Science(Form 2) - Simple Note of Topic Two

Topics: Digestion, Nutrition, Digestive system Pages: 18 (3521 words) Published: February 27, 2011


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.

5. Strach, glycogen and cellulose are made up of glucose molecules joined together in a different manner.

6. Extra carbohydrates in our body are kept in the form of fat.

7. The presence of starch in food can be tasted by using iodine solution. The colour of iodine would change to dark blue starch is present in a food sample.

8. The presence of simple sugar in food can be teated by using Benedict's solution or the Fehling's solution. A brick-red precipitate will be obtained when simple sugar is boiled with the reagents.

(B) Proteins

1. All types of proteins have carbon, hidrogen, oxygen and nitrogen. Some proteins also contain sulphur and phosphorus.

2. Protein molecules are formed from basic units called amino acids. There are about 20 types of amino acids. Some of these amino acids can be produced by the body and some must be consumed from the diet.

3. Protein is a class of food needed for the growth of the body, especially in the building of cell protoplasm.

4. Important functions of protein include :
(a) Building new cells.
(b) Repairing damaged tissue.
(c) Building enzyme, antibodies, hormones and haemoglobin. (d) Supplies energy, especially if carbohydrate and fats are insufficient in the body.

5. Proteins are divided into two categories :
(a) Plant proteins that are found in beans, corn and wheat. (b) Animal proteins that are found in meat, fish, egg white and cheese.

6. Children need more protein compared to adults to support their growth.

7. Protein deficiency will cause kwashiorkor. The symptoms of a kwashiorkor patient are enlargement of the stomach, no appetite for food and diarrhoea.

8. Extra protein is excreted from the body as urea in the urine.

9. The presence of protein in food can be tested by heating a food sample with Millon's reagent. A brick-red...
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