2. Classes of Food
•Food is a collection of chemicals taken into an
organism for the following purposes:
a. It provides energy for cellular activities.
b. It provides raw materials for growth and repair of
worn- out tissues.
c. It keeps the organism healthy.
Food is not only tasty but also useful

3. •The process of making or obtaining food is called
nutrient.
•There are seven classes of food:
•Carbohydrates
•Proteins
•Fats
•Vitamins
•Minerals
•Fibre
•water

5. •Carbohydrates are food substances consisting of
carbon, hydrogen and oxygen in their molecules. The
H:O ratio in carbohydrates molecules is 2:1.
•Carbohydrates include sugars, starch, glycogen and
cellulose.
•Sugars and crystalline compounds that taste sweet and
are water – soluble.
•Examples of sugars are glucose( grape sugar), sucrose (
cane sugar), lactose (milk sugar) and maltose (malt
sugar)
Carbohydrates

6. •Starch is stored in plant cells, rice, potatoes and tapioca
contain plenty of starch.
•Glycogen is also known an “animal starch” because it
is stored in animal cells. Glycogen is stored mainly in
the liver and muscles.
•Cellulose forms the greater part of the cell walls of
plants.
•Starch, glycogen and cellulose are all made up of
glucose molecules.

7. •Starch , glycogen and cellulose are all made up of
glucose molecules.
•Starch and glycogen can be readily converted to
glucose when needed.
Importance of carbohydrates:
•Main source of energy for cell activities.
•Form supporting structures, such as cell walls in
plants.
•Can be converted to protein and fats.

9. •Proteins are food substances that contain
carbon, hydrogen, oxygen and nitrogen. Sulphur and
phosphorus are present too.
•Every protein molecule is made up of basic units
called amino acids.
•Meat, fish and eggs contain animal proteins while
beans, nuts and seeds contain plant proteins.
Proteins

10. •Needed for growth and repair of worn – out or
damaged cells.
•Used for the synthesis and enzymes and some
hormones.
•Important component of antibodies which help the
body to fight diseases.
•A source of energy.
Importance of proteins:

12. •Fats consists of carbon, hydrogen and oxygen. Unlike
carbohydrates, however, fats contain less oxygen in
proportion to hydrogen.
•Fats which are liquid at room temperature are called
oils. Examples are palm oil and coconut oil.
•Each fat molecule consist of a glycerol molecule and
three fatty acid molecules.
•Food rich in fats include butter, margarine, cooking oil
and fatty meats.
Fats

13. •An efficient source and storage of energy . Each gram of
fat provides about twice the amount of energy supplied
by carbohydrates or proteins. Excess fats are stored as
fatty tissue under the skin and around internal organs
such as the kidneys and the heart to protect the organs
from physical injury.
•Act as solvent for fat – soluble vitamins A, D, E and K.
•An important component of cell membrane.
Importance of fats:

14. •Fats under the skin also act as an insulator to reduce
heat loss from the body.
•A diet rich in fats, however, increase the risk of heart
disease.

16. •Vitamins are organic compounds that are required in
very small amounts for maintaining good health.
•Vitamins are not energy providing foods.
•Vitamins are divided into water – soluble vitamins and
fat – soluble vitamins.
•The water – soluble vitamins are vitamin B and C.
•The fat – soluble vitamins include vitamins A, D, E and
K.
•Diseases caused by a lack of vitamins in our body are
called vitamin deficiency diseases.
•We should eat a varied diet to obtain all the different
types of vitamins that our body needs.
Vitamins

17. Vitamins Source Function Deficiency
disease
A Tomatoes, carrots,
fish liver, oil, green
vegetables, egg yolk,
liver
•For night
vision or vision
in dim light.
•Healthy skin
•Bight
blindness
•Skin infections
B Whole grain bread,
cereals, eggs, milk,
green vegetables
•Healthy skin
•Healthy
nervous system
•Development
of red blood
cells
•Release of
energy from
carbohydrates
•Beri – beri
(paralysis
•Dermatitis
(skin disorder)
•Pellagra
(mental
disorder and
skin disease)
•Anaemia
(deficiency in
red blood cells)

18. Vitamins Source Function Deficiency
disease
C Fresh fruits, green
vegetables
•Healthy tissues
•Healing of
wounds
•Resistance of
disease
•Scurvy
(bleeding
gums, internal
bleeding in
muscles and
skin)
D Liver, fish liver oil,
egg yolk, formed in
skin by sunlight.
•Promotes
absorption of
calcium and
phosphorus
•Formation of
healthy teeth
and bones.
•Rickets
(bowed legs
and knock
knees)
•Osteomalacia
(softening of
bones)

19. Vitamins Source Function Deficiency
disease
E Whole grain, wheat
germ, vegetable oil
•Maybe needed
for
reproduction
•Sterility
(failure to
reproduction)
K Green vegetables,
tomatoes, egg yolk,
made by bacteria in
the large intestine
•Essential for
blood clotting
•Prolonged
bleeding

21. •Minerals are inorganic chemical elements that are
needed in small amounts.
•Minerals are required to regulate body processes.
•A lack minerals causes deficiency diseases.
Minerals

22. Minerals Source Function Deficiency
disease
Calcium Milk, cheese, eggs,
anchovies, yogurt,
green vegetables.
•Building
healthy bones
and teeth
•Clotting of
blood
•Normal
functioning of
muscles and
nerves
•Rickets
•Delayed
clotting
•Muscular
spasms
Sodium Table salt, salty fish,
salty eggs, cheese
•Normal
functioning of
nerves
•Maintenance
of tissue fluids
•Muscular
cramps

23. Minerals Source Function Deficiency
disease
Iron Liver, kidneys, egg,
green vegetables
•Needed for the
formation of
red blood cells
•Activate
certain enzymes
•anaemia
Iodine Iodine salt, sea fish,
shellfish
•Needed to
make hormone
of the thyroid
gland
•Control body
growth
•Goitre
(swelling of the
thyroid gland in
the neck)

24. Minerals Source Function Deficiency
disease
Phosphorus Milk, whole
grain bread,
cereals meat.
•Formation of healthy
bones and teeth
•Proper functioning of
muscles
•Formation of chemical
substances that store
energy
•Rickets
•weakness
Potassium Meat, milk,
fish,
mushrooms,
bananas
•Normal functioning of
nerves.
•Maintenance of tissue
fluids
•Regulation of
heartbeat.
•Weak
muscles
•paralysis