Example 1: reading a label
A 60 g packet of crisps contains 20 g of fat per 100 g. How much fat is in the packet?
- Fat in 1 g = 20 ÷ 100 = 0.2 g.
- Fat in 60 g = 0.2 × 60 = 12 g.
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IB DemystifiedMYP Sciences
Nutrition and digestion
A plate of daal, roti and vegetables contains everything your body needs to grow, move and stay healthy, but first it must be broken down. Your digestive system, with the help of enzymes, turns food into molecules small enough to enter your blood.
Recommended for MYP 2 · About 3 lessons · Criteria A, B, C and D
On this page
Learning objectives
By the end of this topic you should be able to:
- describe the nutrients in a balanced diet and what each is for
- carry out and interpret food tests
- describe the organs of the digestive system and their jobs
- explain how enzymes digest food and how nutrients are absorbed
- analyse food labels and enzyme data
- discuss healthy eating choices in schools and communities
Before you start
You will use these skills. If any feel shaky, review them first.
- cells and organs (see Cell organisation)
- acids and alkalis (see Acids, alkalis and indicators)
- percentages and scaling amounts
Key vocabulary
- Nutrient
- A substance in food that the body needs, such as protein or vitamins.
- Balanced diet
- Eating the right amounts of all the nutrients.
- Digestion
- Breaking large food molecules into small, soluble ones.
- Enzyme
- A protein that speeds up digestion (for example amylase, protease, lipase).
- Absorption
- Taking digested nutrients from the small intestine into the blood.
- Deficiency disease
- An illness caused by a lack of a nutrient, such as scurvy or anaemia.
Understanding the ideas
-
What is it?
Food provides energy and materials. Carbohydrates and fats give energy; proteins build and repair the body; vitamins and minerals keep us healthy; fibre keeps food moving; water is needed for every process.
-
Why does it happen?
Large food molecules cannot pass into the blood, so they are digested by enzymes: amylase breaks starch into sugars, protease breaks proteins into amino acids, and lipase breaks fats into fatty acids and glycerol. The small intestine, lined with villi, absorbs the products into the blood.
-
How do we know?
Simple food tests show which nutrients a food contains, and experiments with enzymes show how temperature and pH affect digestion. Nutrition labels tell us how much of each nutrient is in packaged food.
-
Why does it matter?
Poor diets can cause deficiency diseases, such as anaemia, or obesity and diabetes. Choices about school food and adding nutrients to flour can improve the health of whole communities.
-
What does it connect to?
Nutrition links to cells, enzymes, respiration and the circulatory system in biology, and to acids and chemical tests in chemistry.
Food tests
- Starch: iodine solution turns from orange-brown to blue-black.
- Sugars (such as glucose): heat with Benedict's solution; blue turns green, yellow or orange-red.
- Protein: biuret solution turns from blue to purple.
- Fat: shake with ethanol, then add water; a cloudy white layer forms.
- Vitamin C: blue DCPIP solution loses its colour.
Nutrition in the real world
Pakistan and many other countries add iron and folic acid to flour to prevent anaemia. Oral rehydration solution, a simple mix of salts and sugar in water, saves millions of lives from diarrhoea. Food labels help families compare fat, sugar and fibre.
Worked examples
Example 2: an enzyme
Which enzyme digests the protein in daal, and what are the products?
- Protease digests protein.
- The products are amino acids, which are absorbed in the small intestine.
Assessment tips
Nutrition questions often use food labels, diagrams and enzyme experiments. Expect to:
- Describe nutrients, their sources and what they are for.
- Interpret food test results and nutrition labels.
- Explain digestion and absorption using enzymes and villi.
- Analyse enzyme data and plan fair tests.
Common mistakes: confusing digestion with absorption; saying enzymes are killed instead of denatured; mixing up which food test finds which nutrient; and forgetting that fibre is not digested.
Check your understanding
Quick questions on the ideas above. Try each one before using a hint.
Practice questions
Investigation: testing foods for nutrients
Partially guided investigation · about 50 minutes · pairs
- Research question
- Which nutrients (starch, sugar, protein and fat) are present in five common foods: bread, milk, lentils, apple and cooking oil?
- Scientific background
- Each nutrient gives a colour change with its own test reagent, so we can find out what a food contains.
- Hypothesis
- Write your own prediction, with a scientific justification.
- Variables
- Identify your independent, dependent and control variables, and explain how you will control them.
- Apparatus
- Small samples of each food, mortar and pestle, test tubes, iodine solution, Benedict's solution, biuret solution, ethanol, water bath at about 80 °C, dropping pipettes.
- Method
- Grind a small amount of each food with a little water.
- Test a sample with iodine (starch), Benedict's with heating (sugar), biuret (protein) and ethanol then water (fat).
- Record the colour or change for each test.
- Draw a table showing which nutrients each food contains.
Safety. Wear eye protection. Benedict's and biuret solutions are irritants; ethanol is flammable, so keep it away from the hot water bath and flames. Do not eat any food in the laboratory.
Then evaluate: which of your results were hardest to judge, and how could you make the tests more reliable?
Criterion-linked questions
Criterion B: inquiring and designing
Criterion C: processing and evaluating
Criterion D: reflecting on the impacts of science
Challenge questions
Harder problems in unfamiliar contexts. Plan before you calculate.
Topic check
Five questions picked at random from the whole topic. Take a new set whenever you like.
Review your mistakes
Questions you got wrong on this device appear here so you can try them again. Answer one correctly and it leaves the list.
Your progress
Tracked separately for each skill, on this device only.
| Skill | Correct | Status |
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