1. CARBOHYDRATES

Carbohydrates are organic compounds made up of small repeating units called

monosaccharides. These are food substances that provide energy in the body, for example;

sugars, starch and cellulose. The monosaccharides are mainly made up of carbon,

hydrogen and oxygen elements. Carbohydrates are also known as “saccharides” which

means sugars.

Sources of Carbohydrates include; rice, cassava, bananas, sugar cane, honey, sweet

potatoes, yams, maize, wheat (bread and cake), fruits and Irish potatoes.

Figure 1.1: Sources of Carbohydrates

Types of Carbohydrates

Depending on the combination of sugars, carbohydrates are classified into three major

groups, namely;

(a) Monosaccharides (simple sugars). Example; glucose, fructose and galactose.

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Glucose: It is found in germinating maize, grapes, honey and tomato.

Fructose: It is found in all ripe sweet fruits such as banana and pineapple.

Galactose: It is found in mammalian milk.

(b) Disaccharides (compound sugars). Example; sucrose, maltose and lactose. They

are found in sugar cane, fruits and fresh milk respectively.

(c) Polysaccharides (Complex sugars). Example; starch, glycogen and cellulose. They

are found in potatoes, cassava, yams, maize, all cereals, green bananas and beans.

Functions of Carbohydrates

(i) They are used as a source of energy in the body.

(ii) They are necessary for the proper functioning of nervous system, heart and kidney.

(iii) They are used to form genetic materials which are DNA and RNA in the cells.

(iv) They combine with protein and lipids to form glycoproteins and glycolipids which are

important components of cell membrane.

NOTE: Excess carbohydrates in the body are converted into either glycogen or fats in the

liver. Then, the glycogen is stored in the liver and muscles while fats are stored as

fat deposits in the lower abdomen, around kidney and under the skin.

2. PROTEINS

Proteins are organic compounds made up of one or more chains of amino acids. Amino

acids are made up of smaller units that contain carbon, hydrogen, oxygen, nitrogen and

sometimes sulphur and phosphorus elements.

There are two major groups of amino acids making proteins, namely;

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Essential amino acids: are amino acids that cannot be made by the body, they are

obtained from the foods we eat. They are sometimes called first class proteins.

Non-essential amino acids: are amino acids made by the body. They are also called

secondary class proteins because they do not contain all essential amino acids.

Sources of proteins which provide essential amino acids include; beef, chicken, fish, milk,

eggs, beans, ground nuts, mushroom, peas and termites.

Figure 1.2: Sources of proteins

Functions of Proteins

(i) Growth and repair of body tissues. The proteins that we eat are used to make new

cells which will make tissues and organs. New cells which are made are also used

to replace the cells that are old, dead or have become damaged.

(ii) They are alternative source of energy in the body. Proteins become source of energy

mainly when all carbohydrates and fats have been used up during starvation.

(iii) They play a role in the transport of molecules across the cell membrane. This is

because they are major components of the cell membranes.

(iv) They form part of the cell structure and aid in the contraction of muscles.

(v) They are used in the transport of oxygen in the body. Example; haemoglobin, the

iron containing protein found in red blood cells.

(vi) They are used for defense and protection. Protein make antibodies which provide

the body with immunity to fight and defend the body against diseases.

(vii) They help us to digest food and speed up biochemical reactions. Enzymes are

proteins which perform this function.

(viii) They control and regulate various processes in the body. Hormones are proteins

which regulate the body activities. For example; insulin hormone regulates glucose

level in the body.

(ix) They control the process of blood clotting. Fibrinogen protein facilitates this

function. Blood clotting prevents further bleeding from the wound or injury.

(x)

They are components of structure such as muscle fibres, hooves, nails, hairs,

feathers and wool.

3. LIPIDS

Lipids are organic compounds made up of carbon, hydrogen and oxygen elements. They

are insoluble in water but soluble in organic solvents such as ether and benzene.

There are two main forms of dietary lipids, namely:

(i) Fats are obtained from animals and are solid lipids at room or normal temperature.

(ii) Oils are obtained from plants and are liquid lipids at room temperature.

Lipids are made up of fatty acids and glycerol. Three molecules of fatty acids combine

with one molecule of glycerol to form lipid. Fatty acids can be essential or non-essential

.

Essential fatty acids are obtained from the food we eat while non-essential fatty acids can

be made by the body.

The body cannot make essential fatty acids. Therefore, it is important to eat foods that

contain essential fatty acids such as; ground nuts, coconuts, avocados, olives, sunflower

seeds, sesame seeds, milk, palm oil, soya beans, cashew nuts, fish and castor seeds.

Figure 1.3: Sources of lipids

Functions of Lipids

(i)

Lipids are source of energy. They provide more energy than all other food

substances.

(ii)

They are component of cell membranes. That is, they are used to form cell

membranes. Phospholipid is a special type of lipid which is a major component of

cell membrane.

(iii) Lipid offer protection. They surround and protect body organs such as heart and

kidneys.

(iv) They insulate the body against heat loss. Lipids under the skin help to regulate

body temperature by insulating the body against loss of heat especially for animals

living in cold environments.

(v)

They are used to store fat-soluble vitamins. Example; vitamin A, D, E and K are

stored in fatty tissues.

(vi) They are source of metabolic water. When fats and oils are respired they produce

water and energy. This water is known as metabolic water. It is an alternative source

of water for animals living in desert such as camels.

(vii) Essential fatty acids are important for the formation of substances that help to

control blood pressure and activate body’s immune response.

(viii) They help to keep our skins from desiccation (drying out).

4. VITAMINS

Vitamins are complex organic micronutrients that are essential for body growth and

survival. Vitamins can also be defined as the organic compounds that are required by

organisms in small amounts to maintain or keep the normal body healthy. Deficiency or

excess intake of vitamins in the body can lead to health problems.

Categories of Vitamins

(i) Fat-soluble vitamins. They can be stored in the body. For example; vitamins A, D, E

and K.

(ii) Water-soluble vitamins. They are not stored in the body. For example; vitamins B

and C. Vitamin B is of various forms such as; vitamin 퐵₁, 퐵₂, 퐵₃, 퐵₆, 퐵₉푎푛푑 퐵₁₂.

Vitamins are mostly synthesized by green plants. Mammals can synthesize vitamin A and

D using plant molecules obtained in their food. Example of foods containing vitamins are

fruits and vegetables.