Food pyramid, structure and uses of nutrients, diseases caused by some deficiency.

1. A healthy diet
Chapter 2
Biology

2. Nutrients
• A chemical that is needed by the body to keep it in good health is
called a nutrient.
• The human body needs a large number of different nutrients to keep
it healthy.
• Can you list the five groups of nutrients?
• They are:
Carbohydrates
Fats
Proteins
Vitamins and
Minerals

3. • In addition to these nutrients the body also needs water (70% of the
body)
• Water is important as it:
(a) provides support for the cells
(b) carries dissolved materials around the body and
(c) helps in controlling body temperature.
• Fibre is also needed by the body.

4. A healthy diet
• The body needs the range of nutrients mentioned previously to keep
healthy.
• Everyone should eat a balanced diet to eats those nutrients.
• Regular eating of high energy snacks (sweets, chocolate, ice-cream
and chips) between meals unbalances the diet and can lead to the
body becoming overweight.
• High energy snacks should be kept to a minimum.
• Overweight people have to make more effort than normal to move so
they tend to exercise less, which leads to heart problems over time.
• A food guide pyramid reminds you that you should eat large amounts
of foods at the bottom and small amounts from foods at the top.

7. 1) Carbohydrates
• Structure:
1) Made from the elements of
carbon, hydrogen and oxygen.
2) These atoms are linked
together to form molecules of
sugar
• There are different kinds of
sugar molecules but the most
commonly occurring is glucose.
• Glucose molecules link together
to form starch.
• Glucose and starch are the most
commonly known molecules.
• Other examples of known
carbohydrates is cellulose.

8. 2) Fats
• Structure:
Made large nos. of carbon and
hydrogen atoms linked into long
chains together with a few oxygen
atoms.
• There are 2 kinds of fat:
(a) Solid fat: Produced by animals
ex. Lard
(b) Liquid fat: Oil produced by
plants. Ex. Sunflower
oil.

9. 3) Proteins
• Structure:
Made of carbon, hydrogen,
oxygen and nitrogen atoms.
Some of the proteins also have
sulphur atoms.
The atoms of these elements
join together to form amino
acids.
Amino acids join together to
form proteins.

10. 4) Vitamins
• Structure:
Vitamins are needed in small
amounts.
• When vitamins were first
discovered they were named
after letters of the alphabet.
• Later on, when the chemical
structure of the molecules were
found out, they were given
chemical names.

11. 5) Minerals
• The body needs 20 minerals.
• Some minerals such as calcium
are needed in large amounts.
• Other minerals like zinc are
needed in tiny amounts (trace
elements)

12. How the body uses nutrients

13. 1) Carbohydrates
• Carbohydrates contain a large
amount of energy that can be
released quickly.
• They are used as a fuel to keep
the body alive.

14. 2) Fibre
• Cellulose is a carbohydrate
which makes up the walls of
plant cells.
• The cellulose in food is known as
the dietary fibre.
• It is found in foods such as:
- Whole meal bread
- Fruits and
- Vegetables

15. • We cannot digest fibre but it helps move food along the intestines.
• As the fibre moves through the large intestine bacteria feeds on it
(this adds bulk to the food).
• This helps the muscles of the large intestine push the food along.
• Fibres also take up water like a sponge and this makes the
undigested foods which form the faeces soft and easy to release from
the body.
• If a person’s diet lacks fibre, he may suffer from bowel problems
such as constipation.

16. 3) Fats
• Fat are needed for the formation
of cell membranes.
• They contain even larger
amounts of energy than
carbohydrates, but, energy is
released slower.
• In mammals fat forms a layer
under the skin to insulate the
mammal and keep them warm
in cool conditions

17. 4) Proteins
• Proteins are needed for building
the structures inside cells and in
the formation of tissues and
organs.
• They are needed for the repair
of the body, to repair damages
parts (cut skin) and to replace
tissues that are constantly being
worn away (ex. Lining of the
mouth)
• Enzymes are also made up of
proteins.

18. 5) Minerals
• Each mineral has more than one use.
• Example:
1) Calcium: a) make strong bones and teeth.
b) Needed to make muscles work.
c) Helps blood to clot.
(Lack of calcium can lead to weak bones and
high blood pressure)
2) Iron: Used to make haemoglobin.

20. 6) Water
• About 70% of a humans body is
water.
• The body can survive only for a few
days without a drink of water.
• Every chemical reaction in the body
takes place in water.
• The blood is made mainly of water
(transports blood components
around the body).
• Water cools down the body by
evaporation of sweat from the skin.

21. 7) Vitamins
• Each vitamin has one or more
use in the body.

22. Vitamin Effect on the body Good sources
A 1) Allow the eyes to see in dim light
2) Involved in making the mucus lining to the
respiratory , digestive and excretory systems
(protects against infection from micro-organisms)
Milk, liver, cod-
liver oil
B₁ (Thiamin) 1) Prevents digestive disorders
2) Prevents beriberi disease
Bread, milk,
brown rice,
soybean, potato
C Prevents scurvy disease (gums bleed and circulatory
system is damaged)
Blackcurrant,
orange, lemon,
papaya, guava
D Prevents rickets disease (bones become soft and leg
bones of children may bend).

23. The amount of nutrients in food

24. Keeping a balance
• Amount of nutrients in food has been
found out by experiments and
calculation.
• The amounts are usually for 100 g of
food.
• To remain healthy a person must eat
a balanced diet (all nutrients)

25. Malnutrition
• If a diet provides too few nutrients or too
many nutrients malnutrition occurs.
• Lack of vit. C causes scurvy.
• Lack of iron causes anemia.
• Too much protein is broken down and
converted into glycogen (carb.) which is stored
in the liver and part is turned into urea
(excreted in urine)
• Too much carbohydrates and fats causes
obesity (extremely overweight).
• Anorexia nervosa (Fear of gaining weight and
eat a little) can cause death.