5 high-yield, syllabus-aligned questions on Nutrition & digestion, covering 16 individually creditable mark points. Each one shows the answer that scores full marks under our guide, which phrase earns which mark, and a common incomplete answer — so you can see the difference rather than guess at it.
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Every question and solution is reviewed by examiners versed in WAEC and JAMB, each with more than thirty years of experience.
Mark allocations are TopMarks’ own, written against the published syllabus and Chief Examiners’ reports. They are a guide to how these answers are usually credited, not an official marking scheme.
Define2 marks
Define digestion.
TopMarks model answer
Digestion is the breakdown of large, insoluble food molecules into small, soluble molecules that can be absorbed into the bloodstream.
Suggested marking guide
1From large/insoluble to small/soluble molecules
2So that they can be absorbed
Why it scores
Both halves of this definition are load-bearing. The first mark is for the change of STATE — large and insoluble becoming small and soluble. The second is for the PURPOSE — absorption. A definition that says only “food is broken down” describes chewing as much as digestion and earns nothing.
A common incomplete answer
“Digestion is when food is broken down in the stomach.”
What it costs: Nothing. It names neither the change from insoluble to soluble nor the purpose of absorption, and it wrongly confines digestion to the stomach.
Key ideas to include: insoluble, soluble, molecules, absorbed, bloodstream.
State4 marks
State four characteristics of enzymes.
TopMarks model answer
Enzymes are proteins. They act as catalysts, speeding up reactions without themselves being used up. They are specific, each acting on only one substrate. They are denatured by high temperature and work best at an optimum pH.
Suggested marking guide
1They are proteins
2They are catalysts and are not used up
3They are specific
4Affected by temperature and pH
Why it scores
Four marks, four separate properties. “Specific” is the one candidates most often omit, and it is the property that distinguishes an enzyme from any other catalyst — so it is the one the examiner most wants to see.
A common incomplete answer
“They speed up reactions and they are made of protein.”
What it costs: Two marks of four. Both statements are correct and credited, but specificity and sensitivity to temperature and pH are missing.
Explain why the small intestine is well adapted for absorption.
TopMarks model answer
The small intestine is very long and its inner surface is folded into millions of villi, giving a very large surface area for absorption. The wall of each villus is one cell thick, so the diffusion distance is short. Each villus contains a dense network of blood capillaries which carries absorbed glucose and amino acids away, keeping the concentration gradient steep. Each villus also contains a lacteal, which absorbs the fatty acids and glycerol from fat digestion.
Suggested marking guide
1Villi give a large surface area
2Wall one cell thick / short diffusion distance
3Rich capillary network maintaining the gradient
4Lacteal absorbs the products of fat digestion
Why it scores
The lacteal is the mark that separates a good answer from a full one. Most candidates give surface area, thin walls and blood supply, then stop — and lose the fourth mark because they have described the absorption of sugars and amino acids only. Fats are absorbed by a different vessel, and the examiner is waiting for it.
A common incomplete answer
“It has villi which give a large surface area for absorption.”
What it costs: One mark of four. True and credited, but three further adaptations were available and none was attempted.
Key ideas to include: villi, microvilli, one cell thick, capillary network, lacteal, concentration gradient.
State3 marks
State three functions of bile in digestion.
TopMarks model answer
Bile emulsifies fats, breaking large fat droplets into small droplets and so increasing the surface area on which lipase can act. It neutralises the acidic chyme from the stomach and provides the alkaline medium in which pancreatic and intestinal enzymes work. It also aids the absorption of fats and of the fat-soluble vitamins.
Suggested marking guide
1Emulsifies fats to increase surface area
2Neutralises stomach acid and gives an alkaline medium
3Aids absorption of fats and fat-soluble vitamins
Why it scores
Bile contains NO enzyme. That single fact is what this question is really testing. Emulsification is a physical process, not digestion — so an answer that says “bile digests fat” is not a clumsy version of the right answer, it is the wrong answer, and it earns nothing.
A common incomplete answer
“Bile digests fat in the small intestine.”
What it costs: Nothing. Bile has no digestive enzyme; it emulsifies fat so that lipase can digest it. Saying bile digests fat tells the examiner the distinction has not been understood.
Explain why proteins are described as body-building foods.
TopMarks model answer
Proteins are digested to amino acids, which are absorbed and used by the cells to build new protoplasm. They are therefore needed for the growth of new tissues and for the repair of worn-out or damaged tissues. Amino acids are also used to make enzymes, hormones and antibodies.
Suggested marking guide
1Digested to amino acids used to build protoplasm
2Needed for growth and repair of tissue
3Used to make enzymes, hormones and antibodies
Why it scores
The word “explain” means the amino acids must appear. “Protein is for growth and repair” is a statement recalled from a textbook; naming amino acids as the absorbed units that build protoplasm is the biology, and it is where the first mark lives.
A common incomplete answer
“Proteins are used for the growth and repair of the body.”
What it costs: One mark of three. It is the right idea but no mechanism: no amino acids, and no mention of enzymes, hormones or antibodies.
Reading a full-mark answer is the first half. Writing one under time is the other. A free account opens exam-standard practice in Biology with the full solution on every question.