Class 12 Biology Notes Chapter 14 Ecosystem

An ecosystem is a self-sustaining unit of nature where all animals, plants, and microorganisms, along with the weather and landscape, work together to form life.

• It is the summation of all biotic and abiotic components which demonstrate interspecific and intraspecific relationships for the survival of organisms.
• Sir Arthur Tansley first introduced the term ecosystem.
• Species composition and stratification specify how all species interact with each other and their physical environment. 
• Stratification is defined as the vertical distribution of different categories of species occupying different levels in an ecosystem.
• Important functions of the ecosystem include decomposition, nutrient cycling, productivity, and decomposition.
• Biotic factors include producers, consumers and decomposers.
• The consumers are further divided into herbivores, primary carnivores and secondary carnivores.

CBSE Class 12 Biology Chapter 14 Notes on Ecosystem comprehensively covers all topics including ecosystem, components of ecosystem, pyramids of number, biomass, energy and decomposition. Chapter 14 comes under the Ecology and Environment unit with a weightage of 10 marks in the Class 12 Biology Examination 2024.

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Class 12 Biology Chapter 14 Notes – Ecosystem

Structure of Ecosystem

The structure of an ecosystem defines the interaction between biotic and abiotic components, which in turn defines the physical characteristics of each type of ecosystem.

• Abiotic components include all non-living components such as land, water, air, temperature, altitude and turbidity.
• Biotic components include all living components of an ecosystem, such as producers, consumers and decomposers.

Producers

Producers, also known as autotrophs, are organisms that prepare their own food. This group includes all green plants, which create usable forms of energy with the help of water.

Consumers

Consumers, also known as heterotrophs, cannot prepare their own food and must eat other plants and animals to get the required energy. They are further divided into primary, secondary, tertiary and quaternary consumers. 

Decomposers

Decomposers are ecological cleaners that break down dead or decaying organisms and convert them into nitrogen and carbon dioxide. They are also known as saprophytes, which include microorganisms such as bacteria and fungi.

Ecosystem Types

There are two main types of ecosystems, which are as follows:

Aquatic ecosystem

An aquatic ecosystem includes all underwater species, such as sea animals and plants, and the type of water body where the biotic factors survive. It is further divided into freshwater and marine ecosystems.

• Freshwater ecosystems include all plants and animals, such as fishes, algae, and tortoises, that survive only in freshwater, such as rivers, lakes, wells, ponds, and wetlands.
• Marine ecosystems include all marine animals, such as fish and crocodiles, that can survive in high salt concentrations.

Terrestrial Ecosystem

Terrestrial ecosystems include all ecosystems that are found on land. It is further divided into the following categories:

• Forest ecosystem: Forest ecosystems include all animals, insects and birds that coordinate with each other to thrive in the ecosystem.
• Grassland ecosystem: The Grassland ecosystem includes all grasses and herbs. 
• Desert ecosystem: Desert ecosystems include areas that receive little or no rainfall and include animals such as camels, kangaroos, and foxes.
• Tundra ecosystem: The Tundra ecosystem includes trees covered with snow most of the year and is mainly found in arctic areas and mountain tops.

Ecosystem Types

Productivity

Productivity is defined as the rate of biomass production, which is expressed in g^-2 yr^-1 or (kcal m^-2) yr^-1.

• Primary productivity refers to the amount of biomass produced by plants per unit area during photosynthesis. 
• It is further divided into gross primary productivity and net primary productivity.
• Gross primary productivity refers to the amount of carbon dioxide fixed by a gram of chlorophyll in an hour.
• Net primary productivity refers to the difference between gross primary productivity minus respiratory losses, which is given as GPP–R = NPP.
• Secondary productivity refers to the rate of formation and assimilation of organic matter by consumers.

Decomposition

Decomposition is an organic process in which decomposers break down complex organic matter into simpler organic substances, which are finally converted into inorganic compounds. It is included in the biology chapter 14 ecosystem class 12 notes.

Process of Decomposition

• Fragmentation: Fragmentation involves breaking of large particles of detritus into smaller particles with the help of detritivores.
• Leaching: Leaching involves precipitation of soluble inorganic nutrients into the soil.
• Catabolism: Catabolism involves the conversion of fungal and bacterial enzymes into complex organic compounds, which are later converted into simpler organic compounds.
• Humification: Humification refers to the accumulation of a dark-coloured compound called humus.
• Mineralisation: Mineralisation refers to the degradation of humus with the help of microbes to release inorganic compounds.

Energy Flow

The sun is considered one of the important sources of energy for all ecosystems on Earth. It radiates 50 per cent of photosynthetically active radiation (PAR), which is utilized during photosynthesis.

• All herbivores, carnivores, omnivores and decomposers are directly or indirectly dependent on their food producers, which use only 2–10 per cent of the PAR.
• The flow of energy is unidirectional, which means energy flows from the sun to producers and then finally to consumers.
• The energy flow follows the first law of thermodynamics.

In an ecosystem, the energy is transferred in the form of food by the process of degradation as heat during metabolic activities is small and stored as biomass by following the second law of thermodynamics.

Ecological Pyramids

Ecological pyramids, also known as energy pyramids, are graphical representations of the relationships between organisms at different trophic levels.

• Each bar of the ecological pyramid represents the organisms eaten by other organisms.
• It is expressed in numbers, energy, or biomass.
• The ecological pyramid is divided into three types, namely, the pyramid of numbers, the pyramid of biomass, and the pyramid of energy.

Pyramid of Number

The pyramid of numbers, which is usually upright, denotes the number of organisms at each trophic level, irrespective of their size.

Pyramid of Biomass

The pyramid of biomass represents the amount of biomass produced by organisms at each trophic level. The amount of biomass is not upright when large numbers of zooplankton depend on a smaller number of phytoplankton.

Pyramid of Energy

The pyramid of energy is the only category of the ecological pyramid that is always inverted as the flow of energy moves from one trophic level to the other trophic level, where some energy is lost as heat.

Pyramid of Energy

There are Some important List Of Top Biology Questions On Ecosystem  Asked In CBSE CLASS XII