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What makes a balanced diet, how do we test for food groups, and how do enzymes digest our food?

The components of a balanced diet and their functions, the chemical food tests, enzymes as biological catalysts affected by temperature and pH, the digestive enzymes amylase, protease and lipase, the role of bile, and absorption in the small intestine.

A focused CCEA GCSE Single Award Science answer on nutrition and digestion, covering the components of a balanced diet, the chemical food tests, enzymes as catalysts affected by temperature and pH, the three digestive enzymes, the role of bile, and absorption in the small intestine.

Generated by Claude Opus 4.89 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this dot point is asking
  2. A balanced diet
  3. Food tests
  4. Enzymes as biological catalysts
  5. The digestive enzymes and bile
  6. Examples in context
  7. Try this

What this dot point is asking

CCEA wants you to know the components of a balanced diet and their functions, the chemical food tests, how enzymes work as biological catalysts and how temperature and pH affect them, the three digestive enzymes, the role of bile, and how the small intestine is adapted for absorption.

A balanced diet

Eating too much energy-rich food without exercise causes obesity, raising the risk of heart disease and type 2 diabetes. Eating too little of a nutrient causes a deficiency: too little vitamin C causes scurvy and too little iron causes anaemia.

Food tests

Nutrient Reagent Positive result
Starch Iodine solution Orange-brown to blue-black
Reducing sugar Benedict's solution, heated Blue to brick-red precipitate
Protein Biuret reagent Blue to purple or lilac
Fat Ethanol then water Cloudy white emulsion

Enzymes as biological catalysts

Enzymes are affected by two main factors:

  • Temperature. Warming up to an optimum (about 37 degrees in humans) speeds the reaction because particles collide more often and harder. Above the optimum the enzyme denatures: the active site changes shape so the substrate no longer fits, and the reaction stops.
  • pH. Each enzyme has an optimum pH. Stomach protease works best in acid; small-intestine enzymes work best in slightly alkaline conditions. The wrong pH also denatures the enzyme.

The digestive enzymes and bile

Enzyme Substrate Products Made in
Amylase Starch Maltose Salivary glands, pancreas
Protease Protein Amino acids Stomach, pancreas
Lipase Fats Fatty acids and glycerol Pancreas

The small, soluble products are absorbed in the small intestine, which is lined with millions of villi: a large surface area, thin walls and a good blood supply for fast absorption.

Examples in context

Example 1. Why emulsifying fat speeds up digestion. A large drop of fat has a small surface area, so lipase can only act on the outside. Bile emulsifies the fat into many tiny droplets, hugely increasing the total surface area exposed to lipase, so the fat is broken down much faster. This is the surface-area-to-volume idea that appears throughout biology, applied to digestion.

Example 2. Reading an enzyme graph. A graph of amylase activity against temperature rises to a peak at about 37 degrees, then falls steeply. The rise is because warming gives more frequent, more energetic collisions between enzyme and substrate. The fall is because the heat breaks the bonds holding the enzyme's shape, denaturing the active site. Recognising that the curve has a clear peak, not a steady rise, is exactly what CCEA tests in enzyme data questions.

Try this

Q1. State the products of the digestion of fats by lipase. [1 mark]

  • Cue. Fatty acids and glycerol.

Q2. Explain why a high temperature stops an enzyme working. [2 marks]

  • Cue. The enzyme denatures; its active site changes shape so the substrate no longer fits.

Exam-style practice questions

Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

CCEA SAS 20194 marksName the reagent and the positive result for the food tests for starch and for reducing sugar.
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Four marks for two reagents and two correct colour changes.

Starch: add iodine solution. A positive result is a colour change from orange-brown to blue-black.

Reducing sugar: add Benedict's solution and heat in a water bath. A positive result is a colour change from blue to a brick-red precipitate.

Markers reward each reagent named and each positive colour change. A common error is forgetting that Benedict's must be heated, and giving the wrong colour for starch.

CCEA SAS 20215 marksDescribe an experiment to investigate the effect of temperature on the activity of an enzyme, and state what you would expect to happen.
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Five marks for the method, the measured variable and the expected pattern.

Method: mix the enzyme, for example amylase, with its substrate, starch, at a set temperature using a water bath. Take drops at intervals and add to iodine to see when the starch has all been broken down, or time how long the reaction takes.

Repeat at a range of temperatures, for example 10, 20, 30, 40 and 50 degrees Celsius, keeping the volumes and concentrations the same.

Expected results: the rate increases up to an optimum of about 37 degrees, because warming gives more frequent and energetic collisions. Above the optimum the rate falls sharply, because the enzyme denatures and its active site changes shape.

Markers reward a measurable rate, named control variables, the rise to an optimum, and the fall due to denaturing.

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