K325 / 2027

Organisms and their environment

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A caterpillar eats a leaf, and a bird eats the caterpillar. Which statement is correct?

  1. The leaf is a decomposer because it eventually dies.
  2. The caterpillar is a primary consumer and the bird is a secondary consumer in this chain.
  3. The arrow runs from the bird to the caterpillar, because the bird is the one that hunts and eats it.
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The caterpillar is a primary consumer and the bird is a secondary consumer in this chain.

The caterpillar feeds on the producer and the bird feeds on that primary consumer.

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A lower level contains 8,000 kJ and the next level contains 600 kJ of new biomass energy over the same period. What is the transfer efficiency?

  1. 1,333%, because 8,000 should be divided by 600.
  2. 10%, because all chains have the same efficiency.
  3. 7.5%
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7.5%

Correct: 600 / 8,000 x 100 = 7.5%. Use the given values rather than assuming every transfer is 10%.

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Producers in a food chain capture 20 000 kJ. About 10% is passed on at each step. How much energy reaches the secondary consumers?

  1. 2 000 kJ
  2. 20 kJ
  3. 200 kJ
  4. 18 000 kJ
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200 kJ

20 000 x 0.1 = 2 000 kJ for primary consumers, and 2 000 x 0.1 = 200 kJ for secondary consumers.

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Why can a single tree have a narrow bar in a numbers pyramid but a broad bar in a biomass pyramid?

  1. The numbers diagram is always incorrect.
  2. It is one organism but has a large mass compared with individual insects.
  3. The tree makes more energy than it receives, so its biomass bar must be wider.
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It is one organism but has a large mass compared with individual insects.

Counting individuals and measuring their biomass answer different questions.

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One oak tree supports 5 000 caterpillars, which feed 20 birds. Which describes the pyramid of numbers?

  1. Three bars of about the same width, one per level
  2. A narrow base, a wide middle and a narrow top
  3. A narrow base that widens steadily towards the top
  4. A wide base that narrows steadily towards the top
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A narrow base, a wide middle and a narrow top

One tree is a small number, the caterpillars are many and the birds are few.

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Which process transfers carbon from atmospheric carbon dioxide into a plant's organic molecules?

  1. Respiration in the leaf cells.
  2. Combustion.
  3. Photosynthesis.
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Photosynthesis.

The carbon in carbon dioxide becomes part of organic molecules formed by the plant.

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Which explanation of deforestation and warming is most complete?

  1. Clearing only affects oxygen and cannot affect carbon dioxide.
  2. Every replacement seedling immediately stores as much carbon as a mature forest.
  3. Clearing can release stored carbon and reduce future photosynthetic uptake.
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Clearing can release stored carbon and reduce future photosynthetic uptake.

Both the release of stored carbon and the loss of uptake can increase atmospheric carbon dioxide.

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What directly uses dissolved oxygen when organic sewage is decomposed aerobically?

  1. Respiration by decomposer microorganisms.
  2. Photosynthesis by all decomposers.
  3. The formation of a cell wall around the whole river.
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Respiration by decomposer microorganisms.

Greater oxygen demand can lower dissolved oxygen and harm other aerobic organisms.

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Untreated sewage enters a river. Which sequence explains why fish die downstream?

  1. Fish eat the sewage and are killed by the extra protein in it
  2. Algae in the sewage release too much oxygen, which poisons the fish
  3. Sewage blocks out light, so the fish cannot see to find their food
  4. Bacteria decompose the sewage and use up oxygen, so fish cannot respire
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Bacteria decompose the sewage and use up oxygen, so fish cannot respire

Decomposers respire aerobically as they break down the sewage, lowering dissolved oxygen.

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Which statement best explains why fragmentation is not a complete solution to plastic pollution?

  1. Smaller particles can persist and be ingested by other organisms.
  2. All fragments immediately become harmless mineral nutrients.
  3. Small particles sink to the sea floor, where they are out of reach of living things.
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Smaller particles can persist and be ingested by other organisms.

The size has changed, while the material can remain in the environment.

Check your understanding

Which property most supports biomagnification of an insecticide?

  1. Every predator is physically larger than every prey organism.
  2. It persists and is not readily broken down or excreted.
  3. It is immediately converted into harmless products and removed.
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It persists and is not readily broken down or excreted.

Retention allows repeated uptake from many prey to raise concentrations at higher levels.

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Which proposal most directly protects both a fish resource and its capacity to renew?

  1. Protect nursery habitat, regulate catches and monitor population recovery.
  2. Keep harvesting at the same level after destroying its breeding habitat.
  3. Declare a large reserve on paper, without monitoring or limiting damaging activities in it.
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Protect nursery habitat, regulate catches and monitor population recovery.

This links habitat, extraction and evidence about renewal rather than treating any one measure as sufficient.

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Write a short answer, then compare it with a sample and check for missing ideas.

Question 1 of 10

Draw pyramids with parasites

4 marks

An invented woodland chain: 1 oak tree (mass 2000 kg) -> 5000 caterpillars (0.002 kg each) -> 10 birds (0.05 kg each) -> 400 fleas (0.000001 kg each). (a) Describe how you would draw the pyramid of numbers and explain its shape. (b) Calculate the biomass at each level. (c) Describe the shape of the pyramid of biomass and explain why it differs from the pyramid of numbers. [4]

One labelled horizontal bar per level. Biomass = number x mass of one organism, with kg.

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