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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)4 marks

Auxin also responds to gravity by distributing unevenly in the shoot, affecting growth direction.

Description

Auxin and Gravity Response

When a plant shoot is placed horizontally, auxin accumulates on the lower side of the shoot, causing it to bend upwards.

  1. a

    Identify the side of the shoot where auxin accumulates in response to gravity.

    Aim for approximately 1 distinct marking point.

    [1]
  2. b

    Explain how this uneven auxin distribution affects shoot growth direction.

    Aim for approximately 3 distinct marking points.

    [3]

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Paper 4 structured question: Tropic responses

Paper 4Theory (Extended)4 marks

Diagram Description

Auxin Distribution in a Plant Shoot

The diagram shows a plant shoot bending towards a light source. Auxin concentration is higher on the shaded side of the shoot than on the side facing the light.

Side of ShootAuxin Concentration
Light sideLow
Shaded sideHigh
  1. a

    State where auxin is produced in the plant shoot.

    Aim for approximately 1 distinct marking point.

    [1]
  2. b

    Explain how uneven auxin distribution causes the shoot to bend towards the light.

    Aim for approximately 3 distinct marking points.

    [3]