Chapter 29 Ecosystem by TEACHING CARE online coaching classes Chapter 28 Organisms and Populations by TEACHING CARE online coaching classes

Chapter 29 Ecosystem by TEACHING CARE online coaching classes Chapter 28 Organisms and Populations by TEACHING CARE online coaching classes



The word ecosystem was coined by A.G. Tansley in 1935. This term is derived from two words, namely eco and system. Eco refers to environment and system refers to a complex coordinated unit. An ecosystem is a basic functional ecological unit. It consists of living organisms (biotic factors) and non–living substances (abiotic factors). It is an interacting system where the biotic and abiotic factors interact to produce an exchange of materials between the living and non–living factors. An ecosystem is a sum total of living organisms, the environment and the process of interaction between and within all parts of the system (Mathavan, 1974). According to Odum an ecosystem is the basic fundamental unit of ecology which includes both the organisms and the non–living environment each influencing the properties of the other and each is necessary for the maintenance of life. Pond is a suitable example for ecosystem. Lake is another ecosystem. Other examples of ecosystem are river, estuary, ocean, forest, grassland, town etc.

  • Structure : The structure of any ecosystem is formed of two components, namely :
    • Abiotic factors (ii) Biotic factors
  • Abiotic factors : The abiotic factors of an ecosystem include the non–living substances of the eg. Water, soil, air, light, temperature, minerals, climate, pressure etc. The biotic factors of the ecosystem depend on the abiotic factors for their survival.
  • Biotic factors : The biotic factor include the living organisms of the environment. e.g. Plants, animals, bacteria, viruses The biotic factors of an ecosystem are classified into three main groups, namely :

(a) Producers                (b) Consumers            (c) Reducers or Decomposers.

  • Producers : The organisms which carry out photosynthesis constitute the producers of an ecosystem. eg. Plants algae and bacteria. The producers depend on the abiotic factors of the ecosystem for producing energy. They are provided with Chloropyll is used in the synthesis of energy rich compounds with the utilization of abiotic factors like light, CO2, water and minerals. A portion of the energy synthesized, is used by the producers for their growth and survival and the remaining energy is stored for future use.
  • Consumers : Consumers are organisms which eat or devour other organisms. The consumers are further divided into three or more They are primary consumers, secondary consumers and tertiary consumers.
  • Primary consumers : They eat the products like plants, algae and The primary consumers are also called herbivores. Elton referred the herbivores as key industry animals. Rabbit, deer, etc., are primary consumers in a terrestrial ecosystem.


Abiotic factors                                                 Biotic factors

Producers                 Consumers           Reducers/Decomposers





Primary (Herbivores)

Secondary (Pri. Carnivores)

Tertiary (Sec. Carnivores)










  • Secondary consumers : They kill and eat the herbivores. They are also called carnivores. As these carnivores directly depend on herbivores, they are specifically called primary carnivores. Fox, wolf, etc. are the secondary consumers in a terrestrial
  • Tertiary consumers : They kill and eat the secondary consumers. They are also called secondary e.g., Lion, tiger, etc.
  • Reducers or Decomposers : The decomposers are heterotrophs organisms that break up the dead bodies of plants and their waste products. They include fungi and certain bacteria. They secrete enzymes. The enzymes digest the dead organisms and the debris into smaller bits or molecules. These molecules are absorbed by the reducers. After taking energy, the reducers release molecules to the environment as chemical to be used again by the
    • Typical ecosystem (Pond ecosystem) : A pond is a suitable example for ecosystem. It is a lentic fresh– water It contains shallow standing water. The pond ecosystem is formed of abiotic factors and biotic factors.
      • Abiotic factors : The abiotic factors of the pond ecosystem are water, CO2, O2 inorganic compounds, organic compounds, light, temperature, pressure, pH
      • Biotic factors : The biotic factors of the pond ecosystem are producers, consumers and
    • Producers : The producers synthesize the energy from abiotic substances. The producers of a pond include phytoplankton like diatoms, blue green algae (Oscillatoria), green algae, green flagellates (Volvox, Euglena, Chlamydomonas), rooted plants, submerged plants and floating
    • Consumers : Consumers eat other organisms. The organisms which depend on producers are called primary consumers or herbivores. e.g., Zooplankton (Cyclops, Daphnia, larvae of Chironomus etc), Dysticus (insect), Lymnaea (snail) The

primary consumers are eaten by the secondary consumers of carnivores. These carnivores are called primary carnivores because they are the first carnivores in the food chain. e.g., Small fishes, frogs etc. The secondary consumers are eaten by the tertiary consumers or secondary carnivores. e.g., large fish.

  • Reducers or Decomposers : The decomposers are organisms that break up the dead bodies of


organisms and their waste products.

Pond ecosystem




They include microbes like bacteria. They secrete enzymes. The enzymes digest the dead organisms and the debris into smaller bits or molecules. These molecules are absorbed by the reducers. After taking energy, the reducers release molecules to the environment as chemical to be used again by the producers.

  • Types of ecosystem : The ecosystem may be large, as large as the world or small, as small as a cow dung The biosphere of (The total life content of the world) is the major ecosystem. It comprises all other ecosystems.

(i) Mega ecosystem : The biosphere is formed of four mega ecosystems. They are as follows :

  • Marine ecosystem : It is the largest ecosystem of Fresh water ecosystem are two types :
  • Lotic : Runing water ecosystem as
  • Lentic : Still water ecosystem such as pond or It includes saline-water ecosystems like oceans, seas, estuaries, brackish waters, etc.
  • Limnic ecosystem : It includes all fresh water ecosystems like ponds, pools, lakes, rivers, streams,
  • Terresrial ecosystem : It includes the ecosystems of air, forests, grasslands, deserts,
  • Industrial or Artificial ecosystems : These are man made e.g., Crop land, city, town, etc.
  • Macro ecosystems : The four mega ecosystem is further divided into sub units called macro ecosystems. g., Forests. The terrestrial macro ecosystem is formed of many forest ecosystems.
  • Meso ecosystem : The macro ecosystem is further divided into meso ecosystem. For example, the forest ecosystem if formed of many meso ecosystems like deciduous forest, coniferous forests,
  • Micro ecosystem : The meso ecosystem is further divided into micro ecosystems, g., A low land in a forest, a mountain in a forest, etc. All ecosystems in the world are further divided into natural and artificial ecosystems.
  • Natural ecosystems : These are self–regulating systems without much direct human interference and e.g., Ponds, lakes, rivers, seas, oceans, grasslands, deserts, etc.
    • Dynamics of ecosystem : The various components of the ecosystem constitute an interacting They are connected by energy, nutrients and minerals. The nutrients and minerals circulate and recirculate between the abiotic and biotic factors of the ecosystem several times. The flow of energy, on the other hand, is one way, once used by the ecosystem, it is lost. The continuous survival of the ecosystem depends on the flow of energy and the circulation of nutrients and minerals in the ecosystem. Thus the dynamics (functions) of the ecosystem includes the following :


(i) Energy (ii) Primary production (iii) Secondary production (iv) Food chain
(v) Food web (vi) Trophic levels (vii) Energy flow             (viii) Ecological pyramids.
  • Energy : Energy is the ability of do The flow of energy is unidirectional in the ecosystem. The main source of energy for an ecosystem is the radiant energy or light energy derived from the sun. The amount of solar radiation reaching the surface of the earth is 2 Cals/ It is more or less constant and is called solar constant or solar flux. About 95 to 99% of the energy is lost by reflection. Plants utilize only 0.02% of the energy reaching earth. The light energy is converted into chemical energy in the form of sugar by photosynthesis.

6H2O + 6CO2 + Light ® 6C6H12O6 + 6O2

The sugar synthesized is utilized for many purposes :

  • It can be converted into starch and
  • It combines with other sugars to form



  • It combines with inorganic substances (N2, P, S) to form amino acids, protein, nucleic acids, pigments,
  • Some amount of sugar is oxidised during respiration and the energy is released to do various

C6H12O6 + 6O2 ® 6CO2 + 6H2O + Energy.

  • Primary production : Plants convert light energy into chemical energy in the form of sugar by The total amount of sugar and other organic materials produced in plants per unit area per unit time is called gross primary production. During photosynthesis respiration is also going on side by side. During respiration some amount of sugar is oxidised. Hence it is not easy to measure gross primary production. The total organic material actually present (biomass) in plants is called net primary production.

Net primary production = Gross primary production – Respiration. i.e.

Pn = Pg R

Where, Pg = Gross primary production

\            Pg = Pn + R      Pn = Net primary production

R = Respiration

Thus the amount of organic material produced during a given period of time per unit area is called primary production. The productivity is generally expressed in terms of grams or kilocalories per square meter per day or per year. If Pg equals R no storage of energy occurs. When Pg is less than R, productivity decreases. When Pg is greater then R, productivity increases.

Measurement of primary production : Primary production refers to the amount and the rate of energy produced by autotrophs. There are many methods to measure the primary production. They are the following :

  • Harvest method : In this method the plants grown on a particular area are harvested at ground level and their weight is taken. They are dried and again weighed. This is done at regular intervals. The primary production is expressed in terms of biomass or mass per unit area per unit
  • Carbon-dioxide assimilation method : Plants utilize carbon dioxide for So the rate of photosynthesis can be calculated by calculating the amount of carbon dioxide utilized by plants per unit time. The incorporation of carbon dioxide in photosynthesis can be determined by using infrared gas analyzer. With the help of this analyzer, it is possible to measure the amount of carbon dioxide entering or leaving an air tight chamber of known volume.
  • Oxygen production method : This method is used to measure primary production in aquatic ecosytem. In this method the amount of oxygen produced per unit time is taken as an index to measure the rate of For this, light and dark bottle technique is used. Samples of water containing the autotrophs are collected in a light bottle (transparent bottle) and in a dark bottle. The light bottle allows light to enter in the same depth from which the sample is collected. After a certain period of time the amount of oxygen present in the two bottles is calculated by titration using sodium thiosulphate. (Winkler’s method). In dark bottle photosynthesis does not occur but respiration occurs. In light bottle both respiration and photosynthesis occur. The rate of photosynthesis is calculated by calculating the amount of oxygen present in the two bottles.
  • Radio isotope method : This method is similar to the oxygen producing method. In this method a known quantity of C14 is introduced into the light and dark bottles along with the sample and the bottles are





suspended for six hours. During this period the C14 is incorporated into the protoplasm of the autotrophs. The autotrophs are filtered and dried. After drying the radioactivity is measured. The amount of radioactivity is proportionate to the amount of carbohydrate produced.

  • Secondary production : The energy trapped by the producers (primary production) is utilized by the The producers are directly consumed by the herbivores that are eaten by the primary carnivores that in turn are consumed by the secondary carnivores. The consumers store some amount of energy in their tissues. This energy, stored by the consumers, is called secondary production. Only about 10 to 20% of the primary production is converted into secondary production. The remaining 80 to 90% is lost by the consumers in the form of faeces.
  • Food chain : The biotic factors of the ecosystem are linked together by food. For example, the producers form the food for the herbivores. The herbivores form the food for the carnivores. The sequence of the eaters being eaten is called food chain to another trophic

Producers ® Herbivores ® Carnivores

The various steps in a food chain are called trophic levels. Owing to repeated eating being eaten, the energy is transferred from one trophic level.

Phytoplankton ® Zooplankton ® Fishes ® Snakes Tr. L1                          Tr. L2 Tr. L3 Tr. L4

Plants ® Mouse ® Snake ® Hawk = Grassland Plants ® Goat ® Man ® Lion = Forest

This transfer of energy from one trophic level to another is called energy flow. A typical food chain can be seen in a pond ecosystem. The algae and phytoplakton are eaten by the zooplankton. The zooplankton are eaten by fishes which are eaten by snakes.

Types of food chains : The food chains are of two types, namely :

  • Grazing food chain


  • Detritus food chain

A food chain – 1. Producer grass 2. Primary consumer-grasshopper 3- Secondary consumer-Frog 4- Tertiary consumer-snake 5- Quaternary Top consumer-Owl


  • Grazing food chain : This food chain starts from plants, goes through herbivores and ends in carnivores. Plants ® Herbivores ® Primary Carnivores ® Carnivores

This type of food chain depends on the autotrophs which capture the energy from solar radiation. A few chains are given below :

Grass ® Grasshopper ® Lizard ® Hawk Grass ® Mouse ® Snake ® Hawk



Phytoplankton ® Zooplankton ® Fish ® Snake.

The grazing food chain is further divided into two types, namely :

  • Predator chain : In predator food chain one animal captures and devours another The animal which is eaten is called prey and the animal which eats other animals is called predator. The predator food chain is formed of plants, herbivores, primary carnivores, secondary carnivores and so on.
  • Parasitic chain : The plants and animals of the grazing food chain is infected by parasites. The parasites derive their energy from their Thus the parasitic chain within the grazing food chain is formed.
  • Detritus food chain : It starts from dead organic matter and ends in inorganic compounds. There are certain groups of organisms which feed exclusively on the dead bodies of animals and plants. These organisms are called detritivores. The detritivores include algae, bacteria, fungi, protozoans, insects, millipeds, centipeds, crustaceans, mussels, clams, annelid worms, nematodes, ducks, These organisms ingest and digest the dead organic materials. Some amount of energy is trapped and the remainder is excreted in the form of simple organic compounds. These are again used by another set of detritivores until the organic compounds are converted into CO2 and water.

Dead organic materials ® Detritivores ® CO2 + H2O

Linking of grazing and detritus food chains – The two main food chains can not operate independently. They are interconnected at various levels. According to Wilson and Bossert (1971) the stability of the ecosystem is directly proportional to the number of such links. The detritus feeders obtain energy from the dead bodies of animals and plants which are components of the grazing food chain. Again some of the detritus feeders are eaten by the consumers of the grazing food chain. For example, in a pond ecosystem earthworms belonging to the detritus food chain are eaten by fishes belonging to the grazing food chain.

  • Food web : In an ecosystem the various food chains are interconnected with each other to form a net work called food The interlocking of many food chains is called food web. Simple food chains are very rare in nature. This is because each organism may obtain food from more than one tropic level. In other words, one organism forms food for more than one organisms of the higher trophic level.

Examples : In a grassland ecosystem, grass is eaten by grasshopper, rabbit and mouse. Grasshopper is eaten by lizard which is eaten by hawk. Rabbit is eaten by hawk. Mouse is eaten by snake which is eaten by hawk. In addition hawk also directly eats grasshopper and mouse. Thus there are five linear food chains which are inter connected to form a food web.

  • Grass ® Grasshopper ® Hawk
  • Grass ® Grasshopper ® Lizard ® Hawk
  • Grass ® Rabbit ® Hawk
  • Grass ® Mouse ® Hawk
  • Grass ® Mouse ® Snake ® Hawk

This is a very simple food web. But in any ecosystem the food web is more complex. For example, in the grassland itself, in addition to hawk, there are many other carnivores such as vulture, crow, fox, man, etc.




Significance of food web : Food webs are very important in maintaining the stability of an ecosystem. For example, the deleterious growth of grasses is controlled by the herbivores. When one type of herbivores increase in number and control the vegetation. Similarly, when one type of herbivorous animal becomes extinct, the carnivore predating on this type may eat another type of herbivore.

Fig : Food web in a grassland ecosystem (Producers, Herbivores, Carnivores)

  • Trophic levels : Each food chain contains many steps like producers, herbivores, primary carnivores and so Each step of the food chain is called trophic level. The number of trophic levels in a food chain in restricted to 5 or 6. Green plants make first trophic level.

T1 ® Producers – (Trees, Plants, Grass)

C1 or T2 – Herbivorous – (Cow, Grass hopper, Zooplankton) C2 or T3 – Primary carnivorous (Dog, Frog, Lizard)




C3 or T4 – Secondary carnivorous (Hawk, Fox, Snake)

C4 or T5 – Tertiary carnivorous or Top carnivorous (Tiger, Lion, Man) Phytoplankton ® Zooplankton ® Fishes ® Snakes

Tr. L1                  Tr. L2             Tr. L3      Tr. L4

  • Energy flow : The transfer of energy from one trophic level to another trophic level is called energy The flow of energy in an ecosystem is unidirectional. That is, it flows from the producer level to the consumer level and never in the reverse direction. Hence energy can be used only once in the ecosystem. But the minerals circulate and recirculate many times in the ecosystem. A large amount of enregy is lost at each trophic level. It is estimated that 90% of the energy is lost when it is transferred from one trophic level to another. Hence the amount of energy available decreases from step to step. Only about 10% of the biomass is transferred from one trophic level to the next one is a food chain. And only about 10% chemical energy is retained at each


trophic level. This is called 10% law of Lindeman (1942). When the food chain is short, the final consumers may get a large amount of energy. But when the food chain

Energy flow diagram: L = Total light, La = Absorbed light, PG = Gross production, PN = Net production, I = Energy intake, A = Assinilated energy, NA = Non assimilated energy, NV = Unused energy, R = Respiratiory energy loss. Bottom line shows the order of magnitude of energy losses expected or major transfer points starting with the solar in put of 3000 Kcal per square meter per day (ODUM 1963)


is long, the final consumer may get a lesser amount of energy. As shown in the figure. about 3000 K cal of light falls

on the green plants. Of this approximately 50% (1500 K cal) is absorbed. Of the 50% only 1% (15 K cal) is converted at the first trophic level. Thus the net primary production is merely 15K cals. Secondary productivity (P2 and P3) is 10% (1.5 K cal & 0.3 K cal) at the herbivores and carnivores level.

  • Ecological pyramids : The number, biomass and energy of organisms gradually decrease from the producer level to the consumer This can be represented in the form of a pyramid called ecological pyramid. Ecological pyramid is the graphic representation of the number, biomass, and energy of the successive trophic levels of an ecosystem. The use of ecological pyramid was first described by Charles Elton in 1927. In the ecological




pyramid, the producer forms the base and the final consumer occupies the apex. There are three types of ecological pyramids, namely :

(a) The pyramid of number : The number of individuals at the trophic level decreases from the producer level to the consumer level. That is, in an ecosystem the number of producers is far high. The number of herbivores is lesser than the producers. Similarly, the number of carnivores is lesser than the herbivores.


Fig : Pyramid of numbers in a cropland ecosystem                       Fig :Pyramid of numbers in a pond ecosystem



  • In a cropland ecosystem : In croplands the crops are more in The grasshoppers feeding on crop plants are lesser in number. The frogs feeding on grasshopper are still lesser in number. The snakes feeding on frogs are fewer in number.

Crop ® Grasshopper ® Frogs ® Snakes ® Hawks

  • In a grassland ecosystem : In a grassland the grasses are there in large The consumers decrease in the following order.

Grass ® Grasshopper ® Lizard ® Hawk Grass ® Rabbit ® Fox ® Lion

  • In a pond ecosystem : The number in a pond ecosystem decreases in the following

Phytoplankton ® Zooplankton ® Fishes ® Snakes


Top Carnivores

T4                                                e.g. Tigers, Lions

T3                                                                                     e.g. Wolfs

T2                                                                                                     e.g. Birds, Dears


T1                                                                                        e.g. Trees







  • The pyramid of biomass : Biomass refers to the total weight of living matter per unit In an ecosystem the biomass decreases from the producer level to the consumer level.
  • In a grassland : In a grassland the biomass of grasses is the maximum, and it gradually decreases towards the consumer level in the following

Grass ® Mouse ® Snake ® Hawk Grass ® Grasshopper ® Lizard ® Hawk

Fig : Pyramid of biomass in a grassland ecosystem                                                  Fig :Pyramid of energy in a forest ecosystem

  • In a forest : In a forest the biomass or trees is the maximum and the biomass of the top consumer is the The decrease in weight occurs in the following order :

Plants ® Deer ® Fox ® Tiger Plants ® Rabbit ® Fox ® Lion

  • Pyramid of energy : The energy flow in an ecosystem from the producer level to the consumer At each trophic level 80 to 90% of energy is lost. Hence the amount of energy decreases from the producer level to the consumer level. This can be represented in a pyramid of energy level to the consumer level. This can be represented in a pyramid of energy.
  • In a grassland : In a grassland green plants trap the maximum light energy. The energy gradually decreases towards the top consumer

Grass ® Grasshopper ® Lizard ® Hawk Grass ® Rabbit ® Fox ® Lion

Grass ® Mouse ® Snake ® Hawk

  • In a pond : In a pond maximum energy is trapped by the phytoplankton. Then the amount of energy decreases towards the top–consumer

Phytoplankton ® Zooplankton ® Fish ® Snake Phytoplankton ® Zooplankton ® Small fish ® Large fish




  • Inverted pyramids : In most of the ecosystems the number and biomass of producers are more and those of consumers are less. This type of ecosystem has a pyramid where the apex is pointed upwards. This type of pyramid is called upright pyramid. In some ecosystems the number and the biomass of the producers are less and those of consumers are more. This type of ecosystem producers a pyramid where the apex is directed downwards. This type of pyramid is called inverted Inverted pyramid occurs in number and biomass. The pyramid of energy is always upright.

Fig : Inverted pyramid of numbers in a tree ecosystem                         Fig : Inverted pyramid of biomass in a pond ecosystem


  • Inverted pyramid of numbers : When the ecosystem contains lesser number of producers and more number of consumers, the pyramid will be inverted in shape. Inverted pyramid occurs in a tree ecosystem. A single tree (producer) contains many fruit eating birds (primary consumers). The birds contain numerous parasites (secondary consumers).
  • Inverted pyramid of biomass : When the biomass of producers is less and that of consumers is more the pyramid will have inverted shape. It occurs in a pond or lake ecosystem. Here the biomass of diatoms and phytoplankton are negligible as compared to that of crustaceans and small


  • Definition : Each of the major terrestrial ecosystems or distinctive terrestrial areas with their group of climax plants and associated animals constitutes biomes. A biome is the largest terrestrial community. Rainfall, temperature range, nature of soil, barriers, latitude and altitude determine the nature and extent of
  • Major biomes of world : Biomes are often classified in seven categories :
    • Tropical rain forests (ii) Savannahs  (iii) Deserts             (iv) Temperate grasslands

(v) Temperate deciduous forests    (vi) Taiga              (vii) Tundra




  • Tropical rain forests : The tropical rain forest, a biome occurs in regions of high temperature (average 25°C) and high rainfall (200-450 cm per year). These tropical rain forests occur in Central America, around Amazon basin in South America, in Africa and in South-East
  • This biome is characterized by multistoried vegetation (upto five distinct layers or storeys of vegetation). Further maximum biodiversity on land is shown by this biome and it is estimated that one half to two-thirds of all species of terrestrial plants and insects live in tropical
  • Lianas (vascular plants rooted in soil and they only get support of trees for climbing to top) and epiphytes (air plants) are common in this biome due to excess of moisture. Further giant trees of the tropical forest support a rich and diverse community of animals on their
  • No one species dominates in this
  • The productivity of this biome is
  • The trees of this biome posses buttressed trunks and phenomenon of cauliflory (presence of flowers and fruits on main trunk and main branches) is common in this
  • Savannahs : Like tropical forests, savannahs are found near the equator but in areas having less annual rainfall (90-150 cm/year). Some areas near the equator experience prolonged dry seasons. The heat, periodic dryness and poor soils cannot support a forest but have led to evolution of tropical open grasslands with scattered shrubs and
  • The vegetation of this biome support large grazing herbivores like buffalo, zebra, , which are food for carnivores like lions, tigers, etc. The savannah also supports a large number of plant eating invertebrates like mites, grasshoppers, ants, beetles and termites.
  • The termites are one of the most important soil organisms in
  • Indian tropical grasslands are not true savannahs but these are the result of destruction and modification of tropical deciduous forests by cutting, grazing and
  • Deserts : These are the biomes that have 25 cm (10 inches) or less of precipitation
  • Sahara of North Africa, Thar of West Asia and Gobi of Asia are most important
  • Annual plants are abundant in deserts and tide over unfavourable dry season in the form of seeds. Succulent plants are characteristics of Trees and shrubs present in deserts have deep roots.
  • Desert animals have also fascinating adaptations that enable them to adjust with limited water
  • Desert plants show phenomenon of Allelopathy, e., they secret some chemical substances which inhibit the growth of plants growing in their near vicinity.
  • Deserts show poor biodiversity and their productivity is
  • Temperate grasslands : Temperate grasslands experience a greater amount of rainfall than deserts but a lesser amount than savannahs. They occur at higher latitudes than savannahs but like savannahs are characterized by perennial grasses and herbs of grazing

(a) Temperate grasslands have different names in different parts of the world, e.g., Prairies of North America, Steppes of Russia, Veldts of South Africa, Pampas of South America, Pusztas of Hungary and Tussocks of New Zealand.




  • Temperate deciduous forests : Temperate deciduous forests occur in areas having warm summers, cold winters and moderate amount of precipitation (75 – 150 cm annually). The trees of this forest loose their leaves during autumn and remain dormant throughout winter (term ‘deciduous’ derived from Latin word meaning ‘to fall’). These forests are present in Eastern United States, Canada and extensive region in
  • In temperate forest biome, there is an upper canopy of dominant trees like beech, oak, birch, maple, followed by lower tree canopy and then a layer of shrubs beneath.
  • Animal life in this biome is abundant on the ground as well as on the
  • Taiga : The taiga or northern coniferous forests or boreal forests consist of evergreen, cone bearing trees like spruce, hemlock and fir and extend across vast areas of Eurasia, and North
  • The taiga is characterized by long, cold winters with little
  • The harsh climate limits productivity of the taiga The cold temperatures, very wet soil during the growing season and acids produced by fallen conifers needles and Sphagnum inhibit full decay of organic matter, due to which thick layers of semidecayed organic material called peat is formed, which acts as energy source.
  • Tundra : The tundra encircles the top of the This biome is characterised by desert like levels of precipitation (less than 25 cm annually), extremely long and cold winters and short warmer summers.
  • Tundra is uniform in appearance and is dominated by scattered patches of grasses, sedges and Some small trees do grow but are confined to margins of streams and lakes (In general treeless).
  • Tundra is a biome of low diversity and low
  • The precipitation that falls remains unavailable to plants for most of the year because it freezes. During the brief arctic summer, some of the ice melts and permafrost (or permanent ice) found about a meter down from the surface, never melts and is impenetrable to both water and roots. However, the alpine tundra found at high elevation in temperate or tropical regions does not have this layer of
  • Indian biomes : Indian forests are classified into three major types based on temperature are tropical, temperate,

Aquatic biomes


Marine                                                                 Others

  • The marine environment : It is characterized by its high concentration of salt (about 3.5 percent in open sea) and mineral ions (mostly sodium and chloride followed by sulphur, magnesium and calcium).
  • The vertical zones of the ocean are determined on the basis of availability of light for photosynthesis. The lighted upper 200 metres form the photic or euphotic The next zone upto the depth 200–2000 metres gets less light which is insufficient for photosynthesis form the aphotic zone. Below 2000 metre is the area of perpetual darkness, the abyssal zone.
  • Three major environments may be recognized in the ocean basin :
  • The littoral zone : The sea floor from the shore to the edge or the continental
  • The benthonic zone : The sea floor along the continental slope and the aphotic and abyssal
  • The pelagic zone : Constituting the water of the ocean



·         Marine life : It can be grouped into three main categories :

  • Plankton : These are passively drifting or floating Most of these minute organisms, plankton includes photosynthesizing organisms like diatoms (phytoplankton) as well as heterotrophic organisms like small crustaceans (zooplanktons).
  • Nektons : These consist of actively moving organisms with well developed locomotory
  • Benthonic organisms : These are found along the floor of the sea bed and include creeping, crawling or sessile
  • Other (Lakes and Ponds) : Lakes and ponds are stagnant fresh water bodies and are found practically in every Many lakes are direct or indirect result of glaciation. Others are natural or man made depression filled with water. The relatively shallow lakes, called eutrophic lakes, have a rich accumulation of organic products e.g., Dal lake of Kashmir. Generally deep lakes, often with the steep and rocky sides, are poor in circulating nutrients like phosphates. These are called oligotrophic lakes. Some of the lakes contain a saline or brackish water (Sambar lake of Rajasthan).

All the thousands of ecosystems together constitute the biosphere, which exists as a thin envelope around the earth’s surface. The global environment consists of three main sub division :

  • Hydrosphere : All the water (liquid) component of the oceans, seas, rivers and other island water
  • Lithosphere : The solid components of the earth crust, rocks, soil and minerals.
  • Atmosphere : The gaseous cover which envelops the hydrosphere and the lithosphere and the The entire inhabited part of the earth and its atmosphere (including the living and the non-living components) forms the biosphere.

As a result of manipulation by man, the biosphere has become transformed into a human dominated environment of noosphere (noo = mind).

  • The concept of biosphere : It has been evolved by the man and biosphere programme (MAB) of the India has identified 14 areas as biosphere reserves. Of these, the Nilgiri biosphere reserve, including parts of Karnataka, Kerala and Tamil Nadu, was declared in 1986 (first one) and the Nanda Devi biosphere reserve in 1988.

Important Tips

  • The word ‘ecosystem’ was coined by G. Tansley in 1935.
  • Energy is the ability of do The flow of energy is unidirectional in the ecosystem.
  • The main source of energy for an ecosystem is the radiant energy derived from the
  • The energy trapped by the producers is utilized by the
  • Every food chain contains levels like producers, herbivores, primary carnivores and Each level is termed as “Trophic–level”.
  • The number of trophic levels in a food chain cannot be more than 5 or
  • The pyramid of energy is always
  • Upright pyramid occurs in energy number and
  • Flora : A list of all different types of plants exist in an Biosphere whole of the environment (including atmosphere, Lithosphere and hydrosphere) where life exists.
  • Biome: large ecosystem which are always characterised by certain specific geographic features are called
  • Tundra biome is called treeless