2. • An eco-system is a
functional unit of nature,
where living organisms
interact with each other
and also with the physical
environment.
ECOSYSTEM
Do you know?
The term ‘Ecosystem’was coined by Sir
Arthur George Tansley in 1935.

3. STRUCTURE AND FUNCTION
ECOSYSTEM
TYPES OF
ECOSYSTEM
• TERRESTRIAL ECOSYSTEM
Forest, Grassland, Desert ,
etc.
AQUATIC ECOSYSTEM
Pond, Lake, River, Wetland
and Estuary
MAN-MADE ECOSYSTEM
Crop fields and aquarium

4. STRUCTURE AND FUNCTION
ECOSYSTEM
• Entire biosphere is regarded as global eco-system.
• In an eco-system, biotic and abiotic components interact and functions as a unit.
• Vertical distribution of different species at different levels is called stratification. E.g.-
In forest trees occupy the top strata(layer), shrubs the second and herbs and grasses
the bottom layers.

5. STRUCTURE AND FUNCTION
ECOSYSTEM
POND (Aquatic Ecosystem)
A pond is a swallow simple self sustainable water
body that exhibits all basic components of an
ecosystem.
• Abiotic components: Water & soil deposit.
• Climatic components: Solar input, cycle of
temperature, day length etc.
• Autotrophic components: Phytoplankton, some
algae and the floating submerged and marginal
plants.
• Consumers (Heterotrophs): zooplankton, free
swimming and bottom dwelling forms.
• Decomposers: Fungi, bacteria and flagellates.

6. STRUCTURE AND FUNCTION
ECOSYSTEM
POND (Aquatic Ecosystem)
Pond performs all the functions of an
ecosystem. E.g.
 Autotrophs convert inorganic into
organic material using solar radiant
energy.
 Heterotrophs consume autotrophs.
 Decomposition and mineralization of
the dead matters to release them back
for reuse by the autotrophs.

7. STRUCTURE AND FUNCTION
ECOSYSTEM
4 basic
components
of ecosystem
Productivity
Decomposition
Nutrient Cycling
Energy Flow

9. • Solar energy is the basic requirement for an
ecosystem to function and sustain.
• Amount of biomass (organic matter) produced per
unit area over a time period by plants during
photosynthesis is called primary production.
• It is expressed in weight (g-2)or energy (kcal m-2).
• The rate of biomass production is called productivity.
• It is expressed in g-2yr-1 or (kcal m-2) yr-1
• It is divided into gross primary productivity (GPP) &
net primary productivity (NPP).
PRODUCTIVITY

10. • Gross primary productivity (GPP): It is the rate of
production of organic matter during photosynthesis.
A considerable amount of GPP is used by the plants
for respiration.
• Net primary productivity (NPP): It is the available
biomass for the consumption to heterotrophs and
decomposers i.e., NPP is gross primary productivity
minus respiration losses (R).
PRODUCTIVITY

11. • Secondary productivity: It is the rate of
formation of new organic matters by
consumers.
• Primary productivity varies in different
ecosystems because it depends on:
 The plant species inhabiting the area.
 Environmental factors.
 Availability of nutrients.
 Photosynthetic capacity of plants.
PRODUCTIVITY

12. • Annual net primary productivity of whole
biosphere is about 170 billion tons (dry
weight) of organic matter.
• Of this, despite occupying 70% of the
surface, the productivity of the oceans is
only 55 billion tons.
PRODUCTIVITY

14. • It is the breakdown of complex organic matter by
decomposers into inorganic substances like CO2,
water and nutrients.
• It is largely an oxygen-requiring process.
• Raw material for decomposition is called Detritus.
• E.g. dead plant remains (leaves, bark, flowers,
etc.), dead remains of animals, fecal matter, etc.
DECOMPOSITION

15. DECOMPOSITION
STEPS OF DECOMPOSITION
1. FRAGMENTATION
2. LEACHING
3. CATABOLISM
4. HUMIFICATION
5. MINERALISATION

16. DECOMPOSITION
1. FRAGMENTATION
2. LEACHING
3. CATABOLISM
4. HUMIFICATION
5. MINERALISATION
Breakdown of detritus into smaller particles by detritivores
(e.g. earthworms).

17. DECOMPOSITION
1. FRAGMENTATION
2. LEACHING
3. CATABOLISM
4. HUMIFICATION
5. MINERALISATION
Water soluble inorganic nutrients go down into soil horizon and
precipitate as unavailable salts.

18. DECOMPOSITION
1. FRAGMENTATION
2. LEACHING
3. CATABOLISM
4. HUMIFICATION
5. MINERALISATION
Degradation of
detritus into simpler
inorganic substances
by bacterial and
fungal enzymes
Fragmentation, leaching and catabolism occur
simultaneously.

19. DECOMPOSITION
1. FRAGMENTATION
2. LEACHING
3. CATABOLISM
4. HUMIFICATION
5. MINERALISATION
Accumulation of humus (dark amorphous substance)
in soil. Humus is resistant to microbial action and so
decomposes very slowly. Being colloidal in nature, it
serves as a reservoir of nutrients.

20. DECOMPOSITION
1. FRAGMENTATION
2. LEACHING
3. CATABOLISM
4. HUMIFICATION
5. MINERALISATION
It is the release of inorganic nutrients due to the
degradation of humus by some microbes.

21. DECOMPOSITION
Diagrammatic
representation of
decomposition
cycle in terrestrial
ecosystem

22. Factors influencing decomposition:
DECOMPOSITION
• Chemical composition of detritus:
 Decomposition is slow in detritus rich in lignin and
chitin.
It is quicker if detritus is rich in nitrogen and water
soluble substances like sugars.
• Climatic factors (temperature & soil moisture):
Warm and moist environment favour
decomposition.
Low temperature & anaerobiosis inhibit
decomposition resulting in build up of organic
materials.

24. ENERGY FLOW
• Sun is the only source of energy for all ecosystems
(except deep sea hydrothermal ecosystem).
• Of the incident solar radiation, less than 50% is
photosynthetically active radiation (PAR).
• Plants and photosynthetic and chemosynthetic
bacteria (autotrophs), fix solar radiation energy to
make food.
• Plants capture only 2-10% of the PAR. This energy
sustains the entire living world.
• Ecosystems obey 2nd Law of thermodynamics. They
need a constant supply of energy to synthesise the
molecules. It helps to counteract the entropy.

25. ENERGY FLOW
Producers (Autotrophs)
• They are organisms that
synthesise food in a terrestrial
ecosystem, major producers are
herbaceous and woody plants.
• primary producers in an
aquatic ecosystem are
phytoplankton, algae and
higher plants.
• The energy trapped by the
producer is passed on to a
consumer or the organism dies.

26. ENERGY FLOW
Consumers (Heterotrophs)
• These are animals that directly or indirectly
depend on plants or food they include
• Primary consumers (herbivores): feed on
plants. E.g.- insects, bird, mammals, molluscs
etc.
• Secondary consumers (primary carnivores):
feed on herbivores. E.g.- frog, fox, man, etc.
• Tertiary consumers (secondary carnivores):
feed on primary carnivores. E.g.- tiger, lion,
etc.

27. ENERGY FLOW
The Chain of feeding relationship between
different organisms is called a food chain.
FOOD CHAIN IS OF 2 TYPES:
Grazing food Chain (GFC)
Detritus food Chain (DFC)

28. ENERGY FLOW
Grazing food Chain (GFC)
• Here primary consumers feeds on
living plants
Detritus food Chain (DFC)
• Here primary consumer feeds on
dead organic matter (detritus).
• Death of organism is the beginning
of DFC.

29. ENERGY FLOW
Detritus is made of decomposers (saprotrophs) such as fungi and bacteria.
They secrete digestive enzymes that breakdown detritus into simple
inorganic materials, which are absorbed by them. Thus they get energy &
nutrients.
pseudomonas aeruginosa
(Bacteria)
Fungus

30. ENERGY FLOW
• An aquatic ecosystem, GFC is the major
conduit for energy flow.
• In a terrestrial ecosystem, a much
amount of energy flows through the DFC
than through GFC.
• DFC may be connected with GFC at some
levels.
• Some organisms of DFC are pray to the
GFC animals. Animals like cockroaches,
crows, human, etc. are omnivores. Such
interconnections of food chains are
called food web.

31. ENERGY FLOW
4th trophic level (top carnivore) E.g.-
man, lions, etc.
3rd trophic level (carnivore) E.g.- bird,
fishes, wolf, etc.
2nd trophic level (herbivore) E.g.-
zooplankton, grasshopper, cow, etc.
1st trophic level (plants) E.g.-
phytoplankton, grass, trees, etc.
PRIMARY PRODUCER
PRIMARY CONSUMER
SECONDARY CONSUMER
TERTIARY CONSUMER
A specific place of
organisms in the
food chain is
known as their
Tropic level.

32. ENERGY FLOW
Energy flow through different
trophic levels

33. ENERGY FLOW
The amount of energy decreases at successive trophic level.
When an organism dies it becomes dead biomass (detritus). It is the energy source for
decomposers.
Organisms at each trophic level depends on those at the lower trophic level for energy.
Dead
Biomass

34. ENERGY FLOW
The amount of living material in a trophic
level at a given time is called standing
crop.
It is measured as biomass (mass of living
organisms) or number in a unit area.
Biomass of a species is measured in terms
of fresh or dry weight. Dry weight is more
accurate because it is the exact mass of
the body which remains constant.
Number of trophic levels in GFC is
restricted as it follows 10% law (only 10%
of energy is transferred to each trophic
level from the lower trophic level).

36. ECOLOGICAL PYRAMIDS
• The representation of a food chain in
the form of a pyramid is called
ecological pyramid.
• The base of a pyramid represents
producers (1st trophic level). The apex
represents tertiary or top level
consumer.
• Ecological pyramids are 3 types:
pyramid of number
pyramid of biomass
pyramid of energy

37. E.g.- Grassland ecosystem
No. of individuals
3
3,54,000
7,08,000
5,842,000
Primary Producers (PP)
Primary Consumers (PC)
Secondary Consumers (SC)
Tertiary Consumers
(TC)
ECOLOGICAL PYRAMIDS PYRAMID OF NUMBER

38. ECOLOGICAL PYRAMIDS
Dry Weight (Kg/m3)
1.5
11
37
809
21
4
Primary Producers (PP)
Primary Consumers (PC)
Secondary Consumers
(SC)
Tertiary
Consumers (TC)
PYRAMID OF BIOMASS
Primary Consumers (PC)
Primary Producers (PP)
It shows a short decrease in biomass at higher
trophic levels.
Inverted pyramid of biomass
small standing crop of phytoplankton supports large
standing crop of zooplankton.

39. Primary producers convert only 1% of the energy in the
Sunlight available to them into NPP.
Primary Producers (PP)
Primary Consumers (TC)
Secondary Consumers (SC)
Tertiary Consumers
(TC)
ECOLOGICAL PYRAMIDS PYRAMID OF ENERGY
1,000,000 J of sunlight
10 J
100 J
1000 J
10,000 J

40. ECOLOGICAL PYRAMIDS
• Any calculations of energy content,
biomass or numbers has to include all
organisms at that trophic level.
• 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 eco-system at
the same time. E.g.- A Sparrow is a
primary consumer when it gets its fruits
bees and a secondary consumer when it
eats insects and worms.

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

42. Insects feeding on a big tree.
pyramid of biomass in sea is inverted because the biomass of fishes
far exceeds that of phytoplankton.
ECOLOGICAL PYRAMIDS EX. OF INVERTED PYRAMIDS
Pyramid of energy is always upright, because when energy flows from a trophic level
to the next trophic level some energy is always lost as heat at each step.

43. It does not take into account the same
species belonging to two or more trophic
levels.
It assumes a simple food chain that almost
never exist in nature. It does not
accommodate a food web.
Saprophytes are not included in ecological
pyramids even though they play a vital
role in the ecosystem.
ECOLOGICAL PYRAMIDS LIMITATIONS

45. NUTRIENT CYCLING
• Amount of nutrients (C, N, P, Ca, etc.)
present in the soil in a given time is
called the standing state.
• It varies in different kinds of ecosystems
and also on a seasonal basis.
• Nutrients are never lost from
ecosystems. They are recycled again and
again.
• The movement of nutrient elements
through various components of an
ecosystem is called nutrient cycling
(biogeochemical cycles).

46. NUTRIENT CYCLING
• Environmental factors (soil, moisture, pH, temperature, etc.) regulate the
rate of release of nutrients into the atmosphere.
• The reservoir meets with the deficit of nutrients due to imbalance in the
rate of influx and efflux.
Types of
nutrients
Gaseous cycle
Sedimentary cycle
The reservoir is atmosphere.
E.g. Nitrogen & Carbon cycle.
The reservoir is Earth’s crust.
E.g. Sulphur & Phosphorus cycle.

47. Reservoir of carbon
• Atmosphere (about 1%).
• Organism (49% of dry
weight).
• Ocean (71% dissolved
carbon. It regulates the
amount of atmospheric CO2).
• Fossil fuel.
NUTRIENT CYCLING CARBON CYCLE
Carbon cycling occurs through
atmosphere ocean and through
living and dead organisms.

48. 4x1013 kg of carbon is fixed
in the biosphere through
photosynthesis annually.
A major amount of carbon
returns to the atmosphere
as CO2 through respiration.
Process of waste and dead
organic matter by
decomposers also release
CO2.
NUTRIENT CYCLING CARBON CYCLE

49. Some amount of the fixed
carbon is lost to sediments
and removed from
circulation.
Burning of wood, forest
fire and combustion of
organic matter, fossil fuel
and volcanic activity are
other sources for releasing
CO2 in the atmosphere.
NUTRIENT CYCLING CARBON CYCLE

50. Role of human activities in
carbon cycle:
Deforestation, burning
of fossil fuel, etc. has
increased the rate of
release of CO2 in the
atmosphere.
NUTRIENT CYCLING CARBON CYCLE

51. Phosphorus is a constituent of
biological membranes, nucleic acids &
cellular energy transfer system.
Many animals use phosphorus to
make shells, bones and teeth.
NUTRIENT CYCLING PHOSPHOROUS CYCLE

52. The natural reservoir of phosphorus is
rock (in the form of phosphates).
When the rocks are weathered minute
account of phosphates dissolve in soil
solution and are absorbed by the
plants. Herbivores and other animals
obtain this from plants.
The waste products and the dead
organisms are the decomposed by
phosphate-solubilizing bacteria
releasing phosphorus.
NUTRIENT CYCLING PHOSPHOROUS CYCLE

53. NUTRIENT CYCLING PHOSPHOROUS CYCLE

54. NUTRIENT CYCLING PHOSPHOROUS CYCLE
Carbon cycle Phosphorous cycle
Atmospheric input is higher Much smaller
Gaseous exchange is negligible.
There is gaseous exchange b/w organism
& environment.

56. ECOSYSTEM SERVICES
• The products of eco system processes are
called ecosystem services.
• Ecosystem services of a healthy forest:
Purify water & air.
Mitigate droughts & floods.
Cycle nutrients
Generate fertile soils
Provide wildlife habitat
Maintain biodiversity
Pollinated crops
Provide storage site for carbon
Provide aesthetic, cultural and spiritual
values.

57. PYQS
1. S1: Decomposition is a process in which the detritus is degraded to simpler substances by microbes
S2: Decomposition is faster if the detritus is rich in lignin and chitin. [AIIMS-2016]
1. S1 incorrect but S2 correct 3. Both S1 & S2 are incorrect
2. Both S1 & S2 are correct 4. S1 correct but S2 incorrect
2. Keystone species deserve protection because these: [NEET-2022]
1. Are capable of surviving in harsh environmental conditions
2. Indicate presence of certain minerals in the soils
3. Have become rare due to over exploitation
4. Play an important role in supporting other species
3. Which of the following will accelerate phosphorous cycle [NEET-2022]
1. Rain fall and storms 3. Volcanic activity
2. Burning of fossil fuels 4. Weathering of rocks
4. Detritivores breakdown detritus into smaller particles. These are called: [NEET-2022]
1. Decomposition 3. Fragmentation
2. Fragmentation 4. Humification
5. S1: Pyramid of energy is always upright and the most efficient
S2: Pyramid of biomass is generally inverted [NEET-2022]
1. S1 incorrect but S2 correct 3. Both S1 & S2 are incorrect
2. Both S1 & S2 are correct 4. S1 correct but S2 incorrect