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Ecosystems and Energy Flow Paper 3: Challenge
Ecosystems and Energy Flow Paper 3: Challenge
Combined calculations: biomass back to top consumers, multiplying overall efficiency, respiration shares, chain-length comparison 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 3 (challenge) |
02 Questions (10 items)
- FoundationA sea area holds 30 000 kg of phytoplankton. At a tenth per transfer, how much reaches the third-level consumer?
- FoundationPrimary consumers receive 1 250 kJ while producer net production is 12 500 kJ. What is the transfer efficiency?
- FoundationA person eats 800 kJ of beef; the cattle ate 8 000 kJ of feed grown from 80 000 kJ of plants. What is the overall efficiency from plant to person?
- IntermediateA forest has net primary production of 8 000 kJ and primary consumers assimilate 1 120 kJ. What is the efficiency, and is it above or below a tenth?
- IntermediateGross primary production is 40 000 kJ and producers respire 65 per cent of it. What is net primary production?
- IntermediateFrom the same 100 000 kJ, a three-level chain leaves 1000.0000000000002 kJ at the top and a four-level chain leaves 100.00000000000003 kJ. How many times more is the first?
- ChallengeTo support 5 kg of top consumer through three transfers at a tenth each, how much producer mass is needed?
- ChallengeAbout 90 per cent of energy is lost as heat at each level. What does that do to food chain length?
- ChallengeWhy does a food web describe a real ecosystem better than a food chain?
- Error redoError: reading an inverted biomass pyramid as proof that energy can be inverted too. How should it be corrected?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 30.0 kg. | Each level multiplies by 0.1, so three levels leave one thousandth. |
| 2 | 10.0%. | Divide what the next level receives by what was available, over the same time and area. |
| 3 | 1.0%, because the two stage efficiencies multiply. | Overall efficiency multiplies the stage efficiencies rather than adding them. |
| 4 | 14.000000000000002%, which is above 10 per cent. | Measured efficiency can lie above or below a tenth; the rule is only a rough estimate. |
| 5 | 14000.0 kJ. | The larger the respiration share, the less energy is left for consumers. |
| 6 | 10.0 times more: every extra level loses another ninety per cent. | The scarcity of top predators is a direct result of this stepwise loss. |
| 7 | 4999.999999999999 kg. | Five times ten three times is a thousand, which explains why large predators must be scarce. |
| 8 | Available energy falls sharply, so chains usually run four or five levels and cannot be longer. | Chain length is limited by energy, not by what organisms are willing to eat. |
| 9 | Most organisms eat several kinds of food and are eaten by several others, and a web shows those multiple links. | The more complex the web, the better the system usually withstands disturbance. |
| 10 | Only biomass or numbers pyramids invert; an energy pyramid is always upright because energy is lost one way only. | Name which pyramid is meant before discussing its shape. |
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.
In back-calculation multiply by ten per level from the top, and estimate the order of magnitude first so a tenfold slip is caught.Tutor Registration →
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