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Ecosystem - Nutrients and Energy Flow
Ecosystem
An ecosystem is a self-contained area composed of different kinds of organisms which interact with
each other as well as with the physical conditions such as sunlight, air, water, soil and climatic factors
prevailing in the area.
Components of an Ecosystem
An ecosystem consists of two main components:
o Biotic components
o Abiotic components
Types of ecosystems
Natural ecosystem
Aquatic ecosystem
Freshwater ecosystem
Lentic ecosystem
Lotic ecosystem
Marine ecosystem
Pond ecosystem
Terrestrial ecosystem
Forest ecosystem
Desert ecosystem
Grassland ecosystem
Tundra ecosystem
Artificial ecosystem
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Biotic Components of an Ecosystem
The biotic components are the living components of an ecosystem. These include animals, plants
and microorganisms. They constitute the food-obtaining steps or trophic levels of the ecosystem.
TROPHIC LEVELS DESCRIPTION
Trophic level I (Green plants)
They are the starting point of the nourishment chain
for all life forms in the ecosystem.
They produce food through the process of
photosynthesis.
They are regarded as self-food producers or
autotrophs.
These include trees, bushes and grasses.
Trophic level II (Plant-eating
animals/herbivores)
They directly eat plants or their products such as
leaves, grains, fruits, grasses, seeds and flowers as
their food or suck plant sap from their leaves or
stems.
They are also known as primary consumers.
These include animals such as deer, rabbits, rats,
pigeons, parrots, grasshoppers, bees etc.
Biotic components
Producers
Herbivores
Carnivores
Large carnivores
Parasites
Decomposers
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Trophic level III (Flesh-eating
animals/carnivores)
They capture their prey and eat it.
They are also known as secondary consumers.
These include tigers, wolves, snakes, lizards,
certain birds etc.
Trophic level IV (High Order Flesh-
eating animals/large carnivores)
They capture smaller carnivores and eat them.
They are also known as tertiary consumers.
These include peacock, eagle etc.
Parasites
These organisms cannot live independently.
They live inside or on the body surface of another
organism, called the host, and obtain their food or
nourishment from the host.
Worms which live in the guts of animals and fleas
which live on the skin of animals such as dogs are
examples of parasites.
Decomposers
They live on dead and decaying plant and animal
bodies.
They breakdown the complex organic compounds
present in these dead organisms into simpler
substances.
They are also known as microconsumers or
detritivores.
These include certain bacteria and fungi, vultures,
kites, crows, some insects etc.
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Abiotic Components of an Ecosystem
The abiotic components are non-living components of an ecosystem. These include sunlight, air,
water and soil, and climatic factors such as wind, temperature, rainfall and light.
Abiotic components
Sunlight
Air
WaterTemperature
Soil
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Sunlight
The energy obtained from sunlight is essential for the production of food by photosynthesis.
Air
Oxygen from the air is essential to animals for respiration.
Carbon dioxide is useful to plants for photosynthesis.
Air serves as a medium for the flight of birds, insects etc.
Air is an agent for the dispersal of seeds, fruits, flowers, pollen etc.
Water
Water is used by plants and animals for drinking and various other purposes.
Water is the chief constituent of protoplasm in cells.
It is required for various biochemical reactions which occur in organisms.
It helps to transport nutrients and excretory products in organisms.
Temperature
Temperature affects the distribution of living organisms in the environment.
It affects the enzymatic activities in organisms.
Hot, mild or cold temperature influences the kind of body functions of plants and animals
living in such areas.
Most plants and animals survive between 10°C and 40°C.
Soil
Soil provides the substratum for the growth of plants.
It contains water and mineral nutrients such as sodium and potassium required by plants.
Soil also provides a dwelling place for burrowing animals such as rats, snakes and
earthworms which even swallow the mud containing dead organic matter.
In deserts, soil provides support to plants such as prickly pear and date palms.
Even water bodies have some soil at the bottom which is required by organisms living there.
Food Chain
The sequential process of eating and being eaten is called a food chain.
All food chains begin with green plants or the producers. So, the plants or the producers constitute the
first trophic level. Example: Grass
The herbivores or primary consumers which feed on plants constitute the second trophic level.
Example: Grasshopper
The herbivores are next fed upon by the carnivores or secondary consumers. They constitute the third
trophic level. Example: Snake
Finally, the large carnivores, also called the top carnivores or tertiary consumers form the fourth
trophic level. Example: Hawk
The large carnivores die and form the feed of the decomposers. The decomposers feed on these dead
animals and plants. Example: Fungi
There is transfer of food from one organism to the other forming a chain.
A food chain represents unidirectional transfer of energy.
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Examples of Short Food Chains
Rice → Man (Two steps)
Grass → Rabbit → Fox (Three steps)
Maize → Goat → Man (Three steps)
Examples of Long Food Chains
Grass → Grasshopper → Lizard → Crow (Four steps)
Algae → Protozoa → Small fish → Large fish (Four steps)
Green plant → Grasshopper → Frog → Snake → Eagle (Five steps)
Top carnivores (Fourth trophic
level)
Carnivores
(Third trophic level)
Herbivores
(Second trophic level)
Producers
(First trophic level)
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Energy Flow in a Food Chain
In a food chain, along with food, transfer of energy also occurs from one trophic level to the other. The
flow of energy which occurs along a food chain is called energy flow.
All living organisms in an ecosystem require energy for carrying out various life processes such as
breathing, growth and movement. This energy supports various activities of the living world.
All the energy used by living organisms is obtained from the Sun. Solar energy enters the living
components through the autotrophs or green plants, where it gets converted into chemical energy.
However, only 1% of the total energy is actually captured by green plants.
The food energy produced by plants is partially used by them for their growth and development. A
major part of it is lost as heat energy.
The plants are then eaten by primary consumers, the herbivores, and the energy stored in plants is
transferred to these organisms. A part of the energy is used by herbivores for activities such as
digestion, growth and reproduction. Again, most of the energy is lost to the environment in the form of
heat.
When herbivores are consumed by carnivores, a part of the energy is used by the carnivores for their
metabolic activities and growth, while most of it is released as heat energy.
The amount of energy gradually declines as one moves up to each higher trophic level, because at
each level, energy is lost in the form of heat.
Due to the loss of energy at each step, food chains consist of only three to four trophic levels. If there
are many levels, then animals at the end of the food chain will not have enough food and energy to
survive. The solar energy converted by the autotrophs into food energy cannot be reconverted into
solar energy, and the energy which passes from the herbivores to the carnivores can never go back to
the herbivores. The energy lost as heat cannot be returned to the plants and reused during
photosynthesis. Therefore, the flow of energy through a food chain is always unidirectional.
Significance of Food Chain
In all types of food chains, one organism becomes the food of the other organism. As a result, a
situation of eating and being eaten exists. This maintains a check on the population and a balance in
the ecosystem.
Energy in the form of food is continuously transferred between different food chains. This helps to
maintain the equilibrium in an ecosystem.
Food chains help us to understand the interaction and the interdependence of different organisms in
an area.
The loss of energy in food chains and the transfer of energy from one trophic level
to the other can be explained by the Ten Percent Law which states that:
Only 10% of the energy entering a particular trophic level of organisms is available
for transfer to the next higher trophic level.
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Food Web
Similar kinds of organisms may occur in more than one food chain. They eat more than one type of
food to satisfy their requirements. A plant of a particular species can serve as food for a variety of
herbivores.
No food chain can operate in isolation. Individual food chains are interconnected in a complex way.
A network of interconnecting food chains in a natural community of different organisms is called a
food web.
Example of Food Web
Consider six food chains which are interconnected to form a food web. The food web begins with
plants and ends with the top carnivore, the vulture.
In the first food chain, the plants are eaten by the grasshopper, and the grasshopper, in turn, is eaten
by the vulture.
Plants → Grasshopper → Vulture
In the second food chain, the plants are eaten by the rabbit. The rabbit is then consumed by the
vulture.
Plants → Rabbit → Vulture
In the third food chain, the plants are eaten by the rat. The rat is then eaten by the vulture.
Plants → Rat → Vulture
In the fourth food chain, the plants are eaten by the rat, the rat is eaten by the snake, and the snake, in
turn, is eaten by the vulture.
Plants → Rat → Snake → Vulture
In the fifth food chain, the plants are eaten by the grasshopper, and the grasshopper, in turn, is eaten
by the frog. The frog is eaten by the snake, and the snake is consumed by the vulture.
Plants → Grasshopper → Frog → Snake → Vulture
Finally, in the sixth food chain, the plants are eaten by small birds which in turn are eaten by the
vulture.
Plants → Small birds → Vulture
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Significance of Food Web
Food webs permit alternative foods.
They ensure a better chance of survival of an organism if any of its food sources is scarce.
Food Pyramid
A graphical representation of various trophic levels of a food chain in an ecosystem is called an
ecological pyramid or a food pyramid.
Ecological pyramids are of three types:
Pyramid of numbers
Pyramid of biomass
Pyramid of energy
•Pyramid of numbers
•A pyramid of numbers is constructed on the basis of thenumber of individuals which occupy a particular trophic level ina given area at a given time.
•A large number of shrubs and grasses provide food and energyto the deer in grasslands. They are the producers and form thebase of the pyramid.
•As we move higher, there are deer and few lions. However,their number is less as compared to that of grasses andshrubs.
•The lions or the top carnivores are at the top of the pyramidand are found in fewer numbers.
•Pyramid of biomass
•A pyramid of biomass is a graphical representation of biomassor organic matter present per unit area in different trophiclevels.
• In the example of the grassland ecosystem, the biomass ofproducers is the highest of all trophic levels of the ecosystem.The biomass keeps on decreasing as one proceeds from onetrophic level to the next, forming an upright pyramid.
•Pyramid of energy
•A pyramid of energy is a graphical representation of energyflow within an ecosystem.
•The solar energy trapped by producers is converted into foodenergy. This trapped energy flows through the food chain, fromthe producers to the top carnivores. As energy flows, itdecreases with each trophic level, forming an upright pyramid.
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Significance of Food Pyramid
The trophic levels in a food chain can be explained by a food pyramid.
The ecological pyramids help us to understand the structure, functional diversity and energy
conversion efficiency of ecosystems.
The flow of materials in an ecosystem is cyclic, but the flow of energy is unidirectional as the
energy lost as heat cannot be reused by plants during photosynthesis.
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