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Plant Structures and Their Functions

Plant hormones, phototropism and gravitropism

  • 3 things to know
  • Paper 2

Overview

Plant hormones and where auxin is made, phototropism and gravitropism, how auxin makes shoots bend towards light and roots grow downwards and the advantage of each response, and why a shoot with its tip removed no longer bends towards light.

What you need to know

Answer each one before you reveal it.

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Key term

What is a plant hormone?

Key term

What is a phototropism?

Key term

What is gravitropism, and how do shoots and roots respond to gravity?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is a plant hormone?

    Model answer

    A plant hormone is a chemical made by a plant that controls and coordinates its growth and development.

  2. 2

    Where in a plant is auxin produced?

    Model answer

    In the tips of the growing shoots and roots.

  3. 3

    What is a phototropism?

    Model answer

    A phototropism is a growth response in which part of a plant grows towards or away from the direction of light.

  4. 4

    What is gravitropism, and how do shoots and roots respond to gravity?

    Model answer

    Gravitropism is a growth response to gravity: shoots grow away from gravity and roots grow towards it.

  5. 5

    Explain how auxin makes a shoot bend towards a light source at one side.

    Model answer

    Auxin builds up on the shaded side, where it makes the cells elongate more, so that side grows longer and the shoot bends towards the light.

  6. 6

    Explain the advantage to a plant of its shoots growing towards light.

    Model answer

    The leaves receive more light, so the plant can photosynthesise faster and make more food.

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