ECOSYSTEM | STRUCTURE AND FUNCTIONSFlame Institute

The word ecosystem was coined by A.G. Tansley in 1935. 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.

Structure : The structure of any ecosystem is formed of two components, namely :

(1) Abiotic factors : The abiotic factors of an ecosystem include the non–living substances of the environment. e.g., Water, soil, air, light, temperature, minerals, climate, pressure etc. The biotic factors of the ecosystem depend on the abiotic factors for their survival.

(2) Biotic factors : The biotic factor include the living organisms of the environment. e.g., Plants, animals, bacteria, viruses etc. The biotic factors of an ecosystem are classified into three main groups, namely :

(i) Producers : The organisms which carry out photosynthesis constitute the producers of an ecosystem. e.g., Plants algae and bacteria.

(ii) Consumers : Consumers are organisms which eat or devour other organisms. The consumers are further divided into three or more types. They are primary consumers, secondary consumers and tertiary consumers.

(a) Primary consumers : They eat the products like plants, algae and bacteria. The primary consumers are also called herbivores.

(b) 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 ecosystem.

(c) Tertiary consumers : They kill and eat the secondary consumers. They are also called secondary carnivores. e.g., Lion, tiger, etc.

(iii) 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 producers.

(iv) Other heterotrophs

(a) Scavengers or Detrivores : They feed on corpses, e.g., Vulture, Carrion Beetle. They help in quick disposal of dead bodies. In the process they also leave small fragments for decomposers.

(b) Parasites : They obtain nourishment from a living host without capturing or killing the same. Parasites obtain food from all categories of organisms. Common parasites are bacteria, fungi some worm and some insects.

Types of ecosystem

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

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

(i) Marine ecosystem : It is the largest ecosystem of earth. Fresh water ecosystem are two types :

(a) Lotic : Running water ecosystem as river.

(b) Lentic : Still water ecosystem such as pond or lake. It includes saline-water ecosystems like oceans, seas, estuaries, brackish waters, etc.

(ii) Limnic ecosystem : It includes all fresh water ecosystems like ponds, pools, lakes, rivers, streams, etc.

(iii) Terrestrial ecosystem : It includes the ecosystems of air, forests, grasslands, deserts, etc.

(iv) Industrial or Artificial ecosystems : These are man made ecosystems. e.g., Crop land, city, town, etc.

(2) Macro ecosystems : The four mega ecosystem is further divided into sub units called macro ecosystems. e.g., Forests. The terrestrial macro ecosystem is formed of many forest ecosystems.

(3) Meso ecosystem : The macro ecosystem is further divided into meso ecosystem. For example, the forest ecosystem is formed of many meso ecosystems like deciduous forest, coniferous forests, etc.

(4) Micro ecosystem : The meso ecosystem is further divided into micro ecosystems, e.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.

(5) Natural ecosystems : These are self–regulating systems without much direct human interference and manipulations. e.g., Ponds, lakes, rivers, seas, oceans, grasslands, deserts, etc.

Forest ecosystem : Forests are natural plant communities with dominance of phanerogams. In India forests occupy approx. 1/10 of the land area. Indian forests can be divided into the 4 broad categories.

Tropical (wet evergreen, semi-evergreen, moist deciduous and dry deciduous).
Subtropical
Temperate
Alpine

(1) Abiotic components : This includes inorganic and organic substances present in the atmosphere and soil. The climate (temperature, light, rainfall etc.) and soil (minerals) vary from forest to forest. In addition to minerals the occurrence of litter is the characteristic feature of majority of forests. Through litter decomposition approx. 90% energy trapped in the ecosystem by autotrophs dissipates into space as heat energy. The litter fall increases with decreasing latitudes.

(2) Biotic components

(i) Producers : They are represented mainly by trees but shrubs and ground flora are also found. Depending upon the kinds of forest the flora varies.

(ii) Consumers

(a) Primary consumers (herbivores) are small animals feeding on tree leaves, include ants, beetles, flies, bugs, spiders, leaf hoppers etc. neelgai, deer, elephants, moles, squirrels and fruit bats are large animals which feed upon shoots and/or fruits.

(b) Secondary consumers are different kinds of birds, snakes, lizards, feeding on primary consumers.

(iii) Decomposers : Streptomyces (sps. of Angiococus, Bacillus and Pseudomonas) and Fungi (Aspergillus, Polyporus, Alternaria, Fusarium, Trichonderma) are helpful in decomposing the litter. Further litter decomposition found to be slow in cooler and drier areas, therefore, sometimes its accumulation on the soil surface makes a thick layer.

Fresh water pond ecosystem : A pond is a suitable example for ecosystem. It is a lentic fresh–water ecosystem. It contains shallow standing water. The pond ecosystem is formed of abiotic factors and biotic factors.

(1) Abiotic factors : The abiotic factors of the pond ecosystem are water, CO₂, O₂ inorganic compounds, organic compounds, light, temperature, pressure, pH etc.

(2) Biotic factors : The biotic factors of the pond ecosystem are producers, consumers and reducers.

(i) 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 plants.

(ii) 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) etc. The primary consumers are eaten by the secondary consumers or 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.

(iii) Reducers or Decomposers : Several bacteria, fungi and actinomycetes represent this group e.g., Aspergillus, Saprolegnia.

Dynamics of ecosystem : The various components of the ecosystem constitute an interacting system. They are connected by energy, nutrients and minerals. 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 :

(1) Energy : Energy is the ability to do work. 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/sq.cm/min. 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

(2) Primary production : Plants convert light energy into chemical energy in the form of sugar by photosynthesis. 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

\ Pg = Pn + R

Where, Pg = Gross primary production

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.

(3) Secondary production : The energy trapped by the producers (primary production) is utilized by the consumers. 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.

(4) 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 level.

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.

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 :

(i) Grazing food chain : This food chain starts from plants, goes through herbivores and ends in carnivores.

Plants® Herbivores ® Primary Carnivores ® Sec. 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 : (a) Predator (b) Parasitic.

(ii) 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, etc.

(5) Food web : In an ecosystem the various food chains are interconnected with each other to form a net work called food web. 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.

Example : In a grassland ecosystem

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

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.

(6) Trophic levels : Each food chain contains many steps like producers, herbivores, primary carnivores and so on. 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

(7) Energy flow : The transfer of energy from one trophic level to another trophic level is called energy flow. 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 energy 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 is long, the final consumer may get a lesser amount of energy.

(8) Ecological pyramids : The number, biomass and energy of organisms gradually decrease from the producer level to the consumer level. 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 :

(i) 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.

In a cropland ecosystem : In croplands the crops are more in numbers. 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 numbers. 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 order.

Phytoplankton ® Zooplankton ® Fishes ® Snakes

(ii) The pyramid of biomass : Biomass refers to the total weight of living matter per unit area. 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 order.

Grass ® Mouse ® Snake ® Hawk

Grass ® Grasshopper ® Lizard ® Hawk

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

Plants ® Deer ® Fox ® Tiger

Plants ® Rabbit ® Fox ® Lion

(iii) Pyramid of energy : The energy flow in an ecosystem from the producer level to the consumer level. 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 level.

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 level.

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 produces a pyramid where the apex is directed downwards. This type of pyramid is called inverted pyramid. Inverted pyramid occurs in number and biomass. The pyramid of energy is always upright.

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 fishes.

Importance of ecosystem

(1) Energy : Study of ecosystems provides information about amount of energy flowing into them, its harvesting and availability at various levels.

(2) Biogeochemical cycling : Density of ecosystem is governed by degree of biogeochemical cycling and the amount of inorganic nutrients entering the ecosystem from outside.

(3) Food webs : Each ecosystem has a number of food webs. The knowledge of food webs is helpful to restore a degraded ecosystem and prevent unscientific exploitation of different ecosystems.

(4) Protection : Each ecosystem whether natural or man-made requires protection from pollutants and pests.

(5) Inter-relationships : Study of ecosystems gives information about inter-relationships amongst various types of organisms as well as between organisms and their abiotic environment.

(6) Carrying Capacity : By knowing the carrying capacity of an ecosystem, it can be known as to the number of producers and consumers which can be supported by that ecosystem.

(7) Inputs : The shortage of inputs can be known and corrected.

? Producers are also referred to as transducers as they change light energy in to chemical energy.

? Food webs are very important in maintaining the stability of an ecosystem. According to Wilson and Bossert (1971) the stability of the ecosystem is directly proportional to the number of such food links.

? The shallow water region of the shore is called neritic zone, it extends to a width of 16 to 240 kms and to a depth of 200 m.

? Coral reefs are highly productive ecosystem. According to johannes (1970) corals are the most productive, taxanomically diverse and asthetically celebrated of all the communities.

? Estuary is the ecotone of marine habitat and fresh water habitat.

? Epilimnion : Upper stratum of (lake) water exposed to solar radiations–warm in summer and cooler in winter circulates.

? Hypolimnion : Basal stratum of (lake) water which is always cool.

? In detritus ecosystem, producers are absent.

? Ecotone : The zone of transition between two nearby ecosystems is called as ecotone

? Energy content are determined by igniting the plant contents in O₂ bomb calorimeter.

Ecosystem

In ecosystem lithosphere is concerned with

(a) Gases (b) Minerals

Which of the following is producer of plant kingdom

(a) Melia (b) Ficus

The net primary productivity of an ecosystem is

(a) Total weight of green plants – respiratory losses

(b) Total weight of green plants + respiratory losses

(d) None of the above

Primary producer of an ecosystem is

(a) Herbivores (b) Carnivores

Which of the following are consumers of second order

(a) Herbivores (b) Carnivores

When food energy passes from herbivores to carnivores

(a) Some energy is increased (b) Some energy is decreased

What is studied under the ‘‘microcosm’’

(a) Ecosystem (b) Livings

Which of the cycle is concerned with energy flow in the ecosystem

(a) Food cycle (b) O₂ cycle

In a given ecosystem number of individuals in species remain more or less constant over a period of time. The constancy of number is maintained by

(a) Parasite (b) Predators

Which group of living organisms given below is a link in food chain between green plants and hawk

(a) Grasshopper, frog and snake

(b) Grasshopper, rat and snake

(d) Earthworm, hen and rat

Man–engineered ecosystem is

(a) Forest (b) Grassland

Y–shaped energy flow models have

(a) Single channel (b) Two channels

Estuary is

(a) Fresh water zone

(b) Sea water zone

(d) None of these

Shallow lakes with rich organic products are called

[JIPMER 1990]

(a) Eutrophic (b) Oligotrophic

Animals which occupy the same trophic level [CPMT 1991]

(a) Tiger and bear (b) Deer and bees

Food chains are met with only in the

[MP PMT 1999; CBSE PMT 2001]

(a) Sea (b) Cities

The ecosystem of a pond is referred as [CPMT 2000]

(a) Lotic (b) Lentic

1	c	2	b	3	c	4	a	5	b
6	d	7	b

(c) Because here man tries to control the biotic community as well as the physiochemical environment.
(c) Estuary is the tidal mouth of river or coastal bay where there is mixing of fresh and sea water. It is also one of the most productive ecosystems due to rapid circulation of nutrients and quick removal of waste products.
(d) The biotic factors (living organisms) of the ecosystem are linked together by food. Hence food chain are present in the cities, forests and seas.
(b) Lentic is the ecosystem of still water such as pond or lake.

***

The bacteria which attack dead animals are

(a) First link of the food chain and are known as primary producers

(b) Second link of the food chain and are herbivorous

(d) The end of food chain and are decomposers

Which one statement is correct regarding man made ecosystem

(a) They are highly efficient

(b) They are poor in diversity

(d) All are correct

Phosphorus usually becomes a limiting factor at certain times of the year in which ecosystem

(a) Aquatic ecosystem (b) Grassland ecosystem

Food and energy relationships among living components of ecosystem is generally referred as

(a) Biocoenosis (b) Microcosm

Detritus food chain starts from

(a) Dead organic matter (b) Green plants

In ecological crisis, whom interference play important role

(a) Green plants

(b) Human

(d) None of these

Whale is

(a) Primary producer

(b) Carnivorous secondary consumer

(d) Herbivorous

The above represents

(a) Food chain (b) Food web

A natural ecosystem

(a) Depends on man (b) Depends on plants

Which of the following in an ecosystem exhibits one–way flow rather than cyclic flow

(a) Potassium (b) Carbon

Dynamic aspect of an ecosystem is

(a) Producer and energy flow

(b) Producer and mineral cycles

(d) Energy flow and mineral cycles

Which of the following is a man made artificial ecosystem

(a) Grassland ecosystem

(b) Agro–ecosystem

(d) Forest ecosystem

Most important determinant of marine ecosystem is

(a) Rainfall

(b) Geographical location

(d) All the above

Plankton, nekton and benthos are not the components of

(a) River ecosystem (b) Oceanic ecosystem

In lake ecosystem the population rise or its explosion is termed

(a) Tide (b) Bloom

Micro–consumers are

(a) Primary consumers (b) Secondary consumers

The trophic level of Cuscuta, Orobanche and Albugo is

(a) Decomposer (b) Primary producer

The trophic level of mushroom and Monotropa is

(a) Producer (b) Primary consumer

The trophic level of S–bacteria and cyanobacteria is

(a) Producer

(b) Consumer

(d) Phagotroph

If plant (producers) of an ecosystem die, then the system

(a) Cannot produce food

(b) Is seriously affected

(d) Is not much affected

The order of organism in an aquatic food chain is

(a) Bacteria ® Seal ® Diatom ® Fish ® Crustacea

(b) Crustacea ® Seal ® Fish ® Polar Bear ® Diatom

(d) Diatom ® Crustacea ® Fish ® Seal ® Bacteria

An ecosystem resists change because it is in a state of

(a) Homoeostasis (b) Regular illumination

In an ecosystem, there are more prey than predators. This relationship is called

(a) Food webs

(b) Predator–prey relationship

(d) Succession

Pyramid of number becomes partly inverted partly erect for

(a) Aquatic ecosystem (b) Terrestrial ecosystem

Idea of productivity of an ecosystem can be had from

(a) Pyramid of number (b) Pyramid of biomass

The pyramid of biomass and the pyramid of number represent

(a) The rate of energy flow

(b) The rate of food production

(d) Relationship among organisms

The pyramid of energy is the best representation of an ecosystem because it indicates

(a) Relation of all plants and animals

(b) Total energy present in an ecosystem

(d) None of these

Under what condition, the upright pyramid of biomass becomes inverted

(a) Grassland ecosystem (b) Terrestrial ecosyslem

The storage of organic matter not used by heterotrophs is termed as

(a) Gross primary production

(b) Net secondary production

(d) Secondary production

In an ecosystem, the largest population is of

(a) Producers (b) Consumers

Transfer of material and energy from one ecosystem to other ecosystem is best examplified by

(a) Harvesting of fishes

(b) Grazing of pastureland

(d) Silvicultural practices in a woodland

Which of the following has the greatest amount of energy

(a) Insectivores (b) Carnivores

Herbivores are called

(a) Primary consumers (b) Secondary producers

Osmotrophs are also called as

(a) Producers (b) Consumers

The total rate of photosynthesis including the organic matter used up in respiration during definite period is known as

(a) Gross primary productivity

(b) Net primary productivity

(d) None of above

Which one of the following system constitutes the primary producers

(a) Higher plants (b) Algal phytoplanktons

Which one of the following ecosystems is more productive in terms of carbon dioxide fixation

(a) Crop ecosystem (b) Forest ecosystem

The second order consumer in a food chain is

(a) Cattle (b) Deer

In an ecosystem energy flows in

(a) One direction (b) Two direction

The planktonic forms are

(a) Autotrophs (b) Heterotrophs

Which one of the following contains very low concentrations of dissolved inorganic nutrients for algal growth

(a) Oligotrophic lake

(b) Eutrophic lake

(d) Both eutrophic and mesotrophic lakes

Standing state of the ecosystem is

(a) Living and non-living components

(b) Only living components

(d) None of the above

Which ecosystem does not show variations dependent upon geographic location and rainfall

(a) Marine ecosystem (b) Fresh water ecosystem

In food web hyaenas and vultures are

(a) Primary consumers (b) Predators

If all the plants of the world die all the animals will also die due to shortage of [CPMT 1975, 78; AFMC 1989]

(a) Cold air (b) Oxygen

Maximum solar energy may be trapped by [BHU 1978]

(a) Growing grasses

(b) Planting trees

(d) More cultivation of crop plants

A wolf has just eaten a lamb when tiger saw the wolf attacked it and consumed it. The tiger is in ecological terms

[CPMT 1982]

(a) A producer (b) A primary consumer

Green plants constitute [CPMT 1983, 84, 88; MP PMT 1999]

(a) First trophic level (b) Second trophic level

An ecosystem is a complex interacting system of

[JIPMER 1984; MP PMT 1984; AMU 1987]

(a) Individual

(b) Population

(d) Communities and their soil conditions

Eutrophic lakes means [DPMT 1984]

(a) Lake poor in nutrients

(b) Lake rich in nutrients

(d) Lake lacking in water

First link in any food chain is a green plant because

[RPMT 1985; CPMT 1985]

(a) Green plants can synthesize food

(b) They can eat everything

(d) None of the above

The number of primary producer within a specified area would be maximum in

[RPMT 1985; CPMT 1976; MP PMT 1995]

(a) Pond ecosystem (b) Grassland

Nepenthes is a

[CPMT 1986, 90, 93; MP PMT 1995; BVP 2002]

(a) Primary producer

(b) Consumer

(d) None of the above

Which one of the following components of ecosystem comes from outside [MP PMT 1987]

(a) Oxygen (b) Temperature

An ecosystem resist change because it is in a state of

[MP PMT 1987]

(a) Imbalance (b) Homeostasis

In an ecosystem, the population of

[CBSE PMT 1988]

(a) Primary producers are more than that of primary consumers

(b) Secondary consumers are largest because they are powerful

(d) Primary consumers are least dependent upon primary producers

On the global basis the maximum productivity is shown by

[MP PMT 1988; CPMT 2000]

(a) Aquatic ecosystem (b) Grasslands

Which of the following acts as ‘‘nature’s scavengers’’

[CBSE PMT 1997]

(a) Man (b) Animals

The pyramid of number in a grassland ecosystem is

[MP PMT 1998; BHU 2002]

(a) Always erect (b) Always inverted

Cyberviatic is associated with [Pb. PMT 1999; RPMT 1999]

(a) Flow of energy (b) Cycle of energy

Which is the correct sequence in the food chain in a grassland

[MP PMT 1990; AFMC 1999; Pb. PMT 2004; HP PMT 2005]

(a) Grass ® wolf ® deer ® buffalo

(b) Bacteria ® grass ® rabbit ® wolf

(d) Grass ® snake ® insect ® deer

Generally the food chain has how many trophic levels

[MP PMT 1990, 2001, 02; BHU 2001]

(a) One (b) Two

In an ecosystem which of the following are important components [MP PMT 1992]

(a) Energy flow and food chain

(b) Mineral recycling and energy flow

(d) All the above

Among the following, what happens in abiotic components of an ecosystem [CPMT 1990]

(a) Flow of energy

(b) Cycling of materials

(d) Flow of energy and cycling of material

The maximum biological magnification of DDT through food web is seen in [MP PMT 1992]

(a) Algae (b) Bacteria

The pyramid that cannot be inverted in a stable ecosystem, is pyramid of

[CPMT 1991, 99, 2001, 02; MP PMT 2001, 02;

KCET 2000; HP PMT 2005; Orissa JEE 2005]

(a) Number (b) Energy

Snake generally belongs to [CPMT 1991]

(a) Saprophytes (b) Primary consumer

In an ecosystem decomposer include [CPMT 1991]

(a) Bacteria and fungi

(b) Only microscopic organisms

(d) Above two plus macro-organisms

Flow of energy declines from low to higher trophic level in ecosystem, is mainly explained by

[CPMT 1991; MP PMT 1999]

(a) First law of thermodynamics

(b) Second law of thermodynamics

(d) None of the above

Driving force of an ecosystem is [CPMT 1991]

(a) Producer (b) Carbohydrates in plants

The total energy fixed by a gram plant (Cicer arietinum) in an ecosystem on the whole is called [CPMT 1991]

(a) Primary production (b) Gross production

Which of the following is correct sequence in food chain

[CBSE PMT 1991]

(a) Fallen leaves ® bacteria ® insect larvae ® birds

(b) Phytoplankton ® zooplankton ® fish

(d) Grasses ® chameleon ® insects ® birds

The transfer of energy from organism to organism in a natural community establishes [CPMT 1988]

(a) Food chains (b) Biological control

With regard to ecological food chain, man is a [CPMT 1980]

(a) Producer

(b) Consumer

(d) Producer and decomposer

If phytoplankton are destroyed in the sea, then

[DPMT 1984]

(a) Algae will get more space to grow

(b) Primary consumers will grow luxuriently

(d) No effect will be seen

An ecosystem must have continuous external source of

[NCERT 1982]

(a) Food (b) Minerals

The word ‘‘ecosystem’’ was first coined by

[CPMT 1989, 2002; 1995; MP PMT 1997, 2001; BHU 2002]

(a) Weaver and Clements (b) A.G. Tansley

Trophic levels are formed by

[CPMT 1980, 2000; BHU 1984]

(a) Organisms linked in food chain

(b) Only plants

(d) Only carnivores

In a food chain herbivores are

[CPMT 1984; MHCET 2001; BVP 2001]

(a) Primary producers (b) Primary consumers

In a food chain of grassland ecosystem, the top consumers are [NCERT 1979]

(a) Carnivores

(b) Herbivores

(d) Bacteria

Biological equilibrium is an equilibrium among the

[CPMT 1981, 84, 85;MP PMT 1984]

(a) Producers

(b) Producers and consumers

(d) Producers, consumers and decomposers

In a tree ecosystem, the pyramid of number is

[CPMT 1983; RPMT 1997]

(a) Upright (b) Inverted

Largest ecosystem of the world are

[AIIMS 1985; MHCET 2000]

(a) Grasslands (b) Great lakes

Energy storage at consumer level is called

[MP PMT 1990; 2001]

(a) Gross primary productivity

(b) Secondary productivity

(d) Net productivity

Ecosystem is [CPMT 1991; MP PMT 2002; Orissa JEE 2005]

(a) Open (b) Closed

What is maximum in a pond-ecosystem [RPMT 1992]

(a) Primary consumers (b) Secondary consumers

The pyramid of number is based on [CBSE PMT 1993]

(a) Unit per area

(b) Food per individual

(d) None of these

If the plant producer dies in the ecosystem, then the system is

[DPMT 1992]

(a) Seriously affected

(b) Cannot produce food

(d) Hardly affected

The phytoplankton in the ponds act as [DPMT 1992]

(a) Producers (b) Decomposers

The character of an ecosystem is determined by the environmental factor which is shortest supply. This is the

[CBSE PMT 1994]

(a) Law of minimum

(b) Law of diminishing returns

(d) Law of supply and demand

Which must be preserved in an ecosystem, if the system is to be maintained [JIPMER 1994; Kerala PMT 2004]

(a) Producers and carnivores

(b) Producers and decomposers

(d) Herbivores and carnivores

The importance of ecosystem lies in [MP PMT 1993, 95, 98]

(a) Cycling of materials (b) Flow of energy

Ecosystem has two components

[MP PMT 1993, 98, 99; BHU 2000]

(a) Plants and animals (b) Weeds and trees

Ecosystem creates [MP PMT 1993]

(a) Food chain (b) Food web

In lake ecosystem, pyramid biomass is

[MP PMT 1993; Bihar 2005]

(a) Upright (b) Inverted

In forest ecosystem, pyramid of number is [MP PMT 1993]

(a) Upright (b) Inverted

Carnivores are [MP PMT 1993]

(a) Usually primary consumers

(b) Usually secondary consumers

(d) Usually decomposers rather than consumers

The trophic level of lion in a forest ecosystem is

[MP PMT 1994]

(a) T₃ (b) T₄

What energy percentage can be captured by the organisms of next trophic level [CBSE PMT 1999]

(a) 20% (b) 30%

In a pond if there is too much wastage, then the BOD of pond will [CPMT 1994]

(a) Increase (b) Decrease

Which of the following abundantly occurs in pond ecosystem [RPMT 1995]

(a) Producer (b) Consumer

If all decomposers are removed from an ecosystem, what will happen [RPMT 1995]

(a) All consumers will die

(b) Energy cycle will be affected

(d) Only herbivores will die

Which of the following is the most stable ecosystem

[CBSE PMT 1995; BHU 2002; MP PMT 2000]

(a) Mountain (b) Desert

In a biotic community, primary consumers are

[CBSE PMT 1995; BVP 2001; MHCET 2001]

(a) Omnivores (b) Carnivores

Which of the following does not effect the forest ecosystem

[Bihar MDAT 1995]

(a) Deforestation (b) Soil erosion

The pyramid of energy in a forest ecosystem is

[MP PMT 1994, 95, 97, 2002]

(a) Always upright

(b) Always inverted

(d) None of the above

In an ecosystem, there is flow of energy at different trophic levels. This is as follows : [KCET 1994]

(a) Primary consumers — Tertiary consumers — Secondary consumers — Decomposers — Producers

(b) Producers — Primary consumers — Secondary consumers — Tertiary consumers — Decomposers

(d) Producers — Primary consumers — Tertiary consumers — Secondary consumers — Decomposers

We refer to the following as the food chain [KCET 1994]

(a) Large number of animals near a source of food

(b) Transfer of food energy from the green plants through a series of consumer organisms

(d) None of these

In a food chain, lion is a [EAMCET 1995; MHCET 2003]

(a) Secondary consumer (b) Primary consumer

In a pond ecosystem, benthos means

[EAMCET 1995; BHU 2000, 01; AFMC 2001; MHCET 2003]

(a) Primary consumers in the depth of a pond

(b) Zooplankton on the water surface

(d) Epineuston

Transfer of energy from one trophic level to other trophic level is according to the second law of thermodynamics. The efficiency of energy transfer from herbivorous to carnivorous is

[CBSE PMT 1996; AIEEE 2004]

(a) 25% (b) 50%

In a food chain, which of the following produces in the largest amount [CBSE PMT 1996]

(a) Producers (b) Decomposers

If forest area is reduced to half, which one of the following will be a long term effect [CBSE PMT 1996]

(a) The natives (tribals) of that area will die on account of hunger

(b) Cattles of that area will die due to scarcity of fodder

(d) It will be converted into large desert

The first link in any food chain is always a green plant because [MP PMT 1996, 99]

(a) They are widely distributed

(b) They are firmly fixed to the soil

(d) All of the above

Food levels in an ecosystem are called [MP PMT 1996]

(a) Trophic levels (b) Consumer levels

Which one of the following is a correct food chain

[MP PMT 1996]

(a) Grasshopper ® Grass ® Snake ® Frog ® Eagle

(b) Grass ® Grasshopper ® Frog ® Snake ® Eagle

(d) Frog ® Snake ® Eagle ® Grasshopper ® Grass

The correct path of energy flow in an ecosystem is

[MP PMT 1995, 2002]

(a) Producers ® Carnivores ® Herbivores ® Decomposers

(b) Producers ® Herbivores ® Carnivores ® Decomposers

(d) Herbivores ® Producers ® Carnivores ® Decomposers

Which of the following ecosystem has the highest gross primary productivity [CBSE PMT 1997, 2004]

(a) Grassland (b) Coral reef

Biological equilibrium is found among the

[MP PMT 1998; MHCET 2003]

(a) Producer plants

(b) Consumers and producers

(d) Producers, consumers and decomposers

The food chain in which microbes split energy rich compounds of the producer community is [AIIMS 1999]

(a) Parasitic food chain (b) Detritus food chain

In an ecosystem bacteria are considered as [MP PMT 1997]

(a) Microconsumers (b) Macroconsumers

A lake ecosystem is [MP PMT 1997]

(a) Artificial (b) Abiotic

Ecological pyramids are of [MP PMT 1997]

(a) Two types (b) Three types

To eat and be eaten relationship is called as [RPMT 1997]

(a) Food chain (b) Food web

Which of the following ecosystems would be most stable

[RPMT 1997]

(a) Man made forest (b) Fresh water lake

The living organisms of all ecosystems collectively consitute

[RPMT 1997]

(a) Producers (b) Decomposers

The number of individuals of a species in a particular ecosystem at a given time remains constant due to

[MP PMT 1998]

(a) Man (b) Parasites

Ecosystem may be defined as [MP PMT 1999]

(a) Group of plants which act as the energy suppliers

(b) Group of organisms which form population

(d) None of these

Which of the following habitats is most unsuitable for primary productivity [MP PMT 1999]

(a) Meadow (b) Forested river bank

In an ecosystem in abiotic components which of the following occur [MP PMT 1999]

(a) Flow of energy

(b) Cycling of materials

(d) Flow of energy and cycling of materials

The transfer or energy from organisms to organisms in a natural community establishes [MP PMT 1999]

(a) Food chains (b) Biological control

The snakes are included under [MP PMT 1999]

(a) Saprophytes (b) Primary consumers

The zooplanktonic forms are [MP PMT 1999]

(a) Primary consumers (b) Secondary consumers

Energy transfer from one trophic level to other, in a food chain is [CBSE PMT 1999; BHU 2005]

(a) 1% (b) 2%

The maximum biomagnification would be in which of the following in case of aquatic ecosystem [CBSE PMT 1999]

(a) Fishes (b) Birds

The green plants are removed from an aquarium

[KCET 1998]

(a) The fishes will not survive

(b) Fishes will increase in size

(d) None of the above

Energy enters in ecosystem through [CPMT 1998]

(a) Herbivores (b) Carnivores

Ecosystem is defined as [CPMT 1998]

(a) Relation between plants and animals

(b) Relation between biotic and physical components

(d) None of these

Decomposers are [CPMT 1998; BHU 2001]

(a) Autotrophs (b) Heterotrophs

In a terrestial ecosystem such as forest, maximum energy is in which trophic level [CBSE PMT 1998]

(a) T₁ (b) T₂

The rate at which light energy is converted into chemical energy of organic molecules is the ecosystem’s

[CBSE PMT 1998; BHU 1999; Kerala CET 2003]

(a) Net primary productivity

(b) Gross secondary productivity

(d) Gross primary productivity

The relationship in an ecosystem can be depicted in

[AIIMS 1998]

(a) Pyramid of energy (b) Pyramid of biomass

Biomass pyramid of forest is [Pb. PMT 1999; RPMT 1999]

(a) Inverted (b) Upright

In an aquatic ecosystem, maximum biomagnification is seen among the [CBSE PMT 1999]

(a) Fishes (b) Phytoplanktons

The dominant second trophic level, in a lake ecosystem, is

[BHU 1999]

(a) Benthos (b) Plankton

A rat feeding upon potato tuber is [KCET 1999]

(a) Producer (b) Carnivore

Tip of ecological pyramid is occupied by

[MP PMT 1999; CBSE PMT 2001]

(a) Herbivores (b) Carnivores

The lentic ecosystem includes which of following water

[KCET 2000]

(a) Rain (b) Running

Which of the following is source of energy to an ecosystem

[MP PMT 2000]

(a) Solar energy

(b) Sugar stored

(d) ATP

Food chain consists of [MP PMT 2000, 03]

(a) Producer, consumer and decomposer

(b) Producer, carnivore and decomposer

(d) Producer, herbivore and carnivore

Animals which live at the bottom of sea are [BVP 2000]

(a) Nekton (b) Diatom

Green plants are [BVP 2000]

(a) Autotrophs (b) Heterotrophs

Pyramid of energy is [BVP 2000]

(a) Upright (b) Inverted

The flora and fauna in lakes or ponds are [AIIMS 2000]

(a) Lentic biota (b) Lotic biota

During food chain the maximum energy is stored in

[MHCET 2001; Pb. PMT 2004]

(a) Producers (b) Decomposers

Transition zone between two ecosystems or vegetational regions is termed [HP PMT 2005; Kerala CET 2005]

(a) Ecocline (b) Ecotone

The ecosystem consists of [AIIMS 2001; BVP 2001]

(a) Producers (b) Consumers

In a food chain, the total amount of living material is depicted by [BHU 2001]

(a) Pyramid of energy (b) Pyramid of numbers

The biotic part of ecosystem includes [BHU 2001]

(a) Producers (b) Consumers

When the number of organisms at successive levels are plotted, they assume the shape of a pyramid. This is called the pyramid of [CBSE PMT 2001; MHCET 2003]

(a) Energy (b) Number

The two vegetation of ecosystem are separated by

[CPMT 2001]

(a) Ecotone (b) Ecoline

Energy enters into the ecosystem through

[CBSE PMT 2001; CPMT 2003]

(a) Herbivores (b) Carnivores

Which of the following is an artificial ecosystem

[MP PMT 2001]

(a) Rice-field (b) Forest

Which are the biotic components of forest ecosystem

[MP PMT 2001]

(a) Producers (b) Decomposers

Which of the following is most important abiotic factor in pond ecosystem [MHCET 2001]

(a) Water (b) Phytoplankton

The bacteria that attack dead organic matter are

[MHCET 2001]

(a) Producer (b) Herbivore

10% law of flow of energy in ecosystem was proposed by

[MHCET 2001]

(a) Lindemann (b) Carl Mobius

A plant being eaten by a herbivorous which in turn is eaten by a carnivorous makes [CBSE PMT 2002]

(a) Food chain (b) Food web

When peacock eats snakes which eat insects thriving on green plants, the peacock is [CPMT 2002]

(a) A primary consumer

(b) A primary decomposer

(d) The apex of food pyramid

A pond is a [RPMT 2002; MHCET 2003]

(a) Biome

(b) Natural ecosystem

(d) Community of plants and animals

Source of energy in an ecosystem is [CPMT 2002]

(a) Sun (b) ATP

Maximum biomass and variable organism are found in

[Orissa PMT 2002]

(a) River (b) Pond

In food chain initial organisms are [MP PMT 2002]

(a) Top consumers (b) Secondary consumers

In a food web, each successive trophic level has [BHU 2002]

(a) Increased total energy

(b) Less total energy content

(d) Non estimated energy content

Which of the following food chain may not be directly dependent upon solar energy [CBSE PMT 2002]

(a) Grazing (b) Detritus

A food chain starts with [BVP 2002; MP PMT 2004]

(a) Nitrogen fixing organisms (b) Photosynthesis

If bamboo plant is growing in a far forest then what will be its trophic level [CBSE PMT 2002]

(a) First (b) Second

In forest ecosystem, fungi is grouped as [CPMT 2003]

(a) Producer (b) Consumer

Which ecosystem shows maximum genetic diversity

[AIEEE 2003]

(a) Coniferous forests (b) Tropical rain forests

When spontaneous process occurs then free energy of system [DPMT 2003]

(a) Decrease

(b) Increase

(d) Either can increase or decrease

The maximum biomass of living diatoms to be found in

[AIEEE 2003]

(a) Marine pelagic habitats (b) Moist soil and swamps

If decomposers are removed what will happen ecosystem

[BHU 2003]

(a) Energy cycle is stopped

(b) Mineral cycle is stopped

(d) Rate of decomposition of mineral increases

Inverted pyramid is found in [MHCET 2003; Manipal 2005]

(a) Biomass pyramid of aquatic system

(b) Energy pyramid of grassland

(d) Pyramid of number of aquatic system

Which of the food chains directly depends on solar radiations [MP PMT 2004]

(a) Predator (b) Grazing

Which of the following organism form the decomposers

[BHU 2004]

(a) Pteris (b) Bacteria

Which of the following supports a dense population of plankton and littoral vegetation [BHU 2004]

(a) Oligotrophic (b) Eutrophic

A man-made ecosystem is [BHU 2004]

(a) Less in diversity

(b) More in diversity

(d) More stable than natural ecosystem

Decomposers are [Pb. PMT 2004]

(a) Autotrophs (b) Heterotrophs

These belong to the catergory of primary consumers …..

[KCET 2004]

(a) Snakes and frogs (b) Water insects

An ecosystem which can be easily damaged but can recover after some time if damaging effect stops will be having

[CBSE PMT 2004]

(a) Low stability and low resilience

(b) High stability and high resilience

(d) High stability and low resilience

Energy flow and energy transformations in living systems strictly conform to the [Kerala PMT 2004]

(a) Law of limiting factors

(b) Liebig’s law of minimum

(d) Shelford’s law of tolerance

(e) Biogenetic law

Bacteria and fungi in a forest ecosystem are generally

[Kerala PMT 2004]

(a) Producers (b) Decomposers

(e) Tertiary consumers

Area where two ecosystems overlap each other

[Kerala PMT 2004]

(a) Niche (b) Ecotype

(e) Corridor

In an ecosystem [AIEEE 2004]

(a) Cycling of energy and nutrients is a coupled process

(b) Cycling of energy is an independent process

(d) Macro and micronutrients cycle at the same pace

The Great Barrier Reef along the east coast of Australia can be categorised as [AIIMS 2004]

(a) Population (b) Community

In a food chain, the total amount of living material is depicted by [Pb. PMT 2004]

(a) Pyramid of biomass (b) Pyramid of energy

Given below is one of the types of ecological pyramids

This type represents [AIIMS 2005]

(a) Pyramid of numbers in a grassland

(b) Pyramid of biomass in a fallow land

(d) Energy pyramid in a spring

The number of trophic levels in a food chain is limited to 4 or 5 because

(a) The amount of food produced by producer is limited

(b) Consumer’s demand is high

(d) Activity of decomposer is poor

The number of individuals in each trophic level depends upon

(a) The number of individuals at higher trophic level

(b) The number of individuals at the lower trophic level

(d) The amount of sunlight available

Photic or euphotic zone is how much deep from the upper surface of sea

(a) 10 metres (b) 100 metres

Which of the following ecosystems have more productivity in an unit area

(a) Grassland

(b) Marine ecosystem

(d) Tree ecosystem

If less light falls on the pond’s surface

(a) Size of fishes become larger

(b) The size of fish population become smaller

(d) Mutation will take place in fishes

Ecosystem involves

(a) Gain of energy and loss of minerals

(b) Loss of energy and gain of minerals

(d) Loss of energy and loss of minerals

The hypersaline waters are found in [DPMT 1986]

(a) Lakes located in the alpine regions

(b) Lakes located in the arid and semiarid regions

(d) Estuaries

Abyssal zone of oceans is characterized by [BHU 1992]

(a) Presence of sunlight and producers

(b) Absence of sunlight and all living organisms

(d) Absence of sunlight and presence of consumers and decomposers

Which of the following word is related to Homo sapiens [MP PMT 1994]

(a) Herbivor (b) Carnivor

If we completely remove the decomposers from an ecosystem, the ecosystem functioning will be adversely affected because [CBSE PMT 1995]

(a) Mineral movement will be blocked

(b) Herbivores will not receive solar energy

(d) Rate of decomposition of other components will be very high

An ecosystem may be defined as [MP PMT 1999]

(a) A localised association of several plants and animals

(b) Different communities of plants, animals and microbes together with their physico-chemical environments

(d) None of these

X is eating curd/yoghurt. For this food intake in a food chain he should be considered as occupying

[AIIMS 2003]

(a) First trophic level

(b) Second trophic level

(d) Fourth trophic level

In which part of the open sea producers are found

[AMU 2005]

(a) Aphotic zone (b) Abyssal zone

Read the assertion and reason carefully to mark the correct option out of the options given below :

(a) If both the assertion and the reason are true and the reason is a correct explanation of the assertion

(b) If both the assertion and reason are true but the reason is not a correct explanation of the assertion

(c) If the assertion is true but the reason is false

(d) If both the assertion and reason are false

(e) If the assertion is false but reason is true

Assertion : In a food chain members of successive higher levels are fewer in number.

Reason : Number of organisms at any trophic level depends upon the availability of organisms which serve as food at the lower level.

[AIIMS 2003]

Assertion : Ecotone shows more diversity.

Reason : Ecotone is a sharp transition zone between two or more diverse communities.

Assertion : Net primary productivity is gross primary productivity minus respiration.

Reason : Secondary productivity is produced by heterotrophs.

Assertion : Food web consists of several food chains.

Reason : Food web decreases the stability of an ecosystem.

Assertion : Ecological pyramids are also called Eltonian pyramids.

Reason : An ecological pyramid is always upright.

Assertion : The pyramids of number, biomass and energy is always upright.

Reason : It happens because the producers always outnumber and outweigh the herbivores which in turn always outnumber and outweigh the carnivores.

Assertion : The plant biomass which serves as the food of herbivores and decomposers is said to result from the gross primary productivity.

Reason : Gross primary productivity is the rate of total production of organic material (biomass).

Assertion : Pyramid of energy may be upright or inverted.

Reason : Only 10% of energy goes to next trophic level.

Assertion : Thermocline exists between hypolimnion and epilimnion.

Reason : Thermocline acts as a barrier between the two layers.

Assertion : The conversion of productivity at next trophic level is 10%.

Reason : Energy is lost in the respiration process.

Ecosystem

1	b	2	d	3	a	4	d	5	b
6	b	7	a	8	a	9	d	10	a
11	d	12	d	13	a	14	c	15	a
16	b	17	b	18	b	19	d	20	c
21	d	22	b	23	c	24	c	25	b
26	d	27	c	28	c	29	a	30	b
31	d	32	a	33	c	34	c	35	b
36	d	37	c	38	c	39	c	40	a
41	a	42	d	43	d	44	d	45	a
46	d	47	c	48	c	49	a	50	a
51	a	52	c	53	a	54	c	55	c
56	c	57	d	58	a	59	c	60	b
61	a	62	a	63	c	64	d	65	b
66	a	67	a	68	d	69	a	70	a
71	c	72	c	73	d	74	d	75	d
76	b	77	d	78	c	79	b	80	d
81	b	82	b	83	a	84	b	85	c
86	c	87	b	88	a	89	b	90	a
91	d	92	c	93	c	94	b	95	a
96	c	97	c	98	b	99	a	100	a
101	b	102	c	103	c	104	b	105	b
106	a	107	c	108	b	109	d	110	a
111	a	112	c	113	d	114	d	115	d
116	a	117	b	118	b	119	c	120	a
121	c	122	a	123	c	124	c	125	a
126	b	127	b	128	b	129	d	130	b
131	a	132	c	133	b	134	a	135	d
136	d	137	c	138	c	139	c	140	d
141	a	142	d	143	a	144	c	145	a
146	a	147	c	148	b	149	b	150	a
151	d	152	d	153	b	154	a	155	c
156	d	157	b	158	c	159	a	160	a
161	c	162	a	163	a	164	a	165	a
166	b	167	d	168	c	169	d	170	b
171	a	172	c	173	a	174	d	175	a
176	d	177	a	178	a	179	d	180	b
181	a	182	b	183	d	184	b	185	b
186	b	187	a	188	d	189	b	190	a
191	a	192	b	193	a	194	b	195	d
196	b	197	a	198	b	199	d	200	c
201	c	202	b	203	d	204	c	205	c
206	a	207	c

Critical Thinking Questions

1	c	2	b	3	c	4	c	5	b
6	c	7	b	8	d	9	d	10	a
11	b	12	c	13	c

Assertion and Reason

1	d	2	a	3	b	4	c	5	c
6	d	7	e	8	e	9	a	10	a

Ecosystem

(b) The solid component of earth is called Lithosphere and minerals are found in earth.
(a) The total stored energy in the form of organic matter (which is not used by the producer itself) is called net primary productivity (NPP).
(d) The green plants and some bacteria which synthesize organic matter by using solar energy photosynthetically constitute the autotrophic component of the ecosystem they are called producers.
(b) Because it is not eaten by other consumer.
(b) The actual percentage of energy from food at one level when converted to energy from food at the next level may be approximately 10 percent. Much of the other 90 percent of the energy is lost.
(a) Several terms have been introduced to denote this system from the time of Mobius, 1877 called it biocoenosis. It has also named as geobiocoenosis, phytocoenosis, biosystem, ecosom, microcosm, holocene but the term ecosystem has been preferred over others by most of the workers.
(a) In any ecosystem, communities or living organisms interact with their physical environment in such a way that there is well defined flow of energy forming clear trophic (food) levels and material cycles within this system.
(a) Because grasshopper eats green plants and is eaten by frog which is eaten by snake and snake is eaten by hawk.
(d) Because decomposers simplify step by step the organic constituents of each dead body. Their activities make chemical substances available for other living being (producer).
(a) Detritus food chain starts from dead organic matter acted upon by decomposers, which in turn are eaten by detrivores consumers which are eaten by top consumers.
(b) Food chain never occur independently in ecosystem but various food-chains are interconnected with each other forming an interlocked system, which is known as food web.
(d) Because in auto–operated ecosystem, plants and animals both balance their activities in mutual manner.
(c) Because free energy is lost in the environment and further not found in the same condition.
(d) Because both are continuous process.
(b) Because agriculture is a systematic process of plant growing which is produced by man.
(c) They are called micro consumers because in both the conditions living beings are stable.
(d) Because these organisms are not seen by necked eyes.
(c) Because these plants are parasitic in nature.
(a) Because–bacteria is chemosynthetic bacteria and cyanobacteria is a group of photosynthetic protists which can synthesise their own food material.
(b) Because plants are first trophic level (producers) of every food chain.
(d) Diatoms are producer, crustacea is primary consumer, fish is secondary consumer, seal is top consumer and bacteria are decomposers.
(a) The state of equilibrium in an ecosystem is called homeostasis. Every ecosystem is characterised by possessing an inherent property that it resists to any sort of change in its constitution and physical environment.
(b) Because productivity is determined by biomass of organisms.
(c) Pyramids of energy are most fundamental and they indicate overall nature of ecosystem and it is a graphical representation of amount of energy trapped per unit time and area in different trophic levels of a food chain.
(c) Because biomass of each trophic level decreases respectively.
(c) The amount of food energy not utilize by heterotrophs per unit area in a unit time is referred to as net productivity.
(d) Because autotrophs make first trophic level.
(d) Those heterotrophs which act upon and decompose the dead organisms are called decomposers. They are also known as osmotrophs.
(d) All the green plants having chlorophyll are considered as primary producers because they can synthesize food by trapping solar energy.
(c) Because about 90% of the total world photosynthesis (CO₂ fixation) takes place by algae growing mainly in oceans and fresh water.
(c) The herbivores are the primary consumers which live upon green plants. e.g., cattle, deer, goat, mouse etc. Secondary consumer are the carnivores which thrive upon the herbivores. Those carnivores which feed upon other carnivores are top carnivores or tertiary consumers etc. lion, tiger, leopard, etc.
(a) Energy flow is unidirectional i.e., from producers to secondary consumers and not back.
(c) The amount of mineral matter present in an ecosystem at any given time is referred to as standing state or standing quality.
(c) Because all consumers depend on plants (Producers) for food.
(c) Because in large water bodies the number of producers is high. So for synthesizing more food material they need maximum solar energy.
(d) Because lamb is a primary consumer and it is grazing the grass and small herbs and wolf eats lamb so it is secondary consumer. The tiger eats wolf (the secondary consumer) so it is called tertiary consumer.
(a) Because plants have the capacity of synthesizing food (Producers).
(c) Ecosystem is a structural and functional unit of biosphere consisting of community of living beings and the physical environment both interacting and exchanging materials between them.
(a) Green plants are called producer because they can synthesize food material in presence of light (Autotrophs).
(a) Number of producers per unit area is more in pond ecosystem than in grassland ecosystem.
(c) Nepenthese is a chlorophyll containing plant so it synthesizes food by the process of photosynthesis thus it is a primary producer and because of being an insectivorous plant it consumes insects like grasshopper and other small insects, so it is also a consumer.
(d) Because energy in ecosystem comes from sun which is trapped by green plants or producers.
(b) An ecosystem resist changes because it is in a state of greater stability. It is called as homeostasis or an ecosystem maintains a functional balance or relatively stable state of equillibrium amongst its different components. This phenomenon is called balance of nature or homeostasis.
(a) Because 90% of total photosynthesis occurs in oceans and lakes by algae.
(d) The detrivores together with the decomposers (bacteria, actinomycetes & fungi) are sometimes referred to as reducers. The two are also called scavengers because they clean the earth.
(a) In a grassland food chain the number of individuals decrease at the successive higher levels.
(c) Plants represents the first trophic level and the herbivores make the second trophic level. The primary carnivores constitute the third trophic level, and the secondary carnivores, such as large fish, man etc. constitute the fourth trophic level of an ecosystem)
(d) Abiotic components includes inorganic substances or minerals, organic substances and different climatic conditions.
(d) Those pollutants which either degrade very slowly or do not degrade at all are called non-degradable pollutants they usually join the food chain and enter the body of an organism where their concentration always increases. This phenomenon is called biological magnification. These pollutant may degrade or destroy the resources. e.g., DDT, phenolic compounds.
(b) Because at each trophic level only 10% energy is left. Thus the amount of energy decreases and pyramid will be straight and cannot be inverted in any condition.
(d) Because snakes are the secondary consumers.
(c) Decomposers include bacterial, actinomycetes and fungi, which act upon and decompose the dead organisms.
(b) The second law of thermodynamics states that, ‘‘Process involving energy transformation will not occur spontaneously unless there is degradation of energy from nonrandom to a random form’’.
(d) In any ecosystem the basic or ultimate source of energy is sunlight.
(b) Gross productivity is the total amount of chemical energy stored in plants per unit area and per unit time.
(b) Because phytoplankton is eaten by zooplankton which in turn is eaten by fishes.
(a) The transfer of food energy from the producers through a series of organisms (herbivores ® carnivores ® decomposers) with repeated eating and being eaten is known as a food chain.
(b) Because man can not produce the food himself and he depends on plants (producer) for food.
(c) Because phytoplankton is the main producer in the sea.
(a) The trophic structure in any ecosystem is a kind of producer consumer arrangement. Here each food level is called trophic level.
(b) Primary consumers or herbivores of first order are depend upon producers or green plants for their food.
(a) Because carnivorous are not eaten by others.
(c) In tree ecosystem the pyramid of number is intermediate. Here the number of primary consumers is more than producers as well as top consumers.
(c) Oceans have largest flora and fauna hence represent largest ecosystem of world.
(b) The rate of storage at consumer level is referred to as secondary productivity. Infact, it is the rate of re-synthesis of organic food by the consumers.
(a) Ecosystem is normally an open system because there is a continuous and variable entry and loss of energy and materials.
(c) Because phytoplanktons (producer) are largest in number in an aquatic system and pond-ecosystem is an aquatic ecosystem.
(c) Pyramid of number in which number of individuals at each trophic level is shown in pyramid.
(b) Because in a ecosystem only producer can make the food himself by the process of photosynthesis.
(a) Because phytoplanktons are smallest plants found in an aquatic ecosystem and possess chlorophyll.
(c) 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 system.
(c) The ecosystem comprises abiotic and biotic components. The entire living community comprising plants and animals constitute the biotic component whereas the entire physical environment forms the abiotic component.
(b) In pond or lake ecosystem pyramid of biomass are of inverted type as biomass of producers is minimum and of top consumers is maximum.
(a) The pyramid of number in forest is erect or upright as producers are maximum in number and top consumers are least in number.
(c) Because primary consumers are those who consume producer (i.e., green plants) so they are called herbivorous and the animals or consumer who consumes the herbivorous or primary carnivorous are called the secondary or tertiary consumers respectively.
(b) Because lion is a top consumer.
(d) Lindemann gave the law of 10% for energy flow (10% energy transfer law), i.e., only 10% of total energy received by one trophic level is transferred to next trophic level.

110 (a) The sewage water can be corrected by algal bacterial treatment in the oxidation pond. The water pollution is measured in term of BOD. The degree of pollution is directly proportional to BOD. Hence if there is too much wastage in a pond then the BOD of pond will increase.

(c) If decomposes are removed from an ecosystem then bio-geochemical cycle will stop.
(d) 2/3 parts of earth is ocean here, various types of food chains form food webs. This ecosystem is most stable due to buffering action of water.
(d) Because they depend upon producers for food.
(a) Pyramid of energy is always upright in all types of ecosystem as energy goes on decreasing with each and every trophic level.
(c) Lion is also called top consumer.
(a) Benthos are those animals which live at the bottom of a lake. They are primary consumers at the depth of pond.
(c) Habitats of a large variety of organisms would be destroyed and food chains would be disturbed leading to population and ecological imbalance.
(b) Coral reef is the coastal region is the area of maximum productivity and diversity (every group of marine algae and every animal phylum is represented here).
(d) An ecosystem should always maintain a balance, if primary consumers in an ecosystem are absent, then producers will be increased in number and will create over crowding. It results in competition and consequently number of producers will decrease to near normal.
(b) Detritus food chain starts from dead organic matter acted upon by decomposers which in turn are eaten by detrivores consumers which are eaten by top consumers.
(c) It is lentic fresh water natural ecosystem.
(b) Three types i.e., pyramid of number, pyramid of biomass and pyramid of energy.
(a) The transfer of food energy from the producers through a series of organisms with repeated eating and being eaten is known as food chain.
(d) Snakes are the secondary consumers.
(c) As per 10 percent law, only 10% of the energy fixed at one trophic level is passed to next trophic level. For example, when plants are eaten by animals only 10% of energy of the food is fixed into animal flesh; rest is lost through respiration.
(a) Non-degradable chemicals enter the food chain, and their concentration goes up as it moves up in the food chain. This phenomenon is called biomagnification. Naturally in food chain, Phytoplankton ® Zooplankton ® Fishes, it would be highest in fishes.
(c) The ultimate source of energy for biosphere is solar energy which is captured by producers through photosynthesis.
(b) Any heterotrophs, which break down organic matter into simpler organic or inorganic materials is called decomposer.
(d) Gross primary productivity is the total rate of photosynthesis. Light energy is converted into chemical energy including the organic matter used up in respiration during the measurement period.
(b) Biomass of producer is greater than the biomass of top consumers in forest ecosystem.
(a) In an aquatic ecosystem fishes make tertiary trophic level. Due to this reason they have maximum biomagnification in comparison to phytoplanktons.
(c) Phytoplankton is the producer in lake ecosystem and zooplanktons found as consumers. It is a secondary tropic level in lake ecosystem.
(d) Potato is the producer, when rat eats potato then it becomes primary consumer.
(b) Carnivores are the top carnivores represents the penultimate trophic level.
(c) Standing water ecosystem is called lentic type e.g., lake, ponds, pools, and running fresh water ecosystem is called lotic type. e.g., rivers.
(a) Solar energy is the ultimate source of energy in any type of ecosystem.
(a) Green plants are the autotrophs which have capacity to manufacture their own food or which can fix radiant energy of sun into chemical energy.
(d) We know that ecosystem is a unit made up of all the living (producer, consumer and decomposers) and non living components.
(c) Total dry weight of all living organisms in a certain unit area is called biomass.
(b) In the pyramid of number, the number of individual organisms at each trophic level is shown.
(a) The transition zone between two communities is known as ecotone.
(c) Producers are mainly photosynthetic plants, and they can convert light energy to kinetic energy and this energy passes in all trophic levels.
(a) Artificial ecosystem are man made ecosystem e.g., crop land, orchard, urban.
(a) Lindemann proposed the 10% law of flow of energy in ecosystem. According to this law only 10% energy passed from one trophic level to other in a food chain.
(d) Because peacock is the top consumer.
(b) In food web, each successive trophic level has less total energy content as per law of Lindemann. Some energy is lost in transfer from one another level.
(b) The food chain always begins from green plants which synthesize organic food by photosynthesis using solar energy.
(a) Bamboo is a plant, which can produce their food. It is a first tropic level.
(d) Microorganisms like fungi and bacteria are include in decomposer in ecosystem.
(a) In this case the biomass of producers (algae etc.) is minimum which increases at herbivore (rotifers, insects, etc) level and further at carnivore (small fishes etc) level. The biomass of top carnivores (large fishes) is maximum. Thus the pyramid of biomass in aquatic system is inverted.
(d) Decomposers are usually bacterium or fungus that breaks down dead organic matter (cells of dead plants and animals) into simple substances.
(b) Eutrophication means nutrient enrichment. The main factor that cause eutrophication is the release of large amount of phosphate into water body. The enrichment of minerals allow large number of algae, cyanobacteria & aerobic bacteria to grow.
(a) Manmade ecosystem or artificial ecosystem have low diversity and is more vulnerable to sudden changes. Crop ecosystems are man made ecosystems.
(c) In ecosystem energy transfers from one form to another and some energy loss in the form of heat, it follows the II^nd law of thermodynamics.
(a) The concept of biomass refers to organismal mass or the living material.

Critical Thinking Questions

(b) Because in low light condition, the rate of photosynthesis in producer (algae etc.) is decreased. As a result of this activity the quantity of available food material and oxygen for consumer (fishes)are decreased. So the size of the population of consumers i.e., fishes become smaller.
(d) Abyssal zone is a dark zone.
(d) Because they can eat both plants and animals.
(c) Photic zone is upper 200m layer of ocean floor which receives good amount of sunlight. In this zone producers are found.

Assertion and Reason

(d) Each food chain contains many steps like producers, herbivores, primary carnivores and so on. Each step of the food chain is called trophic level. Number of organisms at any trophic level depends upon the availability of food. In grassland ecosystem the maximum number of organisms are found in lower trophic level but in forest ecosystem and parasitic food chain it is reverse.
(a) A sharp transition between two or more diverse communities, for example, between forest and grassland, is known as ecotone. The ecotonal community commonly contains many of the organisms of each of the overlapping communities and in addition, organisms characteristic of and often restricted to ecotone. The tendency for increased variety and density at community junctions is known as the edge effect.
(b) Net primary productivity is the rate of organic matter built up or stored by producers in their bodies per unit time and area. Net productivity is equal to gross primary productivity minus loss due to respiration and other reasons. Rate of increase in energy containing organic matter or biomass by heterotrophs or consumers per unit time and area is known as secondary productivity.
(c) Food web is a network of food chains which become interconnected at various trophic levels so as to form a number of feeding connections amongst the different organisms of a biotic community. Food web is meant for increasing the stability of an ecosystem by providing alternate source of food and allowing the endangered population to grow in size.
(c) Ecological pyramids were developed by Charles Elton and are, therefore, also called Eltonian pyramids. An ecological pyramid can be upright, inverted or spindle shaped depending upon criteria of formation of pyramid(like energy, biomass or number) and the type of food chain involved parasitic, aquatic or terrestrial.
(d) Graphical representation of the trophic structure is done by drawing ecological pyramids. Common parameters used for constructing ecological pyramids are number of individuals (pyramid of numbers), dry weight (pyramid of biomass) and rate of energy flow (pyramid of energy) at successive trophic levels. In most ecosystems, the pyramids of number and biomass are upright e., producers outnumber or outweigh the herbivores, and herbivores outnumber or outweigh the carnivores. However, in certain ecosystems, the pyramid of number (e.g., in tree dominated ecosystems) and the pyramid of biomass (e.g., in deep bodies) may look inverted. The pyramid of energy, however, is always upright. Amongst the three kinds of ecological pyramids, the pyramid of energy, which expresses mainly the rate of food production, can be considered most representative of the functional characteristics. It emphasises that total energy flow at successive trophic level always decreases compared to the preceding trophic level.
(e) The plant biomass which serves as the food of herbivores and decomposers is said to result from the net primary productivity and not the gross primary productivity. Primary productivity has two aspects, gross and net. The rate of total capture of energy, or the rate of total production of organic material (biomass) is known as gross primary productivity. However, while the energy capture process is operating in the green tissues, these as well as other tissues, are consuming energy in respiration. The balance energy or biomass remaining after meeting the cost of respiration of producers, is called net primary productivity.
(e) Energy flow in the ecosystem in a unidirectional manner. There is a decline in the amount of energy passing from one trophic level to the next. Thus pyramid of energy is always upright. According to Lindemann, only 10% of energy goes to next trophic level.
(a) The warmer upper part of the lake or epilimnion becomes temporarily isolated from the colder lower water or hypolimnion by a thermocline zone (temperature stratification) that acts as a barrier to exchange of materials. Consequently, the supply of oxygen in the hypolimnion and nutrients in the epilimnion may run short.
(a) Ten percent law put forth by Lindemann states that while transferring organic food from one trophic level to the next, about ten percent of the organic matter is stored as flesh, the remaining is lost during transfer or broken down in respiration. The net productivity of the next higher trophic level shall be 10% of the first one.