Science(Form 2) - Simple Note of Topic Two

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1. Food is a basic necessity for all living things.

2. Food is important in order to :
(a) Provide energy to carry out physical activities. (b) Provide energy for the physiological activities in life such as reproduction, digestion and excretion.
(c) Build new cells and ti repair tissues in the body. (d) Protect the body from deseases.
(e) Maintain the body temperature.
(f) Promote growth.

3. Food can be divided into seven classes which are :
(a) Carbohydrates
(b) Protein
(c) Fats
(d) Vitamins
(e) Mineral salts
(f) Water
(g) Fibres

(A) Carbohydrates

1. Carbohydrates are formed from the elements of carbon, hydrogen and oxygen.

2. Carbohydrates belong to a class of food that provide energy to the body.

3. Carbohydrates are oxidised in the body during respiration to release energy.

4. Carbohydrates consist of four main forms :
(a) Simple sugar is used directly by living cells to produce energy. Examples of simple sugars are glucose, sucrose and lactose.
(b) Starch, which is a form of carbohydrate, is stored in plants. Examples of plants that store starch are tapioca, banana and wheat. Extra glucose that is produced by photosynthesis is kept in the form of starch.

(c) Glycogen, which is a form of carbohydrate is stored in animals. Glycogen is usually stored in the liver and muscles. Glycogen is only used when the body lacks of simple sugars. (d) Cellulose is the main constituent of the cell wall. Therefore, cellulose is found in abundance in vagetables and fruits cannot be digested by the human digestive system.

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