LIWA

Nutrition

ICSE Class 9 · Biology · Chapter 11

What this chapter covers

Key definitions

Nutrition is the process by which an organism obtains food and uses it for energy, growth, repair and the regulation of body activities.

Food is any substance which, when taken into the body, provides energy, materials for growth and repair, or substances that regulate body processes.

Nutrients are the chemical substances present in food that the body uses for energy, for building and repairing tissues, and for controlling body processes.

Calorific value is the amount of energy released when one gram of a food is completely oxidised in the body.

Carbohydrates are organic compounds made of carbon, hydrogen and oxygen, in which hydrogen and oxygen are usually present in the ratio 2 : 1, as in water.

Fats are organic compounds of carbon, hydrogen and oxygen in which the proportion of oxygen is much smaller than in carbohydrates; each fat molecule is built from glycerol and fatty acids.

Proteins are large organic compounds made of long chains of amino acids, containing carbon, hydrogen, oxygen and nitrogen, and often sulphur.

Amino acids are the building units of proteins; digestion breaks proteins down into amino acids, which are absorbed and then built up again into the body's own proteins.

Mineral salts are inorganic substances, taken in as compounds of elements such as calcium, iron, iodine and sodium, that the body needs in small amounts for building body parts and for regulating body processes.

Vitamins are organic compounds required in very small amounts in the diet for normal growth, health and the regulation of body processes, which the body cannot make in sufficient amounts for itself.

Deficiency diseases are diseases caused by a lack of a particular nutrient, such as a vitamin or a mineral, in the diet over a long period.

Roughage is the indigestible part of plant food, made mainly of cellulose, that passes through the human alimentary canal without being digested; it is also called dietary fibre.

Key points

Questions answered

Define a balanced diet.
A balanced diet is a diet that contains all the classes of food (carbohydrates, fats, proteins, mineral salts, vitamins and water), together with roughage, in the right amounts and proportions to meet the body's needs for energy, growth, repair and health.
Name the six classes of food and state which of them supply energy.
Carbohydrates, fats, proteins, mineral salts, vitamins and water. Carbohydrates and fats are the main energy-giving foods; proteins also give energy when the other two are short.
Why are proteins called body-building foods? Give two other functions of proteins.
Proteins form the structure of new cells and are used to repair damaged tissues, so they build the body. They also form enzymes, which control the body's chemical reactions, and antibodies, which fight infection; hormones such as insulin and the blood pigment haemoglobin are also proteins.
A snack contains 20 g of carbohydrate, 4 g of protein and 8 g of fat. Using 17 kJ per gram for carbohydrate and protein and 37 kJ per gram for fat, calculate its energy value.
20 × 17 = 340 kJ; 4 × 17 = 68 kJ; 8 × 37 = 296 kJ. Total = 340 + 68 + 296 = 704 kJ.
State one function and one deficiency disease of each of: iodine, iron and calcium.
Iodine is needed to make the hormone thyroxine; its lack causes goitre. Iron forms part of haemoglobin, which carries oxygen; its lack causes anaemia. Calcium hardens bones and teeth and helps blood to clot; its lack causes weak bones (rickets in children, with vitamin D lack) and slow clotting.
Why is iodine added to common salt in India?
Many soils, especially in hill regions, are poor in iodine, so local food supplies too little. Salt is eaten by everyone every day in small, steady amounts, so iodised salt gives the whole population enough iodine to make thyroxine and prevents goitre.
Name the vitamin whose deficiency causes each of: scurvy, rickets, beriberi, night blindness, pellagra.
Scurvy: vitamin C. Rickets: vitamin D. Beriberi: vitamin B1 (thiamine). Night blindness: vitamin A. Pellagra: vitamin B3 (niacin).
Give two good sources of vitamin C, and explain why overcooked vegetables are a poor source of it.
Amla and guava (also citrus fruits and tomatoes). Vitamin C is destroyed by heat and by contact with air, and it dissolves in water, so long boiling destroys it and throwing away the cooking water removes what is left.