The Organism and Its Environment || Study of Living Organisms With Environment


The term ecology (Gr – oikos = home, logos = study) was originally given by Reiter, however the credit goes to a German biologist Ernst Haeckel (1869). Ecology deals with the study of organisms in relation to their environment. An ecologist studies the effects of various components of the environment on organisms and vice-versa.

We know that a living being acts as an open system. It constantly exchanges energy and matter with the surrounding. An organism therefore can not be separated o from its surroundings. These surroundings include other living organisms isolated tic factors) and non-living things (abiotic factors) such as light, water, air and soil etc. 

The biotic and abiotic factors together make the environment of an organism. An organism can survive only in an appropriate environment, where it can get sufficient organ food and shelter. Both organisms and their environment interact together and influence each other. The study of this mutual interaction is known as ecology.


Living organisms and non-living objects both are made of the same kinds of elements. are governed and influenced by the same kind of physical laws, such as gravitation, They are governed…electrostatic forces and reactions. However, the living beings are unique magnet they have a well developed, coordinated level of organisation. Hence, the Leung cause these beings are called organisms. 

Unique organisation is the key feature of all living beings. Aggregation, mutual reaction, stability and alteration (change) are all very complex in living beings. life can not be created by just putting together all the required components in the right proportion with required energy. 1he life requires a unique, well coordinated and pro stable organisation. The mystery of ‘being alive’, lies in the highly complicated way in which living matter is organised.

You are familiar with primary levels of organisations (such as atomic level, molecular level, cellular level, tissue level, organ level and organ system level). Here in ecology, we are concerned with higher levels of organisation (such as population level, community level, ecosystem level, biome level and biosphere level).


Species is a group of similar individuals which are capable of interbreeding and are able to produce fertile offspring. Members of a species share a common gene pool Following are different levels of organisation.

Individual or organism level: 

An individual organism is not an independent entity. In fact it is a small part of the natural system. An organism is the basic unit of study in ecology.

Population level: 

All individuals of the same species, found in a particular biogeography in all areas at a particular time forms a population. The members of a amatr population are most frequently able to interbreed. They share a common gene pool. nrfao be conctoitoics)

Community level: 

All kinds of living organisms living in a particular area at a particular time, form a biotic community. A community contains more than one species.

Ecosystem level: 

Ecosystems contain living beings as well as non living components of a particular area at a particular time. An ecosystem must have well defined boundaries. Depending upon the dimensions of the boundary, an ecosystem can be as small as a drop of water or may be as big as the entire ocean. Since the ecosystem involves both living and non living components, the mutual TRC all interaction of different organisms with their environment can be studied only in an ecosystem. Therefore, an ecosystem is called the basic functional unit of| ecology.

Landscape level: 

A landscape is a unit of land with definite natural boundaries but have a mosaic of patches. These patches represent different intermixing ecosystems.

Biome level: 

A biome is a very large regional ecological unit, which is joined by a major vegetation type and characteristic fauna, found in a specific climatic zone. A biome can be viewed as a large distinctive complex of bio-communities created and maintained by a specific climate. According to E. P Odum, a biome is the geographical region on the earth, which has the same average climate and has a specific type of vegetation and peculiar fauna.

A biome is therefore a very large and widespread biocommunity. Important biomes of the world are desert, tropical rainforest, taiga, tundra, deciduous forest, grassland biome, etc.

Biosphere level: 

It represents the total part of earth’s environment where living organisms are present and interact with each other to produce a steady state system. A biosphere can be called a whole planet ecosystem. Sometimes it is also called the ‘ecosphere’.

Features of an Organisation 

Putting together different compounds does not form an organisation. An organisation is characterized by following features

1. Aggregation-

It is the grouping of Smaller units to form a large unit. For example atoms are grouped to form molecules. Molecules to subcellular parts. Subcellular parts aggregate to form a cell and cells form tissues and so on. Aggregation is the primary basis of an organisation.

2. Mutual interaction 

All components of an organisation are not aloof from each other. There exists a close interaction among them. For example: Carbon, hydrogen and oxygen interact to form carbohydrate molecules. Further carbohydrates, nitrogenous bases and phosphates interact to form nucleic acids.

3. Coordination and stability-

it is the most important part of the organisation. The components interact with each other in coordination and bring about the stability of the organisation. Stability or equilibrium is the essential feature.

For example-all cellular organelles such as nucleus, mitochondria, golgi bodies, endoplasmic reticulum, ribosomes etc. coordinate their activities to form a stable cell. Similarly various organs like, heart, arteries, veins and blood coordinate and cooperate with each other to form cardio-vascular system. This coordination is necessary for the equilibrium of the system. If any of the components does not work properly, in coordination, the whole system becomes unstable.

4. Regular alteration (change)-

An organisation must undergo some regular changes to suit the emerging needs. These changes may be due to some environmental stimuli. Such changes are called adaptations. In some cases the changes are due to the change in interacting behaviour of the components.


The environment refers to the whole range of external Conditions, physical and biological in which an organism lives. In other words, the environment is the sum to total of all biotic (living) and abiotic (non-living) factors that surround and potentially influence an 0rganism. Therefore, the environment is the part of our planet in which life exists and with which it exchanges energy and matter. Environment includes a part of the lithosphere (the solid earth), hydrosphere (water) and atmosphere.

An organism can not be isolated from its environment because each organism acts as an open system. It regularly exchanges matter and energy with the surroundings.

Spatial and Time Scales of Environment

All living organisms interact regularly with their environment through the exchanges of matter and energy at different spatial and time scales. Some organisms are smaller in size and they interact with a very small part of the environment. On the other bhand large sized organisms interact with a larger part of the environment. For example-a single bacterium interacts with environmental factors with a fraction of a cubic centimeter space, while a giant tree interacts with a large space. Environmental conditions are not static or constant. These change regularly with time period. Organisms have to cope with these environmental changes over a range of time scales, varying from a few minutes to days, months, years or a much longer period. For example-a population of phytoplankton s may change within a few days, with the change in the

abiotic conditions of the aquatic system. Opposite to this, the population or a terrestrial species (like a mammal) does not undergo noticeable changes even after many because the variations in lithosphere occur very slowly over a long period of time. Environmental conditions are not constant. These keep on changing with time and place. The interaction of organisms is the major cause of the changes in environment conditions. Besides the changes in climate, soil type and topography are also significant factors for the environmental change.


Climate refers to the average weather conditions of a particular area over a long time per Weather reflects only small changes (hourly, daily or weekly changes) ” the properties of the atmosphere (such as temperature, moisture, pressure, rainfall, sunshine and wind).

On the other hand, climate reflects the general patterns of atmospheric conditions, season’s variations and average weather extremes over a long period. There are various factors that decide the climate of an area. Of these, temperature and rainfall are the two most important factors that directly influence the climatic conditions.

These factors in turn result from differential input of solar radiation in different areas. It is clear from the above table, that from tropical to arctic region, the mean temperature declines.s Similarly, when we move from planes to mountains, a similar decline in temperature is observed with the increase in height. A mountain, located in a tropical region will therefore, have tropical, subtropical, temperate and alpine zones respectively, with the rise in height.

Within each climatic zone, average rainfall condition (annual precompilation) also varies considerably. These two factors (temperature and rainfall) are the most important in determining the climate of a zone, which in turn determine the vegetation and soil types of the zone.


The climate of a very small local area is called microclimate. For example, the immediate surroundings of plants and animals in a garden or in a micro-ecosystem is an example of microclimate.

Microclimate usually differs from the regional climatic conditions. For example, In a forest, the dense leaves of many big trees reduce the amount of light reaching the ground. Due to this the soil temperature remains lower than the overall temperature in the forest. In the similar way, the interior of the forest may be more humid than the actual (regional) humidity in that area.


The place where an organism lives is called its habitat. Habitat ot an organism is the best place for it, where it finds maximum food and shelter.

Characteristics of a Habitat 

1. Habitat of an organism provides it, the most favourable conditions.

2. Food supply is optimum.

3. Shelter and support is maximum.

4. Environmental stress is minimum.

Habitat is species or population specific. 

It means that a given place may be habitat for one species (population) but may not be a habitat for the members of another species. For example, the ocean is habitat for marine fish but not for freshwater fish.


Niche (or ecological niche) is the positional status of an organism in an ecosystem. The niche of an organism determines

(i) the range of conditions it can tolerate,

(ii) the resources which it can utilise and

(iii) the role it plays in the ecosystem.

Each species has a distinct niche, i.e., no two species are known to occupy exactly the same niche.

Concept of Niche

It can be explained by a simple example -In human society, there are many human beings. Human beings to a given area occupy the same habitat but their positional status is different. Some people are farmers, some are teachers, some are students and Some others are executing administrative functions. This functional or positional status determines their role in the-society, their resource utilisation capacity and range conditions they can tolerate. Similarly, in an ecosystem, each species/or its members have different positional and functional status. This positional status is called niche.


These include the non-living components of the ecosystem, which determines the habitat and niche of the organisms. They influence the morphology, anatomy, physiology, behaviour, growth and reproduction of the organisms.

Broadly, these can be divided into two types-1. Climatic factors and 2. Edaphic factors. Climatic factors include temperature, light, water, gases etc. while the edaphic factors include soil, pH, salinity, mineral nutrients, geographical location, etc.

1. Atmosphere and Air

Our earth is surrounded by an invisible sphere of gases. This is called atmosphere. All living activities occur within the limits of the atmosphere.

On the basis of variations in temperature and pressure, atmosphere is divided into following layers:

(i) Troposphere: 

It is the lowermost layer of atmosphere, which is nearest to earth’s Crust. It extends upto 8 to 16 km above the earth surface. Its limits are marked by a small tropopause layer.Troposphere contains more than 90% gases of the atmosphere. The temperature and pressure both decline with the height. The temperature averages 15°C near the earth surface and reaches about-57C at the tropopause.

(ii) Stratosphere: 

It extends upto 30 to 50 km from earth surface. The Stratosphere is separated from the troposphere by a narrow tropopause.

(ii) Mesosphere: 

It extends upto 80 km, beyond the stratosphere.

Composition of Air 

Atmospheric gases such as oxygen, carbon di oxide and nitrogen play an important role in biological activities. Oxygen helps in the respiration and thereby in the production of energy. 

Oxygen also helps in the oxidation or decomposition of organic matter.

Carbon dioxide gas helps in various life activities (like photosynthesis) and maintains the greenhouse effect to keep earth warm.

Nitrogen is essential for all organisms. It is the essential component of nucleic acids and proteins. Many bacteria and blue green algae can fix atmospheric nitrogen to ammonium ions which can be utilised by plants for the synthesis of proteins.

Ozone absorbs UV radiations and prevents them from reaching earth’s surface. 

Gases in Water

Gases like oxygen and CO, are partially dissolved in water. Oxygen comes to the water through diffusion from air or from the photosynthetic activity of aquatic plants and algae. Oxygen may be a limiting factor for the growth of phytoplankton and other aquatic organisms.

CO² is highly soluble in water and forms carbonic acid.This acid may react with limestone to form carbonate and bicarbonate ions.

2. Light

Light is also one of the most important abiotic factors. All plants and animals depend directly and indirectly on light. Physically light is radiant energy and is the visible part of the electromagnetic spectrum. Electromagnetic Spectrum

The ultimate source of energy on earth is the solar light. Solar light is the visible part of electromagnetic radiation. These visible radiations have a wavelength range of 400 nm to 700 nm. This part of electromagnetic radiation (visible part) is called Photosynthetically Active Radiation’ or PAR.

Before entering the atmosphere of the earth, the solar radiations carry an energy constant rate of 2 cal/cm/min. This value is called solar constant.

Besides visible light, solar radiations include x-rays, infrared rays, UV rays, etc. These have been shown in the following figure.

Types of ultraviolet radiations

Depending upon the wavelength, three types of UV radiations have been recognised:

(i) Type A–These radiations have a wavelength range 320 to 400 nm.

(ii) Type B-These radiations have wavelength range 280 to 320 nm.

(ii) Type C These have a wavelength range 100 nm to 280 nm.

Out of these, type CUB radiations are lethal to organisms.

Light Zones in Water Bodies

Life activity under water is greatly influenced by the presence of light. In a lake, light can not reach the bottom. This region is called the benthic zone. Photosynthetic activity in this zone is almost completely absent. Slight above the benthic zone there is a profound or dark zone. In this zone also there is no light. Light is available only in the uppermost zone. This zone is called the kinetic zone or open water zone.

Zone of shallow water is called a littoral zone. Light is available in this zone. Therefore, plants and algae are confined mainly to upper zones.

Role of Light in Supporting Life

The quality of light (intensity, duration etc) influence the living organisms in many ways. Some important effects of light have been summarised below


It is the most important function of light. Light is necessary for the formation of food in plants. They convert the light energy (radiant energy) into chemical energy and store it as food. This conversion process is called photosynthesis. The food formed by plants is also for animals. Hence all organisms depend on light for food.


Light induces photochemical reactions, resulting in the formation of skin pigments or melanophores. In organisms, which live in complete absence of light, melanophores are completely absent

Photoreceptor organs: 

Light also induces the formation of photoreceptor organs. Organisms which live in complete darkness have no eyes. For example, adult Fasciola hepatica (Endo-parasite of sheep) has no eyes, but its larva-Miracidium (which is free living) has a rudimentary eye spot. Similarly in many cave dwellers eyes are absent.

Various effects of light on plant life


Increase in light intensity also increases the rate of photosynthesis (while other factors are not the limiting factors). At high light intensity, the rate of respiration also increases. In organisms living in the dark, the rate of metabolism is relatively low.


In plants, light helps in the differentiation of tissues. High light intensity causes the shortening of internodes, smaller leaves and more flowers.

Movement in plants: 

Plants show bending movements towards unilateral light. This effect is called phototropism. Some plants such as Oxalis show bending of leaves at night (nyctinasty).

Feeding time of organisms: 

Most of the organisms are active during light (daytime) for their food capturing. These are called diurnal animals. Some are active at night (dark). These are called nocturnal organisms.

Diurnal rhythms in animals: 

Diurnal rhythms such as awakening, sleeping, feeding, defecation, etc. in animals are also regulated by the light.


In plants the duration of light has a specific effect on flowering and other processes. This effect is called photoperiodism. Response to photoperiod is also found in animals. (Inhibition of embryonic development) in insects is regulated by photoperiod, Photophilous and Sciophilous Plants

On the basis of response to light, plants are of two main types:

1. Photophilous plants

2. Sciophilous plants.

Photophilous plants are light loving plants. They show full activity when optimum light is available. Sciophilous plants on the other hand are shade loving. They show full activity in diffused light. 

Photophilous Plants

1. Plants have shorter internodes.

2. Branching profuse.

3. Stem hard and thick.

4. Mechanical tissue and xylem well developed.

5. Leaves smaller, linear and narrow.

6. Epidermal cell thick.

7. Well-developed palisade tissue in the leaves.

8. Stomata smaller in size, lesser in number, mostly situated on the lower surface.

9. More of mechanical tissue and xylem well developed and. hence have more dry weight.

10. Flowers earlier and flowering is profuse.

11. Plants are hardy and resistant to drought and parasitic infection.

Sciophilous Plants

1.Internodes are longer.

2.Branching poorer.

3.Stem delicate and thin.

4.Mechanical tissue, not well developed.

5. Leaves larger in size and broad.

6.Epidermal cells are thin, chloroplasts present.

7. Palisade tissue less developed

8.Stomata are relatively large, more in number and occur on both the epidermal layers.

9. Mechanical tissue and xylem relatively less, hence dry weight lesser; succulent habit.

10.Flowers late or flowering may be absent. Plants less hard and easily affected by

11. drought and parasitic infection.


Phenology is the study of the timing of seasonal activities of plants in relation to changes in environmental conditions (mainly photoperiodic changes)

3. Temperature

The degree of hotness and coldness is called temperature. It is greatly affected by factors like latitude, altitude, topography, vegetation and slope.

Vertical temperature gradient (temperature variation according to height), is called Lapse rate. Its value is about 6.5 °C per 1000 m elevation. It means that with every 1000m height from earth surface, temperature declines by about 6.5 C.

Organisms can survive only in a narrow range of temperature which helps in their metabolism. Organisms are highly sensitive to temperature changes and accordingly they undergo morphological, behavioural and physiological adaptations to suit the extremes of temperature. A very high and a very low temperature may cause the death of the organism.

On the basis of response to environmental temperature, two types of organisms have been identified:

(i)Cold-blooded Animals (Poikilotherms) or Ectotherms 

These animals do not have a constant body temperature. Their body temperature fluctuates with the temperature of the surroundings. Example-fishes, amphibians and reptiles.

The effect of temperature changes are more apparent in these animals. To avoid excessive cold in winter these organisms undergo winter sleep or hibernation. In summer to avoid heat, they undergo summer sleep or aestivation.

(ii) Warm-blooded Animal (Homeotherms) or Endotherms

These animals have a constant body temperature. Their body temperature does not fluctuate with the temperature of the surroundings. Example-Birds and mammals.

(Human beings have a constant body temperature, which is 37C).

The effects of temperature variations are very less apparent in these organisms, because they remain active in almost all types of weather and normal temperature variations.

Adaptations to avoid Extremes of Temperature in Organisms

(i) Aestivation-Cold blooded animals, to avoid extremes of high temperature, undergo earth surface or in burrOw for many days and months. This is called aestivation (summer sleep).

(i) Hibernation -Cold blooded animals, to avoid low temperature, undergo earth surtace or in burrows for many days and months. This is called hibernation (winter sleep).

(ii) Nocturnal habit-Many organisms to avoid the high temperature in day time, become active at night for food gathering

(iv) Formation of spores, cysts and seeds-Many plants and lower animals produce spores, cysts, eggs, etc which are resistant to extremes of temperatures. Under favourable conditions, spores and cysts are ruptured and organisms come out.

(v) Removal of water- The removal of water helps to prevent the harmful effects of low temperature such as freezing. Dried fruits, and many seeds, avoid freezing by elimination as much as possible. (Un) Thermal migration the movement from one place to another to avoid extremes of cold and heat is very common in animals. It is very well observed in birds.

(vil) Homoeothermic (warm blooded mess)- This is the device used by birds and mammals to keep their body temperature constant. In hot climates they allow evaporation of water from their body surface, which brings a cooling effect. In colds, evaporation is heat loss from the body is minimized by proper physiological mechanisms.

Temperature Tolerance Range

On the basis of their temperature tolerance capacity, organisms are of two types

(i) Eurythermal Those organisms, which can tolerate a wider range of temperature are called eurythermal organisms.

geothermal-Those organisms which can tolerate a very narrow range of temperature are called stenothermal organisms. These are highly sensitive to temperature fluctuations.

Rules Related to Effect of Temperature on Organisms

(i) Van’t Hoff’s rule-High temperature can increase the rate of chemical reaction, while low temperature can decrease the rate of reaction. 

(ii) Bergman’s rule-Temperature can affect the size of body and its parts. A cold temperature causes the increase in size while hot temperature causes the

reduction in size.

(iii) Allen’s rule Temperature also affects the size of body extremities of animals Such as ear, nose, tail, etc. These are shorter in animals living in colder area but longer in organisms living in hot areas.

(iii) Glover rule-This law suggests that organisms living in hot area have dark skin pigmentation while those living in colder area have relatively light pigmentation

(iv) Jordan ‘s rule-Temperature may affect the number of vertebrae in some vertebrates such as a few species of fishes. These fishes in low temperature have more vertebrae and their counterparts in warm water have lesser number of vertebrae.

(v) Jordan’s rule-Temperature may affect the number of vertebrae in some vertebrates such as a few species of fishes. These fishes in low temperature have more vertebrae and their counterparts in warm water have lesser number of vertebrae.

Thermal Stratification in Lakes

The temperature of water bodies such as rivers, lakes, etc. shows seasonal variation. The differences in temperature of water in deep-water bodies (such as a lake) at different depths is called thermal stratification.

The temperature of the upper surface of the water is usually in accordance with the temperature of the outer atmosphere surrounding it. But the temperature at the bottom of the lake may be different.

There is a zone (transition zone) between the upper and lower layers (in a lake) which shows a gradual variation in temperature (from the temperature of upper layer to the temperature of lower layer). This transition zone is called thermocline.

Thermocline clearly divides the water body into an upper zone (called epilimnion) and a lower zone (called hypolimnion).

In summer, the temperature of the upper zone (epilimnion) is higher but the lower layer (hypolimnion) is cooler. This is called summer stratification. In winter, the temperature of upper layer is very lower or even 0 °C. But the temperature of lower layer never reach

the same value. It is usually 4 °C (at this temperature, water has maximum density). This variation in winter is called winter stratification.

Thermal stratification in a lake Between winter and summer there are two seasons-autumn and spring. In both these seasons there is a free mixing of water of the two layers so that the temperature becomes the same throughout the lake. This mixing in autumn and spring is called autumn turnover and spring turnover respectively.

4. Water

Water 1s the prime abiotic factor in all ecosystems. It is especially important in aquatic ecosystems. Water exists in all three states-solid, liquid and gas.

Total amount of water on the earth remains the same, but it moves from one place to another and regulates various processes in organisms.

Water plays an important role in maintaining the climate of an area. It directly controls the humidity and temperature conditions of an area.

Hydrological cycle

Hydrological cycle refers to the movement of water between water bodies, land and air. Most of the water is present in water bodies like ocean, lakes and rivers etc. The water from these bodies is utilised by plants and animals. Much of the water reaches the atmosphere through evaporation. In the atmosphere at high altitudes, the vapours get condensed (due to low temperature) and form clouds. The clouds result in rainfall. In this way cycling of water is maintained in the atmosphere. Plants play an important role in the hydrological cycle through the process called transpiration.

  • In tropical forests, about 75 % of annual rainfall is returned to the atmosphere by plants. 
  • Rainfall is uneven on earth’s surface. Some parts receive very scanty rainfall like deserts), while others receive very high rainfall (forest and rainforest). In India Cheraapunji receives rainfall > 11,000 mm.
  • Role of water in supporting life
  • Water helps the living organisms in following manner: 
  • Water is essential for photosynthesis.
  • It is the main source of oxygen (released in photosynthesis).
  • It is essential for metabolic activities of organisms.
  • Water helps the organisms to get rid of excessive heat. 
  • Water helps the animals to excrete out their waste.
  • Water forms the habitat for many animals and plant varieties.
  • Water helps in the absorption of minerals by the plants from soil.
  • Scarcity of water in desert forces animals to develop xeric adaptations, whereas the abundance of water in aquatic mediums induce organisms to develop aquatic adaptations.

5. Soil

It is the upper shallow layer of earth, which consists of very fine sand particles, organic and inorganic depositions. It forms the habitat of all terrestrial organisms.

Soil helps to anchor the plants. It provides water and mineral ions to the plants.Soil is also the habitat of many microorganisms. Soil texture greatly affects the distribution of organisms.

Soil profile

  • During soil formation various types of layers get deposited one over the other. The process is very slow and takes a very long time. This results in the formation of soil structure, which shows arrangement of different types of layers. When a vertical section of soil is cut, different layers can be seen. This vertical layered structure of soil is called soil profile.
  • Soil profile of grassland, forest and desert biomes differs significantly. The soil is different in colour, clay, organic contents and texture.
  • In grasslands, the roots of the plants penetrate deep into the ground that form a dense root network, which holds moisture and prevents erosion.
  • In temperate forests, the top horizon is a rich mixture of humus and inorganic components.
  • In tropical rainforests, the soil is poor in nutrients due to heavy rainfall, and high temperatures.

Types of layers (horizons) 

A fully formed soil shows many layers or horizons placed one over the other. The smallest three dimensional volume of soil which shows all the horizons or layers is known as pedon. A typical soil profile consists of five following horizons

(i) O horizon: 

This is the uppermost horizon, made of organic matter. The layer has both balls non-decomposed (fresh) as well as partially decomposed matter. It may further be divided into two sub-layers.

(a) Aoo region-

This is the topmost layer. It ballast or consists of freshly added organic matter such as dead leaves, branches, flowers, fruits, etc.

(b) Ao region-

This layer is present below the freshly added organic matter. The organic 1 matter in this layer is in different stages of po decay. Bacteria, fungi, etc. are found in large numbers in this layer.

(iv) horizon: 

This is a laver of mineral substances. However, it consists or One partially weathered material. This horizon is also termed as subsoil.

(v) R horizon: 

This is the lowermost layer or horizon of the soil. It is made of bed rocks which still have unweathered parent material.

Properties and Composition of Soil

A soil broadly consists of four components, 

(i) Small mineral particles, 

(ii) Organic matter, 

(iii) Soil air and 

(iv) Soil water.

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