ICSE Class 9 Biology Chapter 10 Nutrition

Unit-5: Human Anatomy and Physiology

Chapter 10: Nutrition (Nutrition in General)

Syllabus: Classes of food, balanced diet. Malnutrition and deficiency diseases. Functions of carbohydrates, fats, proteins, mineral salts (calcium, iodine, iron and sodium), vitamins and water in proper functioning of the body. Sources of vitamins, their functions, and deficiency diseases. Meaning and importance of a 'Balanced Diet'. Role of cellulose in our diet. Causes, symptoms and prevention of Kwashiorkor and Marasmus.

The Terms Nutrition, Food and Diet

Nutrition means supply of the essential organic and inorganic chemical compounds (proteins, vitamins, salts, etc.) to the body. All such chemical compounds are called nutrients.

Food is any substance which we eat or drink, and which contains the nutrients. Examples: Milk, bread, egg, fish, apple.

Diet. The combination of food items which we eat in our meals. A balanced diet is one which includes food items which supply all the necessary nutrients. [Meal is the food taken at one time to satisfy appetite. Appetite means the desire to eat and hunger is the uneasy sensation due to lack of food.]

10.1 Need of Nutrition

All living organisms require food. It is needed for six main purposes:

(i) Growth: Building up new protoplasm or cells for growth,

(ii) Repair: Providing material for the repair of worn-out or injured cells,

(iii) Energy: Providing energy needed by the body to carry out various life functions.

(iv) Maintenance of chemical composition of cells

(v) Provision of raw materials for the manufacture of various secretions such as enzymes, hormones, sweat, milk, etc.

(vi) Protection from disease and infection.

10.2 Classes of Nutrients (Food Substances)

There are six classes of food substances called nutrients. These are carbohydrates, fats, proteins, mineral salts, vitamins and water.

1. Carbohydrates

Carbohydrates are the compounds of carbon, hydrogen and oxygen, with hydrogen and oxygen always in the ratio of 2:1. They are oxidised in the cells to release energy. Carbohydrates include sugars, starch, cellulose, etc.

Sugars

Sugars are soluble in cold water and taste sweet. Broadly, the sugars in our foods are of two major categories:

A. Monosaccharides or single (simple) sugars with a general chemical formula C6H12O6. These need no digestion and are straightaway absorbed into the body. Three types of such simple sugars are:

(i) Glucose, popularly known as grape-sugar, is the most common and simplest sugar found in organisms. (When we say blood sugar, it means the glucose level in blood).

(ii) Fructose is common in plants and is popularly called fruit sugar.

(iii) Galactose is another simple sugar found in milk.

B. Disaccharides or double sugars have a general chemical formula C12H22O11. These are also three and require digestion.

(i) Sucrose is our commercial sugar. It is commonly obtained from sugarcane in our country. Another source of sucrose is the sugar-beet. Sucrose is a double-sugar made up of two simple sugars, glucose and fructose.

(ii) Maltose or malt-sugar made up of two glucose molecules.

(iii) Lactose or milk-sugar made up of glucose and galactose.

Starch

Starch is an insoluble carbohydrate. It is in this form that plants commonly store carbohydrates. Potatoes, grains (rice, maize, wheat and barley) and bread, are chief sources of starch. The starch has a chemical formula (C6H10O5)n and is called polysaccharide.

Two other insoluble polysaccharide carbohydrates are cellulose and glycogen.

Cellulose is found in cell walls of plants. It is unused in our body but it contributes in providing roughage for proper functioning of the gut.

Glycogen is the form in which carbohydrates are stored in animals (mainly liver and some also in muscles)

Carbohydrates are the principal energy sources in the body. (1 mole of glucose releases 686 kilocalories of energy)

Roughage (Non-digestible cellulose)

The cells of all plants have cell walls made of cellulose. When we eat fruit, raw vegetables and other plant material, cellulose is not digested in our food canal. This is because we have no cellulose digesting enzyme. The undigested cellulose, being fibrous in nature, acts as roughage.

Role of Roughage

- Being fibrous, cellulose absorbs a lot of water and retains it, thus helps in keeping the faecal matter soft and prevents constipation.

- The movement of the undigested food through the intestine becomes easier.

- It stimulates the muscle contraction in the intestinal wall, making the movement of faecal matter easy.

Sources of Roughage

Vegetables, fruit, corn, half-crushed wheat (Dalia) are the chief sources of roughage in our food. Cabbage is one vegetable which provides a lot of roughage.

2. Fats

Fats are also composed of carbon, hydrogen and oxygen. The oxygen content in these nutrients is much less. They produce more energy than carbohydrates do-one mole of fat releases 9.45 Kcal of energy. Common foods rich in fats are butter, cream, vegetable oils, fats of meat and fish liver oils. Fats and oils are made up of fatty acid and glycerol.

Functions of Fat

1. Fat produces energy in the body like carbohydrates.

2. It is an important storage form of food.

3. It serves as a solvent for fat-soluble vitamins

4. Fat under the skin protects the body against a rapid loss of heat (insulation)

3. Proteins

Proteins are large chemical molecules. They contain carbon, hydrogen, oxygen and nitrogen. Nitrogen is the most essential element in proteins. Some proteins may also contain sulphur and phosphorus.

Amino acids are the simple, smaller units of proteins.

Proteins provide chemical material for the growth and repair of body cells and tissues. In the time of emergency they may also be oxidised to release energy.

Foods rich in proteins include lean meat, fat-free muscles, fish, eggs, milk, cheese, nuts, beans, peas, etc. Deficiency of proteins leads to weakness but its severe deficiency causes the two diseases Kwashiorkor and Marasmus.

(i) Kwashiorkor

Kwashiorkor (Hindi Sookha Rog) - It is a severe protein deficiency disease usually affecting young children. This disease is caused when mothers stop breast-feeding their babies at an early age, and the child is given a diet poor in proteins. Mother's milk is rich in protein, and after weaning, the child is given a diet mainly consisting of carbohydrates and poor in proteins. The suffering child may die before the age of five years.

Symptoms of Kwashiorkor:

- Underweight.

- Belly protruding out.

- Skin getting dark and scaly.

- Stunted growth.

- Loss of appetite.

- Repeated diarrhoea.

- Enlarged liver and anaemia.

- Oedema (swelling) of the feet and the face (accumulation of water in the tissues of the feet and the face).

Control/treatment: The child suffering from kwashiorkor should be given a protein-rich diet like pulses, milk, egg, fish and meat. A mixed diet of wheat, gram, peanuts, soybean and jaggery is also useful.

Kwashiorkor

The name "Kwashiorkor" is a Ghanian term (in Africa) which means "the sickness the baby gets when the new baby comes." This is so because the older child's source of protein (mother's milk) is no longer available and now he is usually fed on a starchy diet consisting mostly of fruit and vegetables.

(ii) Marasmus

Marasmus: Marasmus usually affects infants below the age of one year, and is due to the deficiency of carbohydrates, fats and proteins in the diet. This disease is caused due to the sudden stoppage of breast feeding, followed by a diet poor in energy-giving foods like carbohydrates, fats and proteins.

Symptoms:

- Less body weight.

- Degenerations resulting in a very weak body as if formed of muscles, skin and bones only.

- Skin becomes loosely folded.

- Thin face, thinning of limbs.

- Retarded physical and mental growth.

- Ribs appearing prominent.

Table 10.1 Differences between Kwashiorkor and Marasmus

Control/treatment: The child suffering from marasmus should be given a diet rich in proteins and carbohydrates.

4. Mineral Salts

Mineral salts are needed in the diet in small quantities. Table salt contains mainly sodium chloride. Many other mineral elements are obtained from various foodstuffs such as green vegetables and fruit. Some important mineral elements and their nutritional values are as follows:

Calcium and phosphorus for strengthening the bones and the teeth. Calcium is also required in the process of clotting of blood. Phosphorus is required in various chemical processes, as in the production of chemical energy (ATP) during cell respiration. Rich sources: milk, meat, eggs, fish, pulses, vegetables, etc.

Iron for forming haemoglobin; its deficiency leads to anaemia. Source: green leafy vegetables, liver, etc.

Iodine for proper working of thyroid; its deficiency leads to goitre. Source: vegetables, mineral water, etc.

Potassium and sodium for cell permeability, especially in nerve cells. Source: most foods and table salt.

[A detailed list of essential mineral elements, their sources, functions and the related deficiency diseases are given in the Table 12.2 on the next page]

5. Vitamins

Vitamins are chemical substances needed in minute amounts, which help maintain a healthy body. Most vitamins act as catalysts or enzymes in essential chemical changes in the body but each vitamin has also some special function in our body.

Vitamins are contained in foods naturally but a couple of them are also synthesized in the body. Some vitamins (A, D, E and K) are fat-soluble and can be stored in the body, for a longer period of time but some others (B complex containing several vitamins named B1, B2, etc., and C) are water-soluble and cannot be stored for a longer period of time.

Absence or shortage of vitamins in diet over a continued period causes deficiency diseases.

In a low concentration, vitamins have a catalytic and regulatory function in cell metabolism. Excess of vitamins may also be harmful. Excess water-soluble vitamins are easily excreted out.

Table 10.3 on page 92 summarises some important facts about common vitamins.

6. Water

Water is indispensable. About 2/3 of our body weight is water. It serves several functions.

- It acts as a solvent in the body for thousands of substances both organic and inorganic.

- It is used to produce digestive juices.

- It helps in the transportation of digested foods and oxygen throughout the body,

- It is used in the excretion of soluble wastes.

- It is involved in the maintenance of body temperature.

Loss and replacement. Water is regularly lost from the body through sweat, urine, and as water vapour in breath. Therefore, it must be constantly replaced. The liquids we drink and our foods, such as fruit and vegetables, which we eat supply water to the body still we should drink sufficient water every day.

Teacher's Note

Next time you eat a meal, notice how different foods provide various nutrients - the carbohydrates in bread, proteins in meat or beans, and fats in oils work together to keep your body functioning properly throughout the day.

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