ORGANISMS AND ENVIRONMENTFlame Institute

Reiter first used the term ecology in 1868. Ernst Haeckel (1886) first correctly defined ecology as “the science dealing with reciprocal relationship of organisms and the external world”. Prof. R.Misra is known as “Father of ecology in India”. Other famous Indian ecologists include G.S.Puri, S.C.Pandeya. Dudgeon (1921) started ecological studies in India. Study of ecology is important to strike a balance between development and maintenance of natural environment and its biotic communities, use and conservation of resources, solve local regional and global environment problems.

Branches of ecology

(1) Autecology/Species ecology : The study of reciprocal relationships between every stage of development of a population/species and its environment is called autecology.

(2) Synecology : It is the study of reciprocal relationships between composition, organisation and development of communities and their environment.

(3) Applied ecology : It is the study of specialised fields of ecology which are concerned with conservation and economic exploitation of organisms, e.g., agronomy, agriculture, animal husbandry, forestry, wildlife management, conservation ecology and pollution ecology.

(4) Paleoecology : Study of relationship between organisms and environment in the past.

(5) Systems ecology : Branch of ecology dealing with interpretation of ecological concepts and processes in terms of mathematical models and formulae.

(6) Genecology : Study of genetic composition and changes in relation to the origin of ecads, ecotypes, new species, etc.

Levels of ecological organisation : Organisation is the arrangement and coordination of small components into larger components in a hierarchy where each level is formed of components of lower level and itself becomes constituent of still higher level. The hierarchy in the levels of organisation connected with ecological grouping of organisms is called ecological hierarchy or ecological levels of organisation.

(1) Organism : An individual organism is a distinct living entity made up of one or more cells which carries out all the life processes in its body which are quite separate from life processes being performed in the body of others.

(i) Basic unit : Organism is the basic unit of ecological hierarchy.

(ii) Size : It may be microscopic (e.g., Amoeba, Chlorella, bacterium) or macroscopic (e.g., Rose, Mango, Crocodile, Dog, Human being).

(iii) Cellularity : An organism can be unicellular (e.g., Amoeba, Euglena, Chlamydomonas), colonial (e.g., Volvox) or multicellular (e.g., Fish, Lizard, Mango tree).

(iv) Subunits : An organism has a number of subunits in the form of organ systems, organ system with organs, organs with tissues, etc. The subunits coordinate to produce a functional whole. They themselves cannot survive independently.

(v) Life processes : It performs all the life processes independent of life processes being performed in the body of others.

(vi) Self regulation : Each organism is capable of growth, self repair, movement and self regulation of its activities.

(vii) Distinct identity : Organisms possess a distinct identity so that they can be easily identified, counted and measured e.g., Mango tree, Acacia, Sunflower, Mustard, Rat, Deer, Cow.

(viii) Interdependence : Organisms do not live in isolation. They show interactions with other organisms of the same species as well as organisms of other species.

(ix) Environment : Organisms obtain matter and energy from their environment and pass out wastes into it. They are also perfectly adapted to their environment. Environment is also changed to suit the organisms.

(x) Life span : An organism has a definite life span which involves definite series of stages like birth/hatching, growth, maturity, ageing and death.

(xi) Reproduction : New individuals develop from the pre-existing ones through the process of reproduction. Reproduction can be vegetative, asexual and sexual.

(xii) Resemblance : Organisms resemble their parents because they receive the genes for various traits from them.

(xiii) Continuity of race : Individuals die but the race continues due to regular formation of new individuals through reproduction.

(2) Population : It is a grouping of similar individuals in a particular geographical area or space. The different populations of the same organism present in particular geographical areas are called local populations/demes. A local population adapted genetically to its particular environment is called ecotype. There may be several ecotypes of the same organism which show variation amongst them. Various characteristics of a population are : population density, natality (birth) rate, mortality (death) rate, age distribution, biotic potential, dispersion and growth form.

Population density (D) =

N= Total no. of individuals, S= No. of units of space m²/m³.

Factors affecting population

(i) Natality : Birth rate.

(ii) Mortality : Death rate.

(iii) Population growth : Shows two types of curve :

(a) S. shaped curve.

(b) J. shaped curve.

(iv) Emigration : Permanent outward movement. Decreases population.

(v) Immigration : Permanent inward movement. Increases population.

(vi) Migration : Two way movement of entire population. Does not change the size of population.

(vii) Biotic factors : Growth rate of certain population decreases with the increase in density (density dependent) before the carrying capacity of the environment is reached, predators also keep the size of a population under check.

(viii) Carrying capacity : Carrying capacity of an environment is the maximum number of individuals of a population which can be provided with all the necessary resources for their healthy living.

(ix) Biotic potential : Maximum capacity of a population to reproduce under ideal conditions (environmental).

Control of population : It is by three factors :

(i) Geographic factors

(ii) Demographic factors

(iii) Socioeconomic factors.

(3) Species : It is grouping of individuals of one or more populations which resemble one another in all important morphological, anatomical, biochemical and genetic characters besides ability to interbreed freely. The sum of all the populations of same kind of organisms all over the world is called species. It is basic unit of classification and the population is subordinate to species. Only the species has a real existence, other units of classification (e.g., Genus, Family, Order, Class, Phylum and Kingdom) are man made artificial groups.

Exceptions to species concept

(i) Difference in the morphology of developmental stages of an individual.

(ii) Sexual dimorphism : Occurrence of two forms among the organisms of the same species is known as dimorphism. Plants such as the date palm have male and female individuals which bear different types of flowers. Man and woman, peacock and pea hen are two sexual forms of same species. They show sexual dimorphism.

(iii) Polymorphism : The occurrence of many forms of individuals within the same kind of organism (species) is known as polymorphism. e.g. :

(a) Colonies of social insects.

(b) Colonies of coelentrates and Volvox.

Speciation or Origin of species : May be

(i) Due to physical barrier (Allopatric)

(ii) Due to reproductive barrier (Sympatric)

(iii) Mutation

(iv) Polyploidy

(v) Genetic (Wright effect)

Home range : A space to live is a basic need of an organism. Several members of a species may cover a defined area in search of food and mates, which is called home range.

Niche/Ecological Niche (Grinnel, 1917)

It is specific part of habitat occupied by individuals of a species which is circumscribed by its range of tolerance, range of movement, microclimate, type of food and its availability, shelter, type of predator and timing of activity.

A habitat has several ecological niches and supports a number of species. An ecological niche is used by a single species. Two or more species cannot use the same niche despite having a mutualistic association.

Where two different species happen to occupy the same niche, one is excluded, e.g., Paramecium aurelia eliminates Paramecium caudatum while Tribolium confusum exterminates T. castaneaum. This is known as Gause’s Principle or Principle of competitive exclusion.

(4) Biotic community : The assemblage of interdependent and interacting populations of different species present in an area. It has three components –

(i) Plant community or community of producer.

(ii) Animal community or community of consumers.

(iii) Microbial community or community of decomposers. Animal community may show diurnal and seasonal changes. Annual plants also show changes with change of season.

(5) Ecosystem : The sum of the biotic (living) and abiotic (non-living) components of a particular geographical area, collectively called ecosystem.

(6) Biome : It is a large ecosystem or a group of small ecosystems which is delimited by a specific climate or geographical area. A biome may also possess a patch of different ecosystem, e.g., lake in a forest.

(7) Biosphere : Biosphere, also called ecosphere or giant ecosystem is the largest and nearly self-sufficient biological system. It is formed of all the ecosystems of the world. It is also called “life-supporting zone” of the earth.

Environment

The environment is the aggregate of all those things and set of conditions which directly or indirectly influence not only the life of organisms but also the communities at a particular place. Any external force or influence, which surrounds and affects the life of a plant in any way, becomes a factor of its environment. These factors are called environmental factors and may be living (biotic) as well as non-living (abiotic). The abiotic factors affect the structure, life history, physiology and behaviour of organisms. The biotic factors mostly influence growth and reproduction. The environmental conditions which influence the life and development of plants, each part of the environment is called ecological factors. Ecological factors are grouped into four main classes (ecological factors) which are as follows :

Climatic factors : The study of climatic factor is known as climatology. The chief climatic factors are :

(1) Water : Rainfall is the chief source of soil moisture. Water exchange between earth surface and atmosphere is called hydrological cycle. Humidity of the air is expressed in terms of relative humidity. It is measured by hygrometer (Psychrometer). Epiphytes and cryoptogamic plants grow in those regions where relative humidity is high.

(2) Light : Light (solar radiations) is a very important ecological factor as it is the source of energy to the whole biosphere. It enters the biosphere through the process of photosynthesis performed by green plants and other autotrophs. Here organic food is manufactured from inorganic raw materials. Solar energy is changed into chemical energy of food. The radiant energy of sunlight carries out all important functions, without this life except few bacteria would disappear. On this basis of relative light requirements and the effect of light on the overall vegetative development, plants are classified ecologically into following categories :

(i) Heliophytes are popularly called sun plants because they grow in open in full sunlight. They possess a number of characteristics like.

(ii) Sciophytes are shade plants which grow in areas having moderate to low intensity light, as below the shade of other plants. Optimum growth occurs with light of 10-30% of full sunlight.

The plants grow in total darkness are called etiolated (Long, thin, weak and yellow in colours).

(3) Temperature : Temperature influences every reaction and activity of organisms. Temperature shows daily as well as annual variations. The phenomenon of change of temperature between day and night and in different seasons of the year is called thermoperiodicity. It is of two types, diurnal (or daily) and seasonal (or annual). Thermoperiodicity determines periodical phenomena like seed germination, stem growth, flower formation, fruiting, dispersal, maturation of gonads, breeding, egg laying, etc. Low night temperature is suitable for seed germination in many plants, e.g., Rumex, Asclepias. Cooler nights also help in increasing size of tuber in Potato and fruit setting in Tomato. Organisms adapted to live at relatively constant temperature during the whole year are known as stenothermal, e.g., many palms, corals, snakes and some fishes. The organisms which can tolerate large changes of temperature are called eurythermal, e.g., Artemesia, Cyclops, Toad, Wall Lizard.

On the basis of temperature the plants are classified as below :

(i) Megatherms or Climate or Tropical : The vegetation growing in the condition in which high temperature prevails throughout the year (30-40°C). The dominant vegetation is tropical rain forest.

(ii) Mesotherms : Climate-subtropical, the high and low temperature alternates. The dominant vegetation is tropical decidous forest type. Those plants in which leaf fall takes place once in a year are called decidous plants e.g., Ficus religiosa (Sacred tree).

(iii) Microtherms : The vegetation growing in the low temperature (10-20°C) condition. (The temperature remains low throughout the year). The vegetation is mixed coniferous forests type (Taiga).

(iv) Hekistotherms : The vegetation growing in the very low temperature (0-10°C) conditions. The dominant vegetation is Alpine vegetation (Tundra).

The plants growing at very low temperature are called cryophytes or psychrophytes.

(4) Wind : High wind velocity causes soil erosion, breakage and up rooting of trees. Most of the pollutants are dispersed through the medium of air. Wind do harm is blossom trees because it prevents working of insects.

Wind modifies the humidity. Dry winds cause dwarfing of plants. Wind helps in pollination, dispersal of fruits and seeds and prevents frost damage. If the areas subjected to strong winds the leaves of plants become small and rolled and these plants develop an overall shape that offer resistance to wind.

Sometimes shrubs and trees are planted to protect the field against wind. Such structures are known as wind breaks or shelter belts. These plants (Trees) are planted at 90° to the wind velocity.

(5) Atmospheric humidity : Moisture in form of invisible vapours in atmosphere is called humidity.

Atmospheric humidity is generally expressed in terms of relative humidity (R.H.) which is defined as, “amount of vapours in atmosphere as the percentage of total amount which the air or atmosphere can hold at the existing temperature.” Rate of transpiration is inversely related to relative humidity. Area having high humidity have dense vegetation due to lower rate of transpiration. The areas with low relative humidity are dry. They produce sparse vegetation due to high rate of transpiration.

R.H. is influenced by environmental conditions like solar radiation, temperature, wind, etc. If temperature is high, R.H. is low and if temperature is low, R.H. is high.

(6) Atmosphere

Gaseous cover over the earth surface is called atmosphere. Earth’s atmosphere is about upto height of 300 km, out of which 95% of gases is upto height of 20 km and rest 5% in next 280km.

Earth’s atmosphere is having a mixture of gases out of which important ones are :

Table : 9.1-1

(1)	Nitrogen	78.08% (by volume)
(2)	Oxygen	20.84% (by volume)
(3)	Argon	0.93% (by volume)
(4)	CO₂	0.03% (300 ppm)

Earth’s atmosphere is divided into four different zones from below to above :

(i) Troposphere : First 20 km of earth’s atmosphere is called troposphere in which different physical phenomena, i.e., lightening, thundering and cloud formation occur.

(ii) Stratosphere : About 30 km zone over troposphere is called stratosphere.

Temperature increases in this zone (upto 90°C) due to ozone formation. In this zone under the influence of ultra-violet rays, this ozone layer is formed, which prevents entry of harmful UV-rays to reach the earth surface.

(iii) Mesosphere : Next 40 km zone above stratosphere is called mesosphere. Last limit of mesosphere is called mesopause.

(iv) Ionosphere : Uppermost zone of atmosphere is ionosphere and in this zone all the gases are in ionized form.

(7) Fire

Fire may be man caused or natural. It is basically of three types :

(i) Surface fire (ii) Ground fire (iii) Crown fire

Such plants which grow well in fire burnt condition are called pyrophytes or fire loving plants.

Topographic or Geographic factor : Topographic factors are concerned with the physical geography of the earth in an area. The chief topographic factors are as follows :

Micro climate refers to local combinations of factors such as wind, rate of evaporation, humidity, temperature which differ from regional climate.

(1) Altitude : Height of mountain chains. 300 feet rise in altitude decreases temperature by 1°F. There is also increase in humidity and wind velocity. Slope winds are local wind movements which are uphill during the daytime and downhill at night. Shade caused by mountains reduces the total sunlight falling on an areas. Sunlight has more of ultraviolet rays. In high mountains situated in tropical areas, all the vegetation zones are found – tropical, subtropical, temperate and alpine. With the increase in altitude climate changed as decrease in temperature, increase in humidity, increase in precipitation and increase in wind velocity.

Generally the vegetation that develops on base of mountain to top is Tropical ® Temperate ® Taiga ® Tundra. Species diversity generally increase as one proceeds from high altitude to low altitude and from high latitude to low latitude.

(2) Steepness of the slopes : Steep slopes cause fast running of water which result in erosion and do not permit the accumulation of humus so the soil becomes denuded. In such soil plants can not grow properly and vegetation changes to xerophytic plants.

(3) Exposure of slopes : Exposure of slope to sun and wind affects very much the kind of plants growing there. Generally the slopes exposed to sun and wind supports vegetation. That’s why green houses and hot beds are always built in a way to face sun or southern slopes which receive greater amount of solar energy.

(4) Direction of mountains chain : Mountains steer or deflect winds into different directions. Outer Himalayas show frequent rains with luxuriant vegetations while the middle and inner Himalayas are dry with poor vegetation. The southern slopes of Himalayas e.g., Kullu valley are directly exposed to sunlight and has luxurient mesophilous vegetation due to mansoon wind. Where as Northern slopes of Himalayas e.g., Lahul valley exposed to weak light and strong dry wind, thus they have xerophilous vegetation.

Edaphic factor : The study of soil is called edaphology or pedology. The soil can be defined as “the upper crust of earth surface in which plants roots are anchored.” The term soil is derived from the Greek word solum.

(1) Soil formation : It is derived from rocks by weathering which is of three types :

(i) Chemical weathering : It is caused by oxidation, hydrolysis or carbonation.

(ii) Mechanical weathering : It is caused by living organisms, e.g., lichens, grazing animals or earthworm.

(iii) Physical weathering : It is caused by water, wind, gravity, glaciers, etc.

Weathering results into conversion of rocks to small fragments. Humus accumulated and now this can be called as soil. The development of soil is called pedogenesis. Soil is of two types :

(a) Residual soil : If the soil remain at the same place where it is formed.

(b) Transported soil : This soil brought from their place of origin to other place by some agents. It may be :

Alluvial soil : Carried by running water (rivers).

Colluvial soil : Carried by gravity.

Eolian soil : Carried by wind.

Glacial soil : Carried by glacier.

The soils of planes of India is mainly alluvial. In India the principal residual soil types are :

(a) Reddish soil of Vindhyas and South.

(b) Black soils of South West India.

(d) Laterite soil : Oxides of iron and aluminium.

(e) Peat soil : With high percentage of humus 90%.

(f) Black soil : Predominantly with clay and humus (very fertile because most of minerals are present in it).

(2) Soil profile : A fully formed soil shows different layers called horizons. The sequence and nature of these layers is called soil profile (Cross section of soil) which consist of following horizons.

(i) Horizon ‘O’ : It is uppermost horizon made of organic matter. It has both fresh or nondecomposed as well as partially decomposed matter. It consist of following two sub-layers :

(a) O₁ region (Aoo) : It is uppermost layer which consists of freshy added organic matter such as dead leaves, branches, flowers and fruits.

(b) O₂ region (Ao) : It is present below O₁ region. It consists of organic matter which is in different stages of decomposition.

(ii) Horizon ‘A’ : It is rich in mineral elements. A large amount of completely decomposed organic matter is present in this region.

(iii) Horizon ‘B’ : It is dark in colour due to accumulation of leached substances like clay, iron and aluminium from horizon. So it is called as zone of accumulation or zone of illuviation.

Horizon ‘O’, A and B are together called as top soil.

(iv) Horizon ‘C’ : It consists of partially weathered parental rock material. It is called as sub soil.

(v) Horizon ‘R’ : It is the lowermost layer of soil which consist of bed rocks (unweathered).

(3) Composition of soil : The garden soil is made up of :

(i) Mineral matter (40%) : They are derived from rocks (by disintegration). The soil, derived from lime stone, is called chalky soil.

Sandy soils have more coarser particles and lower water holding capacity and better aeration. Sand is most porous. Clayey soils have fine particles which have high water holding capacity and very poor aeration. Clay is least porous (water logged). Loam (50% sand + 25% clay + 25% slit) are best for plant growth.

The best apparatus used to analyse the soil is sieving.

(ii) Organic matter : Humus is total organic matter in the soils. It is rich in N P K. The humus is formed from decay and decomposition of dead plant and animal matter. It is in colloidal state and increase water holding capacity of the soil. The formation of humus is called humification which is caused by microbial activity.

The three distinct layers of humus in soil of forests are :

(a) Litter : All dead fresh organic matter fallen (undecomposed) recently to the ground is called litter.

(b) Duff : The layer, where decomposition is just started, is called as duff as duff layer. Partially decomposed litter is called duff.

(c) Leaf mold or Real humus : When the litter is modified into dark, finely divided, amorphous organic matter by the activities of micro-organisms living in soil is called humus. Humus is maximum in peat soil (90%).

(iii) Soil solution : The soil solution is the primary source of inorganic nutrients for plants. Soil solution helps in exchange of ions. pH of fertile soil is 6 to 7. pH below 5 inhibits bacterial activity. The plants prefer to grow in acidic soil are called oxylophytes e.g., Drosera. The plants prefer to grow in alkaline soil are called halophytes.

The soil rich in nutrients is called eutrophic and soil with less amount of minerals is called as oligotrophic.

(iv) Soil air : 20-25% air or O₂ is necessary for proper growth of plants. The well aerated soil support the plant growth well because :

(a) Root respiration increases.

(b) The capillary potential of the soil increases.

(d) The root growth increases.

(e) Poor soil aeration supresses root hair development and may reduce the rates of absorption of water and minerals.

(v) Soil micro-organims : Soil contains a number of organisms. They are classified into four groups – microflora, macroflora, microfauna and macrofauna.

(a) Microflora : It consists of microscopic nonphagotrophic organisms.

(b) Macroflora : It consists of those fungi which form fructifications, e.g., mushrooms, tubers, truffles. The fungi are otherwise saprohytic in nature.

(c) Microfauna : It consists of microscopic phagotrophic microorganisms like protozoans (e.g., Amoeba, Arcella), rotifers, nematodes (e.g., Rhabditis).

(d) Macrofauna : They are animals residing in the soil. The common ones are insects (ants, beetles, mites, termites), spiders, millipedes, earthworms, snails and burrowing vertebrates.

Biotic factor : Living organisms living together influence each other’s life and these living organisms constitute biotic factors. In these biotic interactions both the organisms may be benefitted or one is benefitted or one is benefitted while another is harmed or both are harmed. These biotic interactions are of two main types :

(1) Positive interactions : Where both the organisms or one organism is benefitted. The main types of positive interactions are :

Mutualism or Symbiosis : Here both the organisms in association are mutually benefitted and further this association is obligatory, i.e., necessary for existence of both organisms. The term symbiosis or mutualism was given by DeBary.

Important examples of symbiosis are :

(i) Dispersal of fruits and seeds by living organisms.

(ii) Pollination by insects, animals, etc.

(iii) Symbiotic nitrogen fixation : In the root nodules of legumes and some non-legumes, Rhizobium bacteria (symbiotic) are present which obtain food and shelter from parent plant and in turn fix atmospheric nitrogen.

(iv) Mycorrhiza or Mycorrhizal association : Association between roots of higher plants and fungal hyphae is called mycorrhiza. It is of two types :

(a) Ectotrophic or Ectophytic mycorrhiza : In this association fungal hyphae are on surface of roots, e.g., in Pinus.

(b) Endotrophic or Endophytic mycorrhiza : Here fungal hyphae are inside the root tissue, e.g., in orchids.

(v) Lichens : These are composite plants in which algal partner and fungal partner are mutually associated.

(vi) Myrmecophilly : Association between ants and higher plants is called myrmecophilly, e.g., jamun, litchi, mango, etc., where ants live. The ants get their food from the plants and in turn act as body-guards.

(vii) Zoochlorellae : Unicellular green alga Chlorella vulgaris lives in gastrodermal cavity of Hydra. The alga gives food and oxygen to Hydra and Hydra in turn gives shelter and nitrogenous substances to alga.

Commensalism : It is the relationship between two living individuals of different species in which one is benefitted while the other is neither harmed nor benefitted except to negligible extent. e.g., epizoic algae, epiphytes and parasitic vascular plants. Jackals follow a lion or tiger while arotic fox follows a seal for obtaining food from pieces or bits left by the predators, e.g. :

(i) Epiphytes or Aerophytes : These are vascular plants which are not rooted in soil and grow upon other plants for support (but not food), e.g., some orchids like Vanda, Dendrobium, etc., members of family Bromeliaceae (bromeliads), Dischidia (here a pitcher like structure is present for accumulation of water), Asplenium (bird’s nest epiphyte), etc.

Three types of roots are present in epiphytes :

(a) Clinging roots for attachment.

(b) Absorptive roots for absorption of nutrients and minerals from organic matter accumulated in crevices of bark.

(c) Aerial roots possess a special tissue having thickenings called velamen, which help in absorption of moisture from atmosphere.

(ii) Lianas : These are vascular plants rooted in soil and get support of other plants or objects for their erectness.

Most common lianas in Indian tropical forests is Bauhinia vauhilii.

(iii) Rhizosphere, Rhizoplane, Phyllosphere and Phylloplane : Soil zone around the roots in which a large number of microbes are present due to secretion of sugars, etc., by roots is called rhizosphere. The root proper surface is called rhizoplane. Similarly air zone around leaves having good population of microbes due to secretion of volatile substance by leaves is called phyllosphere and leaf proper surface is called phylloplane.

Some workers consider these as example of mutualism.

Protoco-operation : It is interaction between two living organism of different species in which both are mutually benefitted but they can live without each other. e.g., tick bird ox pecker and Rhinoceros.

(2) Negative interactions : Here one or both organism in association are harmed. Important examples of these interactions are :

Parasitism : A parasite is an organism which lives in constant association with host and gets its food directly or indirectly without killing the host. This phenomenon is called parasitism. In plants four major types of parasites are present.

(i) Total stem parasite, e.g., Cuscuta.

(ii) Total root parasite, e.g., Rafflesia and Orobanche.

(iii) Partial stem parasite, e.g., Viscum and Loranthus.

(iv) Partial root parasites, e.g., Santalum and Thesium.

Predation : A predator is an organism which gets its food from the host after killing it. It does not live in constant association with host. This phenomenon is called predation.

Important examples of predation are :

(i) Grazing and Browsing

(ii) Carnivorous or Insectivorous plants : These plants grow in marshy conditions where there is lack of nitrogen, so in order to fulfil their nitrogen requirement, they catch small insects by some special adaptations in them.

(iii) Predaceous fungi : In soil there are present some fungi like Dactylella, Dactylaria, Arthobotrys and Zoophagus, etc., which are called predaceous fungi.

Competition : It is a type of cold war in which both the organisms in association are harmed. Competition is for basic necessities of life. Competition may be interspecific or intraspecific but intraspecific competition is more severe because organisms of same species have similar basic requirements.

Amensalism : This is a type of association in which one organism in association is harmed and second is not affected.

Amensalism is of two types :

(i) Antibiosis : Some micro-organisms secrete certain chemical substance which kill or inhibit other micro-organisms. These substances are called antibiotics and phenomenon is called antibiosis.

(ii) Allelopathy : Some higher plants also secrete certain poisonous substances which inhibit the growth of other plants. This phenomenon is called allelopathy, e.g., roots of carrot grass or congress grass (Parthenium argentatum), which is most troublesome terrestrial weed in India secrete trans-cinnamic acid which checks the growth of other plants.

Man as biotic factor : Man is always most important biotic factor. He changes the environment by his activities regularly, e.g., by excessive cutting of trees, fire, domestication of plants and animals, by causing different types of pollution, etc.

? Environmental biology : Depending upon the branch studied, it is of several types like population ecology, ecosystem ecology, pollution ecology, habitat ecology, fresh water ecology (limnology), marine ecology (oceanography), forest ecology, conservation ecology, production ecology, radiation ecology, microbial ecology, space ecology, ecological energetics.

? Father of Plant Ecology is Warming : He wrote the first book on plant ecology – ‘Oecology of Plants’ (1895).

? Schroeter and Kirchner (1896) : Coined the terms autecology and syneocology.

? Ethology : Term used by Hilarie (1859) for ecology.

? Hexicology : Term used by Mivart (1894) for ecology.

? Bioecology : Term used by Shelford and Clements for study of both plant and animal ecology.

? Ecological equivalents : Different organisms occupying similar niches in different geographical areas.

? Speciation or Cladogenesis is the phenomenon of development of one or more new species from an existing one by buildup of resproductive isolation between them.

? Reproductive isolation among adjacent members of a population in the absence of a geographic barrier is parapatric speciation.

? Allopatric speciation is the formation of new species from spatially isolated population.

? Sympatric speciation is the formation of new species from segment of a population due to sudden appearence of the reproductive isolation.

? Ecesis is the establishment of organisms in an area in to which they have come by dispersal or migration.

? Microhabitat is a part of habitat having specific property e.g., forest floor, tree trunk.

? Ecades/Ecophenes : Individuals which have the similar genetic constitutions.

? Ecotypes/Ecological races : Individuals which have the different genetic constitution.

? Keystone species are species which influence ecosystem and determines it’s properties.

? Direct factors : Factors which influence growth and distribution of organisms directly, e.g., light, temperature, soil water, soil minerals, atmospheric humidity.

? Indirect factors : They are factors which express their effect on organisms through direct factors, e.g., wind, rainfall, soil texture.

? Remote factors : The factors influence growth and distribution of organisms generally through indirect factors which in turn affect the direct factors, e.g., topographic factors like attitude.

? Crypsis : It is a type of colouration in which an animal helps to camouflage in its natural environment. It may enable the animal to match or blend with its surroundings.

? Probiosis : Opposite of antibiosis, as stimulating growth of useful intestinal flora.

? Biotype : A clearly demarcated unit of environment showing uniformity of principal habitat conditions is known as a biotope e.g., a sand desert, a sandy or rocky beach etc.

? Snow line : It is zone in latitude and attitude beyond which snow occurs permanently.

? Measurement of rain : Rain gauge.

Ecology (General)

The branch of Botany dealing with the distribution of plants on the earth’s surface is called

(a) Ecology (b) Phytology

Paleo–ecology is referred as the study of

(a) Living organisms with environment

(b) Extinct organisms with their environment

(d) None of these

Population whose members reproduce asexually are termed

(a) Panimictic (b) Amphimictic

The light intensity can be measured by

(a) Sacchi disc (b) Lux photometer

Energy contents of macrophytes may be estimated by

(a) Calorimeter

(b) Energy measuring apparatus

(d) None of the above

Who defined ecology as the study of the relations of all organisms to all its environments

(a) Taylor (b) Odum

Who defined ecology as the study of structure and function of nature

(a) Haeckel (b) E.P. Odum

Who defined ecology as the study of form, function and factor

(a) Odum (b) Climents

Who defined ecology as the reciprocal relationship between organisms and their environments

(a) Misra (b) Haeckel

The idea of food chain was introduced by which one of the following ecologist

(a) Tansley (b) Elton

Which one of the following scientists is famous for his contributions in ecological researches

(a) R.N. Singh (b) M.S. Swaminathan

The functional unit of ecology is the

(a) Organism (b) Biosphere

Index of environmental health is determined by the change in the composition of

(a) Communities (b) Niches

Match the following

I II

(A) Synecology (I) Study of an individual with his environment

(B) Autecology (II) A population of species growing together

(D) Biomass (IV) A group of biotop

A B C D

(a) II III IV I

(b) II I III IV

(d) IV III I II

‘‘Biocoenosis’’ is the study of

(a) Environment

(b) Living

(d) None of the above

Turbidity index of water at different depth is obtained by

(a) Lux photometer (b) Turbidity measuring disc

Study of inter-relationship between a species and its environment of a forest is called

[BHU 1975, 88; MP PMT 1989; KCET 2000]

(a) Forest ecology (b) Autecology

The study of communities of various genera and species is called [JIPMER 2002]

(a) Palaecology (b) Synecology

Which one of the following is wrongly matched

[Kerala CET 2005]

(a) Temperate zone – 20 – 40° latitude

(b) Hypolimnion – Thermal stratification in lakes

(d) Profundal zone – Dark zone

(e) Ecotherms – Cold blooded animals

What percentage of solar radiation is reflected in the outer space by trophosphere

(a) 10% (b) 17%

The animal playing the most dangerous role in an ecosystem is

(a) Snake (b) Lion

Grazing is an example of [NCERT 1979]

(a) Negative pollution (b) Positive pollution

The soil near the surface is usually darker than about one meter down, this is because the top soil [CPMT 1985; AIIMS 1999]

(a) Is richer in Ca and Mg

(b) Contains more organic matter

***

(d) Is drier than the sub soil

Plants growing in shady regions a [JIPMER 1990]

(a) Sciophytes (b) Xerophytes

Rotation of crops is essential for

[DPMT 1991; AIIMS 1999; CPMT 2002]

(a) Increasing the quantity of proteins

(b) Increasing the quantity of minerals

(d) Getting different kinds of crops

The factor governing the structure of earth surface is

[BHU 1995]

(a) Topographic (b) Edaphic

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

(c) “Biocoenosis” is also used for community. Community is the interaction between group of organisms and their environmental conditions.
(b) The study of reciprocal relationships between every stage of development of a population/species and its environment is called autecology.
(b) Synecology is the study of reciprocal relationships between composition, organisation and development of communities and their environment.
(a) Temperate zone is the part of the earth between the tropics and the poles.
(b) Top soil contains decomposed and amorphous organic matter composing of sand with humus.
(a) Those plants which grow best in shade or diffused light are called sciophytes or heliophobous or photophobous or shade loving plants.
(c) If the same crop is grown year after year, fertility of soil is lost due to utilization of same minerals again and again. Soil fertility is usually maintained in the field by rotation of crops i.e., a crop is alternated by a leguminous crop.
(a) Topographic factors are concerned with the physical geography of the earth in an area.

Ruthless exploitation and pollution of the environment has increased the magnitude of waste materials which has disturbed the operations of all important

(a) Biomes (b) Ecosystems

The study of inter-relationship between living organisms and their environment is called [CPMT 1977, 89; AMU 1989]

(a) Ecosystem (b) Phytogeography

Term ‘ecology’ was proposed by

[CPMT 1983; RPMT 1995; MP PMT 2003; KCET 2004]

(a) William (b) Odum

Biotic potential refers to [AIIMS 1986]

(a) Increase of population under optimum conditions

(b) Increase of population under given conditions

(d) Increase of population under climatic conditions

P. Odum is a leading [BHU 1988; HP PMT 2005]

(a) Bryologist (b) Physiologist

The term ‘biocoenosis’ was proposed by

[MP PMT 1988, 2000; KCET 2001]

(a) Tansley (b) Carl Mobious

Ecology takes into account only [JIPMER 1989]

(a) Environmental factors only

(b) Plant adaptations only

(d) All of the above

World environment day is celeberated on

[MP PMT 1991; CPMT 2002; KCET 2004]

(a) 15^th March (b) 15^thApril

Ecological factors which prevent a species from producing at its maximum rate is termed as [AMU 1990]

(a) Survival curve (b) Ecological drift

The ecologically fixed and genetically irreversed species are called [CPMT 1999]

(a) Ecotone (b) Ecological equivalents

Biogenetic law was putforward by [EAMCET 1993]

(a) E. Haeckel (b) Charles Darwins

Agrostology is related with the study of [RPMT 1997]

(a) Agricultural growth (b) Epiphytes

The plants and animals living in a given area form

[CPMT 1998; MP PMT 2002]

(a) Biological community (b) Ecotone

Phytotron is a device by which [AIIMS 1998]

(a) Mutations are produced in plants

(b) Plants are grown in controlled environment

(d) Leaf fall occurs on abscission layer

Name the famous plants ecologist [MP PMT 1998]

(a) Jagdish Chandra Bose (b) Birbal Sahani

On based temperature plants are classified by [RPMT 1999]

(a) Warming (b) Climent

The term ‘niche’ of a species refers to [AFMC 1999]

(a) Specific and habitual function

(b) Specific place where an organism lives

(d) Specific function of organism

The term ecology was coined by [BHU 2001; AFMC 2004]

(a) Linnaeus (b) William

Number of endangered species of angiosperms in India is

[KCET 2001]

(a) 487 (b) 3000

The carrying capacity of a population is determined by its

[BHU 2001]

(a) Birth rate (b) Death rate

Tetonic is the study of [MHCET 2001]

(a) Earthquakes (b) Earth’s crust

A community is defined as [CBSE PMT 2001]

(a) A group of birds (b) A collection of species

Distribution of different plant geographically is called

[AFMC 2002; DPMT 2004]

(a) Allopatric (b) Sympatric

Group of two or more than two plant species is called as

[RPMT 2002]

(a) Plant community (b) Animal ecosystem

Study of environment and animals relation [CPMT 2002]

(a) Ecosystem (b) Phytosociology

Which of the following statements is true regarding individuals of same species [CBSE PMT 2002]

(a) They are interbreeding

(b) They live in same niche

(d) They live in different habitate

Which of the following isolation is important for speciation

[CBSE PMT 2002]

(a) Seasonal (b) Tropical

Species are considered as [CBSE PMT 2003]

(a) Real units of classification devised by taxonomists

(b) Real basic units of classification

(d) Artificial concept of human mind which cannot be defined in abosolute terms

“Exobiology” refers to the study of [BVP 2003]

(a) Exodermis (b) Terrestrial organism

Y–shaped energy flow model was given by

(a) H.T. Odum (b) E.P. Odum

The ecological niche of population is a [MHCET 2003]

(a) Geographical area that it covers

(b) Place where it lives

(d) None of these

Biological concept of species is mainly based on

[BHU 2004; BVP 2004]

(a) Reproductive isolation

(b) Morphological features only

(d) Morphology and methods of reproduction

Name the term used to describe a single dominant species that dictates community structure [Kerala PMT 2004]

(a) Pioneer species (b) Transitional species

(e) Exogenous species

What is a keystone species [CBSE PMT 2004]

(a) A rare species that has minimal impact on the biomass and on other species in the community

(b) A dominant species that constitutes a large proportion of the biomass and which affects many other species

(c) A species which makes up only a small proportion of the total biomass of a community, yet has a huge impact on the community’s organization and survival

(d) A common species that has plenty of biomass, yet has a fairly low impact on the community’s organization

Which one of the following correctly represents an organism and its ecological niche [AIIMS 2005]

(a) Vallisneria and pond

(b) Desert locust (Scistocerca) and desert

(d) Vultures and dense forest

Habitat together with functions of species constitute its

[CPMT 2005]

(a) Trophic level (b) Boundary

The organisms spending most of the time in transitional area between two communities are called [HP PMT 2005]

(a) Exotic species (b) Edge species

Which of the following is correct [Orissa JEE 2005]

(a) 99% of existed species are extinct

(b) 25% of existed species are extinct

(d) 30% of existed species are extinct

The species of plants that play a vital role in controlling the relative abundance of other species in a community are called [Kerala CET 2005]

(a) Edge species (b) Link species

(e) Successful species

Identify the correctly matched pair [CBSE PMT 2005]

(a) Basal convention – Biodiversity conservation

(b) Kyoto protocol – Climatic change

(d) Ramsar convention – Ground water pollution

Environment (Abiotic and Biotic factors)

‘Eco’ term refers as

(a) Biosphere (b) Environment

The major characteristics of the vegetation of a locality are controlled by

(a) Man only (b) Mainly by climate

Ozone layer depletion or hole in ozone layer is being found in

(a) North pole (b) South pole

The resource which regulates the flow of energy in desert ecosystem is the availability of

(a) Light (b) Water

Which of the following ecological factor exerts a direct effect

(a) pH (b) Topography

Maximum water vapour which can be held in atmosphere is

(a) Relative humidity (b) Absolute humidity

What will be the environmental consequence of 25% increase of CO₂ level in our atmosphere

(a) Direct pollution (b) Death of all plants

The average concentration of CO₂ in the atmosphere is

(a) 10 ppm (b) 100 ppm

The main aim of ‘Earth Summit’ organised at Brazil was

(a) To think over ozone layer depletion in stratosphere

(b) To increase oxygen in atmosphere

(d) To use solar energy

Which of the following is capable of causing green house effect in the environment

(a) Nitrogen (b) Hydrogen

In the environment, ozone is known for its

(a) Harmful effects

(b) Useful effects

(d) Inert nature

The soil organisms are

(a) Harmful to the plants growing in the soil

(b) Useful to plants growing in the soil

(d) Both harmful as well as useful to plants growing in the soil

‘‘Biomass’’ is the

(a) Dry weight of organisms

(b) Fresh weight of organisms

(d) None of the above

Prolonged liberal irrigation of agricultural fields is likely to create the problem of [CBSE PMT 2005]

(a) Acidity (b) Aridity

Constant grazing and browsing in an area may ultimately result in the formation of

(a) Dense forest (b) Grasslands

If all the green plants were to disappears from the earth

(a) All the animals will die

(b) Only herbivorous will die

(d) It will not matter to any animal

A characteristic which enables an organism to live in an environment is called

(a) Factor (b) Ecotype

Which of the following factors cannot be regarded as belonging to a non-living environment

(a) Light (b) Temperature

Of the several gases in atmosphere, plant life mostly depends upon

(a) Concentration of O₂ (b) Availability of CO₂

Which of the following is an indirect ecological factor

(a) Temperature (b) Soil structure

Humus is

(a) A mixture of clay sand and loam

(b) Heavy soil with mineral salts

(d) Light soil with lime

The equilibrium of the species is disturbed by

(a) Overgrazing (b) Farming

Mild grazing of plants by herbivores

(a) Retards growth (b) Arrests growth

“Pedology” is the study of [BHU 1979]

(a) Soil (b) Locomotion of animals

One of the effects of dust is to cause [DPMT 1980]

(a) Opening of stomata (b) Closure of stomata

Release of phosphates and nitrates in water bodies(e. rivers and lakes) lead to [AIIMS 1987]

(a) Increased algae growth

(b) Increased growth of decomposers

(d) Reduced algae growth

Plants grow sparsely in arid regions of the world

[CPMT 1987]

(a) Only because of high temperature

(b) Because no seeds fall on their soil

(d) Because the soil is sandy

Ultraviolet radiation from sunlight cause the reaction that produce

[CPMT 1982, 83; MP PMT 1988; CBSE PMT 1990]

(a) Carbon monoxide (b) Sulphur dioxide

Maximum contribution of O₂ is from [CBSE PMT 1989]

(a) Phytoplankton (b) Grasslands

Quantity of CO₂ in the atmosphere is about

[MP PMT 1991; CBSE PMT 1997; RPMT 1997]

(a) 0.003% (b) 0.03%

Which of the following gas is most harmful for plants

[CPMT 1992]

(a) N₂ (b) SO₂

Soil salinity is measured by [BHU 1995]

(a) Porometer (b) Potometer

Which biological factor is responsible for poor vegetation in deserts [CPMT 1993]

(a) Grazing by animals and goats

(b) Low rainfall

(d) Native mankind

If carbon dioxide is withdrawn from the biosphere, which organism would first experience negative effects

[MP PMT 1993]

(a) Primary producers (b) Producers

Which of the following is ecological energy source

[Bihar 1995]

(a) Air (b) Water

(e) Fire

Which of the following is a climatic factor [Pune CET 1998]

(a) Oxygen (b) Temperature

The sun loving plants are referred to as

[CPMT 1998; Pb. PMT 1999]

(a) Halophytes (b) Heliophytes

If there was no CO₂ in the earth’s atmosphere, the temperature of earth’s surface would be [CBSE PMT 1998]

(a) Same as present

(b) Less than the present

(d) Dependent on the amount of oxygen in the atmosphere

Edaphology is the relationship between [AIIMS 1999]

(a) Plant and biosphere (b) Animal and ecosystem

Edaphic factors are related to

[CPMT 1976, 2000; KCET 1994]

(a) Soil (b) Animal

Removal of soil by the action of wind and water is known as

[MP PMT 1988; JIPMER 1987; CPMT 1984]

(a) Soil erosion (b) Soil conservation

An area of soil is thoroughly wetted and allowed to drain until capillary movement of water stopped. The water contents of the soil will give an estimate of its

[AIIMS 1980; MP PMT 1990; AFMC 1987; CPMT 1992]

(a) Capillary water (b) Storage water

Deforestation has an alarming effect on

[DPMT 1984, 86; AIIMS 2001]

(a) Increase in grazing area

(b) Sunlight

(d) Soil erosion or desertification of habitat

The best soil for healthy and vigorous growth of the plant is

[DPMT 1974, 83; BHU 1991; 1995]

(a) Clay (b) Loam

The pH of a fertile soil is usually around

[CPMT 1977, 83, 87; MP PMT 1989; CBSE PMT 2001]

(a) 2 – 3 (b) 6 – 7

The components of a soil are

(a) Inorganic and organic components

(b) Water and air

(d) All the above

Solubility and availability of plant nutrients are more related to

[EAMCET 1981; BHU 1984]

(a) Soil pH (b) Soil porosity

Loss of upper fertile layer of soil is known as [MP PMT 1988]

(a) Pedogenesis (b) Pedosolization

Water logging occurs in [CPMT 1990]

(a) Clay soil (b) Loamy soil

Deep black soil is considered to be highly productive due to high proportion of [CBSE PMT 1991]

(a) Silt and earthworm (b) Clay and humus

Sheet erosion is caused by [CPMT 1990]

(a) Fast running rivers (b) Wind

Mulching helps in [BHU 1983]

(a) Soil fertility

(b) Moisture conservation

(d) Soil sterility

Soil conservation can be best achieved by having

[CPMT 1988]

(a) Wind screens (b) Good plant covers

The process of laterization results into [Bihar 1989]

(a) Degradation of soil (b) Formation of humus

Salinity of the soil is often caused due to [CPMT 1989]

(a) Accumulation of soluble minerals near or in the surface in arid region

(b) Excessive addition of water

(d) Excessive leaching

Insectivorous plants grow on [CPMT 1994]

(a) N₂ deficient soil (b) O₂ deficient soil

Soil formed by transportation of disintegrated parent material from one place to another is called

[Pune CET 1998]

(a) Light soil (b) Alluvial soil

Soil erosion is greater when [Pune CET 1998]

(a) There is no rain

(b) The rainfall is low

(d) The rainfall is received in heavy downpour

When one organism is benefitted without affecting the others is called [CPMT 1977, 83, 2000; DPMT 1984, 92]

(a) Parasitism (b) Commensalism

Biotic factors are [CPMT 1981]

(a) Chemical factors of soil which affect life

(b) Physical factors of soil which affect life

(d) Factors of atmosphere which affect life

Which of the following is not a biotic component

[MP PMT 1990]

(a) Phytoplankton (b) Herbivores

If the strong partner is benefitted and the weak partner is damaged, it is known as [NCERT 1980]

(a) Amensalism (b) Symbiosis

The best source of energy in the environment is [DPMT 1992]

(a) Water (b) Soil

Mycorrhiza, a relationship between fungi and roots of higher plants is [CPMT 1993]

(a) Parasitic relationship (b) Saprophytic relationship

The Orobanche plant is [CPMT 1993]

(a) Partial root parasite (b) Total root parasite

Which one of the following factors is biotic [CPMT 1993]

(a) Photoperiod

(b) CO₂ content to the soil

(d) Rainfall

Which is the main causative factor of desertification

[CBSE PMT 1995]

(a) Developmental activities (b) Tourism

Crop rotation is helpful because [CPMT 1995]

(a) It gives more nitrates in the soil

(b) It gives more sulphates in the soil

(d) It gives more phosphorus in the soil

Stopage of reproduction in an organism by creating hurdle in its biology or physiology or its distruction by use of another organism is known as [CBSE PMT 1996]

(a) Predation (b) Competition

Which of the following statements is incorrect [KCET 1998]

(a) Lichen, an association of fungus and algae is an example of Mutualism

(b) Those Epiphytes which use other plants for support only and not for water or food supply are examples of Commensation

(d) Mutualism, protocooperation, commensalism cannot be included under Symbiosis

When the organisms live together in such a manner that one organism is benifitted, while other has no effects, it is called

[CPMT 1998]

(a) Commensalism (b) Parasitism

Territoriality occurs as a result of

[AFMC 1999; BVP 2000; Pb. PMT 2004]

(a) Parasitism (b) Predation

In an aqueous environment, the microscopic animals are collectively called

[CPMT 1985; MP PMT 1999; CBSE PMT 2001]

(a) Herbivores (b) Carnivores

Soil is a mixture of [Pb. PMT 2000]

(a) Sand and clay (b) Sand and humus

Clay soil is obtained [Pb. PMT 2000]

(a) In desert (b) Around ponds

A bird enters the mouth of crocodile and feed on parasitic leeches. The bird gets food and crocodile gets ribs of blood sucking leeches. Both the partners can live independently. Such an association is [BHU 2001]

(a) Mutualism (b) Amensalism

Ozone hole means [AFMC 2001]

(a) Hole in the stratosphere

(b) Same concentration of ozone

(d) Increase in the concentration of ozone

Which of the following soil is transported by air [CPMT 2002]

(a) Alluvial (b) Aerial

Surface water of lake enrich in having [AFMC 2003]

(a) Organic substance (b) Minerals

Which one of the following is a right matching pair of certain organism(s) and the kind of association [AIIMS 2003]

(a) Shark and sucker fish-Amensalism

(b) Algae and fungi in lichens-Mutualism

(d) Cuscuta (dodder) growing in other flowering plants-epiphytism

Ozone saves the biosphere by absorbing the high energy radiation called [Kerala CET 2003]

(a) Infra-red (IR) (b) Ultraviolet ray (UV)

Humus is found in [CPMT 2003]

(a) Top portion of soil (b) Middle portion of soil

Humus is important for plant growth because [BVP 2003]

(a) It is partially decomposed

(b) It is derived from leaves

(d) It is made up of dead organic matter

The possible beneficial affect of grazing animals is the

[BVP 2003]

(a) Removal of wild animals

(b) Eradication of weeds

(d) Addition of their excrete to the soil

In commensalism [MP PMT 2004]

(a) Both partners are benefitted

(b) Both partners are harmed

(d) None of these

The instrument which measures wind velocity is

[MP PMT 2004]

(a) Lactometer (b) Anemometer

In which one of the following pairs is the specific characteristic of a soil not correctly matched

[CBSE PMT 2004]

(a) Chernozems – Richest soil in the world

(b) Black soil – Rich in calcium carbonate

(d) Terra rossa – Most suitable for roses

Acclimatization is [MHCET 2004]

(a) Pure-line breeding

(b) Pure-line selection

(d) Adaptation to new environment

If the high altitude birds become rare or extinct, the plants which may disappear along with them are [AIIMS 2004]

(a) Pine (b) Oak

Which is not a part of atmosphere [MP PMT 2005]

(a) Light (b) Temperature

An association of two species where both the partners derive mutual benefit from each other is [HP PMT 2005]

(a) Parasitism (b) Symbiosis

Small fish get stuck near the bottom of a shark and derives its nutrition from it. This kind of association is called as

[BHU 2005]

(a) Symbiosis (b) Commensalism

A branch of science in which forest crop can be grown in desired pattern is

(a) Histology (b) Horticulture

Which one of the following words has been used by Prof. R. Misra for ecosystem

(a) Biocoenosis (b) Ecocosm

Species which occupy a similar ecological niche in similar communities occupying different biogeographical regions are

(a) Ecotones (b) Biomes

Study of relationship between communities and environment is called [CPMT 1999; JIPMER 2001]

(a) Ethnology (b) Ecology

The closely related morphologically similar sympatric populations, but reproductively isolated, are designated as

[CPMT 2000]

(a) Clines (b) Demes

The abundance of a species population within its habitat is called [AIIMS 2001, 02]

(a) Niche density (b) Regional density

Which of the following statements is correct for species

[Wardha 2005]

(a) The members of a species occupy the same habitat

(b) They are morphologically similar

(d) They cannot interbreed with members of the other species

Which of the following is not true for a species

[CBSE PMT 2005]

(a) Members of a species can interbreed

(b) Gene flow does not occur between the populations of a species

(d) Variations occur among members of a species

The side effects of heavy and constant grazing is that the

(a) Upper layer of the soil are loosened and are eroded

(b) Lower layer are made more compact and root respiration is interfered with

(d) All the above

Maximum ozone concentration is

(a) One part per hundred (b) One part per thousand

When young plants are grazed too heavily, they get killed because of

(a) Mechanical injury to roots

(b) Roots are starved

(d) Mechanical injury to the branches

Good soil is [CPMT 1972, 78; MP PMT 1988]

(a) Which holds whole of water enters into it

(b) Which allows the limited amount of water into it

(d) Which allows to pass water very quickly from it

Plants are killed in winter by frost [BHU 1977]

(a) Because of dessication and mechanical damage to the tissue

(b) Because no photosynthesis take place at such a low temperature

(d) Because there is no transpiration

In recent years, there has been an increasing incidence of floods in the plains of northern India because

[DPMT 1982, 83]

(a) There has been an increase in annual rainfall

(b) The rate of silting of dams has gone up

(d) Increased areas of land is being self cultivated

In the mountains, there is a lot of moisture and water and still the plants are xerophytes, because [CPMT 1985]

(a) Water turns into snow on mountains

(b) Water runs away due to the presence of slopes and can not be used by plant (physiological dryness)

(d) None of them is correct

The major man made biotic factor is [CPMT 1986]

(a) Ploughing (b) Grazing

Which of the following changes would be likely to make terrestrial life on this planet impossible [CPMT 1989]

(a) A decrease in mean temperature by 10° C

(b) Change in atmosphere permitting all the solar radiation reaching the upper atmosphere to penetrate to the surface of the earth

(d) Disappearance of the moon

The change of the lighter coloured variety of peppered moth Biston betularia to its darker variety (carbonaria) is due to

[CBSE PMT 1995]

(a) Mutation of single Mendelian gene for survival in the smoke–laden industrial environment

(b) Deletion of a segment of gene due to industrial pollution

(d) Translocation of a block of genes in chromosomes in response to heavy carbons

At which lattitude, heat gain through insolation approximately equals heat loss through terrestrial radiation

[CBSE PMT 2005]

(a) North and South (b) 40° North and South

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 : No two species can occupy the same ecological niche in a habitat.

Reason : A habitat can contain only one ecological niche.

Assertion : There is a need to understand the ecological principles.

Reason : One studies the interactions between organisms and their environment in ecology.

Assertion : With increase in population size, environmental resistance tends to increase.

Reason : This is a nature’s way to check the expression of biotic potential.

Assertion : Biotic potential is realised only when the environmental conditions are limiting.

Reason : Under such conditions only, the population size can increase at the maximum rate.

Assertion : Individual is the unit of Ecology.

Reason : Biome occurs at the top of ecological hierarchy.

Assertion : Biotic community has higher position than population in ecological hierarchy.

Reason : Population of similar individuals remains isolated in the community.

Assertion : Speciation is always a very slow process.

Reason : Genetic drift is one of the causes for speciation.

Assertion : Removal of keystone species doesn’t cause any serious disruption in the functioning of the community.

Reason : Keystone species are low in abundance (or biomass) than the dominant species.

Assertion : In S-shaped growth form, the population may abruptly crash after attaining a peak value.

Reason : Exponential growth can not be sustained infinitely due to environmental resistance.

Assertion : Ecological equivalents possess similar types of adaptations.

Reason : Ecological niche is the total interaction of a species with environment.

Assertion : Microclimate generally differs from the prevailing regional climatic conditions.

Reason : Microclimate represents the climatic conditions that prevail at local scale or in areas of limited size.

Assertion : Climate is said to entail the short term properties of the atmosphere (such as temperature, rainfall etc.) at a given place and time.

Reason : Temperature and rainfall are the most important factors which determine the climate of an area.

Assertion : Heliophytes, generally have low photosynthetic, respiratory and metabolic activities.

Reason : This is an adaptation of heliophytes to high intensity of light.

Assertion : Relationship between sea anemone and hermit crab is said to be an example of obligate mutualism.

Reason : Obligate mutualism is a positive (beneficial) interaction between two species.

Assertion : The relationship between sucker fish and shark is considered to be an example of parasitism.

Reason : Sucker fish gets food and shelter from shark and also alters the growth of the shark.

Assertion : Predation and parasitism are considered to be negative interactions.

Reason : Parasites and predators limit the population of their host species.

Assertion : The crown fires are most destructive as they burn the tree top.

Reason : Due to crown fire the temperature of that area may rise upto 700°C. [AIIMS 1995]

Assertion : Living organisms are regarded as closed systems.

Reason : Energy of living organisms can not be lost or gained from external environment.

[AIIMS 2002]

Ecology (General)

1	c	2	b	3	c	4	b	5	c
6	d	7	b	8	c	9	b	10	b
11	d	12	a	13	b	14	d	15	c
16	c	17	a	18	c	19	b	20	d
21	d	22	c	23	a	24	a	25	c
26	a	27	b	28	c	29	d	30	b
31	d	32	a	33	c	34	b	35	c
36	a	37	a	38	d	39	a	40	d
41	b	42	d	43	d	44	c	45	a
46	c	47	c	48	c	49	d	50	b
51	a	52	c	53	b

Environment (Abiotic and Biotic factors)

1	b	2	b	3	b	4	b	5	d
6	c	7	b	8	c	9	a	10	d
11	c	12	d	13	a	14	c	15	c
16	a	17	c	18	c	19	c	20	b
21	c	22	b	23	c	24	a	25	b
26	c	27	d	28	c	29	a	30	b
31	c	32	c	33	b	34	a	35	d
36	b	37	b	38	b	39	c	40	a
41	a	42	c	43	d	44	b	45	b
46	a	47	b	48	c	49	a	50	b
51	c	52	b	53	b	54	a	55	a
56	a	57	d	58	d	59	b	60	c
61	c	62	c	63	c	64	c	65	b
66	b	67	c	68	a	69	c	70	d
71	a	72	d	73	c	74	d	75	b
76	d	77	c	78	c	79	a	80	b
81	b	82	a	83	c	84	d	85	c
86	b	87	d	88	d	89	d	90	c
91	b	92	b

Critical Thinking Questions

1	d	2	b	3	c	4	c	5	d
6	a	7	d	8	b	9	d	10	c
11	b	12	c	13	a	14	c	15	b
16	c	17	b	18	a	19	b

Assertion and Reason

1	c	2	b	3	a	4	d	5	c
6	c	7	e	8	d	9	e	10	b
11	a	12	e	13	d	14	e	15	a
16	a	17	a	18	d

Ecology (General)

(c) Term ‘phytogeography’ is made up of two words phyton = plant and geography i.e. geography of plant distribution.
(c) Apomixis is the formation of new individuals directly through asexual reproduction without involving the formation and fusion of gameter. So, those population whose members reproduce by the process of apomixis are called apomictic.
(c) The famous Indian ecologist, professor R. Misra of Banaras Hindu University has defined ecology as interactions of form, functions and factors.
(c) The term ecology is derived from two greek words, namely Oikos and Logos. Oikos means ‘home’ or ‘habitation’ or a ‘place to live in’. Logos means ‘study’ or ‘discourse’. Hence literally speaking, ecology is the study of organisms at home.
(c) The term ecology is believed to have been coined by Ernst Haeckel (1869) though its first authentic use was made by Reiter (1885).
(a) Biotic potential is the maximum capacity of a population to reproduce under ideal conditions (environmental).
(b) The term biocoenosis is also used for community, which was coined by Carl Mobius (1880).
(d) Ecology is the branch of biology that deals with the inter relationships amongst organisms and interactions between organisms and their environment.
(a) Biological community is the assemblage of interdependent and interacting populations of different species present in an area.
(c) Prof. R. Misra is known as “Father of ecology in India”.
(d) According to Raunkiaer temperature is of the greatest importance in the distribution of plants and the entire vegetation of the earth can be divided in to following 4 classes :

(1) Megatherms (2) Mesotherms

(3) Microtherms (4) Hekistotherms

(b) Ecological niche is specific habitat where an specific species lives.
(c) The carrying capacity of a population is determined by its limiting resources. Carrying capacity is the upper limit of an ecosystem up to which it can provide the basic needs to the population under given circumstances.
(c) A community is an assemblage of populations of plants, animals, bacteria and fungi that live in an area and interact with each other.
(a) Allopatric species are present in different geographical regions, separated by spatial barriers are called allopatric species.
(a) Uniform interbreeding population or group of individuals which freely interbreed among themselves, constitute a species.
(d) The interruption of gene flow (reproductive isolation) between populations is a pre-requisite for the formation of new species.
(b) Species is the basic unit of classification. Only the species has a real existence, other units of classification are man made artificial groups.
(a) A species can be defined as “a group of closely related organisms which are capable of interbreeding to produce fertile offspring. Thus biological concept of species is mainly based on reproductive isolation, which preserve the integrity of the species by checking hybridization.
(c) According to Paine (1969), keystone species are those whose role or activities determine community structure.
(d) Niche is specific part of habitat occupied by individuals of a species which is circumscribed by its range of tolerance, range of movement microclimate, type of food and its availability.
(b) The species which are found primarily, most abundantly or spend most of their time in ecotone or community boundary are known as edge species.
(b) Kyotoprotocol is an inter national conference held in Kyoto, Japan obtained commitments from different countries for reducing overall greenhouse gas emissions by 2008-2012.

Environment (Abiotic and Biotic factors)

(b) Because in desert areas, amount of water is less.
(d) Light, temperature, humidity of air, soil air, etc. are the direct factors. Which have direct effect on organisms.
(a) In ‘Earth summit’ held in 1992 in Rio-de-Janeiro (Brazil), the whole world has adopted a proposal to stop use of CFC by the end of 2000. CFC is strong enemy of ozone and cause depletion of ozone layer.
(d) Green house effect now increasing on earth surface due to certain gases like CO₂, CH₄, NO₂ and chlorofluorocarbons.
(c) Ozone is both harmful and beneficial to life on earth. Ozone near the surface of earth is harmful to life and in stratosphere it saves life from harmful solar radiations.
(a) Because animals depend on plants for food and oxygen. Plants are the producer and they trap the energy from sun and convert it into chemical energy by photosynthesis process and this energy is passed to all the living beings. So when plants will disappear the oxygen cycle will be disturbed and crisis of food will result in death of animals immediately.
(c) Ecological adaptations are special characteristics evolved or developed by organisms in order to live comfortably and successfully under a prevailing set of environmental conditions.
(c) Humus is the upper layer of soil in forest which is rich in organic material.
(c) Because mild grazing breaks apical dominance.
(a) Term ‘pedology’ is derived from two words pedos = soil and logy = study i.e. study of soil.
(b) Due to heavy dust, the amount of sunlight will be decreased as a result of which stomata are closed.
(a) Because phytoplanktons (primary producers) are largest in number.
(b) Generally approximately 0.03% or 300 ppm is present in atmosphere.
(c) CO is major environment pollutant. It is a non-irritant but is highly toxic and impairs respiration. CO combine with haemoglobin of blood and reduces its carry capacity.
(b) Deserts have 25 cm (10 inches) or less of precipitation and show poor biodiversity and their productivity is minimum.
(a) Because primary producer first requires CO₂, for the process of photosynthesis by which they make their food.
(d) In any ecosystem the basic or ultimate source of energy is sunlight (Solar radiation)
(b) The plants which grow best in full sunlight are called sun plants or heliophytes.
(b) layer around earth surface acts as insulator and does not allow heat of the earth to escape into space thus keep the earth surface warm.
(a) Soil; because man and animals are biotic factors and temperature is climatic factor.
(a) Top soil is the vital part of the soil and serves as the chief source of nutrition for plants. Loss or disturbance of top soil by natural agents like water, wind, gravity or ice is called soil erosion.
(c) The amount of water retained by a unit weight of undisturbed soil after complete drainage under controlled conditions is called field capacity or holard.
(d) By deforestation the land is exposed to erosion and desertification.
(b) Because in loamy soil the availability of water and air to plants is sufficient.
(a) Because it is a non-porous soil.
(b) Black soil predominantly with clay and humus. This soil is very fertile because most of minerals are present in it.
(c) Due to heavy rain, top fertile soil is removed in the form of thin sheet.
(a) Insectivorous plants are autotrophic in their mode of nutrition but they grow in marshy or muddy soils, which are generally deficient in nitrogen and in order to fulfil their nitrogen requirement.
(b) Commensalism is the relationship between two living individuals of different species in which one is benefitted while the other is neither harmed nor benefitted except to negligible extent.
(c) Living organisms have effect on other living organisms and these constitute biotic factors or living factors.
(c) It is an association between members of two species in which members of one species capture, kill and eat up members of other species. The former is called predator and later is called prey.
(c) An association of two organism in which both partners are benefitted (but can not live separately) e.g. Mycorrhiza, lichens, etc. This is the process of mutualism or symbiosis.
(b) Because CO₂ is released through plants in soil by repiration process.
(c) Excessive falling of trees and overgrazing remove the vegetation cover and land is exposed to erosion and desertification.
(a) If the same crop is grown year after year, fertility of soil is lost due to utilization of same minerals again and again, thus disturbing the soil structure, which facilitates soil erosion. Legumes are useful in rotation of crops because of having nodulated roots and it gives more nitrates in the soil.
(c) Biological control methods include using natural predators of pests, using resistant varieties, crop rotation, etc.
(d) An interesting behaviour pattern which results in intraspecific competition for space shelter and food etc, effective control of population size.
(c) Microscopic free floating animals are called zooplanktons. Both microscopic plants and animal are known as planktons.
(d) Protoco-operation is the interaction between two living organism of different species in which both are mutually benefitted but they can live without each other.
(b) In lichens, algae and fungi are symbiotically associated. This association is known as mutualism.
(b) Stratosphere zone of earth’s atmosphere contains a layer of ozone which prevents the earth surface from about 99% of incoming solar UV-radiations.
(a) Humus is found in top portion of soil. It is formed by dead organic material by the process of decomposition.
(c) Humus is total organic matter in the soils. It is rich is NPK. The humus is formed from decay and decomposition of dead plant and animal matter. The humus soil is the best soil as it has got high water holding capacity, high porocity, aeration and high organic content.
(d) Although grazing is harmful for plants but grazing may beneficial by adding their excretion into soil, which provides essential mineral nutritions to plants.
(d) Acclimatization is the development of a favourable morphological and physiological response to a change in environment.
(c) Because edaphic factors affects through soil and rest are the climatic factors.
(b) Commensalism is an association between 2 organisms in which one is benefitted without the other being harmed e.g.– Sucker fish has a hold fast and attached itself underside of shark and thus remains protected and also get food left over when shark is feeding on its prey.

Critical Thinking Questions

(d) Silviculture or Forestry is the study deals with the development of forests and utilization of forest products.
(c) The example of ecological quivalents are cow in India and Kangaroo in Australia (both herbivores) are ecological equivalents.
(d) Members of a species can interbreed. Each species is reproductively isolated from every other species.
(b) Gene flow means the spread of genes through populations as affected by movements of individual and their propagules e.g., spores, seeds etc. Gene flow ensures that all populations of a given species share a common gene pool i.e., it reduces difference between populations. The interruption of gene flow between populations is a pre-requisite for the formation of new species.
(a) When a plant is exposed to extremes of temperature it gets injured and the injuries are of three types namely desiccation, chilling and freezing.
(b) Steep slopes cause fast, running of water which result in erosion and do not permit the accumulation of humus so the soil becomes denuded. In such soil plants cannot grow properly and vegetation changes into xerophytic plants. In valleys humus accumulates, so they have luxuriant vegetation and slopes contain xerophytic plants.
(c) Man is always most important biotic factor. He changes the environment by his activities regularly. e.g. by excessive cutting of trees, fire, domestication of plants and animals by causing different types of pollution etc.

Assertion and Reason

(c) The place where an organism lives is called its habitat. Habitats are characterised by conspicuous physical features, which may include the dominant forms of plant and animal life. Habitat may also refer to the place occupied by an entire biological community. For example, a large number of species are found in a forest habitat. On the other hand, the ecological niche of an organism represents (i) the range of conditions it can tolerate (ii) the resources it utilises, and (iii) its functional role in the ecological system. A habitat can contain many ecological niches and support a variety of species. Each species has a distinct niche, and no two species are believed to occupy exactly the same niche.
(b) Ecology is the branch of biology that deals with the study of interactions between organisms and their environment. The word ecology, as given by a German biologist, Ernest Haeckel, in 1869, has its origin from the Greek word, Oikos meaning ‘home’ and logos meaning ‘to study’. In ecology, we study the distribution and abundance of organisms, their interactions among themselves and with the physical environment. The latter is comprised of lithosphere, hydrosphere and the atmosphere. Ecology has progressed from natural history and biogeography to ecosystem ecology. More recently global ecology with an emphasis on climate change, biodiversity, conservation and ecological sustainability has been emphasised. An understanding of ecological principles is needed for the sustainable use of resources and to evolve strategies for the mitigation of environmental problems at local, regional and global levels.
(a) The inherent maximum capacity of an organism to reproduce or increase in number is termed biotic potential (designated by the symbol ‘r). Biotic potential is realised only when the environmental conditions are non-limiting, so that natality rate (birth-rate) is maximum and mortality rate (death –rate) is minimum. Under these conditions, population size increases at the maximum rate. However, nature keeps a check on the expression of biotic potential. For example, if a pair of flies is allowed to reproduce unchecked, the fly population may outweigh the earth in a few years. The environmental check on population size, or its biotic potential is called environmental resistance. With increase in population size, the environmental resistance (against the population) tends to increase.
(d) The inherent maximum capacity of an organism to reproduce or increase in number is termed biotic potential (designated by symbol ‘r‘). Biotic potential is realised only when the environmental conditions are non-limiting, so that the natality rate is maximum and mortality rate is minimum (natality is the increase in number of individuals in a population under given environmental conditions and natality rate is the increase in individuals expressed per unit time. Mortality is the loss of individuals due to death in a population under given environmental conditions and mortality rate indicates the number of individuals dying over a period of time). Under these conditions population size increase at the maximum rate. However, nature keeps a check on the expression of biotic potential. With increase in population size, the environmental resistance (against that population) tends to increase. The environmental resistance represents the limiting effect of abiotic and biotic factors (e.g., water, space, food, competition etc.) that do not allow organisms to attain their biotic potential and keep the population size at a much lower level.
(c) An individual is a distinct living being which carries out all the life processes in its body, separate from those being performed in the body of others. It is a basic unit of ecological hierarchy. Hierarchy means “an arrangement into a graded series.” Biome is a convenient term in wide use for a large regional or subcontinental biosystem characterized by a major vegetation type or other identifying landscape aspect, as, for example, the temperate deciduous forest biome. The largest, and most nearly self-sufficient biological system is often designated the biosphere or ecosphere, which includes all the earth’s living organisms interacting with the physical environment as a whole to maintain a steady-state system.
(c) The organisms of all the species that live in a particular area and interact in various ways with one another form biotic community. Biotic community is a grouping higher than population. It is an assemblage of all the populations of different organisms occurring in an area. The different populations of a community do not remain isolated. They show interactions and inter-dependence.
(e) The phenomenon of development of a new species from a pre-existing one is called speciation. Although it is a slow and gradual process, mutations can give rise to new species all of a sudden, e.g. Ancon sheep, Hornless cattle. Genetic drift is the elimination of the genes of certain characters when a section of population migrates or dies of natural calamity. It changes gene frequency of remaining population. Accumulation of new variations and adaptations to the new habitat would further produce structural and functional changes that could give rise to new species.
(d) Only one or few species in a community are in sufficient abundance (having high density) to dominate and influence other species in terms of numbers and biomass production. Such species are called dominant species. But there are other species which have much greater influence on community characteristics, relative to their low abundance or biomass. Such species are called keystone species. These species play a vital role in controlling the relative abundance of other species. Removal of keystone species causes serious disruption in the functioning of the community.
(e) Population have characteristic patterns of growth with time. These patterns are known as population growth forms. There are two basic population growth forms, designated as J-shaped and S-shaped. In the case of J-shaped growth form and not the S-shaped growth form that the population grow exponentially, and after attaining the peak value may abruptly crash. The exponential growth can not be sustained infinitely, because, not only environment is ever changing, food and space are also limited.
(b) Organisms occupying similar ecological niches but living in different regions are called ecological equivalents. Ecological equivalents possess similar types of adaptations but belong to different taxonomic groups . For example; succulents of American deserts are cacti while those of African desert are euphorbias.
(a) Microclimate generally differs from the prevailing regional climatic conditions, because the microclimate represents the climatic conditions that prevail at local scale or in areas of limited size, such as the immediate surroundings of plants and animals. For example, in a forest, dense foliage reduces the amount of light reaching the ground. This also results in a changed air temperature profile. The day-time air temperature inside the forest is lower than outside. Also the interior of a forest may be more humid than a nearby non-forested area.
(e) It is not the climate but the weather, which is said to entail the short-term properties of the atmosphere, such as temperature, pressure, humidity, rainfall, sunshine, cloud cover and wind, at a given place and time. Weather reflects the hourly, daily or weekly changes in the above properties. On the other hand, climate is the average weather of an area, including general patterns of atmospheric conditions, seasonal variations and weather extremes averaged over a long period. Climate entails longer periods, such as seasons, or years. Temperature and rainfall are the two most important factors which determine the climate of an area. Global variations of temperature and rainfall result from differential input of solar radiations in different regions, and from the redistribution of heat energy by winds and ocean currents. Variations in temperature, rainfall, and humidity in different regions of the globe form global climate patterns, which govern all life on earth.
(d) Plants have special traits that help them to enlarge their tolerance limits to light regimes. Heliophytes are the sun adapted plants which are adapted to high intensity of light, and have higher temperature optima for photosynthesis, as well as have high rate of respiration. On the other hand, shade adapted plants also called as sciophytes generally have low photosynthetic, respiratory and metabolic activities. Plants such as ferns and several herbaceous plants growing on the ground under the dense canopy of trees, are shade tolerant plants.
(e) The interactions between populations of species in a community are broadly categorised into positive (beneficial) and negative (inhibitory) interactions, depending upon the nature of effect on the interacting organisms. An association of two species, in which both species are benefitted, is called mutualism. Mutualism is a functional association, not merely living together. Mutualism may be obligate in which species are completely dependent upon each other, for example, in the case of coral reef, coelentrates and algae live in obligate relationship, or mutualism can be facultative in which one species may survive even in the absence of the other partner species. The relationship between sea anemone and hermit carb is an example of facultative mutualism. The sea anemone grows on the back of the crab, providing camouflage and protection (the sea anemone has stinging cells) and, in turn, the sea anemone is transported about reaching new food sources. This type of mutualism is also called protocooperation.
(a) The relationship between sucker fish and shark is an example of commensalism and not parasitism. Commensalism is a positive (beneficial) interaction between two species where one species is benefitted, while the other neigher gets any benefit, nor is adversely affected under normal conditions. Some organisms live inside or outside the bodies of larger animals in order to protect themselves from the enemies and adverse environment. The sucker fish attaches to shark surface with the help of its dorsal fin, which is modified into a holdfast. The sucker fish is dispersed to distant areas with better food supply. Besides, the fish gets protection from predators due to its association with shark. However, the shark does not get any benefit from sucker fish and it is also not affected adversely.

Parasitism, on the other hand, is a negative interaction in which the species smaller in size (the parasite) lives in or on the larger species (the host) from which it obtains food. Parasitism also involves shelter, in addition to food obtained by a parasite. Plants like Cuscuta (dodder), Loranthus (mistlectoe), Viscum and Rafflesia and parasitic plants, which live on other flowering plants. Parasites may alter the population growth of hosts, shorten the life cycle, weaken the host, and drastically reduce the production to the extent of causing sterility.

(a) Predation and parasitism are considered to be negative interactions, because in both of these interactions one species gains and the other suffers. Predation is the interaction between species involving killing and consumption of prey. The species which eats the other is called the predator, and the one consumed is termed the prey. Predation is commonly illustrated by the herbivore – carnivore interaction, grass deer tiger food chain. For example, tiger, the predator keeps check on deer (prey) population. If the predator population increases, it consumes more prey, thereby reducing the population of prey. The reduction in prey population may reduce the population of predator, resulting from starvation and migration. The reduction in predator population may lead to increase in prey population, since they are not preyed upon. The increased prey population may over – graze the grasses and the shortage of herbage may eventually lead to reduction in prey population. It may ultimately affect population of predators. Thus, these relationships stabilise the prey and predator population in a community.

Parasitism is the interaction in which the species smaller in size (the parasite) lives in or on the larger species (the host) from which it obtains food and shelter. Parasites like leeches, tick, lice, mites feed on the body fluids of the hosts. Parasites, like the predators limit the population of the host species. Parasites are generally host-specific, and do not have choice or alternatives like predators. Parasites are smaller in size and have higher biotic/reproductive potential compared to the predators. Parasites have poor means of dispersal and require specialised structures to reach or invade the host.

(a) Crown fires are most destructive. These destroy the canopies of trees and entire vegetational cover of that particular area. Due to this fire, the temperature, rises upto 700°C and may adversely effect the nearly vegetation.
(d) Living organisms are regarded as open system as these can gain or loose energy from external environment. All living organisms restore their energy either directly from sunlight or indirectly from food.

(155)