This mini-lesson covers the CCEA topic Nutrition & health: a balanced diet and its food groups, food tests (Benedict's, iodine and Biuret), enzymes and how they are denatured, the digestive system and its enzymes, how villi are adapted for absorption, and diet-related health including BMI.
Make a guess: how can you tell glucose, starch and protein apart?
Mission 1What colour would each powder turn?
Mission 2Why is your small intestine lined like a towel?
Mission 3Same mass: healthy for one, risky for another?
Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you're ready.
Nutrition · balanced diet
A balanced diet
A balanced diet contains the right amount of each food group. You should know seven components and what each is for:
Carbohydrates — the body's main source of energy (e.g. bread, pasta, rice).
Proteins — for growth and repair of cells and tissues (e.g. meat, fish, eggs).
Fats / lipids — a concentrated energy store and insulation (e.g. butter, oils).
Vitamins — needed in small amounts for health (e.g. vitamin C, vitamin D).
Minerals — e.g. iron (for haemoglobin), calcium (for bones and teeth).
Water — needed for reactions and to transport substances.
Fibre (roughage) — not digested; keeps food moving through the gut and prevents constipation.
Watch out:fibre and water are part of a balanced diet even though they aren't broken down for energy. Your energy needs change with age, sex/gender and activity level (occupation).
Quick check
Which food group?
?A teenager is growing quickly and needs to build new muscle tissue. Which food group is most important for growth and repair?
Nutrition · food tests · practical
Food tests — reagents & colour changes
CCEA expects you to memorise each test's reagent and its colour change for a positive result:
Extra:DCPIP is used to compare vitamin C content — vitamin C decolourises the blue DCPIP. For fats, the ethanol/emulsion test gives a cloudy white emulsion.
Quick check
Naming the test
?A student adds a reagent to a potato slice and it turns from yellow-brown to blue-black. Which reagent did they use, and what does the result show?
Sort it
Which food test?
Tap a statement, then tap the test it belongs with.
🟦 Benedict's (sugar)
🟫 Iodine (starch)
🟪 Biuret (protein)
Mission 1 check
What colour would each powder turn?
?Three white powders are glucose (a reducing sugar), starch and a protein. Powder X turns iodine blue-black. Powder Y turns Biuret purple. Which test and result would show that powder Z is glucose?
Mission 2 of 3
Why is your small intestine lined like a towel?
Make a guess: why is your small intestine lined like a towel?
Nutrition · enzymes
Enzymes & denaturation
Enzymes are biological catalysts — they speed up reactions and are not used up. They are proteins. Digestive enzymes break large insoluble food molecules into small soluble ones that can be absorbed.
Each enzyme has an optimum temperature and pH. Above the optimum the enzyme is denatured and the rate falls steeply to zero.
Denaturation: at high temperature (or the wrong pH) the enzyme's active site changes shape, so the substrate no longer fits and the reaction stops. This change is permanent — the enzyme cannot recover.
Quick check
Too hot to work
?An enzyme is heated well above its optimum temperature and stops working. What has happened to it?
Nutrition · digestive enzymes
Digestive enzymes & their products
Each food group is broken down by its own enzyme into small, soluble products:
Carbohydrases (e.g. amylase) break starch/carbohydrates into sugars.
Proteases break proteins into amino acids.
Lipases break fats/lipids into fatty acids and glycerol.
Why break food down? Large food molecules are insoluble and too big to be absorbed. Enzymes turn them into small soluble molecules that can pass through the gut wall into the blood.
Quick check
Enzyme & product
?Which enzyme digests protein, and what does it produce?
Nutrition · the digestive system
The alimentary canal
Food travels through the gut, with each part doing a specific job:
Mouth → oesophagus → stomach → small intestine (ileum) → large intestine (colon) → rectum & anus. Bile (from the liver) and pancreatic enzymes enter the duodenum.
Colon (large intestine) — absorbs water; rectum & anus store and remove faeces.
Bile: it is not an enzyme. It emulsifies fats — breaking them into small droplets to give a bigger surface area for lipase to work on.
Quick check
Absorbing water
?After food has been digested and its nutrients absorbed, in which part of the gut is most of the remaining water absorbed?
Nutrition · absorption
Villi — adapted for absorption
The lining of the ileum is folded into millions of finger-like villi. Their features make absorption fast and efficient:
A villus: large surface area, thin lining, good blood supply, and a lacteal for fats.
Finger-like shape + folds → very large surface area for absorption.
Single layer of surface cells → short diffusion distance (thin, permeable membrane).
Capillary network → good blood supply carries molecules away, keeping the gradient steep.
Lacteal → absorbs the products of fat digestion.
Quick check
Why finger-like?
?Villi are finger-like and there are millions of them. What is the main advantage of this shape for absorption?
Mission 2 check
Why is your small intestine lined like a towel?
?An illness flattens the villi in a person's small intestine. They still eat a healthy diet, but they start to lose weight. What is the most likely reason?
Mission 3 of 3
Same mass: healthy for one, risky for another?
Make a guess: how can 80 kg be healthy for one person, risky for another?
Nutrition · diet & health
Diet, health & BMI
An unbalanced diet harms health. Too much saturated fat/cholesterol and too much energy can lead to obesity, type 2 diabetes, coronary heart disease and high blood pressure. Too little fibre causes constipation and bowel problems.
BMI = mass (kg) ÷ height (m)²BMI is a measure of whether someone is a healthy weight
Worked example — BMI
A person has a mass of 72 kg and a height of 1.5 m.
height² = 1.5 × 1.5 = 2.25
BMI = 72 ÷ 2.25 = 32
Tip: square the height first, then divide the mass by it. Never divide by the height on its own.
Calculate
Your turn — BMI
1A person has a mass of 80 kg and a height of 2 m. Calculate their BMI.