• Tropical deciduous forest extends in largest area in M.P.
• In Detritus : ecosystem, producers are absent.
• Ecotone : The zone of transition between two nearby ecosystems is called an ecotone.
• Stability of an ecosystem depends upon diversity. Croplands are mostly monocultures and lack diversity.
• The scientific study of lakes is known as limnology.
• Ecotone is the transitional zone between two vegetation regions.
• There is the highest species diversity in tropical rain forest ecosystem.
• Forest occupy 40% of land is world. In India forests occupy only 22.8% of land area.
• Energy content are determined by igniting the plant contents in O₂ bomb calorimeter.
• Lindemann gave the low of 10% for energy flow (10% energy transfer law).
• The species which are restricted to small areas are called endemic.

 

 Environmental pollution.                                                                                                                                    

According to Odum pollution is an undesirable change in the physical, chemical or biological characteristics of our air, land and water that will harmfully affect the human life and the desirable species so that may waste or deteriorate our raw material resources. Pollution is the deliberate or accidental contamination of the environment with man's waste. Pollution is defined as matter in the wrong place. Pollution produces bad effects on ecological (environmental) balance substances which cause pollution are called pollutants there are two categories :

• Biodegrodable Pollutant : These pollutant can be decompose by micro–organisms. However if they are released in large amount then they begin to accumulate in environment. When their concentration crosses a critical limit then they become toxic and start acting as pollutants.
• Non–biodegradable pollutant : These pollutant can not be decomposed by micro–organism. e.g., DDT, BHC, Aldrin, Plastics, Hg, Salfs Polythene. These pollutants are continiously accumulating in our environment.

Types of pollution : Pollution is classified into the following types :

(1) Air pollution  (2) Water pollution    (3) Land pollution  (4) Noise pollution   (5) Thermal pollution.

1. Air Pollution : Air pollution refers to the undesirable change occurring in air causing harmful effects on man and domesticated species.
   1. Air Pollutants : The common air pollutants are : Dust, Smoke, Carbon monoxide (CO), Ammonia (NH₃), Sulphur dioxide (SO₂), Hydrogen sulphide (H₂S), Nitrogen dioxide (NO₂), Hydrogen cyanide, Hydrogen fluorides, Chlorines, Phosgenes, Arsines, Aldehydes, Ozone, Ionising and radiations. CO₂ is not a normal air pollutant. There is 0.03% CO₂ in the air its higher percentage is the cause of green house effect.

Types of air pollutants : It is two types :

1. Primary air pollutants : Air is polluted by poisonous gases and undesirable substances. They are released by burning fossil fuels. These substances are called primary air pollutants. The primary air pollutants are the following :

• Soot released from unburned fuel.
• Sulphur dioxide (SO₂).
• Benzopyrene (hydrocarbon) released from cigarette smoke.
• Ammonia (NH₃).
• Oxides of nitrogen.

 

 

• Carbon monoxide (CO).
• Lead (Pb).

2. Secondary air pollutants : Secondary air pollutants are poisonous substance formed from primary air pollutants. In bright sun light nitrogen, nitrogen oxides, hydrocarbons and O₂ interact to produce more powerful photochemical oxidants like ozone (O₃), peroxyacetyl nitrate (PAN), aldehydes, sulphuric acid, peroxides, etc. All these constitute photochemical smog, which retard photosynthesis in plants.
   2. Causes of air pollution

1. Agriculture : Hydrocarbons released by plants, pollen grains, insectisides etc. cause air pollution.
2. Dust : Dust in the air is increased by dust storms wind, volcanoes, automobiles, etc.
3. Industries : Combustion of fossil fuels like coal, petroleum, etc. Industrial smoke is the main source of pollution.
4. Automobiles : The combustion of petrol and diesel in automobiles releases harmful gases into the air. They also produce dust.
5. Ionising radiations : Ionizing radiations include alpha particles, beta particles and gamma rays. They are released into the air on testing atomic weapons.
6. Freons : Use of freons and other chloro-fluoro-carbon compounds in refrigerants, coolants and as filling agents in aerosol also cause pollution.
7. Aerosols : Aerosols are small particles of all sorts of solid or liquid substances suspended in the air. They block the stomata of plants and prevent the gaseous exchanges between plants and atmosphere. They may also change the climate of an area.

Biological Indicators : Some plants are sensitive to certain air pollutants. These plants are used to indicate the presence of these substances. These plants are called biological indicators. e.g.,

• The tissues present in the tip of dusheri mango turns black when they are exposed to sulphur dioxide (SO₂) fumes.
• Pinto beans and Petunias are used to indicate the presence of peroxy acetyl nitrate (PAN).
• Tobacco and annual blue–grass plants are used to show the presence of ozone (O₃). Lichens are biological indicaters of air pollution caused by SO₂.
  3. Ecological effects of air pollution

1. Death : When air is polluted with poisonous gases, death comes as a result immediately. Bhopal episode is a good example. Bhopal episode – On 2^nd December 1984 about 3000 human beings died, about 5000 paralysed and thousands of cattles, birds, dogs and cats died in one night at Bhopal. This mass death is due to the leakage of methyl isocyanate (toxic gas) into the air from an insecticide plant managed by Union Carbide Corporation.
2. Chlorosis : The disappearance of chlorophyll is called chlorosis. It is caused by SO₂, nitrogen dioxide, ozone and fluorides.
3. Necrosis : The breakdown of cells is called necrosis. It is caused by SO₂, nitrogen dioxide, ozone and fluorides.
4. Green house effect : CO₂ is released into the air by the combustion of fuels. It is estimated that CO₂ content of the air is increasing at the rate of 0.4% per annum. This will result in an appreciable warming up of the earth. This is called green house effect. It is very likely that this will cause the melting of polar ice caps resulting in a rise of nearly 60 feet on the sea level. Coastal regions and low lying areas all over the world will be go under water.

 

 

• Not only CO₂ but CFC and to some extent methane and oxides of nitrogen disturb the temperature of earth hence they all are described as green houses gases.
• 3.0 pH has been recorded in acid rain.

5. Crop losses : Heavy loss of crop is caused by smog. Smog denotes a combination of smoke and fog. The important components of smog are ozone and PAN (peroxy acetyl nitrate). They damage leafy vegetables, cereals, textile crops, ornamental plants, fruits and forest trees.
6. Respiratory disorders : Excessive ethylene accelerates respiration causing premature senescence (old age) and abscission (accumulation of yellow fluid (pus) in the body). Aldehydes irritate nasal and respiratory tracts. Chlorine and phosgenes (carbonyl chloride) cause pulmonary oedema. Bronchitis is another bad effect of air pollution.
7. Nausea : H₂S smells like rotten eggs and causes nausea.
8. Vomiting : SO₂ causes vomiting.
9. Jaundice : Arsines induce RBC breakdown and jaundice.
10. Oxygen carrying capacity : CO reduces O₂ carrying capacity of RBC by its permanent combination with haemoglobin.
11. Coughing : Coughing is induced by phosgenes (carbonyl chloride).
12. Headache : SO₂ causes headache.
13. Cancer : Cancer is caused by air pollutants like ash, soot, smoke, chromium, nickel and readioactive elements.
14. Mutation : Radioactive elements produce mutation. Ozone produces chromosomal aberrations.
15. Cardiac diseases : Cadmium causes high blood pressure and heart diseases.
16. Pneumonia : Pneumonia is caused by breathing in too much of manganese particles.
17. Depletion of Ozone umbrella : In the atmosphere, about 30 km above the surface of the earth, the ozone molecules (O₃) form an umbrella. It prevents the penetration of harmful ultra violet radiation from the sun and thus protects the life of the earth. It is now feared that there is danger of depletion of the ozone umbrella, which may occur by the use of freons and other CFC-compounds in refrigerants, coolants in domestric refrigenrators and cold storage facilities, and as filling agents in the form of plastics and in aerosol packages. On reaching the ozone umbrella, they destroy ozone molecules as a result of photochemical reactions. Over the past 16 years, the density of the ozone layer has been diminishing at an average rate of 3%. It is calculated that the depletion of ozone layer by 1% results in an increase in the incidence of skin cancer by 5% to 7%. A hole in O₃ layer has been discovered in Antarctica.
18. Acid rain : One of the major environmental issues facing human society at the national and international level is the problem of rain water having low pH. The rainwater is always slightly acidic as CO₂ in the atmosphere gets dissolved in it. However during recent years, it has been noted a further lowering of pH of rain water often as low as 2.4. This lowering of pH is due to the dissolution of acids in the rain water. Precipitation of oxides of sulphur and nitrogen with rain is termed acid rain. Acid rain is caused by air pollution. When atmospheric air contains sulphur dioxide (SO₂) and oxides of nitrogen such as nitrous oxide (N₂O) and nitric oxide (NO), they dissolve in rain water forming sulphuric acid and nitric acid. The rain water falls as acid rain. The main source of releasing

 

 

oxides of sulphur and nitrogen are the power plants based on coal and oil. They contribute more than 60% of all sulphur oxides and 25 to 30% of nitrogen oxides in the atmosphere. Automobiles make a substantial contribution in large cities. Ozone is now recognised as a major factor in the formation of acid rain.

Acid rain affects both materials and organisms. It attacks building materials principally sandstone, limestone, marble, steel and nickel. In plants, it leads to chlorosis (gradual yellowing in which the chlorophyll making mechanism is impeded) or depigmentation of leaves. The concentration of SO₃ in atmosphere is around 0.01 ppm.

Acid rain increases the acidity of lakes and rivers. Vast tracts of forests and lakes in Europe and North America have been destroyed by acid rain. Acidity kills fish, bacteria and algae and the aquatic ecosystem collapses into sterility leaving a crystal clear but ultimately a dead lake.

4. Control of air pollution

1. The emission of exhaust from automobiles can be reduced by devices such as positive crankcase ventilation valve and catalytic converter.
2. Electrostatic precipitators can reduce smoke and dust from industries.
3. Gaseous pollutants arising from industries can be removed by differential solubility of gases in water.
4. A finepray of water in the device called scrubber can separate many gases like NH₃, SO₂, etc. from the emitted exhaust.
5. Certain gases can be removed by filtration or absorption through activated charcoal.
6. Certain gases can be made chemically intert by chemical conversion.
7. At the Government level pollution can be controlled by framing legislations.
8. Vehicles based on compressed natural gas (CNG) should be introduced.

2. Water Pollution : Water pollution refers to the undesirable change occurring in water which harmfully affect the life activities of man and domesticated species.
   1. Water Pollutants : The common water pollutants are : Domestic sewage, Industrial effluents, Pesticides, Herbicides, Fertilizers, Bacteria and Viruses, Plankton blooms and Heavy metals like Mercury, Temperature, Silt, Radioactivity, Oils etc.
   2. Causes of water pollution

1. Domestic sewage : Domestic sewage consists of human faces, urine, and the dirty used–up water in houses. It contains a large number of bacteria and virus. The sewage is released into the rivers on the banks of which most of the cities are situated.
2. Industrial effluents : All industrial plants produce some organic and inorganic chemical wastes. Those nonusable chemical are dumped in water as a means of getting rid of them. The industrial wastes include heavy metals (Hg, Cu, lead, zinc etc), Detergents, Petroleum, Acids, Alkalies, Phenols, Carbonates, Alcoholcyanides, Arsenic, Chlorine, etc.
3. Thermal pollution : Many industries use water for cooling. The resultant warm water is discharged into rivers. This brings about thermal pollution.
4. Agricultural pollution : The fertilizers used for crops are washed into ponds and rivers.

 

 

5. Pesticides : Pesticides are used to control pests in fields and houses. They include DDT, BHC, endrin etc.
6. Radioactive wastes : Liquid radioactive wastes are released into the sea around nuclear installations. The oceanic currents carry the radioactive contaminants every where.
7. Oil pollution : Oil is a source of pollution in sea-water. Oil pollution is due to ship accidents, loading and discharging of oil at the harbour, oil refineries and off-shore oil production. Degree of impurity of after due to organic matter is measured in terms of BOD (Biochemical Oxygen Demand). It is the demand for O₂ to decompose organic wastes in liter of water.
8. Eutrophication : Rich growth of micro-organisms consumes most of the dissolved oxygen, so as to depreve other organisms. It generally occurs at the bottom layers of deep lakes. Addition of excessive plant nutrients intensifies eutrophication. It harmful to fish and other aquatic life.
   3. Control of water pollution : Pollution control by sewage treatment includes the following steps :

1. Sedimentation : When sewage is allowed to stand, the suspended particles settle to the bottom. So by sedimentation the suspended particles are removed from sewage.
2. Dilution : The sewage can be diluted with water. This increases the O₂ contents and reduces BOD and CO₂.
3. Storage : The diluted sewage is stored in a pond. This facilitates the growth of micro-organisms. This renders further oxidation of sewage.
   4. Waste stabilization pond or Oxidation pond : The National Environmental Engineering Research Institute (NEERI) at Nagpur has devised a very economical method for the treatment of industrial and domestic effluents. Domestic and industrial wastes are stored in a dilute condition in shallow ponds called oxidation or stabilization ponds. After a few days micro-organisms and algae flourish. The micro–oranisms decompose the organic wastes by oxidation, and the water is purified. This water is rich in nitrogen, phosphorus, potassium and other nutrients. This water can be used for fish culture, agriculture etc.
   5. Recycling : Pollution can be prevented to a certain extent by reutilizing the wastes. This is called recycling. e.g., :

1. The dung of cows and buffalo can be used for the production of energy (gobar gas).
2. Sewage can be used for irrigation and fish culture after treatment in oxidation pond. Certain pollutants from industrial effluents can be removed by filtrationand selective absorption. Excessive use of pesticides and herbicides should be avoided. At the Government level, legislations should be framed to control water pollution.

3. Land pollution : The undesirable change in the land that harmfully affect the life activities is called land pollution.
   1. Land pollutants : Manure, crop–residues, ashes, cinders (pieces of coal), garbage (waste food), paper, card board and plastics. Plastics are the most important land pollutants. Rubber, leather, cloth, rubbish, bricks, sand, metal, broken glasses, demolished building, dead animals, discarded furniture, automobiles, insecticides, herbicides and other biocides and radioactive elements are some of the important land pollutants. The main sources of land pollution are pesticides, radioactive elements and fertilisers.
   2. Pesticides : Pesticides are chemicals used to kill pests like insects, rats, snails, fungi, herbs, etc. They are collectively called biocides because they kill life. They are of the following types :

• Insecticides : There are chemicals used to kill insect pests.
• Rodenticides : These kill rats.

 

 

• Fungicides : These kill fungi.
• Herbicides : These kill weeds.
• Helminthicides : These kill helminth worms.

1. Chemistry of pesticide : Based on chemical composition, pesticides are divided into following main groups. They are :

• Chlorinated hydrocarbons : DDT (Dichloro diphenyl trichloroethane), aldrin, dieldrin, endrin, benzene hexa chlorids (BHC) and their close relatives form chlorinated hydrocarbon. They are very poisonous, very persistent, highly mobile and highly capable of dissolving in fat. As they have higher affinity for fat, they tend to move out of the physical environment and enter the living organisms. They are non–degradable pollutants.
• Organic phosphorus pesticides : These include arsenic and sulphur compounds. These are much less in use.

2. Ecological effects of pesticides

• Mutation : Insecticides induce gene mutation in human beings (Wurster, 1974).
• Cancer : DDT produces cancer in human tissues.
• Congenital birth defects : Certain herbicides like diozan increase birth defects in both people and livestock.
• Sex hormones : DDT affects sex hormones in mammals and birds.
• Decline of reproduction : In Bermuda petral, a sea bird, the rate of hatching of eggs is much reduced because of the accumulation of DDT. If the accumulation increases further, there will be failure of reproduction in this species in future.
• Calcium metabolism : DDT interferes with calcium metabolism resulting in calcium deficiency. DDT causes hormonal disturbance resulting in delayed ovulation and inhibition of gonad development.
• Biomagnification : The pesticides are non–degradable. They have much affinity towards fat. Hence they tend to move into the living organisms. They are concentrated as they pass up the food chains. For example, at each trophic level, the accumulation of insecticides increases by 10 times. For example if the goat gets one part per million (PPM) of DDT from the grasses, it will have 10 ppm in its tissues. The man, eating the goat will have 100 ppm. The man-eating tiger will have 1000 ppm. If the food chain is still greater, the accumulation will still be higher. This increasing accumulations of insecticides in higher organisms is called biomagnification or biological amplification. DDT causes the pollution of air, water and soil.

3. Control of pesticide pollution

• Minimum use : Pesticides should be used at minimum rates and that to only when required.
• Biological control : Pests should killed either by rearing predators or parasites.
• Sterilization : Juvenile hormones prevent metamorphosis and maturation in insects.
• Decoy plants : Pests can be minimised in high value crops by cultivating low value crops.
• Rotation of crops : Different types of crops should be cultivated in different seasons.

4. Radioactive pollution : This pollution occurs through radiations. Radiations are of two types.

• Non ionising radiations : UV rays, IR rays, etc. UV rays cause skin burning, IR rays increases atmospheric temperature and leads to the green house effect.

 

• Ionising radiation : X – rays, b -rays, g -rays, x - rays cause genetic injury on mutation.

Certain elements continuously disintegrate by emitting ionizing radiations. These elements are called radioactive isotopes. Ecologically important radioactive elements are Strontium-90, Argon-41, Iodin-131, Cobalt- 60, Cesium – 137, Plutonium – 238, etc. Among these Sr-90' is the most dangerous radioactive pollutant.

1. Types of ionizing radiations : Radioactive isotopes release three types of radiations :

1. Alpha particles : These are large particles emitted by radioactive isotopes (as U²³⁸). They travel only short distances. They cannot penetrate the organisms. They cause ionization.
2. Beta particles : These are small particles emitted by radioactive isotopes. They can travel long distances. They can easily penetrate the body tissues and cause ionization.
3. Gamma rays : These are short wavelength rays emitted by radioactive isotopes. They can travel long distances. They can easily penetrate the body tissues and cause ionization. On the basis of the biological effects produced, the radioactive radiations can be grouped into two types, namely internal emitters and external emitters.

• Internal emitters : The alpha and beta particles have low penetrating power. Hence they produce their effect in organisms only when they are ingested into the body. Hence these are called internal emitters.
• External emitters : The radiations with short wave length like gamma rays have high penetrating power. They can affect the internal tissues even when they remain outside by virtue of their high penetrating power. Hence they are called external emitters.
  • Fall outs : Atomic blasts and nuclear explosion release radioactive isotopes into the atmosphere. These radioactive isotopes fall over the earth from the atmosphere continuously for a long time. Hence they are called fall- outs or nuclear fall-outs or radioactive fall-outs. These fall-outs contaminate the air, soil, water, vegetation and animals. The contaminants persist for several years.
  • Ecological effects of radioactivity : Radioactivity causes the following effects : Cancer, Leukaemia, Mental retardation, Congenital malformations, Retarded growth, Deleterious mutations, Infant mortality.

 Biogeochemical cycle.                                                                                                                                        

Organisms are built up on chemical substances. They require certain chemicals like N₂, O₂, H₂, P, C, etc. continuously for their survival. These chemicals enter the organisms from the environment and come out after undergoing changes or without changes. Thus these elements tend to circulate in a characteristic path from the environment to the organism and back to the environment. This cyclical path of the elements from the abiotic system to the biotic system and back is called biogeochemical cycles (Bio = living organism; Geo = water, air, earth). As these chemicals form the components of food, these cycles are also called nutrient cycles.

1. Phases of biogeochemical cycles : Each biogeochemical cycle has two phases, namely the biotic phase (organic phase) and the abiotic phase.

1. Biotic phase : It refers to the flow of chemicals in the living organisms through food chain.
2. Abiotic phase : It refers to the distribution and flow of chemicals in the non-living environment.
   2. Types of biogeochemical cycles : The biogeochemical cycles are classified into two types, namely gaseous cycles and sedimentary cycles.

 

 

1. Gaseous cycles : In gaseous cycles the main reservoirs of chemicals are the atmosphere and ocean. e.g. Carbon cycle, N₂ cycle, O₂ cycle etc.
2. Sedimentary cycle : In sedimentary cycles the main reservoirs are soil and rocks. e.g., Sulphur cycle, phosphorus cycle, etc.
   3. Important biogeochemical cycles
      1. Carbon cycle (ii) Nitrogen cycle      (iii) Oxygen cycle      (iv) Phosphorus cycle (v) Sulphur cycle

1. Carbon Cycle : The cycling of carbon between biotic and abiotic systems is called carbon cycle. It is a gaseous cycle. The main source of carbon is the carbon dioxide (CO₂). CO₂ is present in the air and water. Air is the main reservoir. CO₂ content of air is 0.03%. Its amount remains

constant.

1. Flow of Carbon into the biotic system : Carbon flows into the biotic system in two ways :

• Photosynthesis : Carbon enters the biotic system through photosynthesis. In photosynthesis green plants utilize CO₂ and incorporate the carbon of CO₂ in glucose. Glucose is used for the synthesis of other types of carbohydrates, proteins and lipids. These compounds, containing carbon, are stored up in the plant

tissues. When plants are eaten up by herbivores, the carbon flows into the body of herbivorous animals through food chain. When

herbivores are eaten by carnivores, the carbon enters the body of carnivorus animals.

6CO₂ + 6H₂O ® C₆H₁₂O₆ + 6O₂.

CaCO₃

Fig: Carbon cycle

• Formation of shell : The CO₂ dissolved in sea water is utillized by the marine animals like protozoans, corals, molluscs, algae, etc., for the construction of shell. In these animals CO₂ is converted into calcium carbonate (CaCO₃) which is used for the construction of shells.

CO₂ + H₂O ® H₂CO₃ (Carbonic acid)

H₂CO₃ ® H⁺ + HCO₃ (Bicarbonate)

HCO₃ + Ca⁺ ® H⁺ + CaCO₃ (Calcium carbonate)

2. Flow of Carbon into the abiotic system : The carbon of the biotic system flows into the abiotic system in five ways :

• Respiration : Plants and animals release CO₂ by respiration (biological oxidation).

C₆H₁₂O₆ ® CO₂ + H₂O + Energy

• Decomposition : When plants and animals die, the dead bodies are decomposed into CO₂ by decomposers like bacteria, algae, etc.
• Shells : After the death of marine animals, CaCO₃ stored in the shells is either deposited as sedimentary rocks or dissolved in water to release CO₂ by the reversion of the above said reactions.
• Coal : A certain proportion of carbon from plants is deposited as coal. Carbon from coal returns to air in the form of CO₂ through combustion and weathering.

 

 

• Forest fire : Combustion of wood in the forest, releases carbon from plants in the form of CO₂.

2. Nitrogen cycle : The cycling of nitrogen between abiotic and biotic systems is called nitrogen cycle. It is a gaseous cycle. The main source of N₂ is air which contains 79% N₂.

1. Flow of Nitrogen into the biotic system : Nitrogen is an important nutrient of plants. But plants cannot utilize free N₂ of air. They obtain N₂ from ammonium salts, nitrites and nitrates. These compounds are formed from atmospheric N₂ by a process called nitrogen fixation.

Nitrogen fixation is a process by which atmospheric free N₂ is converted into soluble salts like nitrites and nitrates. It occurs in two ways namely electrochemical fixation and

biological fixation.

• Electrochemical fixation : A certain amount of

Fig : Nitrogen cycle

free N₂ is fixed by the action of lightning. The amount of nitrate formed by this method is about 35 mg/m²/year.

• Biological fixation : It refers to the conversion of free N₂ into soluble salts by the activity of certain organisms. These organisms are called N₂ fixing organisms. The amount of nitrate formed by this method is about 140 to 700mg/m²/year, and in a fertile area it exceeds 20000 mg/m. The N₂ fixing organisms are bacteria, blue green algae, fungi and other micro-organisms. e.g. Rhizobium, Azotobacter, Closteridium, Bacillus, Nitrosomonas, Nitrococcus, Nitrobacter, Anabena, Nostoc, etc.

The fixed N₂ is absorbed by plants through the root system and is incorporated into the proteins. When herbivores feed on these plants, the N₂ flows on the carnivores through food chain.

2. Flow of Nitrogen into the abiotic system : The nitrogen of the biotic system flows into the abiotic system by four methods, namely decomposition, excretion, denitirfication and sedimentation.

• Decomposition : Plants and animals contain nitrogen in their body protein. After death, the proteins of dead bodies are decomposed by decomposers into amino acids and ammonia. The convertion of protein from dead bodies into ammonia by decomposition is called ammonification. This ammonia may be converted into nitrates or free nitrogen.

 

Protein in dead bodies

 

¾¾Am¾mo¾ni ®

fication

 

NH3

N

 

NO3

• Excretion : Animals excrete nitrogenous waste products in the form of ammonia, urea and uric acid. These compounds are decomposed to release N₂.

 

 

 

• Denitrification : The conversion of nitrate into ammonia or free nitrogen is called denitrification. This is done by denitrifying bacteria. e.g., Pseudomonas.These bacteria utilize the O₂ present in the nitrate for the oxidation of carbohydrate.
• Sedimentation : Some amount of nitrate is lost from the ecosystem by sedimentation.

 

 

3. Oxygen cycle : The cycling of O₂ between biotic and abiotic systems is called O₂ cycle. It is a gaseous cycle. Air is the reservoir for O₂. O₂ enters the biosphere through respiration. The O₂ taken into the body is used for oxidation of carbohydrates, proteins and fats. Certain amount of O₂ in atmospheric air is converted into ozone (O₃) the ozone forms an umbrella-like layer in the outer atmosphere. This layer prevents the ultraviolet radiations from reaching the earth's surface.

C6 H12 O

® 6CO₂ + 6H ₂O +

Energy

O2 + O ® O3

Carbon monoxide is released from volcanoes. This CO is unstable. It combines with O₂ to form CO₂.

O₂ combines with a variety of elements to form compounds. For example, it forms CO₂ with carbon, water with hydrogen, nitrates with N₂ ferric axide with iron etc. O₂ returns to air by two main methods, namely photosynthesis and photodissociation.

O2 + C ® CO2

O2 + 2H 2  ® 2H 2 O

O2 + N 2  ® NO3

• Photosynthesis : Green plants synthesize carbohydrate by photosynthesis. During photosynthesis water molecules break up into hydrogen and oxygen. O₂ is released into the atmosphere and H₂ is trapped and turned into carbohydrates.

12H 2 O + 6CO2 ® C6 H12 O6  + 6H 2 O + 6O2

• Photodissociation : Water vapour is dissociated to release H₂ and O₂, in presence of light.

4. Phosphorus cycle : The cycling of phosphorus between biotic and abiotic system is called phosphorus cycle. It is a sedimentary cycle. Phosphorus is an

 

Phosphate in soil

important mineral nutrient. The main source of phosphorus is rocks. Through erosion and weathering phosphorus is made available in the soil. Plants absorb ionic phosphate through roots. In plants it is incorporated into the protoplasmic components like DNA, RNA, AMP, ADP, ATP, GDP, GTP, NADP, phospholipids etc. from plants, it passes into herbivores and animals, the organic

 

molecules containing phosphate are decomposed and

Fig : Phosphorus cycle

 

 

phosphate is liberated as inorganic ion phosphate. It is again used by plants.

The excess of phosphate in the bodies of animals is excreted out through faces. The bird guano (excreta) contains a large amount of phosphate. Phosphate is also released to the soil through the combustion of forest trees and grasses. A large amount of phosphate is lost in the sea by sedimentation. A certain amount of phosphorus gets locked in bones and teeth.

5. Sulphur cycle : The cycling of sulphur between biotic and abiotic systems is called sulphur cycle. It is a sedimentary cycle. Sulphur is an important component of proteins and amino acids.

Sulphur exists in a number of states. Of these, three are important. They are elemental sulphur, sulphides and sulphates. Sulphur is present in rocks.it is made available for plants in the form of inorganic sulphate by weathering and erosion. Sulphur passes into the animals through food chain. By the death of plants and animals, the decomposers again bring the sulphur to the soil for the use of plants.

Some sulphur in dead bodies is released into the air as hydrogne sulphide (H₂S) by the bacteria called Escherichia coli under anaerobic combustion. Similarly incomplete combustion of fossil fuel releases sulphur dioxide (SO₂) into the air.

Certain bacteria (green and purple photosynthetic bacteria) oxidise H₂S of air to sulphate which can be used by plants.

H₂S + 2O₂ ® SO^–₄ + 2H⁺

Certain amount of sulphur is lost in the sediments. If iron is present in the sediments, sulphur combines with it to form iron sulphide.

Fe + S ® FeS

Important Tips

• CO₂ is not a normal air pollutant.
• There is 0.03 % CO₂ in earth’s atmosphere. Rise in the amount of CO₂ causes green-house effect.
• Primary air pollutants : These are CO, SO₂, NH₃, Benzopyrene.
• Secondary air pollutants : These are poisonous substance formed from primary air pollutants. (1) Nitrogen oxide (2) O₃ (3) Sulphuric acid.
• Methyl isocynate was responsible for Bhopal tragedy on December, 1984 which was used in production of savin insecticide in union carbide.
• Hg is known to cause nervousness (reduces the nerve impulse).
• Drinking water rich in nitrates cause methane globenemia (circulatory and respiratory system are affected).
• Ozone day : September 16^th.
• Lichen and mosses are the first plants to die in SO₂ polluted environment and hence act as indicators of air pollution (especially SO₂ pollution). These are thus called indices of atmospheric purity (IAP).
• E.coli, Wolffia, Chara and Utricularia are indicators of water pollution.
•  

Gombusia (fish) was introduced in to several tropical regions to control malaria.

 

Anything which is useful to man or can be transformed into a useful product or can be used to produce a useful thing can be referred to as a resource. A natural resource is the resource obtained from nature. It is these natural resources which form the very basis of entire life on this planet. A natural resource can be of the following two types : living (biotic) or non-living (abiotic).

 

 

• Biotic resources : A resource is directly or indirectly derived from photosynthetic activity of green plants. Food, fruits, wood, fibre, milk, milk products, fish, meat and leather are termed as biotic resources. Coal, oil and natural gas are also biotic resources as they were produced by photosynthetic activity of plants which occurred millions of years ago.
• Abiotic resources : Mineral material, fresh water, rocks, salts and chemicals etc. are termed as abiotic resources as biological activity is not involved in their formation.
  1. Types of natural resources : The natural resources can be classified into three categories :
     1. Renewable resources

1. Renewable resources are those resources which can be regenerated.
2. These are mostly biological in nature and include forestry, agriculture, animals (biomass-based) etc.
3. These can be reproduce itself in nature and we may harvest them continuously through a sustained proper planning and management. Solar energy, wind energy, water energy (tides) and geothermal energy belong to this category, since these are available in an inexhaustible form in nature.
   2. Non-renewable resources

1. They are physical resources like coal, oil deposits, natural gas, minerals, soil, metals etc.
2. These are available in nature only in limited amounts and cannot be reproduced.
3. Coal, petroleum and natural gas are the common sources of energy. They, being of organic origin, are also called fossil fuels.
4. These account for 90% of the worlds production of commercial, energy, hydroelectric and nuclear power accounting for only 10%. The figures are :

Oil	–	39.5%
Coal	–	30.3%
Natural gas	–	19.6%
Hydro-electric	–	6.7%

5. Their formation requires millions of years which can not occur within the human scale of time. Similarly, metals and minerals come from deposits developed by a very slow process of geo-chemical concentration which look millions of years to form.
   3. Inexhaustible resources

1. The total amount of atmosphere, water, rocks and solar energy can never get exhausted.
2. Similarly solar energy is inexhaustible.

At present all the developing countries of the world have started to realize that there is a conflict between environment and development. The problems of human environment derive essentially from these factors :

• The first is the expansion at geometric rates of population.
• The second is a one-sided application of technology to achieve certain goals without the consideration of the effects of this technology on the human environment or on man itself.
• The third is the lack of control over the use of land.

 

 

2. Conservation : It may be defined as the most efficient and most beneficial utilization of the natural resources. Conservation is also defined as the rational use of the environment to provide a high quality of living for the mankind.

1. Aim of conservation : The true aim of conservation, thus, includes

1. To insure the preservation of a quality environment that considers aesthetic, recreational as well as product needs.
2. To insure a continuous yield of useful plants, animals and materials by establishing a balanced cycle of harvest and renewal.

2. Living resource conservation has three specific objectives

1. To maintain the essential ecological processes and the life support system : This system has five elements (air, water, land, flora and fauna) which are interconnected, interrelated and interdependent; deterioration in one inevitably affects the other four elements.
2. To preserve the biological diversity : It includes two related concepts genetic diversity and ecological diversity. The genetic diversity is the amount of the genetic variability among individuals of a single species (intraspecific genetic variability) as also between species (interspecific genetic variability). The ecological diversity means the species richness. It is the number of species of the flora and fauna found in a region (for example, India has about 45,000 species of plants and about 65,000 species of animals).
3. To ensure that any utilization of the species and ecosystems is sustainable : In fact, natural resources may be conserved by efficient utilization which requires a proper balance between the supply and demand. Sustainable utilization means planned utilization so that a continuous yield of the useful plants, animals and materials may be obtained.

3. The conservation of the following resources is necessary

1. Minerals : Until recently little attention was paid to the conservation of mineral resources because it was assumed that nothing could be done to save them anyway. But now these assumptions have proved wrong and it is believed that severe shortages would develop tomorrow. The conservation of minerals, therefore, has become a serious concern for conservationists all over the world.
2. Forests : The need for the scientific management of forests was recognised in our country in the long past. But in our last five-year plans there has been a lack of appreciation of the potential of forestry which could play a great role in the economic growth of the country. Forests not only provide timber, pulpwood and fodder; they are also important in controlling soil erosion, floods etc.

Silviculture is the term for forest management which deals on ecological principles, with the establishment, growth and reproduction of timber trees and other organisms.

3. Wild life : The terms “wild life” refers to any living organisms in its natural habitat. It includes all plants, animals and microorganisms except the cultivated plants and domesticated animals.

• Importance of wild life : Ecological value, Economic value, Scientific value, Gene banks, Sport and Enjoyment, Aesthetic value, Cultural value.
• Causes of destruction of habitat : Destruction of habitat, Hunting, Introduction of exotic species, Disturbance in migratory routes, Legal lapse.

 

 

• Concept of threatened species : The rare species of plants and animals have been categorised as under for conservation purposes by the IUCN (International Union for Conservation of Nature an