FST -1

7th Part

Q.  What is meant by the cycling of materials in an ecosystem? Describe the carbon cycle in detail with the help of a suitable diagram              

A.   Cycling of materials - Living organisms require four nutrients in relatively large amounts, these are carbon. oxygen, nitrogen, and hydrogen. They also require phosphorus and sulphur. These elements are present in our environment in a fixed quantity, therefore they must be recycled in order to sustain life. Also, these elements must move efficiently, from the living to non-living components and vice versa. For example, plants take in carbon as carbon dioxide to produce food. As the herbivores eat plants, carbon is passed on to them, which in turn is passed on to carnivores, and so on. Carbon is eventually returned to the nonliving pool in the ecosystem, through the excretory processes of the producers, the herbivores. the carnivores, and also through the activity of the decomposers. Through such cyclic processes, these nutrients are used over and over again by the organisms. This aspect of the ecosystem function is called the cycling of materials.

Carbon is one of the essential elements of all organic substances and it enters the ecosystem through the process of photosynthesis. Carbon is present as carbon dioxide in the atmosphere. Carbon dioxide forms 0.03 to 0.04% of the atmosphere. The oceans also have carbon dioxide dissolved in their water. There are 12 basic steps of the Carbon cycle.

1. Carbon dioxide enters the food chain through the plants by the process of photosynthesis.

2. Some of the carbon dioxide captured by the plants and converted into organic molecules are returned to the atmosphere via respiration.

3.  Some portion of the carbon is incorporated into the plant body, which is later passed on to the herbivores, etc.

4.  The living beings release carbon dioxide into the air during breathing.

5.  (i, ii) carbon dioxide is also returned to the atmospheric reservoir by the death and subsequent decay of the dead bodies and wastes of animals and plants.

6)  Formation of fossil fuels, like coal. oil. gas is a part of the carbon cycle, wherein carbon is trapped for millions of years. Fossil fuels are the remains of ancient plants and animals that were subjected to high temperature and pressure over millions of years. Man has been using wood, peat, coal, and petroleum as sources of energy, for running transport such as motorcars, airplanes, etc.: for industries. for cooking food and various other purposes. The burning of fossil fuels returns carbon back into the atmosphere. 

7)  Since air is in direct contact with the sea, the carbon dioxide from the air dissolves in the upper layers of water resulting in the formation of carbonates.

8) The plants that grow in seawater, do not get atmospheric carbon dioxide. Therefore, they utilize carbonates present in water as a source of carbon dioxide during photosynthesis.

9)   Food produced by water plants passes through the aquatic food chain. For example, when fish feed on the water plants, carbon passes on from plants to the fish, and ultimately to the other organisms that feed on fish.

10)  Some of the carbon dioxide produced by marine plants and animals during breathing gets dissolved in seawater and can be re-utilized by the plants.

II )  However, some of the carbon dioxides thus evolved escapes to the atmosphere.

12) Organisms like snails, oysters, etc. extract carbon dioxide dissolved in water and combine it with calcium to form calcium carbonate from which they construct their shells. Shells of these dead animals collect in undersea deposits and may eventually be converted to limestone.

Q.  Define by diagram Nitrogen cycle and the Water cycle

A.  

Nitrogen is a vital part of many essential organic compounds especially nucleic acids and proteins. It also forms a major part (79 percent) of the atmosphere. In fact, the atmosphere is the chief reservoir of nitrogen, where it is present in the gaseous form, which, unfortunately, cannot be directly used by plants and animals. Plants actually obtain their nitrogen from nitrates and ammonium salts in the soil to build up proteins, from which animals derive some of their proteins. The amount of nitrates and ammonium salts in the soil, is limited, at a given time, and their supply would quickly exhaust, if it were not for the renewal of supply of nitrogen which goes on continuously.

1) During thunderstorms, some of the oxygen and nitrogen in the air are converted into oxides of nitrogen by the high temperature of lightning. The oxides of nitrogen dissolve in rain water, reach the soil and get converted into nitrates. These nitrates are taken up by plants.

2) Certain bacteria can utilize nitrogen available in the atmosphere and convert them into nitrates. They are called nitrogen-fixing bacteria. Some of these bacteria live freely in soil, others live in small knots or nodules on the roots of certain plants such as beans, peas, peanuts, clover, and alfa etc. These plants have these bacteria carrying nodules on their roots. Farmers make use of some of these plants, to make fodder, and then plough the rest of the plant into the soil, to increase the nitrates in the soil.

3)  Nitrogen fixation by bacteria, i.e., the process of putting nitrogen in a form that plants can absorb, is rather slow, compared with the rate at which plants need nitrogen. In such a situation the demand for nitrogen is fulfilled by adding nitrogen-containing fertilizers to the soil.

4) Nitrogen in the form of nitrates is consumed by plants and is converted into amino acids, which are the building blocks of proteins.

5) Nitrogen enters the food web through plants and passes on to animals which feed on them.

6) Nitrogen eventually returns to soil in the following ways: (i) During excretion, nitrogenous wastes in the form of various ammonium compounds are returned to the soil or water. (ii, iii) Nitrogen trapped in plants and animals returns to the soil by death and subsequent decay of their bodies by the action of bacteria and fungi.

7) In soil, the nitrogen-containing matter is acted upon by bacteria and are converted to ammonium compounds, then eventually to nitrates.

8) Some soils, particularly the ones in bogs. estuaries, lakes, and parts of the seafloor contain denitrifying bacteria that produce the opposite effect of nitrogen fixation. They act on nitrates and release nitrogen to the atmosphere.

9) Volcanoes are one of the important sources of nitrogen. They have been emitting small quantities of nitrogen for centuries and contribute significantly to the nitrogen reservoir of the atmosphere.

Water Cycle -

The ocean is the major reservoir of water which covers about seventy percent of the earth's surface. Ocean water is salty. Freshwater is mostly found in rivers, glaciers and in between rocks below the surface of the earth.

         The water cycle is driven by the sun's heat energy, which causes water to evaporate while gravity draws the water back to earth in the form of rain, snow etc after water vapour condenses. The water cycle is divided into 4 basic steps.

1) All water, which is used by mankind for personal and industrial purposes, is plain or freshwater, which is derived largely from the ocean water through evaporation and precipitation.

2) As the precipitation reaches the earth, some of the waterfalls directly on the ground, some falls on vegetation, on buildings, and on streets. A part of the water that falls on the ground, seeps through the soil, to an impervious layer of clay or rock where it is collected as groundwater. The rate of downward movement of water in the soil is dependent on the type of soil, its slope, type of vegetation and the amount of rainfall. The underground water is utilised by human beings for domestic, agricultural or for industrial purposes.

3) Some of the water falling on the ground runs down the gutters and drains to be carried off to rivers. Some surface runoff water may also get collected in small ditches, lakes, etc.

4) So far we have been discussing the various ways in which water, in different forms, reaches the earth. Now let us understand as to how water reaches back to the

atmosphere.

i) Some amount of rainwater never reaches the ground as it evaporates back into the atmosphere.

ii) Plants also give out large amounts of water back to the atmosphere through their leaves.

iii-v) The water remaining on the surface of the ground and on vegetation as well as the water in the surface layers of streams, lakes mad oceans evaporates and goes back to the atmosphere. As the water vapors in the atmosphere form clouds and drift with the wind,'they eventually meet cold air and condense, this leads to rainfall, snowfall, etc. and thus the water cycle continues. 

Q.  "Land is the most precious resource." Discuss this statement.     

A.  The land is the most precious resource because it produces supports the human population and other living beings on Earth. Soil, which forms the uppermost layer of the land, is the most precious of all resources because it supports the whole life system on Earth. It provides food and fodder in the form of vegetation and stores water essential for life. The land is important to us as around, nearly 44% of land in India is used for agricultural purposes, of which 11-14% is covered with forests that include good as well as degraded forests, and 4% of the land is used as pastures and grazing fields. The remaining 8% is used for various other purposes such as housing, agroforestry, the establishment of industries, the development of roads and reservoirs, etc.. About 14% of our land is barren i.e. it cannot be used for the cultivation of crops. Nearly 1/3 of the barren land has lost its productivity due to alkalinity or salinity of the soil and waterlogging, etc. Soil erosion causes great harm to the productivity of our land because in this process soil is broken up and washed away by water or swept away by the wind. These facts indicate careless and unwise use of land and are a reflection of the mismanagement of our land resources.

Q.  Why is soil considered a basic resource for agriculture? How can saline and alkaline soils be reclaimed (or how to treat soil sickness)?                       

A.  Soil, which forms the uppermost layer of the land, is the most precious of all resources because it supports the whole life system on Earth. It provides food and fodder in the form of vegetation and stores water essential for life. It contains sand, silt and clays, mixed with air and moisture. It possesses rich organic and mineral nutrients which are required for agriculture. The type of soil varies from place to place. Those soils which are rich in organic matter are fertile. Fertility is also dependent on the capacity of the soil to retain water and oxygen. For ex., Deep red soil is good for cultivation of potatoes, bananas, pineapples and rubber etc. Black soil supports crops of sugarcane, groundnut, soyabean, cotton and rice etc.

             (Due to overuse without rest, the soil becomes deficient in the required nutrients and loses its fertility. Rotation of crops and vegetables, such as peas and beans, helps to remove the deficiency of nutrients. Plants such as peas add nitrogen to the soil and thus increase its binding property as well as productivity. The roots and off-shoots of the crops and their remains are left in the field for a certain period of time to protect the soil from erosion.)

                      Excessive irrigation causes complete saturation or waterlogging of the soil. As a result of it, soil loses its productivity, partially or completely. As a consequence of over-irrigation in some areas, salinity and alkalinity of the soil increase, making it "sick". This kind of soil sickness can be controlled by, first of all, sealing off all points of leakage from canals, reservoirs, tanks and ponds, and use of only the required amount of water. Alkalinity and salinity of the soil can also be reduced by the application of some chemicals like gypsum (chalk-like substance, from which Plaster of Paris is made), phosphogypsum (gypsum with phosphates), pyrites (sulfides of copper, iron, etc.) in addition to organic manures and fertilizers. Cultivation of salt-resistant plants such as barley, millets, soya, cotton, spinach, date palm is another way of overcoming the problem of salination of the soil.

Q.  Describe the various non-conventional renewable resources of energy.        

A.  Solar energy - Solar energy can be used directly to give us hot water during winter or for producing electricity to run electric appliances. It can be used for heating rooms in colder regions. It can also be used, with the help of a "photocell" to produce electricity for driving vehicles and illumination of streets. In a desert-like Rajasthan, the earth's surface receives solar energy at a rate of 200 watts per square meter per hour. Since this is an unfailing source of energy, it would be a great advantage to develop cheap and efficient photocells or photovoltaic devices to harness solar energy. A feature of using solar energy is that it can be generated where needed. Solar cookers are being used in many homes to cook food. Photocells are also becoming common for generating electricity.

Wind energy - Like solar energy, wind flow can also be harnessed to obtain mechanical energy for fetching water from the wells or from rivers. Once the windmill is turning due to the force of the wind, it may as well run a generator to get electrical energy. In the coastal and hilly regions, where the wind blows at high speed, a windmill can be used for the supply of electricity to a small town. Windmills have been used for long in many countries, but in India, they have only been recently introduced.

Wave and tidal energy

Waves and tides are other sources of energy which are perpetual and can be converted into electric energy, particularly where seawater can move into a narrow cut, such as cuts provided naturally where rivers flow into the sea. The long flow of water has been widely used in India's hilly regions, where a strong stream of water is made to fall on pedals of motor generating electricity on a small scale. Flour mills of small size built on this principle were used in Kashmir for a long time. In fact, large "hydroelectric" power stations work on the same principle. A natural or artificial waterfall is made to turn a modem kind of pedal wheel, called a turbine, which rotates and causes electricity to be generated.

Geothermal energy

Hot water and superheated steam of hot springs are a natural phenomenon and can be used to generate electricity. In our country there arc 46 hydrothermal areas where the temperature of the spring water exceeds 15D°C. These hot springs can be used to generate electricity for heating homes, or glass-houses to grow vegetables.

Biogas - Cattle dung was used for the production of biogas which is used for cooking. Water weeds like water hyacinth, water lettuce, Salvinia, hydrilla, duckweeds, and algae are found to be a useful supplement to cattle dung. Biogas can be used not only as cooking gas, but it can also be used to raise steam, which can be used for running engines or machines in the factories or for running turbines to generate electricity. It has been found that large biogas plants can supply the needs of a number of families or even small villages. What is left over after generating the gas, can be used as manure. Hence this is also an economical way of getting more energy.

Q.  Eutrophication       

Q. What is an algal bloom                             

A.  Materials such as sewage or organic wastes from milk plants, canneries, slaughterhouses, paper mills, starch factories, and fish processing plants, and runoff from agricultural lands greatly increase the productivity of waters and cause algae to grow in abundance so that sometimes water surface gets entirely covered by algae. This is called 'algal bloom'. In general, the entire water body becomes a green nourishing soup. Eventually, the death of his algae promotes the growth of a very large 'decomposer' population. The decomposers break down the dead algae using a lot of oxygen present in the water. In addition, the living algae also consume oxygen from water at night for their respiration. The action of decomposers, and the algae cause decreased amounts of oxygen available to fishes, ultimately causing them to die. The problem of eutrophication or excessive nourishment leading to loss of life in water bodies mainly occurs in ponds and lakes and not in flowing water.