Biology

1. NUTRIENTS
• Why do we need food?
• Nutrients in food.
• Structure of large molecule.
• Food Test.

2. WHY DO WE NEED FOOD?
• We need food to give us ENERGY
• We need food to keep us
HEALTHY
• We need food to REPAIR and
REPLACE damaged and worn out
Tissues
• We need food to GROW

3. NUTRIENTS IN FOOD
• Carbohydrates
• Proteins
• Fats ( lipids)
• Vitamins
• Mineral Salts

4. CARBOHYDRATES
Simple sugars
Structure
( what are
they made of)
Complex sugars
Polysaccharides
Made up of simple
units
Made up of two simple
sugar joined together.
e.g. MALTOSE,
SUCROSE
Glucose + Glucose
Made up of
many simple
sugars joined
together
e.g. GLUCOSE
Maltose + Water
e.g. Starch,
Glycogen
e.g. FRUCTOSE
Many glucose
molecules
Glucose + Fructose
Sucrose + Water
One starch
molecule +
many water
molecules

5. Simple sugars
Complex sugars
Polysaccharides
Sources
Sweet, honey,
fruits, jam
Sugar cane,
malted cereals
Rice noodles,
potatoes, cakes,
cereals,
vegetables.
Function in
the body
• Supply energy
• Form nucleic acids ( DNA)
• Make lubricant ( mucus)
Effects of too • Become fat as excess carbohydrates are converted to
much on the
fat and stored
body
Effect of too
little on the
body
• Become very weak and will not grow

6. PROTEINS
Structure
• Made up of many amino acids joined together
( what are
they made of) e.g Many amino acids
one protein molecule + many
water molecules
• There are about 20 amino acids found in the structure
of protein.
• Many amino acids link up to form a polypeptide.
• One or more polypeptides link up to form protein molecule.
Source
Lean meat, fish, milk, cheese, egg white, peas, beancurd, nuts.
Function in
body
• Form protoplasm for making new cells so that the body will
grow.
• Repair and replace damaged and worn out tissues.
• Make enzymes and hormones.
• Form antibodies.
• Supply energy
Effect of too
little on the
body
• Muscles are poorly developed
• Become very weak and will not grow

7. FATS
Structure
( what are they
made of)
• Made up fatty acids and glycerol
e.g
3 molecules of fatty acid + 1 molecule of glycerol
1 molecule of fat + 2 water molecule.
Source
Oil, butter, full cream milk, fatty meat, nuts sunflower seeds.
Function in
body
•
•
•
•
•
Effect of too
much on the
body
• Becomes fast as excess fats are stored
Effect of too
little on the
body
• Muscles are poorly developed
• Become very weak and will not grow
Supply energy
Form part of cell surface membrane
Insulate against heat loss
Act as solvent for fat soluble vitamins and hormones
Prevent water loss.

8. WATER
• Water is used as a SOLVENT in living organism.
• Water is important for REGULATING THE
TEMPERATURE OF ORGANISM.
• Water plays a role in SUPPORTING STRUCTURES
AS ORGANISMS.
• Water plays a role in LUBRICATION
• Water plays a role in METABOLISM.
• Water plays a role in the DISPERSAL OF FRUITS.

9. Food Test
Test for starch – IODINE TEST
• Add one or two drops of dilute iodine solution to
the food sample.
• A BLUISH - BLACK colour indicates the presence of
starch
• If starch is absent the iodine solution remains
BROWN

10. Test for reducing sugar –
BENEDICT’S TEST
• Make a solution of the food sample.
• Add an equal amount of Benedict’s solution
(copper II salt ( blue)) to 2 ml of the food solution.
• Mix well and place the tube in a boiling water bath
for two minutes.
• Colour of the solution changes to green yellow to
red ( copper I oxide (red)).
• Colour changes indicates the presence of reducing
sugar

11. Test for protein- BIURET TEST
• Make a solution of the food sample.
• Add an equal volume of 5% sodium hydroxide
solution to 2 ml the food solution.
• Shake the tube to mix the content.
• Add 1% of copper (II) sulphate solution a drop
at a time, shaking the tube after each drop.
• A violet colour indicates the presence of
protein while a light blue indicates the
absence of the protein.

12. Test for fats – ETHANOL
EMULSION TEST
• Grind food items and put it into a test tube. Use
only two drops of the food items if it is liquid.
• Add 2ml of ethanol and mix well. Allow any solid
particles to settle.
• Decant the ethanol into another test tube
containing2 ml of water.
• Mix well and look for a WHITE EMULSION
( CLOUDINESS) Lipids are present .
• Clear solution absence of lipids