Answers · A balanced diet

A balanced diet — answer key

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

1. BQ1 · Practice

Model answer. A balanced diet contains all the nutrients the body needs (carbohydrates, fats and oils, proteins, vitamins, mineral ions, fibre and water), each in the right amount: not too little and not far more than needed. Equal amounts would not be right: the body needs far more carbohydrate than vitamin C.

A full answer includes

A diet that contains all the nutrients the body needs, in the right amounts.

Also accept

all the nutrients, in the right amounts

Watch for

“A balanced diet has equal amounts of every nutrient.” — The body needs very different amounts: far more carbohydrate than vitamin C. "Balanced" means each in the right amount.
“A balanced diet means lots of fruit and vegetables.” — Fruit and vegetables are part of it, but a balanced diet has all the nutrients, including protein, fat and calcium.
“A balanced diet must be made only of fresh foods.” — Frozen, tinned and dried foods can be part of a balanced diet, as in the polar station's crate. What matters is every nutrient in the right amount.

2. BQ2 · Practice

Options as numbered on the pupil sheet: 1 — An infection passed between people; 2 — Too little iron; 3 — Too little vitamin C; 4 — Too little vitamin D or calcium.

Model answer. Scurvy is caused by too little vitamin C in the diet. Rickets, in children, is caused by too little vitamin D or too little calcium, so the bones do not harden properly.

A full answer includes

Scurvy: too little vitamin C in the diet.
Rickets: too little vitamin D or calcium.

Also accept

scurvy: too little vitamin C; rickets: too little vitamin D or calcium

Watch for

“Scurvy is caught from other sailors.” — Scurvy is not infectious. It is caused by too little vitamin C in the diet.
“Rickets is caused by too little iron.” — Too little iron affects the blood. Rickets is caused by too little vitamin D or calcium.

3. BQ3 · Practice

Model answer. Scurvy shows in the gums, skin and blood vessels: the gums bleed, wounds heal slowly or open again, and the skin bruises easily. Soft bones that bend are a sign of rickets, constipation comes from too little fibre, and too little iron means too little haemoglobin.

A full answer includes

Bleeding gums.
Wounds that heal slowly or open again.
Skin that bruises easily.

Also accept

bleeding gums, slow-healing wounds, easy bruising

Watch for

“Scurvy makes bones bend.” — Bending bones are a sign of rickets, from too little vitamin D or calcium.

4. BQ4 · Practice

Model answer. Rickets is a disease of children in which the bones are soft and weak, so the legs may bend. It is caused by too little vitamin D or too little calcium. Children who spend little time in sunlight make less vitamin D in their skin.

A full answer includes

g1: bones.
g2: vitamin D.
g3: calcium.
g4: sunlight.

Also accept

bones; vitamin D; calcium (either order); sunlight

Watch for

“Rickets is caused by too little vitamin C.” — Too little vitamin C causes scurvy. Rickets is about bones: vitamin D and calcium.

5. BQ11 · Practice

Model answer. Fibre comes from the walls of plant cells, so only a food that still contains them can fill the gap. Wholegrain crispbread is made from cereal grains and contains plenty of fibre. Salted meat and sardines come from animals and contain no fibre: an extra box of them would add protein, fat or calcium, and still no fibre. Sunflower oil comes from a plant, but it is only the oil pressed from the seeds, with no cell walls, so it contains no fibre.

A full answer includes

A box of wholegrain crispbread: it is made from cereal grains and contains fibre.

Also accept

wholegrain crispbread: a plant food with fibre

Watch for

“Any extra box makes the crate more balanced.” — A gap is only filled by a food that contains the missing nutrient. Meat, fish and oil contain no fibre.
“Fibre is not needed, because it is not digested.” — Fibre adds bulk, so food keeps moving through the gut; without enough of it, constipation follows.

6. BQ5 · Practice

Model answer. Vitamin D would last 6 weeks and calcium 10 weeks, both less than the 16-week winter, so they would run short. Every other nutrient lasts 18 weeks or more, so those are enough.

A full answer includes

Vitamin D (6 weeks) and calcium (10 weeks).

Also accept

vitamin D, calcium

Watch for

“The nutrient with the most weeks is the problem.” — Lots of weeks means plenty. The problems are the nutrients with fewer than 16 weeks.

7. BQ6 · Practice

Model answer. Sardines are an oily fish rich in vitamin D, and their soft bones, eaten with the fish, are rich in calcium, so they fill both gaps. Extra rice and biscuits add carbohydrate, which was already enough; frozen berries add vitamin C, which was not short.

A full answer includes

Add tins of sardines (oily fish eaten with their soft bones): vitamin D and calcium.

Also accept

sardines: vitamin D and calcium

Watch for

“More of any food makes a diet more balanced.” — Only a food that contains the missing nutrients fills a gap.

8. BQ7 · Practice

Model answer. (a) Scurvy is caused by too little vitamin C in the diet. (b) Oranges and lemons are rich in vitamin C, so they supplied the missing vitamin, and the gums and skin could heal. (c) Ship's biscuit and salted meat kept for months, but they contain almost no vitamin C, so after weeks or months at sea with no fresh fruit or vegetables the sailors were getting far too little.

A full answer includes

(a) Too little vitamin C in the diet.
(b) Oranges and lemons are rich in vitamin C, so they supplied what was missing.
(c) Ship's biscuit and salted meat contain almost no vitamin C, so after weeks or months at sea the sailors' diet had too little.

Also accept

(a) too little vitamin C; (b) citrus fruit rich in vitamin C; (c) biscuit and salted meat have almost no vitamin C

Watch for

“Scurvy is caught from other sailors.” — It is caused by the diet, which is why fruit cured it.
“The sailors were short of food.” — They had food every day; it lacked one nutrient, vitamin C.

9. BQ8 · Practice

Model answer. A balanced diet needs every nutrient in the right amount. Rice and meat contain almost no vitamin C, so twice as much of them still leaves vitamin C short, and adds more carbohydrate, protein and fat than the team needs. The gap is only filled by adding foods with vitamin C, such as frozen berries or frozen vegetables.

A full answer includes

Rice and meat contain (almost) no vitamin C, so more of them leaves vitamin C still short.
A balanced diet needs every nutrient in the right amount; more of nutrients that are already enough does not make up for one that is missing.

Also accept

more rice and meat adds no vitamin C; balance needs every nutrient; more of others does not make up for a missing one

Watch for

“More food always means a better diet.” — A diet is balanced only when every nutrient is there in the right amount. More of the same foods does not add a missing nutrient.

10. BQ9 · Practice

Model answer. The two foods together supply 13 + 11 = 24 weeks of vitamin C. That is more than 16 weeks, so vitamin C lasts the winter (and it is less than twice the winter, so it is not far more than needed).

Checked automatically

Weeks of vitamin C: 24 (exact value)
- Common wrong answer 13 : That is the blackcurrants alone. Add the frozen vegetables too.
- Common wrong answer 2 : That is the difference. Each food adds vitamin C, so add the weeks: 13 + 11.

A full answer includes

13 + 11 = 24 weeks.
Enough: 24 weeks is more than the 16-week winter.

Also accept

24 weeks; enough, because 24 is more than 16

Watch for

“The crate supplies the larger number, 13 weeks.” — Each food adds its own weeks, so add them.

11. BQ10 · Practice

Model answer. (a) Vitamin C would last only 3 weeks and fibre 9 weeks, so both run short. (b) It is not a balanced diet: a balanced diet has every nutrient in the right amount, and here two are too little, even though the rest last the winter. (c) Carbohydrate lasts 45 weeks, far more than the team needs; more carbohydrate does not make up for the missing vitamin C and fibre.

A full answer includes

(a) Vitamin C (3 weeks) and fibre (9 weeks).
(b) Not balanced: two nutrients are short, even though the others last the winter.
(c) Carbohydrate (45 weeks, far more than 16).

Also accept

(a) vitamin C, fibre; (b) not balanced, two nutrients too little; (c) carbohydrate

Watch for

“If most nutrients are enough, the diet is balanced.” — A diet is balanced only when every nutrient is there in the right amount.

12. BT1 · Apply

Model answer. (a) Rickets. (b) Vitamin D is made in the skin in sunlight, and this child gets little sunlight, so makes little vitamin D. The child also has no milk or cheese, the main sources of calcium. Too little vitamin D or calcium means the growing bones do not harden properly. (c) For example: spend time outdoors in daylight; eat oily fish or eggs for vitamin D; have a fortified plant drink or cereal with vitamin D and calcium added; eat other calcium-rich foods such as yoghurt, sardines or tofu.

A full answer includes

(a) Rickets.
(b) Little sunlight on the skin, so little vitamin D is made; no milk or cheese, so little calcium in the diet.
(c) Any two of: play outdoors in daylight; eat oily fish or eggs; have a fortified drink or cereal with vitamin D and calcium; eat other calcium-rich foods such as yoghurt, sardines or tofu.

Also accept

(a) rickets; (b) little sunlight so little vitamin D; no dairy so little calcium; (c) two of: daylight, oily fish or eggs, fortified foods, other calcium foods

Watch for

“Rickets is caused by too little vitamin C.” — Too little vitamin C causes scurvy. Rickets comes from too little vitamin D or calcium.
“Vitamin D only comes from food.” — The skin makes vitamin D in sunlight, so time outdoors matters.

13. BT2 · Apply

Model answer. (a) Meat, fish, eggs and dairy foods bring most of the protein, vitamin D and calcium (and much of the fat and some iron), so these are the nutrients most likely to run short. (b) Beans, lentils and nuts are rich in protein, beans and lentils also contain iron, and nuts are rich in fat. Very few plant foods contain vitamin D, so a plant drink fortified with vitamin D and calcium would supply both. Keep the frozen fruit and vegetables for vitamin C and fibre.

A full answer includes

(a) Protein, vitamin D and calcium (also accept fat or iron).
(b) Beans, lentils or nuts for protein (and iron); a fortified plant drink, with vitamin D and calcium added, for vitamin D and calcium.

Also accept

(a) protein, vitamin D, calcium (fat, iron); (b) beans, lentils, nuts for protein and iron (nuts for fat); fortified plant drink for vitamin D and calcium

Watch for

“Every plant drink contains calcium and vitamin D.” — Only a fortified drink, with them added, is a good source.
“A plant-based crate cannot be balanced.” — It can, if it includes foods that supply each nutrient, such as beans and a fortified drink.

14. BT3 · Apply

Model answer. The box would supply plenty of vitamin C and fibre, and some carbohydrate and iron. But fruit and vegetables contain little protein or fat, and almost no vitamin D, and only a little calcium. A balanced diet needs every nutrient in the right amount, so on its own the box is not balanced. It would need, for example, beans or fish for protein, a source of fat, and oily fish or a fortified drink for vitamin D and calcium.

A full answer includes

Fruit and vegetables supply vitamin C, fibre and some carbohydrate (and some iron in dried fruit and leafy vegetables).
They supply little protein, fat, vitamin D or calcium, so the box alone is not a balanced diet: it would need protein foods, a source of fat, and sources of vitamin D and calcium.

Also accept

good for vitamin C and fibre; little protein, fat, vitamin D, calcium; so not balanced alone

Watch for

“A balanced diet means lots of fruit and vegetables.” — Fruit and vegetables are part of a balanced diet, but they do not supply every nutrient.