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S3 Science: Ecosystems and Energy Flow (Paper 2: intermediate)
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S3 Science: Ecosystems and Energy Flow (Paper 2: intermediate)
The second paper adds photosynthesis, respiration and food webs, and starts working back from the number of steps to the trophic level.
Direct answers Efficiency and step counting alternate, so you must ask how many multiplications are needed before reaching for the calculator.
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: S3 Science: Ecosystems and Energy Flow |
| Level | S3 Science |
02 Questions (10 items)
- FoundationWhat kind of energy does photosynthesis turn light into?
- FoundationWhat is the energy released by respiration mainly used for?
- FoundationWhat is a food web?
- IntermediateGrass holds 20 000 kJ. How much reaches the secondary consumer at ten per cent transfer?
- IntermediateProducers fix 100 000 kJ. How much reaches the fourth trophic level?
- IntermediateWhen the transfer efficiency is only 5 per cent, how much of 40 000 kJ reaches the primary consumer?
- ChallengeEnergy falls from 12 000 kJ to 12 kJ at the top predator. How many ten per cent steps is that?
- ChallengeWhy does a meat diet need more farmland than a plant diet?
- ChallengeHow does an energy pyramid differ from a biomass pyramid?
- Error redoA student works out the fourth trophic level from 10 000 kJ as 1 000 kJ. What is the correct value?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Chemical energy stored in glucose | Light is fixed as chemical energy inside glucose, which feeds the whole food chain. |
| 2 | Life activities such as growth, movement and keeping warm | Respiration releases the chemical energy of glucose to supply cell activity. |
| 3 | A network formed by several food chains linked together | One organism may eat several kinds of food and be eaten by several others, so the chains join into a web. |
| 4 | 200 kJ | Two steps are needed: 20 000 falls to 2 000 and then to 200 kJ. |
| 5 | 100 kJ | Three steps are needed: 100 000 falls to 10 000, then 1 000, then 100 kJ. |
| 6 | 2 000 kJ | Five per cent of 40 000 kJ is 2 000 kJ, and a lower efficiency leaves less for every level above. |
| 7 | Three steps | The chain runs 12 000 to 1 200 to 120 to 12, which is three steps and puts the top predator at the fourth trophic level. |
| 8 | Each transfer keeps only one tenth, so far more plants are needed for the same energy | If the plants of a field pass through livestock first, nine tenths of the energy is already gone. |
| 9 | An energy pyramid is always upright, while a biomass pyramid can be inverted | Energy must fall at every step, but a level with fast turnover can hold less biomass than the one above it. |
| 10 | 10 kJ | Only one step was applied; three are needed, so 10 000 falls through 1 000 and 100 to 10 kJ. |
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.
The intermediate paper works both ways: multiply a lower level by the transfer efficiency to reach the next level, or count the steps from the loss, and keep photosynthesis for storing energy apart from respiration for releasing it.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.