Why does fat store the most energy per gram?

Fat is rich in hydrogen, so oxidising one gram releases about 39 kJ, more than carbohydrate.

What does bile do in digestion?

Bile emulsifies large fat droplets into small ones, raising the surface area for lipase, and contains no enzyme.

S4 Biology: Nutrition and Digestion Paper 1 (teeth, energy and enzymes)

2026-11-03

S · 4

Nutrition and digestion break large molecules into absorbable units and then account for the energy released.

Quick answer　20 teeth; 1,750 kJ; 780 kJ; maltose; 64.6 g; a millionfold; 1,071 kJ; 2.29 times; 1,000 times; bile has no lipase.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10 questions
Suggested time	25 minutes
Difficulty mix	Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1
Chapter	Chapter: S4 Biology: Nutrition and Digestion
Level	S4

02　Questions (10 items)

FoundationAn adult has 32 teeth, of which 8 are incisors and 4 are canines. How many premolars and molars are there?
FoundationA breakfast has 60 g carbohydrate, 20 g protein and 10 g fat. Taking 17 kJ per gram for carbohydrate and protein and 39 kJ per gram for fat, what energy does it give?
FoundationHow much energy is released when 10 g of fat is fully oxidised at 39 kJ per gram?
FoundationInto which sugar does salivary amylase break down starch?
IntermediateA person needs 8,400 kJ a day and fat should supply 30% of it. How many grams of fat is that, to one decimal place?
IntermediateGastric juice has pH about 2 and pancreatic juice about pH 8. By what factor do their hydrogen ion concentrations differ?
IntermediateA meal contains 90 g of protein and 30% passes out unabsorbed. How much energy does the absorbed part supply at 17 kJ per gram?
ChallengeFat gives 39 kJ per gram and carbohydrate 17 kJ per gram. How many times more energy does the same mass of fat supply, to two decimal places?
ChallengeBile breaks one oil drop of diameter 1 mm into droplets of diameter 1 µm. Assuming the total volume is unchanged, by what factor does the total surface area increase?
Error redoA student writes that bile contains lipase and splits fat directly into fatty acids and glycerol. What is wrong?

03　Answers and one-line notes

#	Answer	One-line note
1	20 teeth	Subtracting 8 and 4 from 32 leaves 20, which is 8 premolars plus 12 molars.
2	1,750 kJ	Sixty grams of carbohydrate gives 1,020 kJ, 20 g protein 340 kJ and 10 g fat 390 kJ, so 1,750 kJ in total.
3	780 kJ	Ten grams times 39 kJ per gram gives 780 kJ.
4	Maltose	Amylase cuts starch into the disaccharide maltose, not glucose.
5	64.6 g	Thirty per cent of 8,400 kJ is 2,520 kJ, which divided by 39 gives 64.6 g.
6	a million times	Each pH unit is a tenfold change, so six units means 10 to the power 6.
7	1,071 kJ	Seventy per cent of 90 g is 63 g, and 63 times 17 gives 1,071 kJ.
8	2.29 times	Thirty-nine divided by 17 gives 2.29, so equal masses of fat supply about 2.29 times the energy.
9	1,000 times	A thousandfold smaller diameter means a billionfold more droplets for the same volume, so the total surface area rises a thousandfold.
10	Bile contains no enzyme; it only emulsifies fat, and lipase comes from pancreatic juice.	Bile acts physically by emulsifying, while the lipase that hydrolyses the ester bonds is secreted by the pancreas.

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.

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