What nutrients does the human body need, and how do we test foods for them?
List the main nutrient groups and their functions, describe a balanced diet, and carry out the food tests for starch, glucose, protein and fat
A focused N(A)-Level answer on nutrition. The main nutrient groups and their jobs, what a balanced diet means, and the food tests for starch, glucose, protein and fat.
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What this dot point is asking
SEAB wants you to list the main nutrient groups and their functions, to describe what a balanced diet is, and to carry out the standard food tests. The central idea is that the body needs a range of nutrients in the right amounts, and simple chemical tests can show which nutrients a food contains.
The answer
The main nutrient groups
A healthy diet provides several nutrient groups, each with a job:
- carbohydrates: the body's main source of energy (for example rice and bread),
- fats: an energy store and insulation (for example oil and butter),
- proteins: needed for growth and repair of cells (for example meat, fish and beans),
- vitamins and minerals: needed in small amounts to keep the body working (for example vitamin C and calcium),
- water: needed for many processes and to transport substances,
- fibre (roughage): not digested, but adds bulk and keeps food moving through the gut.
A balanced diet
A balanced diet contains all these nutrient groups in the right proportions for a person's needs. Eating too much energy food (carbohydrates and fats) without using it can lead to becoming overweight, while too little of a nutrient can cause a deficiency. Needs change with age, sex and how active a person is.
The food tests
You should know four tests, each with its reagent and positive colour change:
- starch: add iodine solution. Orange-brown to blue-black shows starch.
- glucose (a reducing sugar): add Benedict's solution and heat. Blue to brick-red (orange) shows glucose.
- protein: add biuret solution. Blue to purple (violet) shows protein.
- fat: rub on paper or use the emulsion test. A permanent translucent (greasy) mark on paper shows fat.
Examples in context
Example 1. Why athletes eat extra carbohydrate before a race. Carbohydrates are the body's main energy source, so athletes eat carbohydrate-rich meals to build up energy stores before a long event. This gives them the fuel they need for sustained effort.
Example 2. Why growing children need plenty of protein. Protein is used for growth and repair of cells. Children are building new tissue as they grow, so they need a good supply of protein from foods such as milk, eggs, fish and beans.
Try this
- Cue. Name the nutrient group that is the body's main energy source. Carbohydrates.
- Cue. State the reagent and positive colour for the glucose test. Benedict's solution, heated; blue to brick-red.
- Cue. Explain why water is part of a balanced diet. It is needed for many body processes and to transport substances around the body.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original4 marks(a) Name the food test for protein and state the colour change for a positive result. (b) Name the food group needed mainly for growth and repair.Show worked answer →
(a) The biuret test is used for protein. Biuret solution turns from blue to purple (violet) if protein is present.
(b) Protein is needed mainly for growth and repair.
What markers reward: the biuret test with the blue to purple colour change, and protein as the nutrient for growth and repair.
Original3 marks(a) State two nutrient groups that provide the body with energy. (b) Explain why fibre is part of a balanced diet even though it is not digested.Show worked answer →
(a) Carbohydrates and fats both provide energy.
(b) Fibre adds bulk to the food in the gut and helps keep it moving, preventing constipation, even though it is not digested or absorbed.
What markers reward: carbohydrates and fats as energy sources, and fibre helping move food through the gut to prevent constipation.
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