Organism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRev

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The term ecology was coined and described by E.Haeckel. The term ecology was first authentically used by Reiter.

Father of ecology                                                                                                                           – Reiter

The term Ethology for ecology was used by                                                                      – Geoffroy Hilaire

The term Hexicology for ecology was used by                                                                          – G.H. Mivart

Study of ecology was initiated in India by                                                                               – W. Dudgeon

Father of Indian Ecology                                                                                          – Prof. Ram Deo Misra

First of all term ecology was employed for for study of plants by                                                   – Warming

The study of interaction or inter-relationship of organism with their environment is called ecology.
Organism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRev

Organism and environment are always interdependent, inter related or mutually reactive.

Branches of Ecology – It is based on organism level

1. Autecology or species ecology – Study of the relation of a species with its environment is known
as autecolocy
2. Synecology or Biocoenology or Community ecology – Study of the relation of the group of different species with their environment. Ex. Population, community, ecosystem, biome ecology.


1. The main aim of ecology is to study the interrelationship between organisms. i.e., Plants, animals and

2. Studies like pollution, soil conservation, soil erosion, proper use of land, afforestation, control on
deforestation, regulation of overgrazing, flood control, maintenance of soil fertility etc., are also done
in the ecology.

3. Thus, the scope of this science is very vast.

4. The living world can be dealt at different level of complexities. A molecular biologists restricts itself to
the level of genes & cells whereas a development biologist deals at the level of tissues, organs & organisms. Whereas an ecologist treats the living organisms largely at the level of population, community
& ecosystem.

5. A population is defined as a group of individuals of a species growing in a given area.

6. A community, on the other hand, is collection of populations of different species growing in a given area.

7. The transition zone between two different communities is known as ecotone.
8. A species may be defined as a uniformly inbreeding population spread over a time. Ecologically, a
species is sub-divided into ecotype and the ecotypes into ecads.


Ecotype/Ecological Race/Ecospecies :

1. Formed due to genotypical responce to a particular habitat.

2. Genetically different but interfertile.

3. Adaptations are genetically fixed and irreversible.

4. Variations are not changed if different ecotypes are grown in same habitat

5. Ecospecies with one or more ecotypes.

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Ecades/Ecophenes :

1. Habitat form or environmentally induced variable form of a species.

2. Ecades of same species differ in appearence variation in size, vagetative part, no. growth habits. of leaves, flowers,

3. Have same genetic stock.

4. If habitat changed, variations also changed.

5. Only sometic, temporary & reversible variations.
Ex. : Euphorbia hirta.

Organism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRev


Organism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRev



Organism : Basic unit of study of ecology.

Species : Similar organisms having the potential fertile for interbreed and producing fertile offspring.

Population : Group of individuals of a plant or animal species inhabiting a given area or group of
individuals of a species.

Community : Assemblage of different populations in an area, interacting with each other.

Ecosystem : Biological communities intergrated with it's physical environment through the exchange
of energy and recycling of nutrients.

Land scape : A unit of land with natural boundary having a mosaic of patches, which represents
different ecosystems.

Biome : Large regional unit or ecosystem characterised by major vegetation type (flora) and associated
founa in a specific climatic zone.

Climate/Weather : Short term properties of the atmosphere (Temperature, Pressure, Humidity, Rainfall,
Sun-shine, Cloud cover and Wind) at a given place and time is weather and average weather of an area is climate. Weather change in hours, day, week while climate is long term for year or months.

Microclimate : Climatic conditions that present at a local scale or in area of limited size.

It is an immediate climate (real climate) of an organism which is different from the average climate of
region. eg. Forest floor, burrow and surface of desert.

Habitat : Place where an organism live on or place occupied by an entire biological community.

Microhabitat : Subdivision of habitat.

Ecological Niche : Word given by Grinnel. The range of conditions that an organism can tolerate, the resource it utilize and it's functional role in ecological system. It is a occupational address or functional status of a species in an ecosystem. Each species has a distinct niche and no two species can occupy same niche in a habitat.

Ecological Equivalents - Organism that occupy the same or similar ecological niche in different
geographical regions are known as Ecological equivalents.

eg. Arctic fox and African Jackel, both are scavengers.
Grazers of North America (Pronghorn Antelope, Bison) and Kangaroo's of Australia.

Biosphere : All the earth's terrestrial biomes and aquatic systems constitute biosphere. It includes
lower atmosphere the land and the oceans, rivers and lakes, where living beings are found.


Ecotone - The transition zone in between two communities is called ecotone or tension zone. It has
greater number of species and density or it is a transition zone between two communities where one
type of community is modified into another type of community is known as ecotone.
Ex. : Sea shore, Estury, Prairie and Forest zone.


Edge effect - Species which occur most abundantly and spend their time in ecotone are called edge
species. The tendency to increase variety and density of some organism at the community border is
known as edge effect. It is due to high availability of resources.
Ex. : Species diversity is high in estury.


Ecocline - Variability or gradient of physical factors seperating an ecosystem from another ecosystem
Ex. : Halocline, thermoclime, chemocline.

Biotic potential (Reproductive potential or potential ability) - The term biotic potential was first used by Chapmann.

Under most favourable environmental conditions the maximum reproductive capacity of an species
is known as biotic potential.

Vitality - Capacity of normal growth metabolism and reproduction for survival of a organism or species.
It depends upon weight of plant, stem height, root length,leaf number etc.

Planktons - Planktons are free floating and small organisms which swim to water currents. They lack
locomotory organs or the locomotory organs may be reduced. It includes –
(i) Phytoplankton - Microscopic, inactive floating plants e.g. Diatoms
(ii) Zooplankton - Microscopic, inactive floating animals e.g. Protozoans, Crustaceans, Larvae.

Nektons - Those aquatic plants and animals which are capacble of swimming actively are called
nektons. They have well developed locomotory organs. It includes -
(i) Phytonektons - usually flagella are present in these plants.
e.g. Chlamydomonas and Dinoflagellates
(ii) Zoo Nektons (animals) - Jelly fishes, sharks, fishes, frog, cuttle fishes.

Benthonic - The sedentary organisms of sea are called benthonic. e.g. Crabs, Snails, Star fishes

Diapause - Delay in development or morphogenesis of larva, embryos in response to regularly and
reoccuring period of adverse environmental conditions.It is Physiological state of dormancy found in
some arthopods, insects, and oviparous fishes.

Hibernation - Winter sleep or period of dormancy
(i) Cold blooded animals
e.g. Amphibians, reptiles
(ii) Hot blooded animals
e.g. Polar bear, North ground squirrels

Aestivation (Summer sleep) - Escape from heat of sun
e.g. Lung fishes, Snails, Goround squirrels in south-west desert

Biodiversity - The term biodiversity refers to the totality of genes, species and ecosystem of a region.

Phenotypic Plasticity
The phenotype is the physical expression of the interaction between genotype of an organism and its
environment. The phenotypes show variations due to difference in the environment conditions with in
the local habitat such type of variatons are known as phenotypic plasticity.

Guild - Organism of same trophic level is known as guild (e.g. Cow, Goat, Rabbit).

Arboreta - Botanical graden where specific trees and shrubs species are cultivated for scientific,
educational and ornamental purpose.

Botanochemicals - Plants can also be used for the manufacture of innumerable synthetic products
called botanochemicals.



Ecology at the organismic level is actually physiological ecology which study that how different organisms
are adapted to their environment in terms of their survival and reproduction.

An organism is the smallest unit of ecological hierarchy and basic unit of ecological study.

It may be small, large, unicellular or multicellular.

It posses fixed life span and organized life cycle (birth to death)


Environment :
Environment is the sum total of all biotic (living) and abiotic (non-living) factors that surround and
potentially influence an organism. Some components of the environment serve as resources, while
other act as a regulatory factor.
The different components of the environment are interlinked and interdependent. The environment can
be understood both at large and global climatic patterns, as well as the local climatic conditions, the

Climate :

The short-term properties of the atmosphere (such as temperature, pressure, humidity, rainfall, sunshine,
cloud cover and wind), at a given place and time, is called as weather. Climate is the average
weather of an area, including general patterns of atmospheric conditions, seasonal variations and
weather extremes averaged over a long period.

Weather reflects the hourly, daily or weekly chages in the above properties, 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 radiation in different
region 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.


Climatic zones

On the basis of variation in mean temperature along latitude, the mean climatic regions are-
(i) Tropical (0º - 20º latittude)
(ii) Subtropical (20º - 40º latitude)
(iii) Temperate (40º - 60º latitude)
(iv) Arctic and Antarctic (60º - 80º latitude)
The mean temperature declines as we move from tropical to arctic region. A similar climatic zonation
occurs with increasing altitude in the mountains. A mountain located in a tropical region will successively
have tropical, subtropical, temperate and alpine zones with increasing altitude. Similarly, in temperate
zone, the high altitudes will have alpine climatic conditions.
Within each temperature-based climatic zone, the annual precipitation (rainfall and/or snowfall) varies
considerably. These two factors, temperature and precipitation, together determine the vegetation
and soil type.

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Note :
The temperature and light values are maximum at the equator, decreases gradually towards the pole. Effect of altitude and latitude are almost same on temperature.
The types of vegetation from sea level to measuring altitude are similar to increasing latitude
(distance from equator).

Microclimate :
The microclimate represents the climatic conditions that prevail at a local scale, or in areas of limited size, such as the immediate surroundings of plants and animals. Microclimate generally differs from the prevailing regional climatic conditions. 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.

Habitat and Niche :
The place where an organism lives is called its habitat. Habitat are characterised by conspicuous physical features, which may include the dominant forms of plant and animal life. We may also understand that habitat may refer to the place occupied by an entire bilogical community. For example, a large number of species are found in a forest habitat.

Plants and animals, as influenced by the environmental conditions of a particular habitat, indicate some specific traits. For example, plants growing on saline soils have several characteristics not found in plants growing on normal non-saline soils.

A habitat can contain many ecological niches and support a variety of species. The ecological niche of an organism represents the rage of conditions that it can tolerate, the resource it utilises, and its functional role in the ecological system. Each species has a distinct niche, and no two species are believed to occupy exactly the same niche.

Physical environment consists of air, light, heat, water, soil and wind. These abiotic factors determine the success of an organism through their effect on structure, life history, physiology and behaviour.
The growth and reproduction of an organism is also affected by biotic factors which includes all other
organisms in habitat.

Atmosphere may be defined as a transparent gaseous envelope surrounding the earth. The vertical profile of the atmosphere shows several concentric layers. These layers vary in density, temperature, composition and properties. The density is highest near the earth’s surface and decreases with altitude.
The thin layer from the surface of the earth upwards are :
(i) Troposphere

(ii) Stratosphere

(iii) Mesosphere

(iv) Thermosphere

(v) Exosphere

(i) Troposphere :
This is the region up to 8-16 km. height from the earth surface. Therefore wind’s clouds, dust particales, spores and pollen and more than 90% of gases of atmosphere are present here.

Temperature decrease with increasing of height upto tropopause (Top of troposphere).

The temperature average 15ºC near the soil surface and lower down to –57ºC at tropopause, which make transistion to the stratosphere.


(ii) Stratosphere :
The region lies up to 16-50 km. from the earth above the trophosphere. There is absence of large convectional current’s (wind) so it is excellent region for air travel.
Ozone layer is present in the stratosphere which protect us from the harmful U.V. radiations from the sun.
Stratopause is transist layer between stratosphere and mesosphere.

(iii) Mesosphere :

The region lies up to 50-80 km. from the earth above the stratosphere.

It show decrease in temperature with height.

(iv) Thermosphere :
This region lies up to 80-150 km. from the earth above the mesosphere is thermosphere, which contains free electrons and ions. All the communication, satellites are launched only in this layer, because ions and electrons transmits or reflects radio waves (Signals) from the surface of earth.

(v) Exosphere :
The outer fringe of the atmosphere known as the exosphere is extremely rarefied and gradually merges with the outer space. So above the thermosphere is exosphere.

Organism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRev

Organism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRev


Organism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRevOrganism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRev


Composition of air -
N2 → 78.8%

O2 → 20.92%

CO2 → 0.033%
Argon → 0.93%

Trace components → 0.04%



Organism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRev

It is a complex physical esnvironmental factor. Light is measured by luxmeter or photometer. It is a electromagnetic spectrum.

Solar Constant - Solar radiation before entering the atmosphere carries energy at a constant rate i.e.,
3 cal cm–2 min–1 known as the solar constant.

In solar radiation wavelength (λ) of light or visible spectrum is 400-700 nm, it is also called
photosynthetically active radiation (PAR)-

The U.V. radiation distinguished in
U.V. - C → 100 to 280 nm - absorbed by stratosphere
U.V. - B → 280 to 320 nm - most harmfull for organisms, cause snowblindness
U.V. - A → 320 to 400 nm

Albido value -

The ability of a surface to reflect the incoming radiation is called albido value (AV) it is 80% for fresh snow, 20-30% for sand, 5-10% for the forest.

Out of the total sun light only 1-5% is utilised in photosynthesis.

Only 2-10% of PAR is utilised by plant in photosynthesis.

Effect of light -

Photokinesis - Regulation of speed of locomotion due to light is called photokinesis.
eg., Larvae of mussel crab move faster if light intensity increases.

Photomorphogenesis in plants. Photoperiodism, seed germination, plant movements and
distribution of plants.

Distribution of plants as heliophytes and sciophytes.

Phenology -

Timing of seasonal activities of plants in relation to change in environmental condition (Flowering in particular season, leaf abscission etc.)

Distribution of animals in aquatic ecosystem - Lake, Pond, Ocean.

Light also affects the seasonal and diurenal activities of animals like foraging, reproductive and migratory activities.

Light affects distribution of plants and animals in aquatic ecosystem.

Light is limiting factor for plants in deep water.

The different stratification is observed in lake, pond, oceanic ecosystems due to distribution of light.


Stratification in lake :

In deep lake, zonation or stratification may be according to the need of light. There are three types of zones differentiated in a deep lake.

A. Littoral Zone - This zone is found at bank of lake with very shallow water or marshy bank is present. Rooted vegetation is found in this zone.

B. Limnetic zone - This is the zone of lake water, where light reaches in sufficient amount to entire surface area. It means this is not too deep. In this region different types of floating plants (phytoplanktons), suspended and submerged plants are present.

C. Profundal zone - It is very deep area of the lake where light does not reach properly up to the bottom. Only heterotrophs are present in this zone.

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Study of Ocean Environment -
All the ocean basins are roughly of the shape of a wash basin or an inverted hat.

Type-I – On the basis of structure :
From the coast line a gradually sloping region extends for about 160 km into the sea. This zone is called continental shelf and has a depth of 8-200 meters. The angle of the slopes then abruptly steepens to form the continental slope. The continental slope levels off into a more or less horizontal ocean floor. The depth of the ocean floor is in the range of several thousand meters.

Type-II – On the basis of availability of light :
The vertical zones of the ocean are determined by the availability or penetration of light for photosynthesis that is-
Photic or Euphotic zone - It is upper lighted zone up to a depth of about 200 meters.
Aphotic zone - Middle region where diffused light penetrate which is insufficient for
photosynthesis. It extends up to the depth of 200-2000 meters.
Abyssal zone - It is deeper part where light do not reach below 2000 meter, is the area of
perpetual darkness.

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Type -III – On the basis of environment :

Three major environment may be recognised in the ocean basin.

The Littoral zone - Comprising the sea floor from the shore to the edge of the continental shelf.

The benthonic zone - Formed of sea floor along with the continental slope and the aphotic and abyssal zone.

The pelagic zone - Constituting the water of the ocean basin.

Note :
The shallow shore region of a marine area is called neritic zone.
The part have been cut off from river is called ox-bow-lake.
Estuaries - The region where, river enter the ocean are known as estuaries.



Temperature is the degree of hotness or coldness of a substance.

Factors which affects the temperature are latitude, altitude, topography, vegetation and slope.

The vertical temperature gradient over earth's surface is called lapse rate. And it's value is 6.5ºC per 1000m elevation.

Temperature has significant effect on climatic conditions, growth responces of plants, activities of organisms.

Plants are affected by temperature like vernalization, thermoperiodism (effect of day-night temperature on various activities) etc.

Temperature also affects plant, animal distribution in aquatic ecosystems like in lake.


Thermal stratification in lakes :
Thermal stratification occurs in deep water body because of difference in temperature of water at
different depth.
Mainly three layer or zone occurs in water-
(i) Epiliminion - The top layer gains warmth.

(ii) Metalimnion/thermocline - Middle region where steady decline in temperature or a gradual change in temperature.

(iii) Hypolimnion - Bottom which is not affected by temperature.

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Difference in temperature of water at different depths results in thermal stratification in deep water bodies. During summer, temperature is higher on the surface water, whereas in lower layer temperature is low.

During winter in a temperature lake, water is at freezing temperature on the surface, whereas in the lower layer temperature is about 4ºC. The surface water is cooled during autumn, and warmed in spring. This results in a free mixing of water in the whole water body, also known as autumn and spring turnover.

During spring and autumn due to turnover of water oxygen and nutrients are redistributed, resulting in a bloom of phytoplankton growth while during winter and summer, growth of phytoplankon is low due to low nutrients and oxygen availability.

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Type of plants and animals on the basis of temperature :
On the basis of temperature vegetation is divided into four groups

1. Megatherms : The plants growings in high temperature througout the year
eg., Tropical rain forest.

2. Mesotherms : The plants growing in alternate high and low temperature.
eg., Deciduous tropical forest.

3. Microtherms : Plants growing in low temperature.
eg., Coniferous forest

4. Hekistotherms : Plant growing in very low temperature.
eg., alpine vegetation


On the basis of temperature animals divide into two groups

(1) Eurythermous or Homeothermal/endothermal/warm blooded - Animals which are able to tolerate wide variation of temperature. eg., Birds, Man, etc.
They regulates their internal body temperature by physiological mean, even the outside temperature fluctuates
Maintainance of relatively constant internal environment under variable environment is called Homeostasis.

(2) Stenothermous or Poikilothermal/ectothermal/cold blooded - Animals which are unable to tolerate wide variation in temperature. eg., Arctic fishes, Reptiles, Amphibians.
Their body temperature tends to match with environment in which they live. So they control their body temperature by physical mean like move in shade. Some ectotherms are nocturnal and feed during night.


 - Organisms and Populations, class 12, biology


The only inorganic liquid occuring on earth which can functions as a resource, condition and habitat.

Water regulates the climate through it's role in rainfall distribution and temperature modification.

It also affects vegetation type and it's composition.

The hydrological cycles regulates movement of water betwen aquatic systems, air and land.

Plant water relation helps in understanding water and it's role is vital activities of plants.
Water presence in soil is of various kinds.

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Soil water

Holard – The total amount of water present in the soil is called holard.

Hygroscopic water : A thin layer of water attached tightly to soil particles due to forces of cohesion or adhesion. This is not available to plants.

Gravitational water : The water that moves downwards due to gravity, it is non available to plants.

Capillary water : Inter particle spaces or porous spaces act as minute capillaries and some amount of water is present in these capillaries due to surface tension. This is capillary water. It is the only form of soil water which is available to plant.

Chemically Combined water - The water which is present as hydroxides of iron, aluminium, silicon,
etc. is called combined water.


Some Terminology :
1. Field capacity - When soil hold all the water except gravitational water, it is known as fieldcapacity. It is upper limit of water availability.
Field capacity = Holard – Gravitational water,
Field capacity = Capillary water + Hygroscopic water + Chemically combined water.

2. Water holding capacity (Storage capacity) - Amount of capillary water retained by any soil.
W.H.C. = Holard – (Hygroscopic water + Combined water + Gravitational water)

3. Permanant Wilting Percent (PWP)/Wilting point : The lower limit of water availability of a soil is called wilting point.
It is generally hygroscopic and combined water.

Note :
(i) The water potential of soil at field capacity is (–0.01 Mpa)         [Mpa = Mega pascal]
(ii) The water potential of soil at wilting point is (–1.5 Mpa)
(iii) Amount of water in soil measured by tensiometer.



 - Organisms and Populations, class 12, biology


1. Soil is the upper most weathered layer of earth's crust.

2. It composed on minerals and partially decomposed organic matter.

3. Soil is formed when rock are weathered in place or transported sediments are deposited by water and wind erosion. It is formed due to interaction among parent rock, climate, living organism, time and topography.

4. Soil plays important role in plant growth by providing water, nutrients and anchorage. It support growth
of plants, crops, grassland and forest.

5. The mineral compostion of soil depands upon the minerals in the parent material and the extent
of weathering.


Soil Profile :

1. O - layer - This is made up of litter.

2. A - layer / Top soil - This layer consists of mainly humus. Minerals are also found here. Most
of microfauna and micro flora are present in this layer of soil. Four feet thick top soil is essential
for growth of plants. The destruction of 'A' layer is called soil erosion.

A-layer is divided in two parts - A1, A2
A1 - The upper part of A layer (A1) is also called humic or melanized zone because dark black humus is present.
A2 - The lower part of A layer (A2) is known, as podosolic or eluvial zone or zone of leaching. It is light coloured region because of little amount of organic matter.

3. B - layer or subsoil - This layer is made up of big soil particles or minerals. This layer has less amount of humus, it contains compounds of iron, aluminium and maganese in higher amount, it is also known as illuvial zone. It is second mineral layer in which the material leached from A2 zone accumulate. So also called as zone of illuviation or accumulation.

4. C - layer - This layer is composed of incompletely weathered rock materials.

5. R - layer - This layer is present in unweathered parental rocks.
A Horizon + B Horizon = Solum

Type of soil on the basis of the mode of their formation -
(i) Residual soil - The soil in which soil formation i.e., weathering and pedogenesis, occurs at same place.
(ii) Transported soil - Soil in which weathering process occurs at one place and pedogenesis occurs at another place.

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Soil Organic Matter :
The dead organic matter present in soil is called humus, which is formed by decomposition of plant and animal remains. Freshly fallen plant and animal material called detritus or litter, partially decomposed litter is called duff. Fully decomposed litter is called Humus.
Detritus/Litter → Duff → Humus

Soil mineral matter :
Soil is the upper most layer of earths crust formed by weathering of rocks. It is the mixture of living or non living material.

Minerals 45% + Water 25% + Air 25% + Organic matter (Living + Non living) 5%
Soil formation is slow process 1 inch soil is formed in 500-1000 years.

Pedogenesis – Development of soil or soil formation.
Pedology (Edaphology) – Study of soil.

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1. Precipitation - It is a source of soil water. The hydrological cycle is the movement of water between earth, air and atmosphere.

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2. Humidity –
Atmospheric moisture in the form of invisible vapour is known as humidity. It is expressed in terms of relative humidity.


Relative humidity –
The amount of moisture in air as percentage of the amount which the air can hold at saturation at the existing temperature.

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Note :
R.H. is measured by Psychrometer.
Wind speed is measured with the help of anemometer.


3. Topography –
In includes the physical features of the earth like altitude, slope, exposure, mountain chains, valleys, plants. It affects distribution of organism by influencing the climatic factor like light, wind, rainfall etc.


The environmental conditions of a habitat are not always constant but change with time. The organisms show various kinds of Adaptations to cope with changed abiotic or environmental conditions.

Acclimatisation -
Acclimatisation is a gradual physiological adjustment of the organism to the slowly changing new nvironmental condition. If there is a shift in some environmental factor beyond the tolerance range of an organism the latter can come to the resting stage or migrate or can undergo acclimatisation.

Shelford law of tolerance -
Every organism has minimum and maximum limit of tolerance (ecological amplitude) with respect to the environmental factor like temperature, sunlight or nutrient concentration. In between these limits the central optimum range is found in which organisms are abundant this is known as optimum zone of tolerance.

The range of demands (requirements), and range of tolerance of a species called ecological amplitude.

If a species posses low ecological amplitude it is less adapted and if high ecological amplitude then
more adapted to environment.

Community is formed by organisms of almost same ecological amplitude.

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Organism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRevOrganism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRevOrganism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRevOrganism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRev

Organism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRev



 - Organisms and Populations, class 12, biology


1. In the polar sea aquatic mamals like seals have a thick layer of fat (blubber) below their skin that acts as an insulator and reduces loss of body heat.

2. Some organisms posses adaptations that are physiological which allow them to respond quickly to a stressul situation. If you had ever been go any high altitude place you must have experienced what is called altitude sickness. Its symptoms include nausea, fatigue and heart palpitation.

3. This due to the low atmospheric pressure at high altitudes, body does not get proper oxygen. In human beings the body compensates low oxygen availability by increasing red blood cells (RBC) production, decreasing the binding capacity of haemoglobin and by increasing breathing rate.


In some animals, the capcity to blend with surroundings or camouflage is a common adaptation. Some on their bodies, which make it difficult to distinguish them from shadows and branches, or from other members of the group.

Hibernation and Aestivation
In very cold or dry environments, animals incapable of migration shift to a physiological dormant state.
Spending winter in dormant condition is called hibernation. On the other hand, spending the dry-hot period in an inactive state is known as aestivation. (Examples are shown in table)

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Two species resemble each other closely, one speceis, called mimic, is palatable to its predator, but resembles another species, called the model, which is distasteful to the predator. In Batesian mimicry, the mimic is defenseless, but has anti-predatory marks, like the model which has a defense against predators;
hence, the mimic is able to protect itself from the attack of the predator. Similarly, the monarch butterfly
(containing poison, toxic to predator) is mimicked by the vicerory butterfly (containing no poison). Mullerian
mimicry is the process when the mimic shares the same defensive mechanism as the model.

Warning colouration :
Concealing form and colouration enables a species to avoide its natural predator. The brightly coloured and highly poisonous dart frogs (Phyllobates bicolour, Dendrobates pumilio) of the tropical rain forests of South America are easily recognised and avoided by the predators.

Adaptations to Water Scarcity :
Two types of adaptations are prominent in animals living in arid regions. viz. lowering of water loss as much as possible and adapting to arid conditions.
For example, the kangaroo rat conserves water by excreting solid urin, and can live from birth to death without even drinking water (By oxidation of fat). The camels show unique adjustments to desert conditions, being very economical in water use, tolerant to wide fluctuations in body temperature, and are able to maintain blood stream moisture even during extreme heat stress.

Adaptations of Cold :
Sessile animals, such as barnacles and molluscs, living in very cold inter-tidal zones of northern shores, and several insects and spiders resist the effect of cold spells by a process known as cold hardening.


Cold Hardening :

Physiological and biochemical process by which an organism prepare for cold weather. These are some means of cold hardening :

The freeze toleranting organisms have ice nucleating proteins, which induce ice formation in the extracellular spaces at very low sub zero temperatures.

Some freeze-avoiding animals can tolerate environmental temperatures below 0ºC by accumulating glycerol or antifreeze proteins that lower freezing point of their body fluids. Presence of such antifreeze compounds allows the fish in Antarctica region to remain active in sea water.

In plants (hekistotherms) cell release water in inter cellular spaces and increase sugar storage in protoplasm which decrease the freezing point.



The plants which are found on the earth, posses some specific characters in order to survive, successfully. A
plant must be above to adjust it self to its environment and grows continuously such type of special characters
are known as adaptability. The ecological factors influence the vegetation of particular area. Plant develops
various types adaptation to protect itself from these factors.

Warming, Classified plants into three groups on the basis of availability of water.

Hydrophytes : Plants found in places where excess of water is present are called hydrophyte.

Xerophyte : Plants found in places where very insignificant amount of water is present are called xerophyte.

Mesophyte : Places where is neither too much water nor less availability of water. Their habitats is having
relative amount of sufficient water.

Note : Ecological adaptations are found in xerophyte and hydrophytes.

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Organism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRevOrganism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRevOrganism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRev

Adaptation of hydrophytic plants :

1. Osmotic Pressure - The osmotic pressure of cells of aquatic plants is very less, so plants are saved from absorption of unwanted water due to low osmotic pressure.
Note : But, osmotic pressure of cells is high in those plants which live in salty water as in sea and sambhar of Rajasthan because it can reduce the loss of water.

2. Mucilage - Mucilage is found on the surface of aquatic plants. Mucilage protects the plants from the action of bacteria and fungus.

3. Cuticle - Cuticle is absent on the surface of aquatic plants. These plants exchanged gases through the
general body surface. But cuticle and wax is present on the floating leaves, so it become hydrophobic.

4. Aerenchyma - Aerenchyma is present in hydrophytes which provide buoyancy to the plants and store
oxygen which is produce in photosynthesis.

5. Chlorenchyma - The chlorenchyma tissue of these plants in well developed. The intensity of light is the
limiting factor in photosynthesis of aquatic plants. The intensity of light decreases in the deep water so,
absorption of more light takes place through well developed chlorenchyma. The whole plant is green excluding roots.
Note : Photosynthetic green roots are present in Trapa.

6. Epidermis - The epidermis of aquatic plants bear chloroplast.

7. Mechanical tissue - Mechanical tissue is less developed in hydrophytes. Sclerechma is either absent or reduced. So, aquatic plants are soft.

8. Conducting tissues - Conducting tissues [xylem & phloem are poorly developed in hydrophytes]
Xylem of these plants is not differentiated completely. Tracheids and vessels less devoleped. Water is absorbed by the whole surface of aquatic plants so the need of conducting tissue is less.
Phloem is also less developed because whole plants prepare its own food.

9. Roots - The root system of hydrophytes are either absent [Wolffia and Utricularia] or reduced [Trapa
and Eichhornia].
Note : Root cap is absent in Eichhornia. In place of root cap, root pocket is present which is filled by air.

10. Leaf - The leaves of suspended and submerged hydrophytes are either dissected [Hydrilla and
Ceratophyllum] or long, soft and ribbon like [Vallisnaria]. Dissected and ribbon's like leaves do not produce resistance to current so that, protected from destruction.

Usually heterophylly is present in emergent hydrophytes. Two types of leaves are found in these plants. The emerged leaves are dissected and aerial leaves are large and complete.

But leaves of floating hydrophyte are long, broad and strong, astrosclereids and trichosclereids are present in these leaves. The leaves becomes solid due to presence of these sclereids.

The leaves of Victoria are strongest and highest in diameter. Their diameter is approximately 1 meter.

11. Stomata -
Astomatic - The leaves of suspended and submerged plants are astomatic. In their leaves stomata are either absent or reduced. These plants exchange gases through the general surface of the body.
Epistomatic - Floating leaves are epistomatic, it means stomata are present only on upper surface of the leaf the lower surface remains in contact of water, therefore stomata are absent on the lower surface.

12. Reproduction : Hydrophytes reproduce vegatatively and sexual reproduction is found less. Sexual
reproduction only takes place in adverse climatic conditions.
Note : The vegetative reproduction takes place vigorously so that these plants becomes a weeds.


Xerophytes :
These plants live in deficiency of water. This deficiency of water may be of two types.

(A) Physical dryness - These plants grow in that region which have very less amount of water is called physical dryness.
In desert, from where only 20 cm rain fall or less than this, takes place and the slopes of hills are also having physical dryness.

Organism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRev
High concentration of salt water, and low temperature habitat is a type of physiological dryness habitat.

Organism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRev


Xerophytes are divided into three groups by Kerney and Shantz on the basis of their habit -
I. Drought Escapers or Ephermerals -
Such type of plants usually grown in desert. These plants complete their life cycle in favourable moisture (humid) season. They leave their mature seed and degenerates before unfavourable condition.
These plants are not facing the scarcity of water, so they are not true (real) xerophytic plants.

Adapatation : These plants do not have xerophytic adaptation. Spines are found on the surface of these plant, which protect them from the grazing animals.
e.g. Argemone mexicana (Yellow kanteli)
Solanum xanthocarpum (Blue or violet kanteli)

II. Drought Resistant or Succulent Xerophytes -
These plants absorb water in moist season and stored in plant organs. They stored maximum amount of water and they continue their life processes on this stored water during the drought, so, these plants are not facing the drought. Therefore, they are also not true xerophytes. They are the most successful plants in places of deficient water supply.

The most of the plants of this group are lithophytes.

Adapatation : The specific type of adaptation are found on these plants for absorption of higher amount of water and to avoid the loss of water.

Root System - The root system of these plant are shallow means spreading near the surface of earth and highly branched. They can absorb very low rainy water. They can also absorb water drops of dew.

Mucilage - Mucilage is present in the plant organs. It is a colloidal substance. Colloids have a great capacity of imbibition of water. Colloids can absorb more water than its weight. These plants becomes succelent due to presence of mucilage and absorption of water.

Stomata - Scotoactive stomata are found in these plants. Such type of stomats remains close during the days and opens at night. The possibility of transpiration is more during the day. They mainly exchange gases during the night.

Modification - In most of the plants, leaves are transformed into spines. The stem function as leaves, in the absence of leaves - it means stem becomes like a leaf. Such type of stem is known as phylloclade e.g. Opuntia.
Those plants in which leaves are not transformated into a spines, that becomes thick and succulent. These succulent type of leaves are called malacophilly. e.g. Aloe, Euphorbia

All the plants of Cactaceae and Crassulaceae families are succulent plants.

Most of the plants of Eurphobiaceae family are succulent.


III. Drought Endurers or Non Succulent Xerophytes -
Psamophytes are included in it. The plants which are found in desert are perennial. They do not store water in their plants organs. However the plant continues to be alive during the drought. Therefore, they are true xerophytes.

Adapatation :

Root System - The root system is very long and penetrate the soil to great depth and is well developed. The
shoot is less developed (Hight root-shoot ratio) as compared to the root, so that it reduces the transpiration.
The roots are well developed in sandy soil. Length of roots are more than shoot.

Leaves - The maximum adaptations are related with the leaves. The leaves are pinnately compound in most
of the plant of this group.


A thick layer of the cuticle and wax is present on the upper surface of leaf.

Rolling leaves : Rolling leaves are found in some of the xerophytic plants. The leaves of these plant fold during the mid day.
For example : Ammophila, Emptera, Poa etc.

Stipules - The stipules of xerophytic plants are modified into spines. These spines protect the plant from the
grazing animals e.g. Acacia (Babool).

Stomata - The stomata are present only on the lower surface of the leaf i.e. leaves are hypostomatic.
Stomata are sunken type. A cavity is present out side the stomata which is called hypostomatic cavity.
These stomata are surrounded by hairs. Such type of stomata prevent the loss of water. The presence of hair
on the leaves are called trichophilly.

Mechanical tissue and vascular tissue - The mechanical tissue and vascular tissue are well developed in
these plants. The intercellular spaces are absent, so that cells are tightly arranged.



Halophytes :
The plants which grow in salty soils or saline soils are called halophyte. Physiological dryness is found
in halophytes.

Adaptation :

1. Stomata : The adaptations of halophytes are similar as succulent xerophyte.
They are succulent and water is stored in plant - organs.

2. Osmotic Pressure :The osmotic pressure of cell sap is highest of these plants. The osmotic pressure
of cell sap reaches 30 mm of Hg - (atmosphere pressure).

3. Chalk Glands : Chalk glands are found on the leaves and roots in some plants of halophytes, which
secretes lime. e.g. Atriplex,

Mangrove Vegetation :
This is a special group of halophyte. They are found in saline marshy areas of sea-shores and near estuaries. Mangrove vegetation is found in Sunder-bans [W. Bengal] in India. Marshy places are physiologically dry due to the presence of salts. Specially, seed of these plants can not geminates in swampy land.

The following adaptations are found in mangrove plants.

(i) Pneumatophores : Marsh is water logged i.e. oxygen is absent in marsh. Oxygen is not available to the roots of the plant in swampy soil so that some special type of respiratory roots are found in Magrove the pneumatophore, they are negative geotropic. Pores are present at the apex of the pneumatophore, they exchange gases through the pores from the atmosphere.

(ii) Vivipary : The germination of seed takes place inside the fruit while it is attached to the parent plant that juvenile plant is present in fruit, falls on the marshy soil.

(iii) Leaves : Leaves in mangrove plants are either absent or less developed and succulent type.
e.g. Rhizophora, Sonneratia, Avisinia, Salicornia, Salsola, Heritiera


Eipihytes :
Epiphytes are extensively distributed in trophical rain forest. Such type of rain forest lies on the equatorial
region around that earth. The main feature of this biome is the good amount of annual rain fall which is more than at lest 140 cm. per year. Such type of forests are found in Assam, W.Bengal, Meghalaya and Andaman Nicobar in India.

Epiphyte are those autotrophic plants which grows on other plants. They do not get water and food from them. Their roots are not present in soil. They absorb atmospheric moisture. Therefore epiphytes are only growing in moistened places. Epiphyte never grows in Rajasthan.

The adaptations are found in epiphytes are
Heterorhizy : These plants are heterorhizomous ie., two type, of roots are found in these plants.
* Clasping Roots : Their function is only to provide support (fix) the plant.
* Hanging Roots : These roots hang in the air these roots have special epidermis which is multilayered
and made up of thick walled cells, this type of epidermis of root is known as velamen. So velamen is an epidermal tissue Velamen tissue is is hygroscopic in nature. It adsorbs atmospheric moisture.

Note :
The plants of Orchidaceae family are known as orchids. Orchids are epiphytes. e.g. Vanda.
Dischidia is known as pitcher plant. The leaves modified into a pitcher in this plants. Rainy water is collected
in the pitcher.

Physchrophytes :

They are also known as hekistotherms. These plants are grown in cold soil (land). Psychrophytes are found in north and south polar regions. The plants grown at 11000 feet or above are only psychrophytes.
They known as Alpines. Such plants are grown on Himalaya.

Cold lands are physiologically dry. Plants are unable to absorb water because temperature of soil is
very less, reasons are as follows -
The viscosity of the water increase due to decrease in temperature.
Water potential of water decreases due to low temperature.
The permeability of plasma membrane decreases at low temperature.

The true characters of xerophytes are found in these plants, such as small leaves, thick cuticle and very
deep root system.
e.g. Rhododendron, Delphinium, Anemone, Primula, Sexifraga.


Adaptation against High pressure → In hydrothermal vents :

No excess body cavities (swim bladder) provide boyancy.

Flesh and bones are Flubby

T.M.O-Tri methylineoxide. Binds with pressure sensitive protiens and protects their pressure inhibition.

Serine phosphaethanol amine - protects protiens from pressure effect.


Adaptation of plants against predators :

Thorns, Hairs, thick stem, Nectorless. silica in grasses.

Chemicals : Cafin, Tannin, Quinin, Opium, Glycosides, Pyrethrin.
Adaptation of Animals aganinst predators :
(i) Cryptic appearence/Camuflage.
Grass hopper-Look like green leaf.
Preying Mantis-Look like dead leaf.



Best pH of the soil for cultivation of plant is 5.5 - 6.5

Excess water produces salinity problem in soil.

Calcifuge Plants → Those plants which can grow in little amount of calcium in soil (pH - 3.8 to 4.0)
eg., Rhododendron, Rumax etc.

Calcarious soil → Soil having excess of calcium carbonate.

Alkaline soil can be corrected by adding gypsum (CaCO4) and heavy irrigation whereas acidic soil can
be corrected by adding lime Ca(OH)2 Availability of nutrients from the soil is related with pH of soil.


Literization :
In the tropical area due to high temperature, high rainfall, litter is decomposed very rapidly in Alayer.
Due to mineralization of Al and Fe are liberated in the upper layer (A-layer) of soil, colour of this soil becomes redish-brown, this process is known as laterization and soil is literite.

Podsolization :
In temperate area temperature is low and high humidity occurs. Humus and minerals contents dissolve and percolate with water and are leached from A layer to B layer. Due to loss of chemicals the colour of soil of A-layer (horizon) turns to light ash colour. This process is known as podosolization and soil is known as podosols.


Gleization :
In tundra region due to low temperature and humid condition humus is formed in less quantity and moves slowly in B-layer. So colour of B-layer becomes blue-grey due to deposition of Fe salt. This process is known as gleization and soil is known as gleys.

Organism and Environment; Chapter Notes; Class 12; Biology Class 12 Notes | EduRev

Many tribes live in high altitude of Himalaya have high RBC's than people living in the plains.

Many xerophytes may accumulate proline (an amino acid) in their cells to maintain osmotic and water
potential in their leaves.

The heat shock protein (chaperonins) provide physiological adaptations to plants to high temperature.This protein helps other proteins to maintain their structure and prevent denaturation at high temperature.

Dunaliella species (green and halophytic algae found in hyper saline lakes) can tolerate saline conditions
by accumulating glycerol in the cells, which helps in osmoregulation.

The main source of CO2 for aquatic plants are Carbonates and bicarbonates.

Effect of Temperature on animal :
Temperature affect the absolute size of an animal and its body parts.

1. Bergman rule - Birds and mammals attain greater body size in cold region and lesser in warm region.

2. Allens rule - The tail, ears, limbs, eyes, snout and hair of mammals are smaller in colder region
and larger in warm region.

3. Jorden's rule - Fishes in cold water posses more vertebrae than those living in warm water.

4. Gloger rule - Warm blooded animals in hot and humid area (tropical region) are more darker in
colour (heavily pigmented) than cold area.

5. Renschs rule - Birds in cold region have narrow wings and in warm region have broader wings.

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