Man needs energy for his various activities as movement, growth, respiration, reproduction and many others.
For physical and metabolic activities energy is essential. In our body many biological activities are going on which are collectively called metabolism.
These activities need energy which obtained Lm food. A food is a substance which is mixture of nutritive and non—nutritive substances.
The main components of food are carbohydrates, fats, proteins, minerals, vitamins and water. These are supplied through cereals, pulses, oils, eggs, sweets, milk, meat, cheese and fruits.
Food is classified mainly on the two bases:
1. On the basis of work.
2. On the basis of nutrients.
On the basis of work food has been classified into three groups:
(i) Energy-giving food:
This includes fat and carbohydrates. This food provides high energy which can be obtained from cereals, sugars, animal fats, vegetable oils etc.
(ii) Body-building food:
This includes proteins and minerals. These are found in pulses, milk products such as cheese, fish, meat, eggs etc. These provide energy which is essential for body-building, growth and repairs of tissues.
(iii) Protective food:
This food protects the body from different diseases and regulates different functions of body. This food is rich in minerals, salts and vitamins. This type of food is available from green vegetables, fruits, milk and eggs. On the basis of nutrients, food may be in the form of carbohydrates, proteins, fat, vitamins and minerals.
Our food contains different nutrients and each nutrient performs its own function. We need proteins carbohydrates, fat, minerals, vitamins and water in proper proportion. Deficiency or excess of any of these causes disorders in the body. Thus a balanced diet is that which provide proper amount and proper proportion of nutrients. Balanced diet of an average adult man is given below in (Table 15.4).
A healthy Youngman who does physical work needs 3,000 calories daily. Such diet should contain 90 gm protein, 90 gm fat, 450 gm carbohydrate and sufficient amount of vitamins, minerals and water. Nutrient value of different foods is given below (Table 15.5).
Today food demand is increasing rapidly due to overpopulation and increased consumption of food. Effort is being made to increase food production all over the world. In many parts of the world a number of ecologically unsound practices are being applied that have resulted in short-term production gains at the expense of long-term food output. Overgrazing, burning of vegetation, deforestation, and expansion of agriculture are some known examples.
Most of us get food mainly through agriculture. Cultivation of crop plants is done by two methods:
1. Shifting cultivation:
This is very old agricultural practice. In this case natural ecosystem is manipulated and cultivation is done in the limited area for short period. In this system cultivated area is temporarily covered by wild vegetation. This type of cultivation is generally practiced in the mountain area where the rainfall is heavy. Most of the tribal populations depend primarily upon shifting cultivation. There are many defects of shifting cultivation. Natural ecosystem is disturbed, yield is poor due to uncared cultivation and crops are infected by many diseases.
The following control measures have been taken regarding shifting cultivation:
(i) Proper management of settlement of tribal population should be made because migration of tribal people needs shifting cultivation and facilities of farming should be provided to them.
(ii) Now agriculture should be clubbed together with silviculture so that land use involves an integrated programme of agriculture, horticulture and forestry.
(iii) Annual crops should be replaced with perennial crops.
(iv) Rotation of crops with perennial crops and then with forest trees has given better results in the sloppy area of hills.
2. Sedentary cultivation:
In this case natural ecosystem is permanently changed. In this system previous plants are removed and then domesticated plants are grown. In dry places soil is gradually depleted with minerals and nutrients which may be restored by adding fertilizers or green manures. Deforestation, overgrazing, fire and desserts are the results of mismanagement of agriculture Soil erosion and lowering of water table are also the results of climatic and geological factors.
Extension and intensification of agriculture are the important steps to increase the yield which have solved the problem of shortage of food and malnutrition. For extension we need better irrigation, improved varieties of crops, agricultural instruments and better roads. Flood control proper drainage, erosion control, mechanization, fertilizers, pesticides and improved varieties of crops are the important steps to increase yield.
Besides these methods, we should select some alternative sources of food. Deficiency of proteins should be compensated from animal source rather than plants. Fishes and eggs are the important sources of protein. Now-a-days everywhere fisheries departments have been established to meet the high demand of fishes.
It also gives enough foreign exchange. Poultry breeding programme is very significant now-a-days because the consumption of eggs is increasing tremendously day by day under poultry, chickens and ducks are included. Some algae, mushrooms, grasses and some aquatics are also rich in protein contents which are consumed by man.
There is a tremendous loss in yield due to plant diseases which are caused by bacteria, viruses mycoplasma and pests. It has been estimated that there is 15-20 per cent loss in yield due to plant diseases alone. Sometimes sudden outbreak of a disease can cause severe loss in the production. Plant diseases are the main problems and barriers to crop production. The damage caused by pests is tremendous and sometimes it is irreparable.