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2.1 : Classes of Food

2.2 : The Importance of a Balanced

Diet

2.3 : Human Digestive System

2.4 : Absorption of Digested Food

2.5 : Reabsorption of Water &

Defecation

2.6 : Eating Habits

Chapter 2

nutrition

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Food is the basic need of

all living things. It is

needed to :-

(a) make new cells

(b) repair damaged cells

(c) provide energy for

daily activities

(d) protect the body

from diseases

1.1 : classes of food

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1.1 : classes of food

Classesof food

Carbohydrate

Fats

Minerals

Fibreater

Vitamins

Proteins

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Carbohydrates

Organic compoundsconsisting of the

elements carbon,

hydrogen andoxygen.

Generally there are 3

types :-(a) sugar

(b) starch & glycogen

(c) cellulose

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Carbohydrates - sugars

Sugars Sources

Glucose Found in all animals, grapes and honey

FructoseCommon in plants, but rarely found in

animals

GalactoseA component of milk-sugar/ lactoserare in

organisms except mammals

Sucrose

Sugarcane stems, sweet fruits & certain

storage roots like carrots & sugar-beet. Notfound in mammals.

Lactose Milk of all mammals including humans

Maltose Malted cereals and sprouting grains

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Carbohydrates - starch

Starch is a storage form of

carbohydrate found only inplants :-

(a) Excess glucose produced

during photosynthesis isstored in plants as

starch

(b)Sources of starch includetapioca, potatoes, sweet

potatoes, rice, maize &

wheat

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Carbohydrates - glycogen

Glycogen is a storage form

of carbohydrate found inanimal & fungi

(a) In mammals, glycogen is

mainly found in themuscles & liver

(b)When glucose in the

body is depleting,glycogen can be easily

broken down into

glucose

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Carbohydrates - cellulose

Cellulose is thecarbohydrate that makes

up the most part of the

cell walls of plants.

(a) A form of fibre,

cellulose is common in

fruits & vegetables

(b)Can only be digested byherbivores. Humans

cannot digest cellulose

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Functions of Carbohydrates

1. As a source of energy.

- During respiration, carbohydratesare oxidized to produce energy. In

fact most of the energy needed by

the body comes fromcarbohydrates.

Carbohydrates(glucose) Oxygen Energy Carbondioxide Water

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Functions of Carbohydrates

2. To form cellulose in plants & other

supporting structures.

3. To form other organic compounds like

amino acids & fats especially when

carbohydrates are in excess.

4. To produce lubricants such as mucus

that covers the surfaces of the nasalcavity

5. To produce nectar that attracts insects

& enables cross-pollination

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Test for Carbohydrates

1. Add 2ml of Benedicts solution into a test tube

containing 2ml of glucose solution.2. Shake the mixture.

3. Immerse the test tube in a beaker of boiling water

for 5 minutes.