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Primary General Studies: Food Chains and Ecology (Paper 3 (challenge))
Primary General Studies: Food Chains and Ecology (Paper 3 (challenge))
Paper three adds reverse energy calculations, biological magnification and population limits at challenge level.
Direct answers Decide first whether the question works forwards or backwards, use division when working backwards, and judge the size of the answer at the end.
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: Primary General Studies: Food Chains and Ecology |
| Level | parts of a closed circuit, conductors against insulators, series against parallel, adding up battery voltage, and electrical safety |
02 Questions (10 items)
- FoundationWhen several food chains cross each other, what do they form?
- FoundationTwo animals eat the same food. What is this relationship called?
- FoundationOne living thing lives on another and harms it. What is this called?
- IntermediateAn eagle needs 300 kJ. At one tenth per level, how much energy do the rabbit and the grass need?
- IntermediateA reserve has 8 000 hectares with 250 plants per hectare. If 2 500 plants feed one deer, how many deer can it support?
- IntermediatePesticide in water is 0.000 05 ppm and magnifies ten times per level. What is it in a big fish after three levels?
- ChallengeThe base holds 100 000 kJ. If the transfer rate rises from 0.1 to 0.15, how much more reaches the top after two levels?
- ChallengeAn island has 100 rabbits growing 20 per cent a year. How many after two years?
- ChallengeEach deer needs 25 hectares. If a reserve should hold at most 120 deer, what is the smallest area needed?
- Error redoA classmate claims a longer chain gives the top predator more energy. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | They form a food web. | A food web is closer to real ecology, because one animal often eats several kinds of food. |
| 2 | It is called competition. | Competitors fight for food and space, so their numbers affect each other. |
| 3 | It is called parasitism. | The parasite gains and the host loses; when both gain, the relationship is mutualism. |
| 4 | The rabbit needs 3 000 kJ and the grass 30 000 kJ. | 300 divided by 0.1 is 3 000, and 3 000 divided by 0.1 is 30 000. |
| 5 | It can support 800 deer. | 8 000 times 250 is 2 000 000 plants, and 2 000 000 divided by 2 500 is 800. |
| 6 | It reaches 0.05 ppm in the big fish. | Three steps of ten give a thousandfold increase, and 0.000 05 times 1 000 is 0.05. |
| 7 | It rises from 1 000 to 2 250 kJ, a gain of 1 250 kJ. | 100 000 times 0.1 times 0.1 is 1 000, while 0.15 twice gives 2 250. |
| 8 | About 144 rabbits. | 100 times 1.2 is 120, and 120 times 1.2 is 144, which is more than simply adding 40. |
| 9 | At least 3 000 hectares. | 120 times 25 is 3 000, and habitat area sets the upper limit on a population. |
| 10 | Energy falls at every level, so a longer chain leaves less for the top predator. | About nine tenths is lost per level, which is why chains rarely run beyond four or five links. |
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.
Paper four clears the conductor, insulator and battery direction misconceptions.Tutor Registration →
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