State the functions, sources and deficiency effects of key minerals, and explain the importance of water in the diet

What this dot point is asking

The syllabus wants you to know why the body needs certain minerals, focusing on calcium and iron, and to explain why water, although it provides no energy, is an essential nutrient. The key idea is that minerals are needed in small amounts for specific jobs such as building bones and carrying oxygen, and that water is needed in large amounts for almost every process in the body.

The answer

What minerals are

Minerals are inorganic nutrients needed in small amounts for specific functions. The three you should know best for O-Level are calcium, iron and sodium.

Calcium

Function

builds and maintains strong bones and teeth, and helps the blood to clot and muscles to work.

Sources

milk, cheese, yoghurt, small fish eaten with their bones (such as ikan bilis or canned sardines), tofu set with calcium, and dark green leafy vegetables.

Deficiency

weak bones and teeth, leading to rickets in children and osteoporosis (brittle bones) in older adults. Vitamin D is needed to absorb calcium properly.

Iron

Function

iron is needed to make haemoglobin, the red pigment in red blood cells that carries oxygen from the lungs to the rest of the body.

Sources

red meat, liver, egg yolk, dark green vegetables, and pulses.

Deficiency

iron-deficiency anaemia, which causes tiredness, weakness, pale skin and breathlessness because the blood carries less oxygen.

Helping absorption

vitamin C improves the absorption of iron, especially from plant foods, so eating a vitamin-C food (such as fruit) with an iron-rich meal increases the iron the body takes up.

Sodium

Sodium, from salt, helps control the body's water balance and is needed for nerve and muscle function. The problem in most diets is too much, not too little: a high salt intake raises blood pressure, increasing the risk of heart disease and stroke. Cutting back on salty foods and added salt is a common health recommendation.

Why water is an essential nutrient

Water gives no energy, but it makes up about two-thirds of the body and is needed constantly:

• Transport: the blood is mostly water and carries nutrients, oxygen and waste around the body.
• Temperature control: sweating uses water to cool the body.
• Digestion and excretion: water is needed for digestive juices and to remove waste as urine.

The body loses water in urine, sweat and breath, so it must be replaced by drinking fluids and from the water in food. Not drinking enough causes dehydration, shown by thirst, headache, tiredness and dark urine. In Singapore's hot, humid climate, fluid needs are higher, especially during exercise.

Examples in context

Example 1. Ikan bilis and small fish. Eaten whole with their soft bones, ikan bilis and canned sardines are excellent calcium sources, valuable for children building bones and for older adults guarding against osteoporosis. They show that calcium does not only come from dairy, which matters for people who avoid milk.

Example 2. Spinach with a squeeze of lime. Dark green spinach provides plant (non-haem) iron, which the body absorbs less easily than meat iron. Finishing the dish with lime, a vitamin-C source, raises the amount of iron absorbed, a simple kitchen technique grounded in the iron and vitamin-C link.

Try this

• Cue. State the function, a source and the deficiency for calcium and for iron. Recall calcium for bones and teeth (weak bones) and iron for haemoglobin (anaemia), with dairy and red meat as example sources.
• Cue. Explain how a person could increase the iron they absorb from a vegetarian meal. Add a vitamin-C food and avoid tea or coffee with the meal.
• Cue. Give three reasons the body needs water and one sign of dehydration. Recall transport, temperature control and digestion/excretion, with dark urine or thirst as a sign.