South Tuen Mun Government Secondary School
Biology Revision Note 3
A Balanced Diet is made up of carbohydrate, protein, lipid, minerals, vitamins, dietary fibre, water in a suitable
proportion.
Food Tests :
Reagents
Uses
Iodine solution
- a brownish yellow solution which stains the cells, the nucleus is very obvious
after staining
- to test for starch : positive result – changes from yellow to dark
blue/black/blue/blue black
Benedict’s solution (heat at a blue solution to test for reducing sugar (reducing sugar is all monosaccharides
100 ℃ water bath is
and disaccharides except sucrose), positive result – changes from blue to brick
required)
red/orange (for a small amount of reducing sugar, the colour will be green or
yellow)
Clinistix paper
Biuret test (add sodium
hydroxide and then copper
the pink end of the paper changes to purple with glucose
to test for protein, positive result – changes from blue to purple/violet
sulphate)
Albustix paper
Spot test (filter paper)
the yellow end of the paper changes to green with protein.
to test for oil / fat, positive result – a translucent spot, the spot disappears in
organic solvent e.g. ether
Emulsion test – add
alcohol and water
to test for oil / fat, positive result – a milky emulsion
DCPIP
to test for vitamin C, positive result – changes from dark blue to colourless
Food
Function
Carbohydrate


Glucose is the immediate source of energy through the process of respiration.
Sucrose is used for transport in plant.



Starch is used for storage of energy in plant.
Glycogen is used for storage of energy in animal.
Cellulose is used to make cell wall and acts as dietary fibre.
Lipid


Phospholipid is used to make cell membrane.
Lipid is used for storage of energy in plant and animal.
Protein




for growth
to repair old or damaged tissues
to make cell membrane
to make antibodies, hormones, enzymes
Food
Function(s)
Deficiency disease
Vitamin A
To make visual purple which is used for
night vision
night blindness
Vitamin C
To make connective tissue, for blood clotting,
for muscle contraction
scurvy
Vitamin D
For the absorption of calcium and
phosphorus
rickets
Iron
To make haemoglobin [in red blood cells]
which is used to carry oxygen
anaemia
Calcium
To make bone and teeth
rickets
Roughage / dietary fibre
e.g. cellulose
To add bulk to food and help peristalsis
constipation, increase risk of colon
cancer
Special diet needs:
 A 12-50 years old girl needs more iron than boys because they lose blood in menstruation, iron is used to
make haemoglobin in blood.
 A pregnant woman needs more iron for foetus to make haemoglobin, more calcium for foetus to make
bone, more protein for foetus for growth, more carbohydrate for foetus to release energy.
 A breast feeding woman needs more calcium and protein to make milk.
 A labourer needs more carbohydrate and lipid for the release of more energy to work.
When a person takes in food with more energy than he/she uses, the extra energy in food will be used to make
fat/glycogen. Glycogen is stored in liver and lipid is stored in the adipose tissue, he/she increases in weight.
When a person takes in food with less energy than he/she uses, he/she will use glycogen/fat to release energy by
respiration, he/she decreases in weight.
The human digestive system (消化系統)
Mechanical digestion
 In the mouth, the teeth grinds the food into smaller pieces.
 In the stomach, the muscle churns the food into smaller pieces.
 In the small intestine, bile salt emulsifies oil into small droplets.
 Importance of mechanical digestion: to increase surface area for chemical digestion
Structure and function of teeth:
Incisor has a shape like a knife for cutting.
Canine is pointed for killing prey, tearing flesh.
Premolar and molar is flat with ridges for grinding food.
Enamel - non-living, hard; function : to protect against tooth decay
Dentine - living cells, soft and cannot resist decay
Cement - function : to attach the tooth onto the jaw
Pulp cavity - contains blood capillaries and nerve fibres
Chemical digestion:
Juice
Site of
production
Saliva
Salivary gland Water
Gastric juice Stomach wall
Pancreatic
juice
Bile
Pancreas
Component
Function
Provide an optimum pH 7 for enzyme action.
Salivary amylase
To break down starch into maltose
Hydrochloric acid
To kill bacteria, provide a optimum pH 2-3 for
enzyme action.
Protease
To break down protein in smaller peptide
Sodium hydrogen
carbonate NaHCO3
To neutralize the acidic food and to provide an
optimum pH 8-9 for enzyme action.
Protease
To break down protein in smaller peptide.
Lipase
To break down lipid into fatty acids and glycerol.
Pancreatic amylase
To break down starch into maltose.
Secreted by
Sodium hydrogen
liver but stored carbonate NaHCO3
in gall bladder Bile salt
To neutralize the acidic food from stomach; to
provide a pH 8-9 for enzyme action.
To emulsify lipid into oil droplets  increase surface
area for lipase to act.
Bile pigment
Intestinal
juice
Small intestine Carbohydrase
Protease
Excretory wastes from haemoglobin
To break down carbohydrate into monosaccharide
e.g. maltose into glucose.
To break down peptide into amino acids
Absorption in small intestine – by villus
Glucose, amino acids, minerals, water soluble vitamins, water are absorbed through the epithelium cell and the
capillary wall into the blood by diffusion and active transport.
Fatty acid and glycerol are absorbed into the epithelium cell. They combine to form fat. Fat and fat soluble
vitamins are moved into the lacteal.
Characteristics of villus to increase the speed of absorption
 one cell thick to reduce the distance of diffusion,
 rich in blood capillary to carry blood away quickly and maintain a high concentration gradient
 many villi and are highly folded to increase the surface area of diffusion; thus the rate of diffusion is very
fast in villus.
Colon – water and minerals are absorbed.
Rectum – for the temporary storage of faeces and for egestion of faeces by peristalsis
Assimilation of absorbed food:
 glucose, amino acids are transported to the liver through the hepatic portal vein
 glucose is used by the liver and body cells to release energy by respiration, excess glucose is changed to
glycogen for storage in liver and skeletal muscle or changed to fat for storage
 amino acids are used to make protein in liver and body cells, excess amino acids cannot be stored
 *in liver, excess amino acids are broken down into ammonia by deamination, ammonia is changed to urea,
urea is excreted in kidney
 fat is broken down to release energy, excess fat is stored in adipose tissue e.g. breast, under the skin, hip
(pat pat), belly