Answers · A balanced diet

Nutrients and what they do — answer key

Check meaning, not exact wording. These are teaching points, not official Cambridge marks.

1. NQ1 · Practice

Options as numbered on the pupil sheet: 1 — Adding bulk so food keeps moving through the gut; 2 — Healthy skin and gums, and helping wounds heal; 3 — Growth and repair of cells and tissues; 4 — Making haemoglobin, which carries oxygen in red blood cells; 5 — A source of energy; 6 — Hard, strong bones and teeth.

Model answer. Carbohydrates are a source of energy. Proteins are used for growth and for repairing cells and tissues. Vitamin C keeps the skin and gums healthy and helps wounds to heal. Calcium makes bones and teeth hard and strong. Iron is needed to make haemoglobin, the red substance in red blood cells that carries oxygen. Fibre adds bulk to the food in the gut, so it keeps moving along and constipation is prevented.

A full answer includes

Carbohydrate: a source of energy.
Protein: growth and repair of cells and tissues.
Vitamin C: healthy skin and gums, and helping wounds heal.
Calcium: hard, strong bones and teeth.
Iron: making haemoglobin, which carries oxygen in red blood cells.
Fibre: adding bulk so food keeps moving through the gut.

Also accept

carbohydrate: energy; protein: growth and repair; vitamin C: skin, gums, healing; calcium: bones and teeth; iron: haemoglobin; fibre: bulk, food keeps moving

Watch for

“Protein is mainly for energy.” — The body can respire protein, but its main job is growth and repair: new cells are built from it.
“Iron makes bones hard.” — Calcium makes bones hard. Iron is needed to make haemoglobin in red blood cells.

2. NQ2 · Practice

Options as numbered on the pupil sheet: 1 — Wholegrain bread, vegetables and beans; 2 — Meat, fish and eggs; 3 — Butter, cooking oil and nuts; 4 — Bread, rice and potatoes.

Model answer. Bread, rice and potatoes are rich in starch, a carbohydrate. Butter, cooking oil and nuts are rich in fat and oil. Meat, fish and eggs are rich in protein. Wholegrain bread, vegetables and beans are rich in fibre, the cellulose of plant cell walls. Many of these foods contain other nutrients too.

A full answer includes

Carbohydrate: bread, rice and potatoes.
Fat and oil: butter, cooking oil and nuts.
Protein: meat, fish and eggs.
Fibre: wholegrain bread, vegetables and beans.

Also accept

carbohydrate: bread, rice, potatoes; fat: butter, oil, nuts; protein: meat, fish, eggs; fibre: wholegrain bread, vegetables, beans

Watch for

“Meat contains fibre.” — Fibre comes from plant cell walls. Meat, fish, eggs and milk contain none.

3. NQ3 · Practice

Options as numbered on the pupil sheet: 1 — Red meat, beans and dark green leafy vegetables; 2 — Oranges, blackcurrants and peppers; 3 — Oily fish such as sardines, and egg yolk; 4 — Milk, cheese and yoghurt.

Model answer. Oranges, blackcurrants and peppers are rich in vitamin C. Oily fish such as sardines, and egg yolk, contain vitamin D. Milk, cheese and yoghurt are rich in calcium. Red meat, beans and dark green leafy vegetables such as spinach contain iron.

A full answer includes

Vitamin C: oranges, blackcurrants and peppers.
Vitamin D: oily fish such as sardines, and egg yolk.
Calcium: milk, cheese and yoghurt.
Iron: red meat, beans and dark green leafy vegetables.

Also accept

vitamin C: oranges, blackcurrants, peppers; vitamin D: oily fish, egg yolk; calcium: milk, cheese, yoghurt; iron: red meat, beans, leafy greens

Watch for

“Milk is the best source of vitamin D.” — Milk is rich in calcium. It has little vitamin D unless vitamin D has been added to it (fortified milk).

4. NQ4 · Practice

Model answer. Protein is used for growth and repair. A growing child builds new cells all the time, for example in muscles, skin and blood, and new cells need proteins, which are made from the amino acids in food.

A full answer includes

Protein is used for growth and repair: to build new cells and tissues.

Also accept

growth and repair; building new cells and tissues

Watch for

“Protein is mainly for energy.” — Energy comes mainly from carbohydrates and fats. Protein is used to build and repair cells.

5. NQ5 · Practice

Model answer. Fats and oils are a source of energy, and the body stores spare energy as fat. A layer of fat under the skin insulates the body, so it loses heat more slowly. Fats are also used to make cell membranes. They do not make bones hard (that is calcium) or carry oxygen (that is haemoglobin, which needs iron).

A full answer includes

A source of energy, which can be stored.
A layer under the skin that insulates the body against heat loss.
Part of the membrane around every cell.

Also accept

energy source and store; insulation under the skin; cell membranes

Watch for

“Fat has no use in the body.” — Fat is a nutrient: it is a source and store of energy, insulates the body and is part of every cell membrane.

6. NQ6 · Practice

Model answer. Calcium makes bones and teeth hard and strong. Vitamin D is needed so that the body can absorb calcium from food in the gut. As well as coming from food such as oily fish, vitamin D is made in the skin when it is in sunlight.

A full answer includes

g1: calcium.
g2: vitamin D.
g3: sunlight.

Also accept

calcium; vitamin D; sunlight

Watch for

“Vitamin D makes bones hard by itself.” — Calcium is what makes bones hard. Vitamin D helps the body take calcium in from food.

7. NQ7 · Practice

Model answer. (a) Iron is needed to make haemoglobin, the substance in red blood cells that carries oxygen around the body. (b) Red meat and beans are good sources; liver, lentils, spinach and other dark green leafy vegetables, and dried apricots also contain iron.

A full answer includes

(a) To make haemoglobin in red blood cells, which carries oxygen.
(b) Any two of: red meat, liver, beans, lentils, dark green leafy vegetables such as spinach, dried apricots.

Also accept

(a) haemoglobin in red blood cells, carries oxygen; (b) two of: red meat, liver, beans, lentils, spinach or leafy greens, dried apricots

Watch for

“Iron makes muscles strong.” — Iron is needed for haemoglobin, which carries oxygen in the blood.
“Only meat contains iron.” — Beans, lentils and dark green leafy vegetables contain iron too.

8. NQ8 · Practice

Model answer. Fibre is mostly cellulose from plant cell walls, which we cannot digest. It stays in the gut and adds bulk to the food there. The muscles of the gut wall can grip the bulky food and push it along, so food keeps moving through the gut and constipation is prevented.

A full answer includes

Fibre adds bulk to the food in the gut.
The muscles of the gut wall can push the bulky food along, so it keeps moving and constipation is prevented.

Also accept

adds bulk; gut muscles push food along; prevents constipation

Watch for

“Fibre is useless because it is not absorbed.” — Fibre does its job inside the gut: it adds bulk so food keeps moving.
“Fibre gives us energy.” — We cannot digest fibre, so it releases no energy for us.

9. NQ9 · Practice

Model answer. Water is needed as a solvent: many substances dissolve in it, and the chemical reactions in cells take place in solution. The plasma of the blood is mostly water, which carries dissolved substances round the body. Urine carries waste such as urea out of the body in water. Sweat cools the body as its water evaporates. Water releases no energy and does not make bones hard.

A full answer includes

Water is a solvent: substances dissolve in it, and the reactions in cells happen in solution.
Water carries substances around the body in the blood plasma.
Water carries waste out of the body in urine.
Sweat cools the body as water evaporates.

Also accept

solvent for reactions; transport in plasma; waste in urine; cooling by sweat

Watch for

“Water is not a nutrient, because it gives no energy.” — Water is a nutrient: the body needs it every day as a solvent, for transport and to cool down, even though it releases no energy.

10. NQ10 · Practice

Model answer. Vitamin C is needed to make a protein that holds the skin, the gums and the walls of blood vessels together, so it keeps the skin and gums healthy and helps cuts and wounds to heal.

A full answer includes

Vitamin C keeps the skin and gums healthy and helps wounds to heal.

Also accept

healthy skin and gums; wound healing

Watch for

“Vitamin C makes bones hard.” — Calcium makes bones hard. Vitamin C is for healthy skin and gums and for healing.

11. NT1 · Apply

Model answer. (a) Calcium and vitamin D. Calcium makes bones and teeth hard and strong. Vitamin D, which has been added to this milk, helps the body to absorb calcium from food in the gut. (b) Milk does contain protein, but the label shows it also contains fat, carbohydrate (milk sugar), calcium and vitamin D. Most foods contain several nutrients, so naming one does not describe the food.

A full answer includes

(a) Calcium makes bones and teeth hard; vitamin D (added to this milk) helps the body absorb the calcium.
(b) Milk contains several nutrients: protein, but also fat, carbohydrate (sugar), calcium and vitamin D; most foods contain more than one nutrient.

Also accept

(a) calcium hardens bones and teeth; vitamin D helps absorb calcium; (b) milk contains several nutrients, not only protein

Watch for

“A food is either a protein food or a carbohydrate food.” — Most foods contain several nutrients. Milk has protein, fat, sugar and calcium.
“All milk is rich in vitamin D.” — This milk has vitamin D added. Milk without added vitamin D contains very little.

12. NT2 · Apply

Model answer. Vitamin D is made in the skin when sunlight falls on it. In the dark northern winter there is almost no sunlight, so the skin makes very little vitamin D. Oily fish and cod liver oil are among the few foods rich in vitamin D, so they supply the vitamin D the skin cannot make. The body needs vitamin D to absorb calcium from food, for strong bones and teeth.

A full answer includes

Vitamin D is made in the skin in sunlight; in the dark winter the skin makes very little.
Oily fish (and cod liver oil) is a good food source of vitamin D, so it makes up for the vitamin D the skin cannot make.
Vitamin D is needed to absorb calcium, for strong bones and teeth.

Also accept

little sunlight so little vitamin D made in the skin; oily fish supplies vitamin D; vitamin D needed to absorb calcium for bones

Watch for

“Oily fish is eaten for its calcium.” — Here the point is vitamin D: the dark winter stops the skin making it, and oily fish is rich in it.
“Vitamin D only comes from food.” — Most people make much of their vitamin D in their skin in sunlight.

13. NT3 · Apply

Model answer. (a) Beans, lentils, nuts and tofu contain plenty of protein. (b) Beans, lentils, dark green leafy vegetables such as spinach, and dried apricots contain iron. (c) A plant drink that has calcium added (fortified), tofu, or dark green leafy vegetables. (d) Few plant foods contain vitamin D naturally, so a fortified plant drink or cereal with vitamin D added; the skin also makes vitamin D in sunlight.

A full answer includes

(a) Beans, lentils, nuts or tofu.
(b) Beans, lentils, spinach or other dark green leafy vegetables, or dried apricots.
(c) A fortified plant drink (calcium added), tofu, or dark green leafy vegetables.
(d) A fortified plant drink or cereal with vitamin D added (and sunlight on the skin).

Also accept

(a) beans, lentils, nuts, tofu; (b) beans, lentils, leafy greens, dried apricots; (c) fortified plant drink, tofu, leafy greens; (d) fortified drink or cereal (or sunlight)

Watch for

“Every plant drink contains calcium and vitamin D.” — Only drinks with calcium and vitamin D added (labelled fortified) are good sources of them.
“Plants contain no protein.” — Beans, lentils and nuts are rich in protein.

14. NT4 · Apply

Model answer. (a) Fibre is the cellulose from the walls of plant cells. Cheese, dried meat and sweets contain none, and white bread has only a little, so the food in her gut has little bulk. The muscles of the gut wall push food along by gripping bulky food; with too little fibre the food moves slowly and she becomes constipated. (b) On the hottest days she sweats more, and the water in sweat cools her as it evaporates. That water, and the water she loses in urine and breath, must be replaced, because the body needs water every day: as the solvent for the reactions in its cells, in the plasma that carries dissolved substances, and to carry waste out in urine. (c) For example: wholegrain bread instead of white bread adds fibre; fresh fruit such as apples or oranges adds fibre and water; dried fruit or nuts add fibre and are light to carry.

A full answer includes

(a) Her food has very little fibre: cheese, dried meat and sweets have none and white bread has little, so the food in her gut has little bulk, moves slowly, and constipation follows.
(b) Sweat cools her as its water evaporates, so on hot days she loses more water; it must be replaced, because the body needs water as a solvent for the reactions in cells and for transport in the plasma.
(c) Any two foods with a reason, e.g. wholegrain bread instead of white bread (fibre); fresh fruit such as apples or oranges (fibre and water); dried fruit or nuts (fibre); vegetables (fibre and water).

Also accept

(a) little fibre, so little bulk and food moves slowly; (b) water lost in sweat, which cools her, must be replaced (solvent, transport); (c) two of wholegrain bread, fresh fruit, dried fruit, nuts, vegetables, each with fibre or water

Watch for

“She became constipated because she ate too much food.” — The amount is not the problem: her food has almost no fibre, so it has too little bulk to keep moving through the gut.
“She only needs water when she feels thirsty, because water gives no energy.” — Water releases no energy, but she loses some every day, and the body needs it as a solvent, for transport in the plasma and for cooling by sweat.