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Ecosystems and Energy Flow Paper 4: Error Clinic
Ecosystems and Energy Flow Paper 4: Error Clinic
Ten recurring errors: miscounted levels, net against gross production, decomposers read as an energy cycle, a wrong denominator for efficiency, and misread chain length and pyramid shape.
Direct answers Answers and explanations for all ten questions
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: DSE Biology Ecosystems and Energy Flow |
| Level | Paper 4 (error clinic) |
02 Questions (10 items)
- FoundationError 1: gross primary production is 50 000 kJ and each transfer keeps a tenth. How much reaches the third-level consumer?
- FoundationError 2: gross primary production is 24 000 kJ and respiration uses 9 000 kJ. What is net primary production and what share of gross is it?
- FoundationError 3: a student claims decomposers return energy to producers, forming a cycle. Where is the mistake?
- IntermediateError 4: 14 000 kJ is available at one level and 1 400 kJ is assimilated at the next. What is the transfer efficiency, and what is the commonest slip?
- IntermediateError 5: eating 10 kg of maize directly against eating 10 kg of beef, roughly how many times more energy is available?
- IntermediateError 6: a top consumer holds 6 kg of biomass in a three-level chain. What producer biomass does it require?
- ChallengeError 7: 180 000 kJ passes through four transfers. How much is left at the top, and why is the real figure usually lower?
- ChallengeError 8: a transfer efficiency rises from 12 per cent to 15 per cent. What is the percentage increase, and how does it differ from three percentage points?
- ChallengeError 9: producer biomass is 45 000 kg and three transfers follow. What biomass reaches the top, and does the unit change?
- Error redoError 10: treating the energy pyramid and the biomass pyramid as the same thing and assuming both are always upright. How should they be separated?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 50.000000000000014 kJ. Start at the producer and multiply by a tenth once per level, three times for level three. | Count the levels first, then decide how many times to multiply by a tenth. |
| 2 | Net primary production is 15000 kJ, which is 62.5 per cent of gross. | Net production subtracts respiration only, before any grazing, so the two must not be confused. |
| 3 | Decomposers break organic matter into inorganic substances, so matter is reused, but the energy has left as heat and does not return. | Matter cycles in an ecosystem while energy flows one way; the two are handled differently. |
| 4 | Efficiency is 10.0 per cent. The commonest slip is dividing by the wrong base, such as total production rather than energy available at the level below. | The denominator is always the energy available at the level below, the numerator the energy actually assimilated. |
| 5 | About 10.0 times more; 10 kg of beef sits on roughly 100 kg of plant feed. | Each level keeps only a tenth, so a shorter chain supports more people. |
| 6 | About 5999.999999999998 kg, because backward calculation multiplies by ten per level, a thousandfold over three levels. | Backward and forward calculation use the same tenfold step, only the direction differs. |
| 7 | 18.000000000000004 kJ in theory; less in practice because some energy goes to decomposers and not every organism is eaten. | Answer the calculation and the ecological reality separately: the formula gives a ceiling, actual flow stays below it. |
| 8 | A 25.0 per cent increase, which is three percentage points; both statements are true but mean different things. | Check whether the question asks for a relative change or an absolute gap. |
| 9 | About 45.000000000000014 kg, still in kilograms; no conversion is needed. | Multiplying by a tenth never changes the unit; only mass-volume conversions do. |
| 10 | The energy pyramid is always upright because energy falls at every step; a biomass pyramid can invert, as with fast-turning marine phytoplankton. | Before judging the shape, ask whether the pyramid counts numbers, biomass or energy. |
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.
Most errors come from separating the level count from the tenfold step; always count levels before reaching for the calculator.Tutor Registration →
Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.