Grade 11 Botany Note

Biota and Their Environment


Ecology (fromGreek) is the scientific analysis and study of interactions among organisms and their environment, such as the interactions organisms have with each other and with their abiotic environment. Ecology is adisciplinary field that includes biology and earth science.The word "ecology" was coined in 1866 by the German scientist Ernst Haeckel (1834–1919).          

Ecology may be defined as the study of the relationships of plant and animal with each other and their environment. Ecology is not synonymous with environment, natural history, orenvironmental science. It is closely related to evolutionary biology, genetics.       

Ecological Factor:

Environment means each and every thing outside the plant which influences in any way, directly or indirectly the life of the plant. It includes all external forces i.e. light, temperature, soil, water and other organism etc. Each part of the environment is called ecological factor. It consists of Abiotic and biotic factor.

(A) Abiotic Factors

1. Climatic factors

a) Light: The first and foremost requirement of life is energy. On our planet the main source of energy is the sun. The solar energy that sustains all life on the earth is received in the form of electromagnetic waves.

Light effects regulate the plant activities in various ways and are responsible for the photochemical activities of the plants like photosynthesis, transpiration, movement, germination, reproduction and geological distribution. The quality of light, its quantity and duration influence the above described activities of plants.


b) Temperature: Heat, like light is a form of energy. Sunlight falling on the surface causes heating effect. All organisms are constantly receiving heat energy from outside and heat is not accumulated in the body. Heat travels in space in the form of radiation. Earth itself acts as second source of heat energy.

Some sources other the sun also can produce heat which effects atmosphere. Temperature affects wind velocity, evaporation and rainfall, sea current, soil formation from rocks and other vital activities. The temperature is highly variable time and space. For most of the organism, the favorable temperature range lies between 00C to 50C. Temperature is variable facture and influenced by time, latitude, slope, direction and industrialization. Temperature affects the morphology, physiology, biochemistry and distribution of the plants. The transpiration rate is directly proportional to temperature. Seed germination, bud sprouting, growth, flowering, fruiting and maturation of seeds required optimum temperature.


c) Wind Velocity: The strong moving current of air or wind is an ecological factor of great significance. Wind velocity directly influences transpiration of plants. It is also helpful in dispersal of pollen grains, seeds and fruits. Some plants that grow in areas subjected to strong wind all the year round develop an overall shape that offers least resistance to wind.


d) Atmospheric Gases: The atmosphere is essential for all living beings. The air surrounding earth, within 15kms affects weather and influence organism. All atmospheric gases are usually available in proper amount to living organisms because, concentration of gases dose not vary in the environment, hence they are not considered as part of changing environment.

The atmosphere contains following gases:

1. Oxygen (O2): 20.8%

2.Carbon dioxide (CO2): 0.03%

3. Nitrogen (N2): 79%

4. Water vapors (H2O): 0.1%


e) Rainfall: The hot air masses moving from the sea, lake, and pounds are extremely moist. This warm and moist air while moving up to elevations or cooler place becomes cool and condensed. This precipitation of atmospheric moisture is the ultimate source of water for plants.

Plants are highly sensitive to combined effect of rainfall and temperature. In equatorial and tropical regions dense vegetation or forest due to heavy rainfall.


f) Atmospheric Humidity: water vapours are always present in the atmosphere. Presence of vapours is known as atmospheric humidity. When atmosphere holds the maximum quantity of moisture at a fixed temperature and pressure then it is known as absolute humidity. The humidity of a particular area is influenced by temperature, pressure, air velocity, vegetation and soil water.


2. Edaphic Factor: Plants get their food and water from the soil. The root hairs of plants adhere to the soil particles and absorb water. The process of braking down of small rocks into soil is called weathering. The nature and properties of mineral components of soil greatly depends upon the nature of parent rocks and the process of weathering.


Soil profile: At any place where parent material is weathering over a period of time, there develops layers of soil one over the other in progressive state of maturity. Such a vertical section of soil is known as soil profile. The soil profiles are characteristic of mature soil and are named as A, B, C horizons from the surface downwards.


Organic Matter: The organic matter in the soil is received from the dead bodies of plant and animals. Many micro-organism acts on the dead body and convert it into humus and ultimately back to minerals and increase the fertility of the soil. The fertile soil contains more organic matter.


Soil Water: Rain is the principle source of water for the soil. Water which flow down due to the force of gravity is known as gravitational water. This kind of water is not available to the plants but it is big soil water reservoir and is trapped out through tube wells.


Soil Air:  Soil air is essential for the process of absorption of water by plants. Soils which contain more oxygen show a rapid absorption of water while oxygen deficient soil shows slow absorption of water. Roots also require oxygen for respiration.


3. Topographic Factors:

Altitude of the place: Temperature decreases with an increase in altitude of the place. On mountains for every rise of 1000 meters a lowering of 6-70C has been observed. There is more rain in High Mountain.


Slope of land: Rain water runs away rapidly on the slope due to which the soil cannot absorb sufficient water and remains dry. The possibility of soil erosion also increases with the slope. So onlyfew plants grow on slope land.


Direction of Mountains: If the slopes receive less light and dry winds blows then these are best suited for xerophytes e.g. north facing slopes of Himalayan range. Moisture laden winds precipitate if any mountain range comes in the way of wind and such mountains have dense vegetation.


Biotic Factor: Plants living together or with animals make a community. The members of a community are related with each other and with the environment of that area in which they live.


(B) Biotic Factor: Biotic factors mean all the living organism of the ecosystem including bacteria, algae, fungi, parasites, saprophytes, symbiotic and animals. This living organism further divided into:

1. Autotrophs (producer): Those organism which can prepare their own food by utilizing raw material and sunlight or in other word those organism having chlorophyll and capable of making their own food. They shouldn’t have to depend on other for food. This includes all green plants, photosynthetic bacteria and cyanobacteria. These also maintain oxygen and carbon dioxide cycle.


2. Heterotrophs (Consumer):  In simple word they are those organisms which consume the production of producer or in other word that organism which do not have chlorophyll and they have to depend on other for their daily food. On the basis of nature of the food they are classified into:

a) Primary consumer: these includes herbivorous which directly feed upon the plants e.g. Rabbit, deer, goat etc.

b) Secondary Consumer: This includes the primary carnivores which feed upon the herbivorous e.g. Fox, fishes etc.

C) Tertiary Consumer: These includes the secondary carnivores which eat upon secondary consumer e.g. Tiger, Lion etc.


3. Decomposer: Those organisms which decompose the complex organic compound present in dead body are known as decomposer. They are saprophytes or reducers. They includes microorganism like bacteria, fungi etc. They produce digestive enzyme to breakdown the organic material. So decomposers are responsible for the recycling of the material in the ecosystem.


Interaction between biotic factors:

Biological interactions are the effects organisms in a community have on one another. In the natural world no organism exists in absolute isolation, and thus every organism must interact with the environment and other organisms. An organism's interactions with its environment are fundamental to the survival of that organism and the functioning of the ecosystem as a whole. They show positive as well as negative interaction.


1. Positive interaction

Interspecific interaction:

a) Mutualism (Symbiosis): when two species live together in close association and they are benefited from each other, the relationship is called Mutualism.Mutualism is an interaction between two or more species, where species derive a mutual benefit, for example an increased carrying capacity. Similar interactions within a species are known as co-operation. Mutualism may be classified in terms of the closeness of association, the closest being symbiosis, which is often confused with mutualism. One or both species involved in the interaction may be obligate, meaning they cannot survive in the short or long term without the other species, e.g. nitrogen fixing bacteria in the root nodule of leguminous plant.

b) Commensalism: It is an association of two species where one organism is get benefited and other is not harmed or get any benefit.. It occurs when one organism takes benefits by interacting with another organism by which the host organism is not affected. A good example is a remora living with a shark. Remoras eat leftover food from the shark. The shark is not affected in the process, as remoras eat only leftover food of the shark, which does not deplete the shark's resources.

c) Protocooperation:The cooperation between species where both species are benefited. However it is not obligatory.Protocooperation is where two species interact with each other beneficially; they have no need to interact with each other - they interact purely for the gain that they receive from doing this.

d) Neutralism: Neutralism describes the relationship between two species that interact but do not affect each other. It describes interactions where the health of one species has absolutely no effect whatsoever on that of the other. Examples of true neutralism are virtually impossible to prove.  However, the term is often used to describe situations where interactions are negligible or insignificant, e.g. the leaf eating and sap-sucking insects live together but there is no interaction.


Intraspecific interaction:

a) Colonization: Some species of plants and animals live in colony for protection from predator or from natural condition or for food, e.g. nostoc and obelia.

b) Social Organization: Social organization refers to those organism which live in colony and work together in groups to complete theirworks such as food gathering to survive in different climatic condition and other various purpose. For e.g honey bees and ants.

c) Aggregation: The capacity among animal to concentrate in large numbers by their movement is called aggregation.


2. Negative Interaction:

a) Predation: This is a direct interaction of two species. In ecology, predation is a biological interaction where a predator (an organism that is hunting) feeds on its prey (the organism that is attacked).Predators may or may not kill their prey prior to feeding on them, but the act of predation often results in the death of its prey and the eventual absorption of the prey's tissue through consumption.[2] Thus predation is often, though not always, carnivory.

b) Parasitism:A parasite is organisms which live on another organism and depends completely on it for the survival. Parasitism is a non-mutual symbiotic relationship between species, where one species, the parasite, benefits at the expense of the other, thehost. Unlike predators, parasites do not kill their host, are generally much smaller than their host, and will often live in or on their host for an extended period. Both are special cases of consumer-resource interaction Parasites show a high degree of specialization, and reproduce at a faster rate than their hosts. Classic examples of parasitism include interactions between vertebrate hosts and tapeworms.

c) Competition:In ecosystem, there is always competition between organisms for their survival and other various purposes like reproduction, shelter etc. Competition can have both beneficial and detrimental effects. It arises whenever at least two parties strive for a goal which cannot be shared or which is desired individually but not in sharing and cooperation. 

d) Antibiosis: Antibiosis is a biological interaction between two or more organisms that is detrimental to at least one of them; it can also be an antagonistic association between an organism and the metabolic substances produced by another. Examples of antibiosis include the relationship between antibiotic and bacteria and the relationship between animals and disease-causing pathogens.


Food chains:

The transfer of food energy from the procedure through a series of organism (herbivores to carnivores to decomposer) with repeated eating and being eaten is known as a Food chain. Procedure utilizes the radiant energy of sun which is transformed to chemical form (ATP) during photosynthesis. The energy stored in food matter manufactured by green plants is then utilized by the plant eaters- the herbivores, which constitute the second trophic level-the primary consumer level, and are called the primary consumer (herbivores). Herbivores in turn are eaten by the carnivores, which constitute the tropic level and are called secondary consumers (carnivores). These in turn may still be eaten by other carnivores at tertiary consumers level i.e. by the tertiary consumer (carnivores) and finally eaten by top consumer, e.g. Hawk is top consumer. In nature, food chain generally is of 3 types.

1. Grazing food Chain: this type of food chain starts from the living green plant goes to grazing herbivores and on to carnivores. Ecosystems with such type of food chain are directly dependent on an influx of solar radiation. This type of chain thus depends on autotrophic energy capture and the movement of this captured energy to herbivores. Most of the ecosystem in nature follows this type of food chain.

The primary carnivores eat herbivores of the ecosystem. And likewise, tertiary consumers eat primary carnivores. The total energy assimilated by primary carnivores or gross tertiary production is derived entirely from the tissues of herbivores, and its disposition into respiration, decay and further consumption by other carnivores is entirely analogous with that of herbivores. It seems clear that much of the energy flow through grazing food chain can be described in terms of the categories or trophic levels outlined as follows.

Autotrophs            Herbivores               Pri. Carnivore Secondary Carnivore


2. Parasitic food chain: it goes from large organism to smaller ones without outright killing as in case of predation.


                                      Fig:  Parasitic food chain

3. Detritus Food Chain: the organic wastes, exudates and dead matter derived from the grazing food chain are generally termed detritus. The energy contained in this detritus is not lost to the ecosystem as a whole, rather it serves as the source of energy for a group of organism that is separate from the grazing food chain and generally termed thedetrius food chain. The detritus food chain represents an exceedingly important component in the energy flow ecosystem.

In the detritus food chain the energy flow remains as a continues passage rather than as a stepwise flow between discrete entities. The organism of the detritus food chain are many and include algae, bacteria, fungi, protozoa, insects, molluscs and some vertebrates.

Food webs: Food chains in natural conditions never operates as isolated sequences but are interconnected with each other forming some short of interconnecting pattern which is referred to as a food webs. Under natural conditions, the linear arrangement of food chains hardly occurs and these remain indeed interconnected with each other through different types of organism at different trophic level. For e.g. in grazing food chain of grassland, in the absence of rabbit grass may be also eaten by mouse. The mouse in turn may be eaten directly by hawk or by snake first which is then eaten by hawk. Thus, in nature there are found alternatives which all together constitute some sort of interlocking pattern of food web.

                     Fig: food web in a grassland ecosystem.

Ecological Pyramids:Each particulars type of ecosystem has a tropic structure the interaction of food chain phenomenon and size metabolism relationship. Trophic structure and functions are shown graphically by means of ecological pyramids. In ecological pyramids the first or procedure level constitutes the base and successive levels (primary, secondary consumers etc.) the tires which make the apex. The ecological pyramids are of three general types:

1. Pyramids of Number: They show relationship between producer, herbivores and carnivores at successive trophic levels in terms of their number. The pyramid may be upright or inverted depending upon the size of the producer in the community. Large procedure are fewer in number than the smaller organism.

In grassland, the procedures which are mainly grasses are always maximum in number. This number then shows a decrease towards apex as the primary consumers (herbivores) like rabbits, mice, insects etc.  Are lesser in number than the grasses; the secondary consumer, snakes and lizards are again lesser in number than the rabbits and mice, finally the tertiary consumers hawks or other birds are least in number. Thus, the pyramids become upright. Similarly, in a pond ecosystem the pyramid is upright. Here the procedure which are mainly the phytoplankton’s as algae, bacteria etc. are maximum in number; the herbivores, which are smaller fish are lesser in number than the procedure and the secondary consumer such as small fish eating each other, water beetles etc. are lesser in number than the herbivores. Finally the top consumers, the bigger fish are less in number.



                                       Fig: Pyramid of number


2. Pyramids of biomass: The total fresh or dry weight of all living organisms in a certain unit area is called biomass. They are comparatively more fundamental as they instead of geometric factor show the quantitative relationships of the standing crops. In grassland and forest there is generally a gradual decrease in biomass of organism at successive levels from the procedures to the carnivores. Thus pyramids are upright. However, in a pond as the procedure are small organisms their biomass is minimum and value gradually shows an increase towards the apex of the pyramid, thus making the pyramid inverted in shape.

                                            Fig: pyramid of biomass



3. Pyramid of energy: Of the three types of ecological pyramids, the energy pyramids give the best picture of overall nature of the ecosystem. This type of pyramid shows energy accumulation pattern at different trophic levels. Here, number and weight of organisms at any levels depends not on the amount of fixed energy present at any one time in the level just below but rather on the rate at which food is being produced.


Fig:  Pyramid of energy


Ecosystem:An ecosystem is a community of living organisms (plants, animals and microbes) in conjunction with the non-living components of their environment (things like air, water and mineral soil), interacting as a system. The term "ecosystem" was first used in a publication by British ecologist Arthur Tansely.


Pond Ecosystem

A pond as a whole serves a good example of a freshwater ecosystem. A pond indeed exhibits a self-sufficient, self-regulating system. It has a structure having the abiotic and biotic components

Abiotic Components: The chief substances are heat, light, ph. value of water and basic organic and inorganic compounds such as carbon dioxide gas, oxygen, calcium, nitrogen etc. some properties of nutrients are in solution state but most of them are present as stored in particular matters as well as in living organisms. Amounts of various organic compounds are also estimated for biomass determination.

Biotic Components: The various organisms that constitute the biotic component are as follows-

1. Procedure: These are autotrophic green plants and some photosynthetic bacteria. The procedure fixes energy and with the help of material derived from the water and mud. They produce complex organic substances as carbohydrates, proteins, lipids etc. The procedures are two types:

a) The rooted or large floating plants which includes partly or completely submerged, floating and emergent hydrophytes. The common plant species are Trapa, typha, chara, hydrilla, azolla, salvinia etc.

b) The minute, floating or suspensed lower plants. Majority of them are such filamentous algae, e.g. zygonema, spirogyra, oedogonium, anabaena etc.

2. Consumer: They are heterotrophs which depend for their nutrition on the organic food producer, the green plants. Most of the consumers are herbivores, a few as insects and some large fish are carnivores feeding on herbivores. The consumers in a pond are as follows.

a) Primary Consumers (herbivores): Also known as primary macro consumers, these are herbivores feeding directly on living plants (producer). These may be large or minute. The primary consumer of pond is Euglena, Dileptus, beetles, mites etc.

b) Secondary consumer (carnivores): They are the carnivores which feed on the primart consumers. These are chiefly insects and fish. Most insects as water beetles feed on zooplanktons.

c) Tertiary Consumer: these are some large fish as game fish that feed on the smaller fish and thus become the tertiary carnivores. It is common to observe the large fish feeding on smaller fish and thus occupying the tertiary consumers level.

3. Decomposer:  They are known as microc onsumers, since they absorb only a fraction of the decomposed organic matter they bring about the decomposition of complex dead organic matter of both plants and animals to simple form. Thus they play an important role in the return of mineral elements again to the medium of the pound. The decomposers of pond are Aspergillus, alternaria, penicillum, cladosporium, saprolegina etc. the most common decomposer.



                                             Fig: Pond Ecosystem






Grassland Ecosystem:

This is a type of terrestrial ecosystem. Grassland occupy a comparatively fewer area roughly 19% of the earth’s surface. The various components of a grassland ecosystem are as follows-

Abiotic Component:

These are the nutrient present in soil and the aerial environment. Thus the elements like C, H, O, P, S etc. are supplied by carbon-dioxide, water nitrates, phosphates and sulphates etc. present in air and soil of the area.

Biotic Component:

Procedure: They are mainly grasses as species of Dichantium, Cynodon, setaria, sporoblous etc. Besides them a few forbs and shrubs also contribute to primary production.

Consumer:There occur in the following sequence-

a) Primary Consumers:  The herbivores feeding on grasses are mainly such grazing animals as cows, deer, sheep, rabbit etc. Besides them there are also present some insects as Leptocorisa, cicinella, termites etc.

b) Secondary Consumer: These are the carnivores feeding on herbivores. These include the animals like fox, jackals, snakes, frogs etc. sometime the hawks feed on the secondary consumers, thus occupying tertiary consumers level in food chain.

Decomposer: The microbes active in the decay of dead organic matter of different forms of higher life are fungi as species of Mucor, aspergillus, penicillium etc. they brings about the minerals back to the soil thus, making them available to the procedure.




 In nature, different kinds of organisms grow in association with each other. A group of several species living together with mutual tolerance and beneficial interaction in a natural area is known as a community. In a community, organisms share the same habitat growing in a uniform environment.Forest, grassland, desert orpond is natural community.

Characteristics of a community:

Like a population, a community too has its own characteristics, which are not shown by its individual component species. These characteristics which have meaning only with reference to community level of organization are as follows-

1. Species Diversity: Each community is made up of many different organisms- plants, animals, microbes which differ taxonomically from each other.

2. Growth from and structure: Community is described in terms of major growth forms as trees, shrubs, herbs, mosses etc. in each growth form as in tree, there may be different kinds of plants as broad- leaves trees, evergreen trees etc. these different growth forms determines the structural pattern of a community.

3. Dominance: In each community all the species are not equally important. There are relatively only a few of these, which determine the nature of the community. These few species exert a major controlling influence on the community. Such species are known as dominants.

4. Succession: Each community has its own developmental history. It develops as a result of a directional change in it with time.

5. Trophic structure: nutritionally each community a group of autotrophic plants as well as heterotrophic animals exists as a self-sufficient, perfectly balanced assemblage of organism.




Under natural conditions the vegetative occupying a given habitat is called plant community. Since the community is not stable it passes through many development stages in definite sequence and in definite direction generally from simple to complex and rarely complex to simple. Ecological succession is the observed process of change in the species structure of an ecological community over time. The time scale can be decades or even millions of years after amass extinction.

The community begins with relatively few pioneering plants and animals and develops through increasing complexity until it becomes stable or self-perpetuating as a climax community. The engine of succession, the cause of ecosystem change, is the impact of established species upon their own environments. Succession that begins in new habitats, uninfluenced by pre-existing communities is called primary succession, whereas succession that follows disruption of a pre-existing community is called secondary succession.

Types of succession:

 Depending upon the nature of bare area on which it develops, the succession may be two kinds:

1. Primary Succession: Primary succession is one of two types of biological and ecological succession of plant life, occurring in an environment in which newsubstrate devoid of vegetation and usually lacking soil, such as a lava flow or area left from retreated glacier, is deposited. In other words, it is the gradual growth of an ecosystem over a longer period.

2.Secondary Succession: This type of succession starts on secondary bare, area which was once occupied by original vegetation but later became cleared of vegetation by the process called denudation. Secondary succession occurs on substrate that previously supported vegetation before an ecological disturbance from smaller things like floods, hurricanes, tornadoes, and volcanic eruptions which destroyed the plant life.


General process of succession

The whole process of a primary autotrophic succession is actually completed through a number of sequential steps which follow one another. The steps are:

1. Nudation:

This is the development of a bare area without any form of life. The area may develop due to several causes such as landside, erosion, deposition or other catastrophic agency. The cause of Nudation may be,

A) Topographic: due to soil erosion by gravity water or wind the existing vegetation may disappear.

B) Climatic: Strom, frost, wind, fire may also destroy the vegetation.

C) Biotic: Man is the main important, responsible for destruction of tree, agriculture etc. which destroy the whole population.

2. Invasion:

This is the successful establishment of a species in a bare area.

A) Migration:the seeds,spore or other propagates of the species reach the bare area. This is migration process.

B) Establishment (Ecesis):After reaching to new area, the process of successful establishment of the species as a result of adjustment with the condition prevailing there is known as ecesis.

C)Aggregation: After ecesis as a result of reproduction, the individuals of the species increase in number and they come to each other. This process is known as aggregation.


3. Competition and coaction:

After aggregation of a large number of individuals of the species at the limited place, there develops competition mainly for space and nutrition. Individuals of a species affect each other’s life in various ways and this is called coaction.


4. Reaction:

This is the most important stage in succession. The mechanism of modification of the environment through the influence of living organisms on it is known as reaction. As a result of reactions changes take place in soil, water, light conditions, temperature etc. of the environment. Due to all these the environment is modified becoming unsuitable for the existing community of communities that replaces one another in the given area is called a sere and the communities is called seral communities.


5. Stabilization (climax):

Finally there occurs a stage in the process, when the final terminal communities becomes more or less stabilized for a longer period of time and it can maintain itself in equilibrium with the climate of the area. This final community is not replaced and is known as climax community and the stage as climax stage. The developmental stage is called a seral stage. These stages are in fact continuous with each other and the whole sequence from beginning till the climax is known as a Sere. The species which colonies the bare area in the beginning of succession are called Pioneers.


Biogeochemical Cycle

Simply it, cyclic moment of the chemical compound. A biogeochemical cycle or substance turnover or cycling of substances is a pathway by which a chemical substance moves through both biotic compartments of earth. A cycle is a series of change which comes back to the starting point and which can be repeated. Water, for example, is always recycled through the water cycle, The water undergoes evaporation, condensation and precipitation, falling back to Earth. Elements, chemical compounds, and other forms of matter are passed from one organism to another and from one part of the biosphere to another through biogeochemical cycles.


Carbon Cycle:

Carbon is basic constitute of all organic compound. The ultimate source of carbon in nature is carbon dioxide present in the atmosphere and in dissolved state in the water on earth. All living things are made of carbon. Carbon is also a part of the ocean, air, and even rocks. Because the Earth is a dynamic place, carbon does not stay still. It is on the move. In the atmosphere, carbon is attached to some oxygen in a gas called carbon dioxide. Plants use carbon dioxide and sunlight to make their own food and grow. The carbon becomes part of the plant. Plants that die and are buried may turn into fossil fuels made of carbon like coal and oil over millions of years. When humans burn fossil fuels, most of the carbon quickly enters the atmosphere as carbon dioxide.

Carbon dioxide is a greenhouse gas and traps heat in the atmosphere. Without it and other greenhouse gases, Earth would be a frozen world. But humans have burned so much fuel that there is about 30% more carbon dioxide in the air today than there was about 150 years ago, and Earth is becoming a warmer place.

                                                  Fig: Carbon Cycle


Nitrogen cycle

 Nitrogen is important as constitute of proteins and nucleic acids that play the basic role in metabolism, growth, reproduction and transmission of heritable characters of living organisms. Most plants get the nitrogen they need from soil. The main component of the nitrogen cycle starts with the element nitrogen in the air. Two nitrogen oxides are found in the air as a result of interactions with oxygen. Nitrogen will only react with oxygen in the presence of high temperatures and pressures found near lightning bolts and in combustion reactions in power plants or internal combustion engines. Nitric oxide, NO, and nitrogen dioxide, NO2, are formed under these conditions. Eventually nitrogen dioxide may react with water in rain to form nitric acid, HNO3. The nitrates thus formed may be utilized by plants as a nutrient.

Nitrogen in the air becomes a part of biological matter mostly through the actions of bacteria and algae in a process known as nitrogen fixation. The ammonia is further converted by other bacteria first into nitrite ions, NO2-, and then into nitrate ions, NO3-. Plants utilize the nitrate ions as a nutrient or fertilizer for growth.

Ammonia may be directly applied to farm fields as fertilizer. The reaction of ammonia and nitric acid produces ammonium nitrate which may then be used as a fertilizer.

To complete the cycle other bacteria in the soil carry out a process known as de-nitrification, which converts nitrates back to nitrogen gas. A side product of this reaction is the production of a gas known as nitrous oxide, N2O.

                                             Fig: Nitrogen Cycle


Greenhouse Effect:

The greenhouse effect is a natural process that warms the Earth’s surface. When the Sun’s energy reaches the Earth’s atmosphere, some of it is reflected back to space and the rest is absorbed and re-radiated by greenhouse gases. The absorbed energy warms the atmosphere and the surface of the Earth. Greenhouse gases include water vapour, carbon dioxide, methane, nitrous oxide, ozone and some artificial chemicals such as chlorofluorocarbons (cfcs).

If it were not for greenhouse gases trapping heat in the atmosphere, the Earth would be a very cold place. Greenhouse gases keep the Earth warm through a process called the greenhouse effect

 The Earth cools down by giving off a different form of energy, called infrared radiation. But before all this radiation can escape to outer space, greenhouse gases in the atmosphere absorb some of it, which makes the atmosphere warmer. As the atmosphere gets warmer, it makes the Earth's surface warmer, too.



1. The greenhouse effect results in increase in temperature of earth surface.

2. By greenhouse effect can melt the polar eyes due to which the sea level increase and that can make difficulty for the country like Maldives.

3. It can alter the monsoon season.

4. It can decrease the crop production due to rise in temperature.


Ozone (O3) Layer:

The accumulation of oxygen in atmosphere due to photosynthesis by green plant results in the formation of ozone layer.The ozone layer is a belt of naturally occurring ozone gas that sits 9.3 to 18.6 miles (15 to 30 kilometers) above Earth and serves as a shield from the harmful ultraviolet B radiation emitted by the sun.

Ozone is a highly reactive molecule that contains three oxygen atoms. It is constantly being formed and broken down in the high atmosphere in the region called the stratosphere.Chlorofluorocarbons (cfcs), chemicals found mainly in spray aerosols heavily used by industrialized nations for much of the past 50 years, are the primary culprits in ozone layer breakdown. When cfcs reach the upper atmosphere, they are exposed to ultraviolet rays, which cause them to break down into substances that include chlorine. The chlorine reacts with the oxygen atoms in ozone and rips apart the ozone molecule.One atom of chlorine can destroy more than a hundred thousand ozone molecules.

i)  O2                                                       O + O;        O2 + O                                        O3

ii) CFCl3                                               Cl + CFCl2 (UV)

                                                (Chlorine Atom)

iii) Cl + O3                                            ClO + O2 (UV)

                                                                (chlorine Monoxide)

iv) ClO + O                                                                Cl + O2

Consequence of Ozone layer depletion:

- UV lights can damage living cells and can cause mutation.

- It can cause blindness.

- It can also cause skin cancers.

- Ozone layer depletion can result in rise in earth’s temperature.


Acid Rain: Acid rain is a rain or any other form of precipitation that is unusually acidic meaning that it possesses elevated levels of hydrogen ions (low pH). It can have harmful effects on plants, aquatic animals and infrastructure. Acid rain is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids. Governments have made efforts since the 1970s to reduce the release of sulfur dioxide into the atmosphere with positive results. Nitrogen oxides can also be produced naturally by lightning strikes and sulfur dioxide is produced by volcanic eruptions. The chemicals in acid rain can cause paint to peel, corrosion of steel structures such as bridges, and erosion of stone statues.

Controlling Measures:

The acid rain can cause many problems so these can be solved by reducing emission of sulphur dioxide and nitrogen oxides.

1. By reducing the uses of fossil fuels.

2. By purifying the polluted air.

3. By controlling the uses of old vehicles.


Mountain Ecosystem: Nepal is a country of mountain ranging from 60m to world highest peak which clearly indicates the larger number of species in it. In mountains region is formed by sedimentary rock. Soil of this region is not fully mature. In mountains region the soil layer is very thin, because of steep higher mountains. The climate is extremely cold, dry and windy at this area. It varies greatly in different altitudes of the mountains region.


Abiotic Components: These includes physical factor like temperature, wind velocity, moisture, pressure and light intensity. The chemical factors include inorganic and organic substance present in soil.

Biotic Components:


The mountain is a favorable for plants growth which make mountain rich in ecosystems. However in High Mountain due to snow fall the plant vegetation is scattered and small. Mountain regions possess sub-alpine and alpine vegetation. The producer of this ecosystem isjuniperus spp, rhododendron spp, aconitum, meconopis, primula etc.

Consumer: the primary consumer of this region are red panda, musk deer, blue sheep and secondary consumer are black dear, snow leopard, leopard cat, snow patridges, insects, worms etc.

Decomposer: The microbial organisms such as bacteria and fungi acts as decomposer. They decompose the dead organic body of plants and animals into simple inorganic forms.

The ecological pyramid of number of this ecosystem is inverted.

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