Chapter 14 ecosystem by mohanbio

• Ecosystem:-
• A functional unit of nature where interactions of living
organisms with themselves and with physical environment
takes place.
• The term ecosystem was coined by A.G.Tansley.
• Types:
• Artificial ecosystem: man made ecosystem. Ex: crop field,
aquarium.
• Natural ecosystem: Terrestrial ecosystem and Aquatic
ecosystem.
• Terrestrial ecosystem is classified into forest, grassland, desert
etc.
• Aquatic ecosystem is classified into freshwater and salt water
ecosystem.
• Freshwater ecosystem are lentic - ponds, lakes and lotic -
river, streams.
• Salt water ecosystem are wetlands, estuaries, marine

• Stratification:- Vertical distribution of different
species occupying different levels in an ecosystem is
called stratifiction.
1. Top trees.
2. Shrubs.
3. Herbs.
4. Grass.

• Structure and function of ecosystem.
• 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- synthesis there own food.
Photoautotroph and chemoautotroph.
• Consumers – pri consumer (herbivores), sec
consumer (pri.Carnivores), tertiary consumer
(sec.Carnivores) etc.
• Decomposers. Bacteria and fungi.

• The major function of ecosystem are,
• Productivity.
• Decomposition.
• Energy flow.
• Nutrient cycling.

• Productivity
The rate of biomass production per unit area during a given
period of time 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 bcoz, 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 fecas 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:
• Chemical composition - 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 conditions – warm and moist environment
favour decomposition. Low temperature and
anaerobiosis inhibit decomposition.
• Food chain: Transfer of energy / food from the
producer through a series of organisms is known as
food chain.
• Food chains represent energy flow through ecosystems.
• Different steps in a food chain are called trophic levels

• Grazing food chain (GFC):
• The food chain that begins with producers
continued with herbivores is called grazing food
chain
• Eg. Grass ------- Goat ----------- man.
• Detritus food chain (DFC):
• The food chain that begins with dead organic
matter is called detritus food chain (DFC).
• Dead leaf -------earthworm ------ Bird.
• Saprophytes: These are decomposers (fungi,
bacteria) which feed on detritus.

• Trophic level:- Each Step of the food chain is called
trophiclevel.
• Standing crop:
• Each trophic level has a certain mass of living
material at a particular time is called standing crop.
• The standing crop is measured as the mass of living
organisms (biomass) or the number in a unit area.
• Food web:
• The natural interconnection of food chains forms a
web called food web.

• Energy flow:
• Sun is the only source of energy for all ecosystem.
• Plants capture only 2 to 10% of photosynthetically
active radiation(PAR) for photosynthesis.
• Energy is transferred in ecosystem in the form of food.
• "Flow of energy is unidirectional but nutrient flow is in
a cycle"
• Energy flow is always from the sun to 'producers' and
to the different trophic levels. so it is unidirectional. But
the nutrients are moving from the living to non-living
and vice-versa.
• Major energy is used for metabolic activity. Only less
amount of energy is stored as biomass.
• Lindeman’s 10% law:
• Only 10 per cent of the energy is transferred to each
trophic level from lower trophic levels is called 10% law

• Ecological pyramid:- graphical
representation of energy, biomass or
number of different organisms in an
ecosystem is in the form of pyramid
is called ecological pyramid .
• characteristic features of ecological
pyramids.
• The base of the pyramid is broad and
it is narrow at the apex.
• The relationship can be expressed in
terms of number, energy or biomass.
• The base of the pyramid represented
by producer and apex is the top
consumer, other trophic levels are in
between.
• In most ecosystems, all the pyramids
of number, energy and biomass are
upright.

• Inverted pyramid:
1. The pyramid of number in a
tree ecosystem is inverted.
2. The pyramid of biomass in
sea also inverted because the
biomass of fishes is more
than phytoplankton.
• Pyramid of energy is always
upright, can never be inverted.
Because when energy flows
from a particular trophic level
to the next, some energy is
always lost as heat at each
step.

• Ecological succession:- The gradual and predictable
change in the species composition of a given area.
• Primary Succession: A Succession that starts where no
living organisms are there.
• Secondary succession : A Succession that starts in areas
which have lost all the living organisms that existed
there.
• Hydrarch succession:- That takes place in wetter areas.
• Xerarch succession:- That takes place in dry areas.
• Pioneer species:- The species that invade a bare area.
Ex: lichines, phytoplankton,
• primary succession on rocks are lichens which are able
to secrete acids to dissolve rock, helping in weathering
and soil formation.

• Nutrient cycling/ biogeochemical cycling:-
Movement of nutrient elements through the
various components of an ecosystem as between
biotic and non-biotic components.
• Gaseous cycle:- Cycle which have its reservoir of the
nutrient in atmosphere.
• Ex: Carbon cycle, Nitrogen cycle.
• Sedimentary cycle:- Cycle which have its reservoir
of the nutrient is earth crust.
• Ex: Phosphorus cycle, Sulphur cycle.

1. Carbon constitutes 49 % of dry weight of organism.
2. 0.003% of CO2 is present in atmosphere.
3. Carbon is fixed in the biosphere through
photosynthesis.
4. Carbon returns to the atmosphere as CO2 through
respiratory activities of the producers and
consumers.
5. Decomposers also contribute Some amount of CO2
from dead organic matter
6. Burning of wood, forest fire , combustion of
organic matter, fossil fuel, and volcanic activity are
additional sources for releasing CO2 in the
atmosphere.

1. Phosphorus is a major constituent of organism.
2. It found in nucleic acids and cellular energy transfer
systems (ATP).
3. Many animals also need large quantities of this
element to make shells, bones and teeth.
4. The natural reservoir of phosphorus is rock. In which
it contains in the form of phosphates.
5. When rocks are weathered, minute amounts of
phosphates dissolve in soil solution and are absorbed
by the roots of the plants.
6. Herbivores and other animals obtain this element
from plants.
7. The waste products and the dead organisms are
decomposed by phosphate-solubilising bacteria
releasing phosphorus.

• ecosystem services.
• The products of ecosystem processes are called as
ecosystem services.
• Ex: Forest ecosystems purify air and water,
• It avoids droughts and flood.
• It cycle nutrients and generate fertile soils.
• It provide wildlife habitat, maintain biodiversity.
• It provide storage site for carbon.
• It also provide aesthetic, cultural and spiritual
values.

Chapter 14 ecosystem by mohanbio

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