Why pure drinking water, clean food, hygienic habits and environmental sanitation are necessary for the prevention of infection diseases?

Infectious diseases are caused due to various types of microbes. Microbes present in the environment gain entry into the body via air, water and food They multiply in the body and make the person sick. The sick person releases them in greater number in the environment thus infecting many people.Our body has a defence system which is capable of fighting against the genns. Modem drugs assist ow defence system. Disease results from a disturbance in the balance between man and his environment. Improvement in the health status of our people requires clean drinking water, adequate living conditions and proper sanitation.

Major Problems area of Agriculture in Aodern India.

A considerable portion of our agricultural lands are affecied by the problem of alkalinity and salinity of soils. In such soils, salts are present in large enough quantities that they interfere with crop growth. Alkaline soils can be used as well as improved, by growing suitable trees, and grasses. Later, alkali-resistant varieties of rice or wheat can be grown. The key factor in the management of saline soils is drainage. If such lands are welldrained, saline-resistant varieties of sorghum, maize and wheat can be profitably grown.Modem agriculture aims at pnxlllcing maximum amount of food with the minimum amount of time, space and energy. There are number of problems associated with the present day agriculture. The foremost is that of energy. There is considerable dependence on our non-renewable resources. These resources being finite, would soon get depleted. Also, adequate facilities for efficient transportation, processing, and packaging would help in making the products easily available to the consumers.

Differentiate between primary and secondary pollutants.

Now-a-days, you might have heard every one talking about pollution. What does pollution mean? Pollution is the addition to the environment (air, water, soil) of substances or energy (heat, sound, radioactivity, etc.) at a rate, and in quantities that are harmful to life. Pollution has a long history. It became noticeable when larger and larger numbers of people began to live in cities. Unplanned growth of the cities,led to difficulties in the disposal of garbage and sanitary wastes. Living .;pace was often shared with animals as is sometimes done in lndia even now. Mud, slush and dusty roads added to the pollution. Air, water and soil, acquired many harmful substances, in the form of wastes, from human activities.

The waste materials (pollutants) that cause pollution are of two types:

i)                   those that remain in an unchanged form for a long time and are known as persistent pollutants,e.g. pesticides, nuclear wastes, and plastlcs etc. Many of these are toxic; those that break down, into simple products, and are known as non-persistent pollutants, e.g., garbage. If this break down process is facilitated by living organisms, then such pollutants are referred to as biodegradable pollutants, e.g., wastes fromanimal sheds.

Natural resources available on our earth.

Our resources are basically of two kinds, viz, renewable and non-renewable. Let us see what they mean. Some of the resources of the earth are replaced from time to time by natural multiplication as for example, is vegetation. In other words, these resources are inexhaustible and are therefore called renewable resources. Forests, pastures, wild life. and aquatic life are renewable resources. Water is also a renewable resource because it recycles. There are some
other resources, such as minerals which once used are lost for ever. They cannot be regenerated. Mineral deposits were formed slowly in millions of years. Once a deposit is used, it cannot be regenerated. For example, petrol gets burnt up and cannot be recovered. These are known as non-renewable resources. Similarly, the formation of soil is a very slow and long term process and it takes thousands of years. It is, therefore, not renewable in the life span of even several generations of people. Hence it is also a non-renewable resource.

Describe as to how the age of fossils of plant and animals etc. is determined.

The method most commonly used, now, for estimating the age of fossils is radio-carbon dating. Radioactive isotope of carbon is commonly known as carbon- 14. Since carbon- 14 is chemically the same as ordinary carbon, both arc absorbed by plant and animal tissues in the same proportion as they arc present in the atmosphere as carbon dioxide. Plants use this carbon dioxide in making their food. Animals eat the plants. Hence, the proportion of carbon-14 in the tissues o f plants and animals is the same as in the atmosphere, as long as the plant or the animal is living. But as soon as it dies, no more carbon can enter its body as photosynthesis or food intake stops. Following death, the carbon-14, already present in the body, decays steadily into ordinary carbon. So the smaller the number of carbon-14 atoms remaining, the older is the fossil. This technique has been applied to materials of known age, and thus its accuracy was tested giving confidence in the age determinations of unknown samples. The carbon-14 method is applicable only to organic materials which still contain carbon. It cannot be used for fossils in which all organic matter has decayed. In that case the age of the fossil can be estimated by determining the presence of other radioactive elements like fluorine, or phosphorus.