FST -1

8th Part

Q.  Make a clear and well-labeled diagram to explain the energy flow through an ecosystem.                            

Q.  In a food chain explain why the number of trophic levels is seldom more than four and five. 

A.     The principal source of energy for any ecosystem is sunlight. Solar energy is converted by plants into food materials and is stored within the body of the plant. All food materials that we or other animals consume are manufactured directly or indirectly by plants. Thus, the energy that we obtain from plants either by burning wood or by eating them, represents the solar energy trapped by the plants. We are dependent on the stored resources of solar energy. When we eat meat, we obtain energy that had been stored by plants several years before and then taken up by an animal like a goat through grazing. When we cut firewood for fuel, we obtain energy accumulated & stored by trees for perhaps a century or more. When we bum coal or petroleum, we obtain solar energy stored by plant life, millions of years ago. Now let us trace the energy flow through an ecosystem.

The energy from the producer to the last level decreases considerably. The energy passed on to the next trophic level is represented by letter E of three different sizes, each by its size indicates the comparative amount of energy. The arrows in the upper half of the diagram indicate the loss of energy in the form of heat given out by different organisms. The arrows in the lower half show the energy loss via the wastes secreted and energy trapped in dead bodies of the organisms. Decomposers use these wastes and dead bodies as sources of food and derive energy from them. They also give out some unused heat energy.

          Energy flowing through an ecosystem is thus first captured by the producers. From the producers, the energy passes to various consumers, via food. At the end of the chain, we find that very little energy is left for the last trophic level because some energy is always lost in going from one level to the next. This loss of energy limits the number of trophic levels in the ecosystem, and so they are seldom more than five. This also clearly shows why the steps in a food chain are limited to four or five.

Q.  Define the ozone layer. How did the ozone layer gets depleted?  

A.        The presence of a thin layer of ozone is important for life on the earth. There is an ozone layer about 25 kilometers above the earth's surface. Ozone is a form of oxygen. Each molecule of ozone contains three atoms of oxygen (0,) while there are only two atoms in the ordinary oxygen (0,) molecule. The ozone layer creates a protective shield around the Earth as it absorbs a great deal of ultraviolet radiation coming from the sun. It thus saves us from skin bums, skin cancer, and other harmful effects. An increased level of ultraviolet radiation would cause more skin cancer, affect crops, interfere with the oxygen cycle and even distort weather patterns.

                   There are many reasons for the depletion of ozone. The foremost is the widespread usage of chlorofluorocarbons. These are gases that readily liquify when compressed. This makes them useful in refrigerants, ac, propellants in aerosol cans, and in plastic foams. Chlorofluorocarbons are very stable and accumulate in the atmosphere, where they react with ozone. Nitrogen oxides also play a significant role in ozone destruction. Jet planes flying in the upper atmosphere release fumes containing Nitrogen oxide which destroys the Ozone.

Q.  Write the physical features of oceans and coasts and the ecological crises in the oceans and the coastal areas.      

A.                  Physical Features of the Oceans

               Oceans are the oldest and the largest ecosystems of the earth. They cover more than 70 percent of the earth's surface. The depth of oceans varies, from shallow near the coasts to deep in the middle. There are trenches, valleys, hills under the ocean waters. 

               Ocean waters are never still. Wind exerts a frictional force on the surface of the water and generates waves that keep the surface water in motion. Tides are another type of movement of the oceanic water, noticeable in coastal regions. The water level of the sea rises and falls twice a day. The gravitational pull of the sun and the moon is the principal cause of the formation of tides. Coastal waters rise to a high point called the high tide when the sun and the moon are on the same side of the earth, and the tide is low when the sun and the moon happen to be on the opposite sides. Ocean currents are yet another form of water movement. Currents are generated in several ways: by changes in the density of seawater, due to temperature differences, by the effect of earth's rotation and also prevailing winds. These currents transport seawater over long distances, more or less like rivers on the surface of the earth. 

            Ocean water is salty. It has about 35 parts of salt (by weight) per 1000 parts of water. Ordinary salt or sodium chloride is the major salt component of the oceanic water. Salts of magnesium, calcium, and potassium are also present. This substantial amount of salt in seawater is the result of the accumulation of small bits of salt that are carried by rivers from the lands they drain.

                Oceanic waters have a minimum temperature well below zero Celsius, near the poles, and a maximum of about 28 Celsius in the tropics. The atmosphere exerts a pressure of about 1 kilogram per square cm (= 1 Atmosphere Pressure) at the surface of the sea or land. This pressure increases due to the weight of water by 1 Atmosphere, for every 10 meters of the depth of water.

                  Ecological Crises in Oceans and Coasts

Coastal and marine areas all over the world including those in India are under stress because two-thirds of the world's population lives near the coasts, and 60% of the marine food is harvested from the zone near the coasts. Most of the sewage, garbage, and industrial wastes find their way into the sea. So the industry produces massive amounts of "waste" which is allowed to reach the sea. As a result, huge quantities of dead fish were found floating in the Arabian Sea on the west coast due to poisonous outflows from a fertilizer factory.

          The rivers, which join the seas, bring sand from the hills and plains, and thus a lot of silt gathers near the coasts. Rivers also bring to the seawater, runoff from the fields, which, today. means a certain amount of fertilizers and pesticides. A new factor has recently come to light and that is chemicals from nuclear power plants and the nuclear industry. This waste has radioactive chemicals that can demolish and destroy living organisms in ocean waters. A number of times it has been reported that ships, particularly tankers, transporting oil leaves a trail of oil along their routes. A thin layer of oil thus covers wide areas of the surface seawater, depriving living organisms of oxygen.

Q.  Describe the various ways of management of soil.        

A.     Soil is a precious resource that takes millions of years to form, and hence proper management of soil is very necessary. The management of the soil is two-fold, i.e. (a) to minimize or check soil erosion and (b) restore the productivity of the soil.

Control of soil erosion

The most significant measures of erosion control include - 

(i) growth of grasses, shrubs, and trees on soils and 

(ii) construction of a drainage system that can prevent free, uncontrolled flow of water. 

               Uncontrolled water flow causes the formation of narrow channels or gullies and it further leads to the development of deep narrow valleys leading to ravine land for ex. the famous Chambal ravines. This can be controlled by constructing a series of check dams that prevent the flow of running water and widening of gullies. Construction of a broad wall of stone along the coasts of Maharashtra, Kerala, Andhra Pradesh, and Orissa has proved to be very effective in controlling erosion by sea waves and currents.  

                Movement of sand by drifting winds in the deserts and sandy coasts can be prevented by putting barriers of trees and shrubs across the path of the wind. In the mountain and hilly areas, planting of self-propagating trees and shrubs, not only strengthens the slope of the hills but also provides fuelwood and fodder to the general population. Alternate cultivation of beds of crops with strips of erosion-resistant vegetation like grasses, shrubs. trees, maize, sugarcane, cotton, and tobacco, etc. bring about stability of the terraced fields on mountainous and hilly areas. The most effective step in controlling erosion and mass movement, such as landslides in the hills, is the construction of a network of the drainage ditches which are filled with fragments of stones or bricks so that water flows out through them. The hill slopes are stabilized by constructing walls around them which allows the free passage of water. On the vulnerable slopes, a cover of vegetation is provided and here, seeds are covered with coir netting pegged firmly to the ground. Netting checks erosion holds the soil material together and adds nutrients. The quick growth of grass stabilizes the soil.

Q.  How does photochemical smog form?           

A.  Photochemical smog, a secondary Pollutant, results when the two pollutants, nitrogen oxide and hydrocarbons found in automobile exhausts, react with one another in the presence of sunlight to produce nitrogen dioxide (N02), ozone (03) and a compound called PAN (Peroxylacetyl nitrate), which then appear as a yellowish-brown haze. Breathing ozone affects the respiratory and nervous system. It causes respiratory distress, affects eye membranes and stimulates tears. It also causes a headache. Ozone also damages rubber articles, textiles and discolors paintings. It has been recently found that smog is harmful to timber. PAN is

especially damaging to plants. Plants exposed to PAN exhibit leaf mottling.

Q.  (i) Explain six ways by which water bodies of a country get polluted.
(ii) How does aquatic fauna get killed due to 
(a)heavy metal pollution and (b) eutrophication?             
A. 1.  Power plants, fertilizer factories, steel mills, paper mills, refineries, sugar factories, and automobile factories are examples of industries that mostly dump their wastes in rivers or into the sea thus polluting water resources.
2. Community wastes (sewage and garbage) from urban and rural settlements account for four times as much dirty water as industrial wastes. Most of these wastes are discharged untreated into the water sources.
3.  Water which is used to irrigate agricultural fields where fertilizers, pesticides, insecticides, and other agrochemicals are used, contributes much to the pollution of water sources. This water, on absorption also pollutes the underground sources.
4. Nuclear and thermal power stations use large quantities of water for cooling purposes. They discharge the resultant hot water often containing chemicals, into water streams. This results in an increase in temperature of the water of the stream, which is injurious for fish, and other aquatic organisms.
5. Pollution of river water by ferries which leave a certain amount of oil on river surfaces and similar pollution by ships on the high seas interferes with the supply of oxygen needed for plants, and animals such as fish, etc. in water. Offshore exploration for petroleum and accidental oil spills cause similar problems for under-water life.
6. Acid water from mines, and also from rain pollutes water in rivers and in the sea.
7. Suspended particles in the air, such as the pesticides sprayed through an aircraft are brought down into the water bodies by rain and thus cause pollution of water.
        Heavy metals such as lead and mercury coming out of industrial wastes pollute the under ground water. Excessive use of fertilisers, insecticides, pesticides in the fields, which gradually seep down to the ground water also pollute it. Such heavy metals like Mercury is not easily excreted. Once it enters the food chain its concentration goes on increasing at each level. For example, from plants+ large fish -+human beings. Large no. Of fishes die due to it and also becomes unsafe for consumption.