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This paper covers the whole of Topic 7. Like a real Cambridge paper, the seven questions range across every sub-topic — diet, the digestive system, physical and chemical digestion, and absorption — and they are deliberately mixed rather than grouped. All three Topic 7 papers do; they differ in the angle they come at it from, not in what they cover.
Question 1 — Balanced Diet, Deficiency and the Nutrients That Do No Work
Total: 12 marks
(a)[3]
Define a balanced diet, and state two factors that change how much of it a person needs.
Model Answer — 1(a)
a diet containing all the nutrients required — carbohydrate, fat, protein, vitamins, mineral ions, fibre and water [1]
in the correct amounts and proportions [1]
any two of: age, sex, activity level, body size, pregnancy or breastfeeding [1]
⚠ If you missed marks here: Balanced does not mean equal. A diet is balanced for a particular person, which is why the two factors are worth a mark of their own — a sleeping infant and a footballer can both be eating a balanced diet and be eating nothing alike.
(b)[4]
For vitamin C and for calcium, state one good dietary source and describe its importance in the body.
Model Answer — 1(b)
vitamin C: citrus fruit / blackcurrants / peppers / fresh green vegetables [1]
needed to form the connective tissue that holds cells together — healthy skin, gums and blood vessel walls, and healing of wounds [1]
needed for strong bones and teeth (also for blood clotting and muscle contraction) [1]
⚠ If you missed marks here: Sources have to be foods, not nutrients — “vitamin C is found in vitamin tablets” earns nothing. The importance marks want a job, not a disease: writing “prevents scurvy” describes what happens without it rather than what it does.
(c)[3]
A young child whose diet contains plenty of calcium is kept indoors and develops rickets. Explain this fully.
Model Answer — 1(c)
vitamin D is made in the skin in sunlight, so a child kept indoors makes very little [1]
vitamin D is needed for the absorption of calcium from the small intestine [1]
so the calcium in the diet is not absorbed, cannot be laid down in bone, and the bones stay soft and bend under the child’s weight [1]
⚠ If you missed marks here: The whole answer turns on the word absorption. Vitamin D never becomes part of a bone; it makes the calcium available. An answer that says “vitamin D strengthens bones” misses the mechanism and cannot explain why a calcium-rich diet made no difference.
(d)[2]
Fibre is neither digested nor absorbed. Explain why it is still an essential part of the diet.
Model Answer — 1(d)
it adds bulk to the contents of the alimentary canal, giving the muscles of the gut wall something to grip and push against, so material is moved along [1]
this prevents constipation and keeps the contents moving at a healthy rate [1]
⚠ If you missed marks here: If a molecule cannot be digested it can never be absorbed, and if it is never absorbed it can never be respired — so any answer that has fibre releasing energy contradicts the first line of the question. Fibre’s value is mechanical, not nutritional.
Question 2 — The Alimentary Canal, the Associated Organs and the Five Processes
Total: 12 marks
(a)[4]
Name, in order, the four regions of the alimentary canal through which material passes between the stomach and the anus.
Model Answer — 2(a)
duodenum [1]
ileum [1]
colon [1]
rectum [1]
⚠ If you missed marks here: Cambridge names the two parts of the small intestine and the three parts of the large intestine separately, so “small intestine then large intestine” is worth two marks at best. The order is forced by the biology: digestion is finished in the duodenum before absorption happens in the ileum.
(b)[3]
Name the associated organ that carries out each of these: producing bile; storing bile; secreting a juice containing amylase, protease and lipase.
Model Answer — 2(b)
produces bile: liver [1]
stores bile: gall bladder [1]
secretes the juice: pancreas [1]
⚠ If you missed marks here: Three organs, three different verbs. Writing that the gall bladder makes bile is the standard slip, and it makes the liver’s role in the digestive system disappear entirely. Note also that none of these three organs is part of the alimentary canal — food never passes through any of them.
(c)[3]
Define absorption, assimilation and egestion.
Model Answer — 2(c)
absorption — the movement of nutrients from the intestines into the blood [1]
assimilation — the uptake and use of nutrients by cells [1]
egestion — the removal of undigested food from the body as faeces [1]
⚠ If you missed marks here: Absorption and assimilation are exchanged more often than any other pair in Topic 7. Fix the order in your head: absorbed into the blood, then assimilated into a cell. A nutrient cannot be used by a cell it has not yet reached.
(d)[2]
Explain why the loss of undigested food in the faeces is egestion and not excretion.
Model Answer — 2(d)
excretion is the removal of the waste products of metabolism — substances made by the body’s own chemical reactions [1]
the material in faeces was never absorbed and never entered the cells, so it has taken no part in metabolism [1]
⚠ If you missed marks here: The state of the material is irrelevant — solid does not mean egested. What decides the word is where the material came from. Bile pigment in faeces really is excreted, which is why the mark is for the origin of the material and not for the fact that it leaves through the anus.
Question 3 — Teeth, Churning and the Meaning of “Physical”
Total: 12 marks
(a)[2]
Define physical digestion and state why it is necessary.
Model Answer — 3(a)
the breakdown of food into smaller pieces without any chemical change to the food molecules [1]
it increases the surface area of the food for the action of enzymes in chemical digestion [1]
⚠ If you missed marks here: The phrase “without chemical change” is doing all the work in this definition: a chewed piece of bread is smaller but is still starch. Leave it out and you have written the definition of chemical digestion instead, and then part (a) contradicts everything that follows.
(b)[4]
Describe how the shape of an incisor and the shape of a molar each suit the job that tooth does.
Model Answer — 3(b)
an incisor is chisel-shaped with a sharp straight edge [1]
used for biting or cutting pieces off the food [1]
a molar is broad with cusps or ridges on a large flat surface [1]
used for grinding or chewing the food into small pieces [1]
⚠ If you missed marks here: Each mark needs the structure and the function joined together — naming the tooth and saying “for chewing” leaves half the answer unwritten. Note that canines and molars can never do each other’s job: a point cannot make a clean cut and a flat surface cannot grip.
(c)[4]
Name the part of a tooth that fits each description: the hard non-living layer covering the crown; the region containing the nerves and blood vessels; the living tissue forming the bulk of the tooth beneath that hard layer; the layer covering the root that attaches it to the jaw bone.
Model Answer — 3(c)
enamel [1]
pulp (pulp cavity) [1]
dentine [1]
cement [1]
⚠ If you missed marks here: Enamel and dentine are constantly swapped. Enamel is outside, non-living and cannot repair itself; dentine is inside, living, and forms most of the tooth. If you can remember that a chipped tooth never grows back, you have the enamel mark, because only non-living tissue behaves that way.
(d)[2]
Describe the part the stomach plays in physical digestion.
Model Answer — 3(d)
the muscular wall contracts, churning and mixing the contents [1]
this breaks the food into smaller pieces and mixes it with gastric juice, increasing the surface area for enzymes [1]
⚠ If you missed marks here: The question says physical, so pepsin and hydrochloric acid earn nothing here however correct they are. A very common answer describes everything the stomach does; a mark scheme only credits the part that was asked for.
Question 4 — Amylase, Protease and Lipase — Substrate, Product, Place
Total: 12 marks
(a)[2]
Define chemical digestion and state why it is necessary.
Model Answer — 4(a)
the breakdown of large insoluble molecules into small soluble molecules [1]
only small soluble molecules can be absorbed through the wall of the intestine into the blood [1]
⚠ If you missed marks here: Insoluble to soluble is the point of the whole process. An answer that says food is “broken down” without naming the change in size and solubility is describing what everyone can see rather than what the syllabus asks for.
(b)[6]
For each of amylase, protease and lipase, state the substrate it acts on and the product or products it forms.
Model Answer — 4(b)
amylase acts on starch [1]
forming maltose (a simple reducing sugar) [1]
protease acts on protein [1]
forming amino acids [1]
lipase acts on fats and oils [1]
forming fatty acids and glycerol [1]
⚠ If you missed marks here: Two traps here. Amylase gives maltose, not glucose — the last step is done by maltase on the membranes of the epithelium lining the small intestine. And lipase gives two products; a mark scheme reading “fatty acids and glycerol” will not award half of it.
(c)[2]
State where lipase is secreted and where it acts.
Model Answer — 4(c)
secreted by the pancreas [1]
acts in the small intestine (duodenum) [1]
⚠ If you missed marks here: Cambridge asks for secretion and action separately because for pancreatic enzymes they are different places. Answering “the pancreas” for both is the standard error and it makes the pancreatic duct pointless — nothing is digested inside the pancreas.
(d)[2]
Describe the two functions of the hydrochloric acid in gastric juice.
Model Answer — 4(d)
kills harmful microorganisms taken in with the food [1]
provides the acidic pH at which the enzyme in gastric juice, pepsin, has its optimum activity [1]
⚠ If you missed marks here: The acid does not digest anything itself. Writing “the acid breaks down protein” hands the enzyme’s job to the environment, and it is the reason candidates then cannot explain why the stomach needs pepsin at all.
Question 5 — The Villus — Building a Surface for Absorption
Total: 10 marks
(a)[2]
State the region in which nutrients are absorbed, and describe where water is absorbed.
Model Answer — 5(a)
nutrients are absorbed in the small intestine [1]
most water is absorbed from the small intestine, but some is also absorbed from the colon [1]
⚠ If you missed marks here: The water statement is worded carefully by Cambridge and the two halves are both needed. “Water is absorbed in the colon” is a true sentence that scores nothing, because it leaves out the region where most of the job is done.
(b)[4]
Describe the structure of a villus.
Model Answer — 5(b)
a finger-like projection of the lining of the small intestine, about 1 mm long, present in very large numbers [1]
its wall is a single layer of epithelial cells, whose surfaces carry microvilli [1]
it contains a network of blood capillaries [1]
and a lacteal running up the centre [1]
⚠ If you missed marks here: Describe means give the parts, not the advantages — “it has a large surface area” answers a different question. Notice how many candidates draw the capillaries and forget the lacteal, then cannot answer any question about the fate of digested fat.
(c)[2]
State the role of the blood capillaries and the role of the lacteal in a villus.
Model Answer — 5(c)
capillaries absorb and transport glucose and amino acids (and water-soluble vitamins and mineral ions) away from the intestine [1]
the lacteal absorbs and transports fatty acids and glycerol, the products of fat digestion, into the lymphatic system [1]
⚠ If you missed marks here: Two vessels means two different cargoes, and putting everything into the capillaries makes the lacteal impossible to justify. This is also the reason lymph looks milky after a fatty meal — a detail that makes the answer memorable.
(d)[2]
Apart from surface area, describe two features of a villus that speed up absorption, and explain each.
Model Answer — 5(d)
the wall is only one cell thick, so the diffusion distance into the blood is very short [1]
the rich blood supply carries absorbed nutrients away quickly, keeping their concentration in the blood low and maintaining the concentration gradient [1]
⚠ If you missed marks here: Surface area, diffusion distance and concentration gradient are three separate adaptations, and questions often exclude one to see whether you know the other two. An answer that simply repeats “the villi give a large surface area” ignores the word “apart” and scores nothing.
Question 6 — Reading a Dietary Record
Total: 12 marks
A dietician recorded the mean daily intake of a 15-year-old girl over four weeks and compared it with the recommended values for someone of her age and activity level.
nutrient
recommended per day
her mean intake per day
energy
10 500 kJ
8 200 kJ
protein
45 g
51 g
calcium
800 mg
310 mg
iron
14.8 mg
6.2 mg
vitamin C
40 mg
12 mg
fibre
25 g
9 g
(a)[2]
Calculate her iron intake as a percentage of the recommended value. Show your working and give your answer to the nearest whole number.
Model Answer — 6(a)
working: 6.2 ÷ 14.8 × 100 [1]
= 42 % (41.9 %) [1]
⚠ If you missed marks here: The percentage must be taken of the recommended value, so the recommended figure goes on the bottom. Dividing the other way gives 239 %, which should look wrong immediately — a sanity check on the size of the answer catches this every time.
(b)[4]
Using the table, name two deficiency conditions she is at risk of developing, and for each explain the link between the nutrient and the condition.
Model Answer — 6(b)
anaemia [1]
because iron is needed to make haemoglobin, so less oxygen is carried and she would feel tired [1]
scurvy [1]
because vitamin C is needed to make the connective tissue that holds cells together, so gums bleed and wounds heal slowly [1]
⚠ If you missed marks here: Naming the condition alone earns half the marks. Note also that protein and energy are not the answer here: her protein intake exceeds the recommendation, and a below-target energy intake is a shortfall rather than a named deficiency disease.
(c)[3]
Describe the likely effect of her fibre intake, explain why it happens, and suggest one change to her diet.
Model Answer — 6(c)
she is likely to suffer constipation, as her intake is only about a third of the recommended value [1]
there is too little bulk for the muscles of the gut wall to grip, so material moves along slowly and more water is absorbed from it [1]
suggestion: more wholegrain cereals, fruit and vegetables [1]
⚠ If you missed marks here: The mark for the mechanism needs the word bulk or an equivalent description of the muscles having something to push against. Suggestions must be foods rich in fibre; “eat more fibre” simply repeats the question back.
(d)[3]
She begins taking a calcium supplement but after several months her bones are still weak. Suggest what else may be lacking, and explain fully why the supplement alone did not work.
Model Answer — 6(d)
vitamin D may also be lacking [1]
vitamin D is needed for the absorption of calcium from the small intestine into the blood [1]
without it the extra calcium is not absorbed and is egested in the faeces rather than being laid down in bone [1]
⚠ If you missed marks here: This part is really testing the difference between eating a nutrient and absorbing it. A nutrient that stays in the lumen of the gut has never been inside the body, so it leaves by egestion — and that word, not excretion, is the one the mark scheme wants.
Question 7 — One Slice of Buttered Toast, From Duodenum to Cell
Total: 10 marks
A person eats a slice of buttered toast. Two hours later the partly digested meal passes from the stomach into the duodenum, where it meets bile and pancreatic juice.
(a)[3]
Describe what happens to the fat in the butter in the duodenum, naming the substances involved.
Model Answer — 7(a)
bile emulsifies the fat, breaking large droplets into many small droplets and so increasing the surface area [1]
bile is also alkaline and neutralises the acidic mixture arriving from the stomach, giving a suitable pH for the enzymes [1]
lipase from the pancreas then breaks the fat down into fatty acids and glycerol [1]
⚠ If you missed marks here: Bile has two separate jobs and both are examinable: one physical, one chemical. Candidates who remember only emulsification lose the pH mark, and candidates who remember only the pH lose the surface area mark.
(b)[2]
Explain why bile is described as emulsifying fat rather than digesting it.
Model Answer — 7(b)
bile contains no enzymes, so it cannot catalyse the breakdown of any molecule [1]
it changes the size of the droplets, not the fat molecules themselves, which are unchanged after emulsification [1]
⚠ If you missed marks here: This is the most commonly dropped mark in the whole topic. “Bile digests fat” is refused however good the surrounding answer is. The test to apply is simple: has a molecule been changed? If not, the process was physical.
(c)[3]
Describe the route taken by the products of fat digestion from the contents of the ileum into the transport system of the body.
Model Answer — 7(c)
they pass through the epithelium of a villus, which is only one cell thick [1]
they enter the lacteal in the centre of the villus rather than a blood capillary [1]
the lacteal carries them into the lymphatic system, which eventually empties into the blood [1]
⚠ If you missed marks here: The lacteal is the mark most often lost, because candidates who have only ever drawn capillaries send everything into the blood directly. Glucose and amino acids do go into the capillaries; the products of fat digestion do not.
(d)[2]
Using the toast as your example, distinguish between absorption and assimilation.
Model Answer — 7(d)
absorption: the glucose produced from the starch in the toast moves from the ileum into the blood [1]
assimilation: that glucose is taken up by a cell and used — for example respired in a muscle cell to release energy [1]
⚠ If you missed marks here: An answer that gives the two textbook definitions without applying them to the toast does not answer the question as set. The examiner is checking that you can see the two events happening in sequence to one particular molecule.
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