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Cambridge IGCSE Biology practice

Paper 4 structured question: Tropic responses

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Tropic responses

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Paper 4Theory (Extended)6 marks

Plants use chemical regulation to control growth direction in response to environmental stimuli such as light and gravity.

Diagram Description

Auxin Distribution in a Shoot

A diagram shows a shoot with auxin concentrated on the lower side during gravitropism, causing the shoot to bend upwards.

  1. a

    Identify the stimulus that causes auxin to accumulate on the lower side of the shoot.

    Aim for approximately 1 distinct marking point.

    [1]
  2. b

    Explain how the accumulation of auxin on the lower side causes the shoot to grow upwards.

    Aim for approximately 5 distinct marking points.

    [5]

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Paper 4 structured question: Tropic responses

Paper 4Theory (Extended)6 marks

Description

Phototropism and Gravitropism

Phototropism causes shoots to grow towards light, while gravitropism causes shoots to grow upwards against gravity. Both responses involve the redistribution of auxin, which promotes cell elongation on one side of the shoot, causing bending.

  1. a

    State the direction of shoot growth in phototropism and gravitropism.

    Aim for approximately 2 distinct marking points.

    [2]
  2. b

    Explain how auxin causes shoots to bend during phototropism.

    Aim for approximately 4 distinct marking points.

    [4]