Matric Notes Class IX Biology Carbohydrates

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Carbohydrates

They are organic compounds. They are found in all organisms. They are commonly known as sugars. They contain three elements carbon, hydrogen and oxygen in which hydrogen and oxygen exists in 2:1 ratio that is why they are called hydrates of carbon or carbohydrates. One gram of carbohydrates provides 3800 calories of energy.

Forms of Carbohydrates

Carbohydrates occur in three forms.

1. Monosaccharide
2. Disaccharides
3. Polysaccharides

1. Monosaccharides

Monosaccharides are simple sugars. Their common example is glucose. Glucose is main source of energy in our body cells.

2. Disaccharides

Disaccharides are formed by condensation of two monosaccharide units e.g. sucrose is formed by the combination of glucose and fructose. Maltose is another disaccharide.

3. Polysaccharides

Why many monosaccharides link together, they form polysaccharides. A single polyusaccharide may have many hundred units of monosaccharides. The common examples of polysaccharides are glycogen and starch. Glycogen occurs in animals and starch in plants. Another polysaccharide is cellulose, present in the cell walls of plants. It is the most abundantly occurring carbohydrate.

Sources of Carbohydrates

Carbohydrates containing starch are obtained from cereals and their products like wheat, rice, maize, oats and barley. They are also obtained from carrots, radish, turnip, beet, beet root and potatoes. Simple sugar called glucose is obtained from grapes. The sugar derived from fruit is called fructose. Then from beet and sugar cane is called sucrose and that from milk is lactose.

Importance of Carbohydrates in Human Body

One gram carbohydrate food provides 3800 calories to our body. The Carbohydrates are the cheapest and easy source of energy. Surplus carbohydrates are stored as glycogen in the liver and muscles, or converted to fats and stored in the fat cells beneath the skin and causes obesity.

Children, laborers and people, involved in physical labor need more carbohydrates in their daily diet whereas other should avoid them because their excess in the body can cause blood pressure, diabetes, obesity and heart diseases, therefore, carbohydrate products should be taken with care.