S2 Science: Digestion And Nutrients (Paper 3 (challenge))

S2 Science: Digestion and Nutrients (Paper 3 (challenge))

2026-11-14

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Tutor Prep Guide · The role of each part of the digestive tract, enzyme action and temperature, bile emulsifying fats, absorption by villi, and food tests for starch, reducing sugars, protein and fat

S2 Science: Digestion and Nutrients (Paper 3 (challenge))

This paper covers energy percentages and gram conversions, pH dilution, BMI, lactose intolerance, and food tests that must be read together.

Direct answers　Grams equal energy divided by kcal per gram, a hundredfold dilution raises pH by 2, BMI is mass over height squared, lactose intolerance means no lactase, and two food tests must be read together.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	20
Difficulty mix	Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1
Chapter	Chapter: S2 Science: Digestion and Nutrients
Level	S2

02　Questions (10 items)

FoundationA teenager takes 2500 kcal a day with 55 percent from carbohydrate. How many grams is that? (carbohydrate gives 4 kcal per gram)
FoundationA 60 kg student needs 0.8 g of protein per kilogram of body mass a day. How many grams, and how many kcal is that?
FoundationFat gives 9 kcal per gram and carbohydrate 4 kcal per gram. How many times denser is fat in energy?
IntermediateGastric juice has a pH of 2. If it is diluted a hundred times, what is the new pH?
IntermediateA student of height 1.6 m weighs 64 kg. What is the BMI?
IntermediateWhat causes lactose intolerance and what symptoms follow?
ChallengeThe small intestine is about 6 m long. How many cm is that, and why does the length help?
ChallengeA drink turns brick red with Benedict solution after heating but shows no colour change with iodine. What does it contain and what not?
ChallengeThree meals of 800 kcal give how many kcal a day? If an extra 3500 kcal is eaten in a week, roughly how much fat is gained? (about 7700 kcal per kg of fat)
Error redoWhich statement is right? A: digestion happens only in the stomach; B: digestion starts in the mouth and is completed mainly in the small intestine.

03　Answers and one-line notes

#	Answer	One-line note
1	1375 kcal, about 343.75 g	2500 times 0.55 gives 1375 kcal, and dividing by 4 gives 343.75 g.
2	48 g, which is 192 kcal	0.8 times 60 gives 48 g, and at 4 kcal per gram 48 times 4 gives 192 kcal.
3	2.25 times	Nine divided by four gives 2.25, so the same mass of fat stores more than twice the energy.
4	About 4	Diluting a hundred times divides the hydrogen ion concentration by a hundred, so pH rises by log10 of 100, which is 2.
5	25.0	BMI is mass divided by height squared, and 64 divided by 2.56 gives 25.0, which is the lower edge of overweight.
6	The small intestine lacks lactase, so undigested lactose is fermented by bacteria in the colon causing bloating, pain and diarrhoea	Lactose that is never split cannot be absorbed, so it stays in the gut, draws in water and produces gas.
7	600 cm, and the length plus the villi give an enormous absorbing area and enough time to absorb nutrients	Six times a hundred gives 600 cm; the length gives time and the villi give area, so absorption is efficient.
8	It contains reducing sugar and no starch	Read both tests together: a positive result is a colour change and a negative one means the substance is absent.
9	2400 kcal a day, and the extra 3500 kcal is about 0.455 kg of fat	Three meals give 2400 kcal, and 3500 divided by 7700 gives 0.455 kg.
10	B is right	The mouth chews and starts starch digestion, the stomach mainly digests protein, and most chemical digestion and absorption happen in the small intestine.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

For digestion questions ask three things: whether the question is about structure, an enzyme or a nutrient, which part of the tract the reaction happens in, and whether the colour change of a food test is being used.Tutor Registration →

Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.