14.5 Coordination in plants

14.5 Tropic responses

• Define gravitropism as a response in which parts of a plant grow towards or away from gravity

• Define phototropism as a response in which parts of a plant grow towards or away from the direction from which light is coming

• Investigate gravitropism and phototropism in shoots and roots Supplement

• Explain phototropism and gravitropism of a shoot as examples of the chemical control of plant growth

• Explain the role of auxin in controlling shoot growth, limited to:

1. auxin made in shoot tip (only)

2. auxin spreads through the plant from the shoot tip

3. auxin is unequally distributed in response to light and gravity

4. auxin stimulates cell elongation

• Describe the use in weedkillers of the synthetic plant hormone 2,4-D