IB MYP Sciences – Metabolism Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – the IB holds copyright in its own papers. Use these alongside the official past papers available through your school or the IB store.

These practice questions cover metabolism for IB MYP Sciences, aligned to the International Baccalaureate Organization, Middle Years Programme Subject Brief – Sciences, from 2014, which lists “metabolism” among the on-screen examination topics. MYP Sciences has no SL/HL split, and the set suits MYP years 4 and 5. The MYP has no prescribed content list – schools design their own units – so your teacher will share the task-specific clarifications for assessed work.

Each question is labelled with the criterion it trains. Real MYP work is judged against criterion level descriptors (eight achievement levels, 1–8, in four bands), so the [1] points below are a revision aid, not IB marks. All data are fictional.

Related: metabolism study guide · metabolism revision notes · MYP Sciences hub · printable checklist · criteria in practice questions

Questions

1. (Criterion A) Define the term enzyme and name the part of an enzyme that the substrate binds to. [2]

2. (Criterion A) Write the word equation for aerobic respiration and state the part of the cell where most of it happens. [3]

3. (Criterion A) Compare anaerobic respiration in human muscle with anaerobic respiration in yeast. [3]

4. (Criterion A) For each of the following, give the product(s) of digestion: (i) starch by amylase, (ii) protein by protease, (iii) lipid by lipase. Then state one role of bile. [4]

5. (Criterion A) Explain why the rate of an enzyme-controlled reaction rises from 20 °C to 37 °C, then falls sharply at 50 °C. [4]

6. (Criterion A) Give four differences between photosynthesis and aerobic respiration. [4]

7. (Criterion C) A student measured oxygen bubbles per minute from pondweed at six light intensities, in water with a low and a high concentration of dissolved carbon dioxide. Temperature was kept at 25 °C.

Light intensity (arbitrary units)	1	2	3	4	5	6
Low CO₂ / bubbles min⁻¹	8	16	22	24	24	24
High CO₂ / bubbles min⁻¹	8	16	24	32	38	38

(a) Identify the limiting factor at light intensities 1 and 2. Use the data to justify your answer. [2] (b) Identify the limiting factor for the low-CO₂ plant at light intensities 4 to 6. Justify your answer. [2] (c) Calculate the percentage increase in rate at light intensity 6 when carbon dioxide is raised from low to high. Give your answer to 3 significant figures. [2] (d) Suggest one factor that could be limiting the high-CO₂ plant at light intensities 5 and 6. [1]

8. (Criterion B) Design an investigation into how temperature affects the rate of anaerobic respiration in yeast. Yeast, glucose solution, water baths and a gas syringe are available. Include a research question, a hypothesis with a scientific reason, the variables, a method and one safety point. [10]

9. (Criterion C) A student added potato discs to hydrogen peroxide at five concentrations. Catalase in the potato breaks down hydrogen peroxide into water and oxygen. Oxygen was collected for 60 s.

H₂O₂ concentration / %	Trial 1 / cm³	Trial 2 / cm³	Trial 3 / cm³
1	6.2	5.8	6.0
2	11.8	12.4	12.1
3	17.7	18.3	12.0
4	22.9	23.5	23.2
5	24.1	24.6	24.2

(a) Identify the anomalous result and justify your choice. [2] (b) Calculate the mean volume of oxygen at 3% and at 5%. [2] (c) Calculate the mean rate of oxygen production at 5%, in cm³ s⁻¹, to 3 significant figures. [1] (d) Describe the trend in the mean results, using data. [2] (e) Explain why the volume barely increases between 4% and 5%. [2] (f) Suggest one specific improvement to the method. [1]

10. (Criterion C) The time for amylase to break down all the starch in a sample was measured at different pH values.

pH	4	5	6	7	8	9
Time / s	250	125	50	40	80	200

(a) Calculate the rate, as 1000/time, at pH 7 and at pH 8. [2] (b) State the optimum pH shown by these data. [1] (c) Explain why the rate at pH 9 is lower than at pH 7. [2]

11. (Criterion D) Biological washing powders contain enzymes such as proteases and lipases. Evaluate their use, discussing benefits and limitations, and reach a judgment. [7]

Answers

1. A protein that acts as a biological catalyst, speeding up a reaction without being used up [1]. The substrate binds to the active site [1]. Examiner insight: “Catalyst” alone is incomplete – say biological catalyst or protein, or the definition point is not credited.

2. glucose + oxygen [1] → carbon dioxide + water [1]. Mostly in the mitochondria [1]. Examiner insight: Energy is not a product substance; writing “→ energy” as a product in place of water loses the products point.

3. Both release less energy per glucose than aerobic respiration and need no oxygen [1]. Muscle produces lactic acid only [1]. Yeast produces ethanol and carbon dioxide [1]. Examiner insight: “Compare” needs a similarity as well as differences; two differences alone cap the answer below full credit.

4. (i) maltose (then glucose) [1]; (ii) amino acids [1]; (iii) fatty acids and glycerol [1]. Bile emulsifies fats into small droplets, or neutralises stomach acid [1]. Examiner insight: Writing “fatty acids” without glycerol, or calling bile an enzyme, loses the point.

5. From 20 °C to 37 °C, particles have more kinetic energy and collide more often [1], so more enzyme–substrate complexes form per second [1]. At 50 °C, bonds holding the enzyme’s shape break and the active site changes shape [1], so the substrate no longer fits and the enzyme is denatured [1]. Examiner insight: “The enzyme dies” earns nothing; the explanation must link the rate fall to the changed active site.

6. Any four, one point each: photosynthesis is anabolic, respiration catabolic [1]; photosynthesis uses carbon dioxide and water, respiration produces them [1]; photosynthesis happens in chloroplasts, respiration mainly in mitochondria [1]; photosynthesis needs light, respiration happens all the time [1]. Also accept: photosynthesis stores energy, respiration releases it; only cells with chlorophyll photosynthesise, all living cells respire. Examiner insight: Each difference must state both sides; “respiration happens in mitochondria” alone is half a comparison.

7. (a) Light intensity [1]. Rate doubles from 8 to 16 when light doubles, and raising CO₂ makes no difference there [1]. (b) Carbon dioxide concentration [1]. The low-CO₂ rate stays at 24, but the high-CO₂ plant reaches 38 at the same light, so extra CO₂ raises the rate [1]. (c) (38 − 24)/24 × 100 [1] = 58.3% [1]. (d) Temperature, or carbon dioxide concentration still limiting [1]. Examiner insight: Justifications must quote values from the table; “the graph levels off” without numbers is treated as unsupported.

8. Indicative points, one each:

• Research question: How does temperature (20, 25, 30, 35, 40 °C) affect the volume of CO₂ produced in 5 min by yeast in glucose solution? [1]
• Hypothesis: volume rises with temperature up to an optimum, then falls [1], because respiration is controlled by enzymes: collisions increase, then the enzymes denature [1].
• Independent variable: temperature, set with water baths and checked with a thermometer [1].
• Dependent variable: volume of CO₂ in 5 min, read from a gas syringe in cm³ [1].
• Control variables: mass of yeast and concentration and volume of glucose solution, measured the same each time [1]; time and equipment kept the same [1].
• Method: leave yeast and glucose in the bath for 10 min to reach temperature before connecting the syringe [1]; at least five temperatures, three repeats each, calculate means [1].
• Safety: take care with hot water baths; wipe up spills to avoid slips [1]. Examiner insight: A hypothesis without a scientific reason and control variables without a method of control are the two points most often missing in design answers.

9. (a) 12.0 cm³ at 3% [1]; it is far below the other two trials (17.7 and 18.3) and does not fit the trend [1]. (b) 3%: (17.7 + 18.3)/2 = 18.0 cm³ (anomaly excluded) [1]; 5%: (24.1 + 24.6 + 24.2)/3 = 24.3 cm³ [1]. (c) 24.3 ÷ 60 = 0.405 cm³ s⁻¹ [1]. (d) Mean volume rises steadily from 6.0 cm³ at 1% to 23.2 cm³ at 4% [1], then only increases by 1.1 cm³ to 24.3 cm³ at 5% [1]. (e) At high concentration nearly all active sites are occupied at any moment [1], so enzyme amount, not substrate, now limits the rate [1]. (f) e.g. cut discs with a cork borer and scalpel to the same size and mass, so the surface area of catalase exposed is the same each time [1]. Examiner insight: Including the anomaly gives a 3% mean of 16.0 cm³; if you exclude a value you must say so, or the mean is marked wrong.

10. (a) pH 7: 1000/40 = 25.0 [1]; pH 8: 1000/80 = 12.5 [1]. (b) pH 7 [1]. (c) pH 9 is far from the optimum, so the active site changes shape [1]; fewer substrate molecules fit and fewer enzyme–substrate complexes form [1]. Examiner insight: Answers that give the times rather than calculated rates in (a) earn nothing; follow the method the question specifies.

11. Indicative points, one each:

• Benefit: enzymes break down protein and fat stains into small soluble molecules that wash away [1].
• Benefit: they work at lower temperatures, so less energy is used heating water [1].
• Benefit: lower wash temperatures can protect delicate fabrics [1].
• Limitation: enzymes denature at high temperatures, so they are less useful in very hot washes [1].
• Limitation: proteases can damage protein fibres such as wool and silk [1].
• Limitation: some people may have skin irritation or allergic reactions if residue remains [1].
• Judgment: useful for everyday low-temperature washing, but not for protein fabrics or sensitive users [1]. Examiner insight: An evaluation with only benefits, or no final judgment, cannot reach the top of the range however many benefits are listed.

Where marks are usually lost

• “Enzymes die” instead of “enzymes are denatured”.
• Carbon dioxide given as a product of muscle anaerobic respiration.
• Comparisons that describe one process only.
• Graph and table descriptions with no quoted values.
• Anomalies left in means, or removed without comment.
• Hypotheses with no scientific reason.
• Control variables listed without saying how each is controlled.
• Rates given without units (cm³ s⁻¹, bubbles min⁻¹).
• Percentage change divided by the new value instead of the original.
• Evaluations with no final judgment.

Next steps

• Metabolism revision notes
• Metabolism study guide
• MYP Sciences course hub
• Printable MYP Sciences checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

International Baccalaureate Organization, Middle Years Programme Subject Brief – Sciences, from 2014. The brief lists metabolism as an on-screen examination topic and describes the Investigation skills task (criteria B and C, 50 marks).