Cambridge O Level Biology · Syllabus 5090 · Human Nutrition
Nutrient
What is Nutrient?
A substance in food that the body requires for energy, for growth and repair, or for the correct working of its processes. Carbohydrates, lipids and proteins are required in large amounts; vitamins and mineral ions are required in small amounts. Dietary fibre and water are required too, although neither is a nutrient in the strict sense because neither is absorbed and used in the same way.
This definition is part of the Human Nutrition chapter in Cambridge O Level Biology.
Nutrient in context
Human nutrition is the study of how food is taken in, broken down and used. A balanced diet supplies every required nutrient, plus fibre, water and energy, in suitable proportions. Digestion converts large, usually insoluble food molecules into small soluble ones. Absorption moves those small molecules through the wall of the intestine into the blood or lymph. Assimilation is what the body's cells then do with them. Material that was never digested leaves the body unchanged as faeces — that is egestion, and it is not excretion.
Common mistakes with Nutrient
- “A balanced diet is the same for everyone.” Why it is wrong Requirements change with age, biological sex, activity level, pregnancy, state of health and body size. A balanced diet for a six-year-old is not a balanced diet for an adult doing heavy manual work. Write instead "A balanced diet supplies all the required nutrients, plus fibre and water, in suitable proportions for that person."
- “All nutrients enter the blood in the same way.” Why it is wrong Water enters by osmosis; glucose and ions enter by diffusion when a gradient allows and by active transport when it does not; the products of lipid digestion enter the lacteal, not a blood capillary. Write instead Name the process that fits the substance in the question, and say why that process is the one required.
Questions students ask about Nutrient
Is fibre a nutrient?
Not in the strict sense: fibre is not digested, not absorbed and supplies no energy. It is still required in the diet, because it adds bulk that the muscles of the gut can grip, keeping material moving and preventing constipation. A definition of a balanced diet that leaves out fibre and water is incomplete.