CLASS XII
BIOLOGY
LESSON GIST
CHAPTER: ECOSYSTEM
[NCERT, PAGE NO: 241-249,255]
➢ Ecosystem: - A functional unit of nature where interactions of living
organisms with themselves and with physical environment takes place.
➢ Types:
1. Artificial ecosystem: manmade ecosystem - Ex: crop field,
aquarium
2. Natural ecosystem: Terrestrial ecosystem and Aquatic ecosystem.
3. Terrestrial ecosystem is classified into forest, grassland, desert etc.
4. Aquatic ecosystem is classified into freshwater and saltwater
ecosystem.
5. Freshwater ecosystems are lentic - ponds, lakes and river, streams.
6. Saltwater ecosystem are wetlands, estuaries, marine
➢ Stratification: - Vertical distribution of different species occupying
different levels in an ecosystem is called stratification - Top trees, Shrubs,
Herbs, Grass.
➢ The structure of ecosystem consists of biotic and abiotic components. The
abiotic components are non-living components. They are air, water, solar
radiation, temperature etc. The biotic components are: Producers-
synthesise their own food. Consumers – primary consumer (herbivores),
sec consumer (pri. carnivores), tertiary consumer (sec. carnivores).
Decomposers-Bacteria and fungi.
➢ The major functions of ecosystem are:
• Productivity • Decomposition • Energy flow • Nutrient
cycling
➢ The rate of biomass production per unit area during a given period is
called productivity. It is measured in terms of weight (g-2) or energy
(kcal m – 2). It is used to compare productivity of different ecosystems.
, ➢ Primary productivity: It is the amount of biomass produced per unit area
in a given time period by plants during photosynthesis.
➢ GPP-Gross Primary Productivity: It is the rate of production of organic
matter during photosynthesis.
➢ NPP-Net Primary Productivity. R- respiration loss. GPP – R = NPP
GPP is not equal to NPP because, considerable amount of GPP is utilized
by plants in respiration.
➢ Secondary productivity - It is the rate of formation of new organic matter
by consumers in a given period of time.
➢ Decomposition: It is the process of breaking down of dead organic matter
into smaller organic and inorganic molecules by decomposers (bacteria,
fungi).
➢ DETRITUS: Raw materials of decomposition as dead plants, animals and
animal faeces is called detritus.
➢ DETRITIVORES: Animals that feed on decaying organic matter
(detritus). Examples: earthworms, termites, snails etc.
➢ Steps of Decomposition:
1. Fragmentation of Detritus: It is the process of breakdown of detritus
into smaller particles. It is done by detritivores.
2. Leaching: Soluble inorganic nutrients dissolve in water and goes down
to soil, get precipitated is called leaching.
3. Catabolism: Decomposers (bacteria, fungi) release enzymes to
decompose detritus into simpler inorganic compounds.
4. Humification: Simplified detritus converted to humus a) Humus is a
dark, amorphous substance. b) Highly resistant to microbial action. c)
Undergoes decomposition very slowly. d) Reservoir of nutrients (due to
colloidal nature).
5. Mineralisation: Humus is degraded to releases inorganic substances
(CO2, H2O etc) and nutrients (Ca2+, Mg2+, K + etc).
➢ Factors affecting rate of Decomposition: decomposition rate will be slow
when detritus is rich in lignin and chitin. The rate increases when detritus
is rich in nitrogen and water-soluble substances like sugars. Climatic
BIOLOGY
LESSON GIST
CHAPTER: ECOSYSTEM
[NCERT, PAGE NO: 241-249,255]
➢ Ecosystem: - A functional unit of nature where interactions of living
organisms with themselves and with physical environment takes place.
➢ Types:
1. Artificial ecosystem: manmade ecosystem - Ex: crop field,
aquarium
2. Natural ecosystem: Terrestrial ecosystem and Aquatic ecosystem.
3. Terrestrial ecosystem is classified into forest, grassland, desert etc.
4. Aquatic ecosystem is classified into freshwater and saltwater
ecosystem.
5. Freshwater ecosystems are lentic - ponds, lakes and river, streams.
6. Saltwater ecosystem are wetlands, estuaries, marine
➢ Stratification: - Vertical distribution of different species occupying
different levels in an ecosystem is called stratification - Top trees, Shrubs,
Herbs, Grass.
➢ The structure of ecosystem consists of biotic and abiotic components. The
abiotic components are non-living components. They are air, water, solar
radiation, temperature etc. The biotic components are: Producers-
synthesise their own food. Consumers – primary consumer (herbivores),
sec consumer (pri. carnivores), tertiary consumer (sec. carnivores).
Decomposers-Bacteria and fungi.
➢ The major functions of ecosystem are:
• Productivity • Decomposition • Energy flow • Nutrient
cycling
➢ The rate of biomass production per unit area during a given period is
called productivity. It is measured in terms of weight (g-2) or energy
(kcal m – 2). It is used to compare productivity of different ecosystems.
, ➢ Primary productivity: It is the amount of biomass produced per unit area
in a given time period by plants during photosynthesis.
➢ GPP-Gross Primary Productivity: It is the rate of production of organic
matter during photosynthesis.
➢ NPP-Net Primary Productivity. R- respiration loss. GPP – R = NPP
GPP is not equal to NPP because, considerable amount of GPP is utilized
by plants in respiration.
➢ Secondary productivity - It is the rate of formation of new organic matter
by consumers in a given period of time.
➢ Decomposition: It is the process of breaking down of dead organic matter
into smaller organic and inorganic molecules by decomposers (bacteria,
fungi).
➢ DETRITUS: Raw materials of decomposition as dead plants, animals and
animal faeces is called detritus.
➢ DETRITIVORES: Animals that feed on decaying organic matter
(detritus). Examples: earthworms, termites, snails etc.
➢ Steps of Decomposition:
1. Fragmentation of Detritus: It is the process of breakdown of detritus
into smaller particles. It is done by detritivores.
2. Leaching: Soluble inorganic nutrients dissolve in water and goes down
to soil, get precipitated is called leaching.
3. Catabolism: Decomposers (bacteria, fungi) release enzymes to
decompose detritus into simpler inorganic compounds.
4. Humification: Simplified detritus converted to humus a) Humus is a
dark, amorphous substance. b) Highly resistant to microbial action. c)
Undergoes decomposition very slowly. d) Reservoir of nutrients (due to
colloidal nature).
5. Mineralisation: Humus is degraded to releases inorganic substances
(CO2, H2O etc) and nutrients (Ca2+, Mg2+, K + etc).
➢ Factors affecting rate of Decomposition: decomposition rate will be slow
when detritus is rich in lignin and chitin. The rate increases when detritus
is rich in nitrogen and water-soluble substances like sugars. Climatic
