OCR GCSE Biology A: Material cycling and decomposition in ecosystems (J247) – 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 – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover statements B4.1a to B4.1d of the OCR GCSE (9-1) Gateway Science Biology A specification (J247), Version 4.0: cycling of materials, the role of microorganisms, the carbon and water cycles, and the rate of decomposition. None of these statements is printed in bold, so all questions suit both tiers. Learn the content first from the study guide or the revision notes. Course hub: OCR GCSE Biology. Printable checklist. Try a free diagnostic to find weak topics.

Questions

1. Name two materials that cycle between the abiotic and biotic parts of an ecosystem. [2]

2. Explain the role of microorganisms in the decomposition of a dead tree. [4]

3. A fox eats a rabbit that has eaten grass. Trace the path of one carbon atom from the air into the fox, and describe how it could later get back to the air. [5]

4. The water cycle involves several processes.

(a) Name the process by which plants lose water vapour from their leaves. [1] (b) Explain why precipitation is important to organisms living on land. [3]

5. Suggest what would happen to the growth of producers in a woodland if all the decomposers died. Explain your answer. [4]

6. A bag of straw has a mass of 320 g. After 8 weeks the mass is 224 g.

(a) Calculate the percentage loss of mass. [2] (b) Calculate the mean rate of decay in grams per week. [2] (c) Give the fraction of the original mass that remains, in its simplest form. [1]

7. A student wants to find how temperature changes how fast leaves decay. Describe how the student could carry out the investigation. [6]

8. Samples of 100 g of fallen leaves were kept moist with plenty of air for 10 days at different temperatures. The table shows the mass lost.

Temperature (°C)	5	15	25	35	45	55
Mass lost (g)	3	11	26	41	19	2

(a) Describe how you would plot a graph of these results. [2] (b) Describe the pattern shown by the results. [2] (c) Calculate how many times faster the rate of decay is at 35 °C than at 15 °C. Round your answer to two significant figures. [2] (d) Explain the result at 55 °C. [2]

9. A gardener places 500 g of the same plant waste in each of five trays with different water contents. The table shows the mass lost after 4 weeks.

Water content (%)	10	30	50	70	90
Mass lost (g)	20	96	165	110	30

(a) Calculate the percentage of the starting mass lost in the tray with 50 % water. [1] (b) Calculate the mean rate of decay in the tray with 30 % water, in grams per week. [2] (c) Explain why the mass lost is low at both 10 % and 90 % water content. [2]

10. In a peat bog, dead plants build up and decay very slowly.

(a) State what the term anaerobic means. [1] (b) Explain why the plant remains in the bog decay so slowly. [3] (c) Explain why turning a compost heap with a fork speeds up decay. [2]

11. A compost heap started with a mass of 600 g (this is a small model heap). Its mass was measured every 10 days.

Day	0	10	20	30
Mass (g)	600	510	459	441

(a) Calculate the mean rate of decay, in grams per day, for each 10-day interval. [3] (b) Calculate the percentage loss of mass over the 30 days. [2] (c) Suggest two reasons why the rate of decay falls as time passes. [2] (d) State what happened to most of the carbon in the mass lost. [1]

12. Explain how the water cycle helps to maintain a pond as a habitat. [3]

Answers

1. Carbon [1]. Water or nitrogen [1]. [2] Examiner insight: Name the materials themselves; answers such as “gases” or “nutrients” are too vague to be credited.

2. The microorganisms (bacteria and fungi) secrete enzymes onto the dead wood [1]. The enzymes break large insoluble molecules into small soluble molecules [1]. The microorganisms absorb the products and respire, releasing carbon dioxide into the air [1]. Mineral ions that are not used are returned to the soil, where plants can take them up [1]. [4] Examiner insight: A strong answer says what is released and where it goes; “they break it down” alone does not explain the role.

3. Grass takes in carbon dioxide and photosynthesis makes carbon compounds such as glucose [1]. The rabbit eats the grass, so the carbon passes to the rabbit [1]. The fox eats the rabbit, so the carbon passes to the fox [1]. Carbon dioxide returns to the air when the organisms respire [1], and when dead organisms and waste are decomposed by microorganisms, which respire [1]. [5] Examiner insight: Name each process (photosynthesis, feeding, respiration, decomposition) and say what form the carbon is in; a diagram of arrows without labels is hard to credit.

4. (a) Transpiration [1]. [1] (b) Precipitation supplies fresh water to the land [1]. Plants take it up through roots, and it dissolves and carries mineral ions into the plant [1]. Animals drink it, and it keeps rivers, lakes and soil moist for habitats [1]. [3] Examiner insight: Linking the process to an effect on organisms is what turns “it rains” into an explanation; name more than one benefit when three marks are available.

5. Dead organisms and waste would not be broken down [1]. Mineral ions would not be returned to the soil [1]. The soil would run short of mineral ions, so producers would grow poorly [1]. Carbon would stay locked in dead material rather than returning to the air as carbon dioxide for photosynthesis [1]. [4] Examiner insight: A “suggest” question rewards a clear chain of cause and effect; the prediction alone is not enough.

6. (a) Mass lost = 320 - 224 = 96 g [1]. Percentage = 96 / 320 x 100 = 30 % [1]. [2] (b) Rate = 96 / 8 [1] = 12 g per week [1]. [2] (c) 224 / 320 = 7/10 [1]. [1] Examiner insight: Show the subtraction before dividing, and include units on the rate; a correct bare number may gain less credit than a worked one.

7. Weigh equal masses of the same type of leaf and place each in a mesh bag or container [1]. Use the same size of leaf pieces [1]. Keep the bags at different temperatures, such as 5, 15, 25, 35 and 45 °C [1]. Keep moisture and air supply the same for every temperature [1]. Reweigh each bag at regular intervals and record the mass lost [1]. Repeat each temperature and calculate a mean; wash hands after handling decaying material [1]. [6] Examiner insight: Say which variable is changed, which is measured and which are controlled; listing “keep everything the same” without naming variables is weak.

8. (a) Put temperature on the x-axis and mass lost on the y-axis, both labelled with units [1]. Pick scales so the points spread across most of the grid, such as 0 to 60 °C and 0 to 45 g, and plot the points accurately [1]. [2] (b) Mass lost rises from 3 g at 5 °C to a maximum of 41 g at 35 °C [1], then falls to 19 g at 45 °C and 2 g at 55 °C [1]. [2] (c) Rate at 35 °C = 41 / 10 = 4.1 g per day and at 15 °C = 11 / 10 = 1.1 g per day [1]. 4.1 / 1.1 = 3.7 times faster [1]. [2] (d) At 55 °C the enzymes of the decomposers are denatured [1], and many microorganisms are killed, so little decay occurs [1]. [2] Examiner insight: In a “describe” answer, quote figures from the table for the peak and the end values; do not explain until the question asks for it.

9. (a) 165 / 500 x 100 = 33 % [1]. [1] (b) 96 / 4 [1] = 24 g per week [1]. [2] (c) At 10 % water the microorganisms have too little water for enzyme action and growth [1]. At 90 % the air spaces are filled with water, so there is little oxygen and aerobic decay is slow [1]. [2] Examiner insight: Give a different reason for each end of the range; repeating “not the right amount of water” does not distinguish them.

10. (a) Without oxygen [1]. [1] (b) The bog is waterlogged, so there is very little oxygen [1]. The decomposers cannot respire aerobically, and decay is by anaerobic microorganisms, which are slow [1]. So the plant remains are not broken down and build up as peat [1]. [3] (c) Turning mixes air into the heap [1], so more oxygen is available for aerobic respiration and decomposers break down material faster [1]. [2] Examiner insight: Name oxygen as the limiting factor rather than writing that the bog is “wet” or “cold”.

11. (a) Days 0 to 10: (600 - 510) / 10 = 9.0 g per day [1]. Days 10 to 20: (510 - 459) / 10 = 5.1 g per day [1]. Days 20 to 30: (459 - 441) / 10 = 1.8 g per day [1]. [3] (b) Loss = 600 - 441 = 159 g [1]. 159 / 600 x 100 = 26.5 % [1]. [2] (c) The easily broken-down material is used first, leaving material that is harder to decompose [1]. Conditions may change, for example the heap may dry out, cool or run short of oxygen [1]. [2] (d) Most of the carbon was released as carbon dioxide by the respiration of the decomposers [1]. [1] Examiner insight: When asked for rates over several intervals, work each interval separately; using the whole 30 days misses the change in rate.

12. Evaporation and transpiration remove water from the pond [1]. Precipitation and run-off replace it [1]. This keeps a supply of fresh water in the pond, so the organisms that live there can survive [1]. [3] Examiner insight: Mention both loss and replacement of water; naming only rain misses why the cycle keeps the habitat steady.

Where marks are usually lost

• Writing “decomposers eat dead things” without secreted enzymes or absorbed products.
• Omitting that mineral ions are returned to the soil.
• Forgetting that decomposers respire and release carbon dioxide.
• Describing a carbon cycle without naming processes.
• Saying that decay increases with temperature without an optimum or denaturing.
• Giving “too wet” as a reason for slow decay without mentioning oxygen.
• Giving a rate without time units, or using the wrong time interval.
• Calculating a percentage of the final mass instead of the starting mass.
• Mixing up aerobic and anaerobic.

Next steps

• Read the study guide and the revision notes.
• Return to the OCR GCSE Biology hub and tick off the checklist.
• Take one of our free 10-minute diagnostics.
• Book a free trial class if you want to go through any of these with a teacher.

Official syllabus

OCR GCSE (9-1) Gateway Science Biology A (J247), Version 4.0 (August 2026), for first assessment in 2018, published by OCR: statements B4.1a to B4.1d and mathematical learning outcomes BM4.1i to BM4.1v.