1 . There are 7 types of food:
- Fibre or roughage .
2 . Carbohydrates can be divided into two:
- Starch (To test for starch, use iodine solution, the colour will change from orange to blue-black if starch is present).
- Glucose (To test for glucose, use benedict’s reagent, the colour of the reagent will change if glucose is present).
3 . Proteins:
- To test for the presence of proteins, use biuret’s reagent. If the colour of the reagent changes to violet, it means that proteins are present.
4 . Fats:
- Its presence can be tested by using the filter paper experiment or the alcohol test. A grease spot can be seen if fats are present using the filter paper experiment.
5 . Minerals:
- They are the inorganic salts which do not provide energy but are indispensable to bodily functions.
- Examples of minerals are calcium, phosphorus, sodium, chlorine, potassium and iron.
6 . Vitamins:
- They are not energy-providing food nor are they body-building food.
- They are for maintaining normal health and development.
- Lack of vitamins can cause diseases such as scurvy and rickets.
7 . Fibre or roughage:
- They are the indigestible fibrous materials, e.g. cellulose, present in the diet.
- It provides bulk to the intestinal contents and helps peristalsis.
- Insufficient of fibre can cause constipation.
8 . Water:
- They are the essential constituent of protoplasm.
- Insufficient of fibre can cause constipation.
9 . A balanced diet is a type of diet which consists of all types of food at the correct amount.
10 . Factors affecting the diet of individuals:
- Body size.
11 . Malnutrition (Unbalanced diet):
- Obesity -extremely overweight.
- Constipation – difficulty to remove faeces
12. Carbohydrates and fats are the main source of energy. While proteins are used for growth i.e. to make new cells and repairing damaged tissues.
13. Carbohydrates are from glucose and starch. Fats are from fatty acids and glycerol. Proteins are from amino acids.
Cholesterol is a kind of sterol which is essential for the formation cell membrane.
14. Vitamin C maintains healthy skin, gum and the lining of blood vessels. Lack of Vitamin C can cause scurvy. Vitamin C helps our cells to stick together.
15. Vitamin D helps the absorption of calcium. Lack of Vitamin D can cause rickets.
16. For strong bones and teeth.
1) Clotting of blood.
2) Calcium is a type of mineral, it has the function:
17. Lack of calcium can cause rickets.
18. Iron is also a type of mineral, it has the function of making haemoglobin in red blood cells.
19. Lack of red blood cells can cause anaemia.
20. Stages of nutrition:
5.3 Digestion and the digestive system
1 . Digestion is the process of breaking down food into its simplest form. This is necessary so that food substances are small enough to be carried by the blood and able to pass into the cells.
2 . Mouth:
- Chews food up into easy-to-swallow balls.
3 . Salivary glands:
- Produce an enzyme called amylase to start the breakdown of starch.
- Saliva contains mucous (sticky, slippery substance).
4 . Oesophagus (Gullet):
- The food chutes from the mouth to the stomach.
5 . Stomach:
- It pummels food with its muscular walls.
- It produces pepsin (an enzyme for digesting proteins) and renin (an enzyme for digesting milk proteins), they are also called the protease enzyme.
- It produces hydrochloric acid for three reasons:
- 1) To kill bacteria.
- 2) To give the right pH for pepsin and renin to work (pH2-acidic).
- 3) To neutralise the alkaline effect of saliva.
- Hydrochloric acid, pepsin and renin are called the gastric juice.
6 . Small intestine:
- 1) Secretion of pancreatic juice which consists of the pancreatic amylase, trypsin (protease), lipase and bile.
- 2) Bile are emulsifying agent created in the liver, stored in the gall bladder and transferred to the duodenum through the bile duct to emulsify fats.
- 3) Sodium bicarbonate are secreted into the duodenum to neutralise the acidic effect of hydrochloric acid
- 1) Secretion of intestinal juice which consists of the intestinal amylase, maltase, lipase and protease.
- 2) It is where the foods are completely digested into its simplest form.
- 3) Carbohydrates are digested into glucose, proteins are digested into amino acids, and fats are digested into glycerol and fatty acids.
- 4) This is also where the “food” is absorbed into the blood.
- 5) It is long and folded to increase surface area. Tiny finger-like things called villi cover the inner surface to increase the surface area for absorption.
7 . Large intestine:
- 1) Excess water is absorbed from the food.
- 1) To store faeces.
8 . Anus:
- The faeces (the indigestible food) are expelled.
B) Salivary gland.
C) Buccal cavity
H) Small intestine.
- Ascending colon.
- Transverse colon.
- Descending colon.
K) Large intestine.
M) Gall bladder.
1 . Absorption is the process by which digested food are transferred into the blood stream through the villi of the ileum.
2 . The capillaries of the villi will join up to form the hepatic portal vein which carries blood to the liver.
3 . Glucose & amino acids will be sent to parts of the body that need them.
4 . Excess glucose will be converted by the liver into a storage substance called glycogen & stored in the liver.
5 . Glycogen can be converted back to glucose when the body needs more glucose.
6 . Any more excess glucose will be converted to fats and stored in the adipose tissues under the skin.
7 . Excess amino acids will undergo a process called deamination which is done by the liver.
8 . Deamination is the process by which amino acids are broken down into glucose and urea. Urea is a nitrogenous substance which is sent to the kidneys for disposal.
1 . Assimilation is the process by which some of the absorbed food materials are converted into new protoplasm or used to provide energy.
2 . Uses of glucose and fats:
- For energy (to respire).
- Making new cells.
- Repair & replace damaged tissues.
- Production of other proteins such as enzymes and hormones.
- Fats are used to form part of a cell such as the cell membrane and the nuclear membrane.
- Fats are used as insulators