Tropisms and Auxin

IGCSE Edexcel Biology
2.83-2.85 Plant Responses
Key Concept: Shoots and roots grow in response to stimuli, with auxin controlling shoot phototropism.

Section A: Tropisms

1. Define phototropism and geotropism. [4]
2. Describe how shoots and roots respond to light and gravity. [4]

Section B: Auxin

3. Explain the role of auxin in shoot phototropism. [4]
Total marks: 12

Mark Scheme

1. Phototropism: growth response to light; geotropism: growth response to gravity [4]
2. Shoots grow toward light and away from gravity; roots grow away from light and toward gravity [4]
3. Auxin accumulates on the shaded side of the shoot, causing cells to elongate, bending the shoot toward light [4]