Nutrition — ICSE Class 9 Biology Important Questions

Answer: (c) Protein.

Proteins are body-building nutrients; their amino acids are used to build new cells and repair worn-out tissues.

Answer: (b) Scurvy.

Lack of vitamin C (ascorbic acid) causes scurvy, marked by bleeding, spongy gums and slow healing of wounds. It is prevented by eating citrus fruits and amla.

Answer: (c) Starch.

Iodine solution turns blue-black in the presence of starch; this is the standard iodine test for starch.

Answer: (c) Iodine; for making the hormone thyroxine.

Goitre is caused by iodine deficiency; iodine is needed by the thyroid gland to make thyroxine, so the person is advised to use iodised salt.

Answer: (a) Roughage (dietary fibre) is not digested, yet it is needed because it adds bulk, stimulates peristalsis and helps egest undigested waste, preventing constipation. R correctly explains A.

A balanced diet is a diet that contains all the essential nutrients — carbohydrates, proteins, fats, vitamins, minerals, water and roughage — in the correct proportions and amounts required to keep the body healthy.

A growing child needs more protein because proteins are body-building nutrients required for the rapid formation of new cells and tissues during growth, whereas an inactive adult mainly needs protein only to repair worn-out tissues.

(i) Vitamin A: deficiency causes night blindness (difficulty in seeing in dim light). Good source: carrots, papaya, milk and butter.

(ii) Iron: deficiency causes anaemia (reduced haemoglobin, pale skin, weakness). Good source: green leafy vegetables, liver, jaggery and dates.

The six main classes of nutrients are carbohydrates, proteins, fats, vitamins, minerals and water (roughage/fibre is often added as a seventh component).

Chief functions of three of them:

1. Carbohydrates — the main source of energy for all activities of the body.
2. Proteins — body-building nutrients used for growth and repair of tissues.
3. Fats — a concentrated store of energy; they also insulate the body and protect organs.

(Vitamins and minerals are protective, and water is the medium in which all reactions take place.)

Rickets is prevented by vitamin D from sunlight, milk and fish oils; beri-beri by whole grains and pulses; scurvy by citrus fruits and amla.

Although both boys take in the same amount of energy (calories), only the second boy eats a balanced diet.

The first boy's food (polished rice and sugar) is almost pure carbohydrate. It supplies energy but is deficient in proteins, vitamins, minerals and roughage:

• Lack of protein means his body cannot grow or repair tissues properly, so he becomes weak.
• Lack of vitamins and minerals lowers his resistance and can cause deficiency diseases, so he falls ill often. (Polished rice, for example, lacks vitamin B1, risking beri-beri.)

The second boy's meal supplies protein (pulses, milk), vitamins and minerals (vegetables, fruit) and roughage as well as energy, so all his body's needs are met.

This shows that health depends not just on the quantity of energy but on getting all nutrients in the right proportions — the meaning of a balanced diet.

1. Carbohydrates

• Function: the main and quickest source of energy for all body activities (each gram gives about $17\,\text{kJ}$17\,kJ). Excess is stored as glycogen or fat.
• Source: rice, wheat, potato, sugar.

2. Proteins

• Function: body-building nutrients; supply amino acids for the growth of new tissues and the repair of worn-out cells; also make enzymes and hormones.
• Source: pulses, milk, eggs, meat, fish, soybean.

3. Fats

• Function: a concentrated store of energy (each gram gives about $38\,\text{kJ}$38\,kJ); insulate the body against heat loss and cushion delicate organs; carry fat-soluble vitamins.
• Source: ghee, butter, oil, nuts.

4. Vitamins

• Function: needed in tiny amounts to regulate body processes and maintain health; protect the body from deficiency diseases (e.g. vitamin C prevents scurvy).
• Source: fruits and vegetables (e.g. citrus fruits, green leafy vegetables).

5. Minerals

• Function: protective and body-building; e.g. calcium and phosphorus for bones and teeth, iron for haemoglobin, iodine for thyroxine.
• Source: milk (calcium), green vegetables and liver (iron), iodised salt (iodine).

A diet with all these in the right amounts, along with water and roughage, is a balanced diet.

(i) Test for starch (iodine test)

• Reagent: dilute iodine solution.
• Method: add a few drops of iodine solution to the food sample.
• Positive result: a blue-black colour appears if starch is present.

(ii) Test for reducing sugar / glucose (Benedict's test)

• Reagent: Benedict's solution (blue).
• Method: add Benedict's solution to the sample and heat in a water bath.
• Positive result: the blue colour changes through green and yellow to a brick-red precipitate if reducing sugar is present.

(iii) Test for protein (Biuret test)

• Reagent: dilute sodium hydroxide (NaOH) followed by a few drops of dilute copper sulphate ($CuSO_4$CuSO_4).
• Method: add NaOH to the sample, then add copper sulphate solution.
• Positive result: a violet / purple colour develops if protein is present.

(iv) Test for fat (grease-spot / translucent test)

• Method: rub the food sample on a piece of paper (or shake with ethanol and add water).
• Positive result: a permanent translucent (greasy) spot on the paper that does not dry off shows fat is present (with ethanol, a milky white emulsion forms).

These four tests together allow the main nutrients in a food sample to be identified.

(i) Patient A has rickets, caused by a deficiency of vitamin D (which is needed for the absorption of calcium and phosphorus for strong bones).

(ii) Patient A can get vitamin D by:

1. Exposure to sunlight, which lets the skin make vitamin D.
2. Eating vitamin-D-rich foods such as milk, butter, egg yolk and fish-liver oil.

(iii) Patient B is suffering from anaemia, caused by a deficiency of the mineral iron.

(iv) Iron is needed for the formation of haemoglobin in red blood cells, which carries oxygen from the lungs to all the tissues of the body.