Ecosystem, Chapter Notes, Class 12, Biology | EduRev Notes

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Class 12 : Ecosystem, Chapter Notes, Class 12, Biology | EduRev Notes

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A.G.Tansley - The term "Ecosystem" first of all coined by A.G. Tansley.

According to Tansley - Ecosystem is symbol of structure and function of nature.

E.P.Odum - Father of ecosystem ecology.

According to E.P.Odum - Ecosystem is the smallest structural and functional unit of nature or environment.

Karl Mobius - Used term Biocoenosis for ecosystem.

Thienmann - Used term Biosystem for ecosystem.

Sukhachov - Used term Biogeocoenosis for ecology.

Misra - Used term Ecosom for ecosystem.

Forbes - Used term Microcosom for ecosystem. For artificial ecosystem in laboratory.

ecosystem, biology

Diagrammatic representation of the basic types of ecosystems, all of which together constitute the giant ecosystem- the biosphere. Note, in the centre, the generalised scheme of the structure and function of any unit ecosystem of the biosphere.

Definition - Total living (biotic) and non living (aboitic) componants of the environment present in a particular area is called ecosystem.

In any ecosystem, communities or living organisms interact with their physical environment in such a way that there is a well defined flow of energy forming clear trophic (food) levels and material cycles within this ecosystem.

Ecosystem is normally an open system because there is a continuous and variable entry and loss of
energy and materials.

An ecosystem may be small like a drop (microsystem) of water and as large as sea or tract of forest.

An ecosystem may be temporary as a fresh water pool or a field or permanent like a forest or sea.

Thus any area of nature that includes living organisms and nonliving substances interacting, so that a flow of energy leads to characteristic trophic structures and cycling of materials makes the ecosystem.

Any ecosystem must have the following peculiarities.:
There is an energy source for all living organisms in an ecosystem.
Adequate amount of food and essential nutritional element should be present for living organisms
in an ecosystem.
There should be a continuous cyclic flow of energy and materials in form of food chains between
organisms and environment.
There are regular changes in the climatic conditions (temperature, humidity, light etc.) in an


Homeostasis - Ecosystem is a dynamic system because continuous interaction is going on in between aboitic and biotic components so ecosystem is present in equilibrium position. Ecosystem is also self maintainable and self regulatory system, it means an ecosystem maintains a balance in between different trophic levels. Each trophic level control the other trophic level in an ecosystem. If any change take place in any trophic level of ecosystem, the other trophic levels of this ecosystem may react according to it. So ecosystem always remain in equilibrium. This feature of system is known as Homeostasis.

Cybernetics - A science of self control as (homeostasis) in an ecosystem is called cybernetics.
The boundaries of ecosystem are indistinct and have a overlapping character over each other.
Ecosystem is the smallest structural and functional unit of nature or environment. It is a self regulatory
and self sustaining unit.


 - Ecosystem, class 12, biology

(A) Natural Ecosystem

(B) Artificial Ecosystem


(A) Natural Ecosystem -
(a) Terrestrial Ecosystem -
eg. forest, grassland, tree, desert ecosystems.
(b) Aquatic Ecosystem -

Aquatic ecosystem is again of two type-
(i) Lentic ecosystem - Stagnant fresh water, lake, pond, swamp.
(ii) Lotic - Running fresh water ecosystem. eg., rivers


(B) Artificial Ecosystem - Man made eg., cropland, Gardens etc.
On the basis of size, type of ecosystem :
(a) Mega ecosystem- Ocean/Sea

(b) Macroecosystem - Forest
(c) Microecosystem - Pond

(d) Nanoecosystem - Drop of water.



(A) Abiotic component

(B) Biotic component

(A) Abiotic component
Rainfall etc.

(B) Biotic component
Formed by living things. eg., plants, animals, microbes.


Type of Biotic Components :

1. Producers -
All the autotrophs of ecosystem are called producers. They prepare their own food. The green plants are the main producers. In the process of photosynthesis, producers absorb solar energy and convert it into chemical energy so producers are also called transducers or converters.
Energy enters into the ecosystem through the producers. The solar energy is the only ultimate source of energy in ecosystem. This energy is available for the remaining living organisms.

Other eg. of producers are-
Chemoautotrophs : (iron bacteria, sulphur bacteria, nitrifying bacteria)
In aquatic ecosystem : Floating plant called phytoplankton are the major autotrophs.
Phytoplankton may produce as much food as produced by the larger shrubs and trees in unit area.

2. Consumer -
All the heterotrophs of the ecosystem are known as consumers. They directly (herbivores) or indirectly (Carnivores) depend on the producers for food.
Type of consumer
(i) Macro consumers

(ii) Micro consumers

(i) Macro consumers (Phagotrophs or holozoic)
They digest their food inside the body. ie., first ingestion then digestion.
Macro consumers are of following types-
(a) Primary consumers - Such living organisms which obtain food directly from producers or plants are known as primary consumers.
eg., herbivores of ecosystem, Cow, Grazing Cattle, Rabbit.
They are also known as secondary producers as they synthesize complex materials in the cells, by the digestion of food which is obtained from the plant.


(b) Secondary consumers or primary cornivores - Animals which feed upon primary consumers and obtain food. Those cornivores which kill and eat the herbivores, are called predator. eg., Dog, Cat, Snake

Note :
The organism which completely depends on dead animals are not example of predators but they are the scavangers or detrivores. eg., Vulture, Crow, Fox.
All the herbivores are predators.
All the carnivores are not predators like crow.
(c) Top Consumers - Those animals which kill other animals and eat them, but they are not killed & and eaten by other animal in the nature. eg., Lion, Man, Hawk, Peacock.

ecosystem, biology

(ii) Micro Consumers/Decomposers or Saprotrophs/osmotrophs-
Those living organisms which decompose the dead body of producers and consumers are known as decomposer or reducers or transformer or osmotrophs.
Note :
The main decomposers in ecosystem are bacteria and fungi.

Decomposers play a significant role in mineral cycle. Decomposers are responsible for converting complex organic material of dead animals or plants into simpler organic matter through the process of decomposition and release mineral substances into the soil where these are reused by the producers. So that soil is considered as the best resource of minerals.

In Bacteria and fungi, process of decomposition completely takes place outside the body. They release enzymes from their body on dead remains and decompose it into simpler organic substance and then absorb it so these are called as osmotrophs (absorptive).

In aquatic system whale is secondary consumer. It is an example of filter feeder because it feeds on plankton.

Vulture is a scavenger not predator because it never kills any animal. Vulture is also a decomposer. In Vulture, the break down of the food material takes place inside the body and then released into the soil in the form of waste material and minerals.

Plant parasites are known as primary consumers while animals parasites (E.coli bateria, Entamoeba hisotlitica, liver fluke, tapeworm) are known as secondary consumers.

All the insectivorous plants play the double role i.e., producer as well as secondary consumer because they sythesise their own food through photosynthesis and they eat insects simultaneously.

Man and peacock are omnivores.

Organisms which use milk or curd are known as secondary consumer.

Sparrow occupy 2 trophic level -

(i) Primary consumer-as eating seeds,
(ii) Secondary consumer-as eating insects.

Frog -

(i) Larva - Herbivore,

(ii) Adult - carnivore



Structure of Ecosystem :
Biotic and abiotic components are physically organized to provide characteristic structure to a ecosystem

It is species composition and stratification (lake stratification, forest stratification, ocean stratification).

Another way to represent the structure of ecosystem is through food relationship of producers and
consumers constituting the Standing Crop.

The nutrients necessary for growth of living organisms, accumulated in biomass and in abiotic componants like soil called Standing State.

Function of Ecosystem :

Ecosystem posses a natural tendency to persist, which is due to it's variety of functions (activities under taken to ensure persistance).

For example leaves carryout photosynthesis, root absorb nutrients from soil, herbivores utilize plant production and serve as food for carnivores, decomposers carryout decompositions and product used by producers. All these functions are came out in ecosystem in balanced and control manner called Processes.

So key aspect of function of ecosystem are -
(A) Productivity

(B) Decomposition
(C) Energy flow

(D) Nutrient cycling




 - Ecosystem, class 12, biology

(A) Productivity :
(i) Primary productivity -

Primary production is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It is expressed in term of weight (g–2) or energy (Kcal m–2). The rate of biomass production is called productivity. It is expressed in term of g–2yr–1 or (Kcal m–2) yr–1 to compare the productivity of different ecosystem. It can be divided into GPP and NPP.


(a) Gross primary productivity (G.P.P.) - It is the total amount of energy fixed (organic food) in an ecosystem (in producers) in unit time is called G.P.P. including the organic matter used up in respiration during the measurement period. It is also known as total (Gross) photosynthesis. A considerable amount of GPP is utilised by plants in respiration.

(b) Net primary productivity (N.P.P.) - It is the amount of stored organic matter in plant
tissues after respiration utilisation.

ecosystem, biology

NPP is the available biomass for the consumption of heterotroph.


(ii) Secondary productivity - Secondary productivity is the rate of formation of new organic matter by consumers.

(iii) Net community productivity or Net productivity - The rate of storage of organic matter not used by the heterotrophs.
NCP   =     N.P.P.   –      HR      (HR = Energy used by Heterotrophs or consumers)
Primary productivity depends on the plant species inhabiting a particular area. It also depends on a variety of environmental factors availability of nutrients and photosynthetic capacity of plants. Therefore it varies in different type of ecosystem. The annual net primary productivity of the whole biosphere is approximately 170 billion tons (dry weight) of the  organic matter, productivity of the ocean are only 55 billion tons.
In per unit area maximum productivity found in tropical rain forest.
In water, least productive ecosystem is very deep lakes and highly productive ecosystem is coral reef.
Nitrogen is the limiting factor in ocean and phosphorus is the limiting factor in lake productivity.
In land           - Highest productivity, Tropical rain forest           i.e., 5 kg/msq/year.
                     - Lowest productivity is of Deserts, tundra.
Most productive Agro-ecosystem is Sugarcane and rice ecosystem      - 3-4 kg./msq/year.



 - Ecosystem, class 12, biology

(B) Decomposition :
Decomposition (Formation of Humas) : Decomposers break down comlex organic matter into inorganic substance like carbon dioxide, water and nutrients and the process is called decomposition. Dead plant remains such as leaves, bark, flower and dead remains of animals, including fecal matter, constitute detritus, which is the raw material for decomposition. The important steps in the process of decomposition are fragmentation, leaching, catabolism, humification and mineralisation.

Detritivores (eg., earthworm) break down detritus into smaller particles. This process is called fragmentation. By the process of leaching, water soluble inorganic nutrients go down into the soil horizon and get precipitated as unavilable salts. Bacterial and fungal enzymes degrade detritus into simple inorganic substance. This process is called as catabolism.

It is important to not that all the above steps in decomposition operate simultaneously on the detrius. Humification and mineralisation occur during decomposition in the soil. 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. The humus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralisation.

Decomposition is largely an oxygen-requiring process. The rate of decomposition is controlled by chemical composition of detritus and climatic factors. In a particular climatic condition, decomposition rate is slower if detrius is rich in lignin and chitin and quicker, if detritus is rich in nitrogen and water-soluble substances like sugars.

Temperature and soil moisture are the most important climatic factors that regulate decomposition through their effects on the activities of soil microbes. Warm and moist environment favour decomposition where low temperature (< 10ºC) and an anaerobiosis inhibit decomposition resulting in build up of organic materials.

Decomposition requires years at very high altitude or lattitudes. Rate of decomposition is low in prolonged dry soil like in tropical desert.

The actual rate of decomposition depands on environmental conditions and detritus quality.

Nutrient Immobilisation - In the process of decomposition, some nutrients get tied up with the biomass of microbes and become temporarily unavailable to other organisms. Such incorporation of nutrients in living microbes (bacteria and fungi) is called nutrient immobilisation.

Nutrients gets immobilized for variable periods and gets mineralised later after the death of microbes. This immobilization prevents nutrients from being washout form the ecosystem.


Two types of Humus -
(i) Mor (Coarse terxtured humus)- It is raw humus and is formed in acidic soil (PH - 3.8 – 4.0) in which decomposition of litter is slow because it has less number of decomposer organism.
(ii) Mull – This is completely decomposed litter. i.e., humus because rate of decomposition is fast due to high PH of soil. (Best PH of the soil 5.5 to 6.5)



Energy Flow  - Ecosystem, class 12, biology

(C) Energy Flow :
Energy flow is the key function of ecosystem. The storage and expenditure of energy in ecosystem is based on the two basic laws of thermodynamics.
(i) Energy is neither created nor destroyed but only transformed from one state to another state.
(ii) The law of entropy - The transfer of food energy from one to another organisms leads to loss of energy as heat due to metabolic activity.

Energy in food is in concentrated form, heat energy is highly dispersed. It must be understood that all changes in energy forms can be accounted for energy flow in any system.

It is useful to examine the relationship between incident radiant energy and the energy captured by the producers in the food they menufacture. Only the visible light, or the photosysnthetically active radiation (PAR), which carries about 50 percent of the energy of total incident solar radiation, is available to producers for absorption.

Under favourable environmental conditions, only about 1-5 percent energy of incident radiation
or 2-10 percent of PAR is actually captured by the photosynthetic process (gross primary
productivity), and the remaining portion is dissipated. Since the simultaneously occuring
respiratory processes are energy consuming and use up the part of the photosynthetic gain,
the net capture of energy (Net primary productivity) is reduced to only 0.8-4 percent of the
incident total radiation, or 1.6-8 percent of PAR. Only the energy captured can be used by other
trophic levels.

ecosystem, biology


Food Flow Model :
A simplified representation of energy flow through ecosystem has been made in figure presented.
Two aspects with respect to energy flow in ecosystem need careful consideration. First, the energy flows one ways, i.e., form producers to herbivores to carnivores; it cannot be transferred in the reverse direction.

Second, the amount of energy flow decreases with successive trophic levels. Producers capture only a small fraction of solar energy flow decreases with successive trophic levels. Producers capture only a small fraction of solar energy (1-5 percent of total solar radiation), and the bulk of unutilised energy is dissipated mostly as heat. Part of the energy capture in gross production their standing crop (respiration) and for providing food to herbivores (herbivory). The unutilised net primary production is ultimately converted to detritus, which serves as energy source to decomposers.

Thus, energy actually used by the herbivore trophic level is only a small fraction of the energy captured at the producer level. On an average, in different ecosystems, the herbivore assimilation or productivity approximates 10 percent of gross productivity of producers.

The enrgy assimilated by the herbivores is used in respiration and a fraction of unassimilated energy is transferred to decomposers (eg., Faecal matter). The remaining herbivore level energy available at carnivore trophic level is again partitioned leaving a very small fraction to support the next trophic level (top carnivore).

The respiration cost also increases sharply along successive higher trophic levels. On an average, respiration in producer consumes about 20 percent of its gross productivity. Herbivores consume about 30 percent of assimilated energy in respiration. The proportion of assimilated energy consumed in respiration rises to about 60 percent in carnivores. Because of this tremendous loss of energy at successive higher trophic levels, the residual energy is decreased to such an extent that no further trophic level can be supported. Therefore, the length of food chains in an ecosystem is generally limited to 3-4 trophic levels.

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Food Chain
In ecosystem every organism depends on other organism for food material and all organism are (herbivores to carnivores) arranged in a series in which food energy is transferred through repeated eating and being eaten. It is called food chain. In food chain, energy flow is in the form of food.

In a food chain, food material or food energy is transfer from one trophic level to next trophic level.

Four trophic levels are present in the ecosystem, because level of energy decreases during the flow of energy from one trophic to the another trophic level.

First trophic level [T1] = Producers
Second trophic level [T2] = Primary consumers
Third trophic level [T3] = Secondary consumers
Fourth trophic level [T4] = Top consumers

Five trophic levels found in highly complex ecosystem in which tertiary consumer is present in between the secondary consumers and top consumer. Then the fifth trophic level (T5) is formed by the top consumer.

In food chain energy flow is unidirectional (preducers to herbivores).

Shorter food chains will provide greater energy.

Generally the decomposers (Bacteria and Fungi) are not included in the food chain but when
included then included as the last trophic level.


Type of Food Chains :
In nature three type of food chain are present-
1. Grazing food chains or Predatory food chain - Most of food chain in nature are of this type. This food chain begins with Producers (plants) and in successive order it goes from small organism to big organism.

ecosystem, biology

Note :

Both above food chains are directly dependent on solar radiation (as a primary source of energy) and have rapid energy flow.

3. Detritus food chain or Saprophytic food chain - This food chain begins with decomposition of dead organic matter by decomposers so it is also known as saprophytic food chain.
In this food chain primary consumers are bacteria and fungi.
Dead organic matter → Bacteria, fungi
Note :
In mangrove vegetation this food chain goes up to big organism.
Dead mangroves leave → Bacteria & fungi → Amphipds, molluscs, crabs, nematodes →small fishes →fish eating birds.
It does not depends on light.

In an aquatic ecosystem, GFC(Grazing Food Chain) is the major conduit (source) of energy flow. As against this, in a terrestrial ecosystem, a much larger energy flow through the detritus food chain (as it is small) than through the grazing food chain.


Food Web
In big ecosystem many food chains are interlinked together on different trophic levels to form food web. In food web transfer of food energy is unidirectional but from many different alternative pathways.

In food web members of a particular trophic level obtain their food according to their choice and taste but that type of facility is not present in food chain. It means they have more than one option or alternative for getting food.

As mush as food web is complex that ecosystem is more permanent or stable, such type of ecosystem is not destroyed naturally and continues for long time. This ecosystme is not affected by loss of any organism of any particular trophic level. Those ecosystems which have simple food web are not very stable it means that they can be finished at any time, if there is a change in any particular trophic level.

ecosystem, biology



 - Ecosystem, class 12, biology

Pyramids of Ecosystem
Graphical representation of ecological parameters at different trophic levels and trophic structure in ecosystem is called pyramids. These parameters are Number, Biomass and Energy. First of all, pyramid was formed by Charis Elton; So we called it Eltonian pyramids.
These Pyramid are of three types
(1) Pyramids of number,

(2) Pyramids of energy,

(3) Pyramids of biomass.

(1) Pyramids of number -

In this type of pyramid the number of individual organism in various trophic level is shown. These pyramid are mostly upright, because number of producers [T1] is maximum and number of herbivores and carnivores decrease towards apex or at successive trophic levels, such as Grassland ecosystem and aquatic ecosystem.

ecosystem, biology

But in a tree ecosystem the pyramid of numbers is inverted. This is called parasitic ecosystem. Because birds (herbivores) depend on the tree (producer) and parasites (consumer) like bugs, lices depend on birds, therefore with increase in the number of trophic levels, the number of the organisms increase sequentially.

ecosystem, biology

Note :
Maximum number of producers are present in aquatic ecosystem. The number of organism at any trophic level depends upon the availability of organisms which are used as food on lower level so availability of food is main factor.

Pyramid of number shows biotic potential of a ecosystem. The number of members of any particular species in favourable conditions is called their biotic potential. When the numbers of the members of any species increases over the limit then it is called population explosion. Because of this existence of the species comes in danger.Human population is also near this condition at present.

(2) Pyramid of Biomass -
Pyramids of biomass represent the total amount of biomass of each trophic level of ecosystem, mostly these pyramids are also upright (erect) eg., tree ecosystem, forest ecosystem.

ecosystem, biology


(3) Pyramids of energy -
It represent amount of energy at different trophic levels, energy pyramids are always upright or erect because there is a gradual decrease in energy at successive trophic levels. According to the 10% law of Lindeman, the 90% part of obtained energy of each organism is utilized in their various metabolic activites and heat and only 10% energy is transferred to the next trophic level. So 90% energy is lost at each trophic level, therefore top consumers like lion etc. are ecologically weakest but physically they are strong.

ecosystem, biology



Nutrient Cycling and Biogeochemical Cycle - Ecosystem, class 12, biology

(D) Nutrient Cycling / Biogeochemical Cycle :
Bio              – Living organism
Geo – Rock, Soil, Water
Chemcial – Material or Nutrients

All the types of material required by ecosystem in addition of energy, are available continuously to ecosystem through recyling. Thus there is a constant exhcange of materials between the living organism and their abiotic environment through the recyling of materials. This phenomenon is called Biogeochemical cycle.

The mineral elements taken up from the enviroment (soil as well as air) by the green plant, (the producers), are again returned to the environment through consumers and decomposers.

The following types of cycles are found in an ecosystem

Gaseous Cycle - C, H, N, O cycle. Reservior is in the atmosphere (air) or in Hydrosphere(water).

Sedimentary cycle - P, S, Ca cycles reservoirs are in earth’s crust (lithosphere)

In these cycles, the bulk material remains in the inactive reservoir on earth crust like sediment of sea or water bodies.

Nutrient cycles can be conveniently considered under the following three aspects as shown in above figure.

Input of Nutrients : Ecosystem receives nutrients form external sources and stores them for further used though biological processes. For example, nutrients in dissolved state are gained from rainfall (wet deposition), or in particular state from dust fall (dry deposition). Symbiotic biological fixation of nitrogen in soil also represents an input. Weathering of soil parent materials, which releases available nutrients from their fixed state, is another example of input.


Output of Nutrients : Nutrients are moved out of an ecosystem and many become input to another ecosystem. For example, considered loss of nutrients like calcium and magnesium (from soil particle) occurs through runoff water, or through soil erosion. Significant amount of nitrogen may be lost in gaseous form by the denitrification process in soil. Harvesting of agricultural crops or transportation of logs from forest, represent nutrient loss from these ecosystems.

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In an undisturbed ecosystem, (ie., an ecosystem in which human activities are absent or nearly so) the input of nutrients may approximately equal the output of nutrients, rendering the nutrient cycle more or less balanced.

Generally, the absolute amounts of nutrient moving in (input) and moving out (output) of the ecosystem are much less than the amount of nutrients cycled within (amongst different components) the ecosystem. Sever disturbances in the ecosystem (e.g., Tree felling, insect outbreak, fire, soil erosion, etc.) may make the nutrient cycles unbalanced and the ecosystem unstable. The soil can be lost rapidly by erosion after removal of natural vegetation.

Internal Nutrient Cycling : Plants absorb varying amounts of nutrients from the soil. Due to decomposition of dead organic matter, nutrients are continuously regenerated and strored in soil and available to the plant. A dynamic state exists in soil, with nutrient regeneration and absorption occuring simultaneously.


The transfer of nutrients form the soil to plants by the process of nutrient absorption is known as uptake. The absorbed nutrients are metabolically incorporated in plants during growth. Periodically, nutrients are recycled i.e., brought back to soil through litter fall from vegetation, animal remains and faecal matter, etc. The overground, as well as root detritus decompose to regenerate the nutrients.

Eventually, nutrients contained in the detritus on soil surface and within, are regenerated by decomposition in plant-available forms.
When the uptake of nutrient exceeds the amount recycled (e.g., as in the case of a young growing forest), a fraction of the uptake is retained in the standing crop. This retension of balance nutrients in the standing crop leads to increase in nutrients content of the ecosystem. Thus, in a nutrient cycle :
Retention = Uptake – Recycle.

Rates of nutrient uptake, recycle and retention vary widely in different ecosystems. A large number of chemical methods are available for determining the amounts of different nutrients per unit weight of biomass of soil. By determining changes in the nutrient concentrations and biomass with time, the nutrient budget of the ecosystems can be computed.



 - Ecosystem, class 12, biology

Carbon Cycle :
It percent of carbon dissolved in ocean and this ocean reservoir regulates amount of CO2 in atmosphere.

The main source of carbon is atmosphere and in hydrosphere it is rocks of carbonates. Carbon present in lithosphere in the form of coal and petroleum. The carbon released from them is present in the atmosphere in the form of carbodioxide. The green autotrophs utilize CO2 from the air to synthesize food materials which is obtained by other organisms as food. Carnivors obtain their organic food from the herbivores. These carbonic matter produce


CO2 through the oxidation or respiration which dissolve in air or water and again utilized by the plants.

Annually 4 × 1013 kg carbon is fixed in biosphere through phosynthesis in biosphere.

ecosystem, biology


Nitrogen Cycle
Atomsphere is the only source of nitrogen 78% nitrogen is present in atmospheric air. Plants absorb nitrogen in the form of nitrate ions mainly.

Nitrogen cycle is completed in following steps
1. Nitrogen fixation -
In this process first of all some bacteria and blue green algae converts atmospheric nitrogen in to nitrogenous, compounds viz ammonia, amino acid or nitrate salts.
Bacteria – Rhizohbium, Aerorhizobium, Azospirillum
                Frankia, Clostridium, Azotobacter

Blue green algae – Oscillatoria, Anabaena, Aulosira, Nostoc → In flooded rice field in tropics


Note :
(1) Azotobacter is aerobic bacteria
(2) Clostridium is anaerobic bacteria
(3) Symbiotic relationship where the nitrogen fixing bacteria does not penetrate deep into host tissue, known as associative symbiosis. Azospirillum with grass paspalum notatum.

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3. Nitrogen assimilation –
Plants absorb nitrate from the soil and form protein. When consumers eat these plant proteins is transferred into consumer.

4. Ammonification –
Protein present in litter, is converted into ammonia by some ammonifying bacteria.
e.g. Bacillus vulgaris, Bacillus mycoides, Bacillus ramosus

5. Denitrification –
Some quantity of nitrate which is not used by plants is converted into nitrogen by denitrifying bacteria. e.g. Thiobacillus denitrificans, Pseudomonas denitrificans

Note : some nitrate washed out from the ecosystem through seepage.


 - Ecosystem, class 12, biology

Phosphorus Cycle

ecosystem, biology

Phosphorus is the main constituent of protoplasm,plasma membrane, bones and teeth. Main source of phosphorus is rocks. If comes from the weathering of phosphorus containing rock in the soil. Plants absorb this phosphrous from the soil and transfer this phosphate to animals and after the death of animals it is released again into the lithosphere by the action of decmposers.

Sometime some of the elements like phosphorus and calcium reach into the sea through water, from where they transform into rocks. They separate from the cycle for a long time so it is also known as sedimentary cycle.

But when these rocks break after sometime then this phosphorus is again made available to the sea plant or sea weeds, which pass into fish and sea birds. The excretory materials of birds on the rocks of sea shore is called Guano and and it is a source of phosphorus.

Plants absorb phosphate from the soil in the form of orthophosphate (Po43–)

Phosphorous cycle differ from nitrogen and carbon cycle in atmospheric input of phosphorous through rainfall is much smaller and gaseous exchange of phosphorous between organism and environment is negligeble, which both are considerable in Nitrogen and Carbon cycle.


Water Cycle
Water is indispensable for life. Sea is the main source of water on earth. Water is always present in the atmosphere in the form of water vapour. Water is also evaporated from other places from where it reaches into the atmosphere. These vapours form clouds in the atmosphere, condensation of water vapour forms clouds, moist, fog and ice at high altitudes. It comes again on he earth in above forms.

ecosystem, biology

Water cycle plays a significant role on the earth. Plants and animals receive water or absorb water. Water  participates in various metabolic activites of the body of organisms and again it is formed. Water is converted into food through the photosynthesis in plants. Water is also present in protoplasm of all organisms. This water again comes into the atmosphere through transpiration from the plants and evaporation and sweating from the animals. Thus this cycle goes on continuously. The oxygen cycle and hydrogen cycle is also found in the
ecosystem as above cycles.


Note :
1. Water cycle is diectly operated by solar radiation and it is under the control of forests.
2. The term "Cycle" is used for the movement of matter and the term "Flow " is used for the movement of energy.

Large ecosystem is called biome, mainly large aquatic and terrestrical ecosystem are called biomes. Altitude and latitude determine the boundary of biome.

ecosystem, biology

Types of world biom : From the poles towards the equators.
(i) Tundra Biome : 60-80ºN latitude.
(ii) Northern coniferous forest or Needle leaf forest : 40-60ºN latitude (Taiga or North wood)
(iii) Temperate Deciduous forest : 40-60ºN latitude or Temperate broad leaf forest.
(iv) Tropical Rain forest : 20-40ºN latitude.
(v) Tropical deciduous forest : 20-40ºN latitude.
(vi) Chaparral (Mediterranean scrub forest) Biome
(vii) Tropical Savanna Biome
(viii) Grassland Biome
(ix) Desert Biome.

Major Grasslands are :
Prairies - North America
Pampas - South America
Steppes - Europe and Asia
Tussocks - New zealand
Veldts - Africa


Main desert biomes are :
Sahara - North Africa
Tibet, Gobi, Thar - Asia
Gobi desert is cold desert.
Sahara and Thar deserts are hot deserts.

Major forest Biomes of India :
(i) Tropical Rain Forest Biome : Western Ghat and North-Eastern Himalaya.
(ii) Tropical Deciduous Forest : In Northern and Southern parts in plain and hilly areas.
(iii) Temperate Broad leaf forest : Western Himalaya.
(iv) Temperate Needle leaf or Coniferous forest : Himalaya.


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* Month in which rainfall is < 50 mm.

All the living and non living (Biotic + Abiotic) components of the earth (biomes) combine together to consitute a big eccosystem called Biospher. Biosphere is alos called Ecosphere.
The term ecosphere for biosphere was used by Cok.
1. Lithosphere –
The living components and non-living components present on the earth surface consititutes the lithosphere.

2. Hydrosphere –
All living components and non living components present in water consitutes the hydrosphere.

3. Atmosphere –
All livign components and non living compoments of air consituted the atmosphere.


ecosystem, biology


Note :
1. Biosphere (space ship or earth) is closd system for mineals and biosphere is an open system in regards with the energy.
2. Noo Sphere (Noo-mind, Sphere-domain) - Because of development of human civilisation biosphere is changed in to human dominating environment called noo sphere.





(i) Ecological efficiency - The percentage of energy transferred from one trophic level to the next is called ecological efficiency or food chain efficiency.

ecosystem, biology

(ii) Assimilation efficiency - It is the production of consumed energy that is assimilated.

ecosystem, biology

(iii) Net production efficiency -

ecosystem, biology

(iv) Photosynthetic efficiency -

ecosystem, biology

ecosystem, biology

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