Neet aspirants CLASS 12 useful video.

1. ECOSYSTEM
By Minaxi Patil

2.  Ecosystem is "a biological
community of interacting
organisms and their physical
environment.“
OR
 It is the sum total of interacting
biotic and abiotic factors that are
capable of independent existence.
The term ecosystem was coined by
ARTHUR TASNSLEY in 1935.
OR
 A group of organisms interacting
among themselves and with
environment is known as ecosystem.
 Ecology is the study of ecosystems.

3. Types of ecosystem
On the basis of development ecosystem is of 2 categories
AQUATIC ECOSYSTEM
e.g. crop field, gardens
TERRESTRIAL ECOSYSTEM
TERRESTRIAL ECOSYSTEM
AQUATIC ECOSYSTEM
e.g. Forest, grassland, desert
e.g. ocean, pond, lake, wetland,
river, estuary, coral reef
e.g. aquarium
1 NATURAL
ECOSYSTEM
2 MANMADE
ECOSYSTEM
Or
ANTROPOGENIC

4. FOREST ECOSYSTEM GRASSLAND ECOSYSTEM
DESERT ECOSYSTEM
 TERRESTRIAL
ECOSYSTEM

5.  AQUATIC
ECOSYSTEM
FRESH WATER ECOSYSTEM BRACKISH WATER ECOSYSTEM
POND, LAKE, RIVER. ESTUARY
MARINE WATER ECOSYSTEM
OCEAN, CORAL REEF
WETLAND
MARSHY WATER ECOSYSTEM

6.  MANMADE
ECOSYSTEM
GARDENS CROP FIELD
AQUARIUM

7.  DIFFERENCES BETWEEN NATURAL AND ANTROPOGENIC ECOSYSTEMS
NATURAL
 It is self-sustainable.
 It has high range of genetic
diversity.
 The food chain is complex and
long.
 The nutrient cycles are complete
and occur naturally.
 It has low productivity.
 e.g. forests , coral reef etc.
MANMADE
 It is not self-sustainable.
 It has limited genetic diversity due to
human intervention.
 Food chains are shorter and often
incomplete.
 The nutrient cycles are generally
incomplete.
 It has high productivity.
 e.g. farmland , aquarium etc.

8.  STRUCTURE AND FUNCTION OF ECOSYSTEM
Structure of an ecosystem is explained by the relationship between
biotic ( living ) and abiotic ( non living ) components.
Ecosystem has two major components
1 Biotic Components
2 Abiotic Components

9. 1 Biotic Components:
The living organisms (or) living members in an ecosystem
collectively called biotic components (or) biotic community.
Ex: • Producer (Plants) - Autotrophs
• Consumer (Animals)
• Decomposers (Micro-organisms)
Photoautotrophs
chemoautotrophs
Heterotrophs
saprotrophs

10.  Producers:
All autotrophs like plants, phytoplankton, etc. that can
produce their food using sources like sun, water, carbon
dioxide, or any other chemical elements

11. •Consumers:
These are the organisms that take their nutrition from the food that is made by the
producers.
Primary Consumers: These organisms feed directly from the producers. They are
herbivorous animals like deer, rabbit, cow, buffalo, and giraffes.
Secondary Consumers: These organisms feed on the primary consumers for their
nutrition. These are carnivorous and omnivorous animals like crows, dogs, cats,
snakes.

12. Tertiary Consumers: These organisms feed on secondary consumers.
These are only carnivores where they only consume meat usually by preying on
prey.
E.g., lion, tiger, cheetah
Quaternary Consumers:
These organisms feed on the tertiary consumers for their nutrition.
E.g; Eagle, which consumes a snake that consumes a frog that consumes a fly.

13.  Decomposers:
All microorganisms, such as bacteria and fungi, that depend on decaying and
dead matter for food fall under this category. It contributes to environmental
cleanup and ecosystem nutrient recycling.
These nutrients support plant development and subsequently ecosystem
maintenance.

14. 2 Abiotic Components:
The non-living components (physical and chemical) of
ecosystem collectively form a community called abiotic
components (or) abiotic community.
Ex:
(a) Climatic Factors: Which include rain, temperature, light,
wind, humidity etc.
(b) Edaphic Factors: Which include soil, pH, topography
(latitude, altitude, direction of mountain), Minerals etc.

16. Species composition and stratification are the two main
structural component of an ecosystem.
Species Diversity is simply the number and relative abundance of
species found in a given biological organization.
Identification and enumeration of plant and animal species
of an ecosystem gives its species composition.
Species composition
structural component of an ecosystem

17. Stratification: ( strata – layer)
The vertical distribution of different species occupying different
levels in an ecosystem is called stratification.
The vertical layering of habitat; the arrangement of vegetation in
layers.
Stratification generally found in TRF ( tropical rain forest). There
are 5-6 strata are found.

19.  Some important structure in ecosystem:
Standing state and standing crops.
 Standing state
It is a amount of inorganic matter found in an ecosystem.
It is a raw material for standing crop.( amount of nutrients)
e.g. N, P, K carbon, etc
 standing crops
It is a amount of living matter present in unit area of an ecosystem.
It is measure in counting and biomass.
e.g. in a particular area biomass of trees is a standing crops.
( maximum standing crop is in TRF).

20. The components of an ecosystem are seen to function as a
unit when the following factors are considered :
 Productivity
 Decomposition
 Energy flow
 Nutrient cycling
 Functional component of Ecosystem

21. The rate of biomass production or the amount of food energy produced
or obtained or stored by a particular trophic level per unit area in a unit
time is called productivity.
It can also be defined as the energy accumulated in plants by
photosynthesis.
The unit of productivity is gm/m2/year or kcal/m2/year.
There are two types of productivities –
 Primary productivity
 Secondary productivity
 Community productivity

22.  Primary Productivity:
It is the productivity at the producer level. It can be termed as the amount of
organic matter produced by the plants from solar energy in a given area during a
given period of time.
Approximately 1-5% of solar energy that falls on the plant is converted to organic
matter.
Green plants fix solar energy and accumulate it in organic forms as chemical
energy. As this is the first and basic form of energy storage, the rate at which the
energy accumulates in the green plants or producers is known as primary
productivity.
Primary Productivity = Dry matter produced or energy captured
area of land/ time

23. 1) GPP (Gross Primary Productivity):
The total solar energy trapped in the food material by
photosynthesis/chemosynthesis is referred to as gross primary productivity
(GPP).
A fraction of gross primary productivity is utilized in respiration of green
plants.
Gross primary productivity minus respiration losses (R), is the net primary
productivity (NPP).
 Primary productivity is of two types:
1) Gross Primary Productivity (GPP)
2) Net Primary Productivity (NPP)

24. 2) NPP (Net Primary Productivity):
The amount of energy-bound organic matter created per unit area and
time that is left after respiration is net primary productivity (NPP).
The rate at which the energy or organic matter is stored in a producer
after respiration is called NPP.
Net primary productivity is the available biomass for the consumption to
heterotrophs (herbivores and decomposers).
Thus, NPP = GPP-R (R= Energy lost in respiration.)
 The annual net primary productivity of the whole biosphere is
approximately 170 billion tons (dry weight) of organic matter.
 Of this, despite occupying about 70 per cent of the surface, the
productivity of the oceans are only 55 billion tons. Rest of course, is
on land. (115 billion tons)

25.  Secondary productivity
The rate of formation of new organic matter by consumers.
The rates at which the heterotrophic organisms resynthesize the energy-
yielding substances are called secondary productivity.
The energy stored at consumer level for use by the next trophic level is
known secondary production.
 Community productivity
This is the rate of net synthesis of organic matter by a community per unit
time and area. ( plants + animals ).
It can also be referred to as the energy accumulated in the plants by
photosynthesis.
CP = NPP – Heterotrophic consumption

26.  In land ecosystem ,lowest productivity is of desert and tundra.
 In water least productivity ecosystem is very deep lake and high
productivity is coral reef.
 It is a unidirectional movement of energy towards higher trophic
level and loss heat to environment.

27. Difference between productivity and standing crop
PRODUCTIVITY
 It is a rate of biomass formation
 It is measured as
Kcalories/m2/year (energy) or
grams/m2/year (dry organic
matter)
 E.g. biomass formation of
diatom is more than mango tree.
STANDING CROP
 It is the amount of biomass
at given time.
 It is measured as calories
or grams per m2.
 E.g. biomass of mango
tree is more than diatoms.

28. The Productivity in Ecosystem is depend on :
 A variety of environmental factors, such as light - solar radiations
( in TRF > aquatic), soil moisture ( in desert < TRF ,because of dry
soil), temperature (in low temp., polar < TRF ), etc .
 Availability of nutrients e.g. in oceans available nutrients is less (
N, P, K) therefore productivity is less than land.
 Photosynthetic capacity in plants e.g. in c4 plants > than c3.
 Plant species inhibiting a particular area (flora)

29.  Decomposers break down complex organic matter into inorganic
substances like carbon dioxide, water and nutrients and the process is
called decomposition.
 Dead plant remains such as leaves, bark, flowers and dead remain of
animals, including faecal matter, constitute detritus, which is the raw
material for decomposition called as detritus.
 Decomposition gives rise to two product
humus and minerals.
In terrestrial ecosystem decomposition takes place at upper layer of soil,
But, in aquatic ecosystem decomposition takes place at bottom of water
body.

30.  The important steps in the process of decomposition are
Fragmentation
Leaching
Catabolism
Humification
Mineralization

31.  Fragmentation
It is a process in which detritivores (e.g., earthworm & other
soil animals ) break down detritus into smaller particles.
This is an important step, because smaller fragments have
more surface area to support the growth of bacteria and
fungi.

32.  Leaching
The process of leaching, water soluble inorganic nutrients go down
into the soil horizon and
get precipitated as unavailable salts.
During this process, water percolating through soil removes soluble
substances, such as sugars and several other nutrients, from the
fragmented detritus due to leaching action.

33.  Catabolism
Bacterial and fungal enzymes degrade detritus into simpler inorganic
substances. This process is called as catabolism. It is important to note
that all the above steps in decomposition operate simultaneously on the
detritus.
During process of catabolism, the extracellular enzymes released by
bacteria and fungi carry out enzymatic conversion of the decomposing
detritus to simpler compounds and inorganic substances.

34.  Humification
Humification leads to accumulation of a dark coloured 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.
It is acidic in nature ( humic acid ).
It is rich in lignin and cellulose.
Humus serves as a reservoir of nutrients.
This layer can’t simply dissolve because it is particularly resistant to the actions
of microbes.
The humus layer is very beneficial, contains a lot of nutrients, and gives the soil
fertility.

35.  Mineralization
The humus is further degraded by some microbes and release of inorganic
nutrients occur by the process known as mineralization.
This step marks the end of the process of decomposition. In this step, the
humus is broken down into inorganic nutrients and hence the process of
decomposition is complete.
A process, which results in the release of inorganic substances, such as CO2,
H2O and other nutrients like NH4
+/Ca++, Mg++, K+, etc., in the soil.

36. SCHEMATIC REPRESENTATION OF DECOMPOSITION

37.  Factors influencing decomposition
 Detritus
Rich in lignin and chitin – decrease rate of decomposition.
Rich in nitrogen and water soluble substances (sugar) – faster rate of
decomposition.
 Temperature – In low temp. – decrease rate of decomposition
In high temp. – increase rate of decomposition
 Moisture - In less moisture – decrease rate of decomposition
In high moisture – increase rate of decomposition
 Aeration – Aerobic - high rate of decomposition
Anaerobic - low rate of decomposition

38.  ENERGY FLOW
The source of energy is sun except deep sea hydrothermal ecosystem.
The chemical energy of food is the main source of energy required by
all living organisms.
This energy is transmitted to different trophic levels along the food
chain.
This energy flow is based on two different laws of thermodynamics:
 First law of thermodynamics, that states that energy can neither be
created nor destroyed, it can only change from one form to another.
 Second law of thermodynamics, that states that as energy is
transferred more and more of it is wasted.

40.  The primary source of energy is solar energy. It is amusing to find that we
receive less than 50 % of the sun’s effective radiation on earth.
 This effective radiation is termed as the Photosynthetically Active Radiation
(PAR).
 and only around 2-10 % of it is used by plants for the process of
photosynthesis. (GPP)
 During the process of energy flow in the ecosystem, plants being the producers,
stored organic products (1.6-8 %, NPP) and passed on to the primary
consumers in the food chain, followed by the secondary consumers.
 Plants convert energy from 1 form to another, known as transducers.
 Finally, when tertiary consumers consume the carnivores, again energy will be
degraded.
 Thus, the energy flow is unidirectional in nature.

41. 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
consumer) to the second and carnivores (secondary consumer) to the
third.
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. The amount of energy decreases at
successive trophic levels
Each trophic level has a certain mass of living material at a particular
time called as the standing crop.
 TROPHIC LEVEL (T)

42. Moreover, in a food chain, the energy flow follows the 10 percent law.
According to this law, only 10 percent of energy is transferred from one
trophic level to the other; rest is lost into the atmosphere.
 10 percent law.

43. The transfer of food energy from the producers, through a series of
organisms (herbivores to carnivores to decomposers) with repeated
eating and being eaten, is known as food chain.
In nature, basically two types of food chains are recognized
1) Grazing Food Chain
2) Detritus Food Chain.
Key industry animal – it convert plant matter to animal matter is
herbivores ( heterotrophs)
Secondary producers are herbivores in food chains
 FOOD CHAIN

44. 1) Grazing Food Chain (GFC)
It starts from the green plants(T1) that make food for herbivores(T2) and
herbivores in turn for the carnivores(T3).
Ecosystems with such type of food chain are directly dependent on an
influx of solar radiation. It takes place in terrestrial and aquatic
ecosystem.
The detritus food chain 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.
2) Detritus Food Chain (DFC)

45. Aquatic Terrestrial

46.  In an aquatic ecosystem, Grazing
Food Chain (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 (DFC) than through the
GFC.
 Parasitic /auxiliary /accessory/subsidiary food chain
It begins with the host and usually end in parasite. the food chain
begins with herbivores and ends with the smaller parasites.
The energy flows from larger organisms to smaller organisms, i.e.,
from host to parasite.

47.  FOODWEB
Simple food chains are very rare in nature because each organism
may obtain food from more than trophic level.
Thus, in an ecosystem, the various food chains are interconnected to
each other to form a network called food web.
In food web transfer of energy is unidirectional ,but from many
different alternative pathway.
A food web illustrates all possible transfers of energy
and nutrient among the organisms in an ecosystem, whereas food
chain traces only one pathway
of food. Food webs are very important in maintaining the stability of
an ecosystem.

49.  Ecological Pyramid
The concept of number pyramid (Eltonian pyramid)is given by Charles Elton (1927)
Bodenheimer presented the pyramid form for biomass in 1938.
Hutchinson and Linderman suggested the pyramid structure for productivity in
1942.
 A graphical representation of diverse living species at various trophic levels is an
ecological pyramid.
The various forms of ecological pyramids are determined by the amount of energy
or biomass available for every trophic level.
 pyramids are classified into three types based on the
quantity of organisms, biomass, and energy.
1) Pyramid of numbers
2) Pyramid of biomass
3) Pyramid of energy

50.  Pyramid of Number
It denotes the number of organisms found in each trophic level.
The number pyramid is always upright, but in situations such as the
detritus food chain, it does not show an upright position. (inverted)
The number of organisms decreases as one moves up the pyramid.
Because there are a lot of producers, it's at the bottom.
Grassland ecosystem Tree ecosystem

51.  Pyramid of Biomass
The amount of biomass produced by each trophic level is depicted in this ecological pyramid.
in the oceans, where large numbers of zooplankton rely on phytoplankton, the biomass
pyramid is always inverted.
In this pyramid, producers have the most biomass, followed by primary consumers, who have
less biomass than producers. secondary consumers have less biomass than primary
consumers, and at the top of the pyramid, biomass is present.
The biomass pyramid in a sea is also inverted because fish biomass exceeds phytoplankton
biomass.

52.  Pyramid of Energy
The energy pyramid is always upright because energy flow in a
food chain is unidirectional and some energy is lost in the
environment as trophic levels increase.
This energy pyramid depicts the flow of energy from consumers
to producers.

53.  ECOLOGICAL SUCCESSION
Ecological succession is a series of changes that occur in an
ecological community over time.”
The species that invade a bare area are called pioneer species. Or
The first plant to colonize an area is called pioneer community.
These changes lead finally to a community that is stable in
environment is called a climax community.
It is mature more complex and long lasting community.
The entire sequence of communities that successively change in a
given area are called sere(s).
The stage leading to the climax community from pioneer community
is called seral stages or seral communities.

54.  PRIMARY SUCCESSION
 It takes place an over where no community has existed previously.
Such area includes bare rock, newly formed deltas and sand
dunes, emerging volcano islands and lava flows, etc.
 In this succession on terrestrial site ,the new site first colonized by
pioneer species such as microbes, lichens, and mosses.

55.  PRIMARY SUCCESSION IN WATER

56.  SECONDARY SUCCESSION
It takes 50-100 years (for grassland) and 100-200 years (for forest).
It Is a Sequential development of biotic communities after the complete or
partial destruction of the existing community.
A mature or intermediate community may be destroyed by natural events
such as floods, droughts, fires, or storms or by human interventions
such as deforestation, agriculture, over grazing etc.

57.  Succession of Plants
Based on the nature of the habitat succession is of 2 types.
It is in water (very wet areas) succession of plants is called Hydrarch.
It is in dry areas succession of plants is called Xerarch.
Hydrarch succession takes place in wetter areas and the successional
series progress from hydric to the mesic conditions.
xerarch succession takes place in dry areas and the series progress from
xeric to mesic conditions.
Hence, both hydrarch and xerarch successions lead to medium water
conditions (mesic) – neither too dry (xeric) nor too wet (hydric).

58.  Nutrient cycle
All nutrients in the earth are recycled/circulate between biotic and abiotic
component of biosphere called biogenetic nutrients. The major nutrients
such as oxygen, carbon, nitrogen, phosphorous, and Sulphur are
essential ingredients that make up organisms.
The amount of these nutrient present in soil at any given is called
standing state.
The cyclic exchange of material between the living organisms and their
non-living environment is called Biogeochemical Cycle.
Nutrient cycles are of two types:
(a) Gaseous cycle - The reservoir for gaseous type of nutrient cycle exists
in the atmosphere (e.g., nitrogen, carbon cycle)
(b) Sedimentary cycle – The reservoir is located in Earth’s crust.
(e.g., Sulphur and phosphorus cycle)

59. Carbon in the atmosphere is present in the form of carbon dioxide.
carbon constitutes 49 per cent of dry weight of organisms and is next only to
water.
The total quantity of global carbon, we find that 71 per cent carbon is found
dissolved in oceans.
The atmosphere only contains about 1per cent of total global carbon.
The conc. Of co2 in atmosphere is 0.03 % ,and is utilized in photosynthesis by
plants.
It has been estimated 4 × 1013 kg of carbon is fixed annually in the biosphere
through photosynthesis.
Fossil fuel also represent a reservoir of carbon.
Carbon cycling occurs through atmosphere, ocean and through living and
dead organisms.
 CARBON CYCLE

60. Oceanic Carbon Cycle
 Ecologically, oceans take in more carbon than it gives out. Hence, it is called
a “carbon sink.” Marine animals convert carbon to calcium carbonate and
this forms the raw building materials require to create hard shells. When
organisms with calcium carbonate shells die, their body decomposes,
leaving behind their hard shells.
 These accumulate on the seafloor and are eventually broken down by the
waves and compacted under enormous pressure, forming limestone.
 When these limestone rocks are exposed to air, they get weathered and the
carbon is released back into the atmosphere as carbon dioxide.
Carbon Cycle on Land
 Carbon enters the atmosphere through natural processes such as respiration
and industrial applications such as burning fossil fuels.
 The process of photosynthesis involves the absorption of CO2 by plants to
produce carbohydrates. Carbon compounds are passed along the food chain
from the producers to consumers.
 The majority of the carbon exists in the body in the form of carbon dioxide
through respiration. The role of decomposers is to eat the dead organism and
return the carbon from their body back into the atmosphere.

62.  PHOSPHOROUS CYCLE
 Phosphorus is a major constituent of biological membranes, nucleic
acids and cellular energy transfer systems. Many animals also need
large quantities of this element to make shells, bones and teeth.
Steps of Phosphorus Cycle
1. Weathering
2. Absorption by Plants
3. Absorption by Animals
4. Return to the Environment
through Decomposition

64.  ECOSYSTEM SERVICES
Ecosystem services are the positive benefits that people obtain
from ecosystems. They support, directly or indirectly, our survival
and quality of life.
The 5 Ecosystem Services
•Food and drink.
•Natural medicines.
•Water supply.
•Materials.
•Renewable and non-renewable energy.

65. THANK YOU