2.5 Plant Responses

What are plant tropisms?

The growth of a plant in response to a stimulus.

What is positive tropism?

The growth of a plant towards a stimulus.

What is negative tropism?

The growth of a plant away from a stimulus.

What are the two main types of plant tropism?

- Phototropism
- Gravitropism

Define phototropism.

A plant's growth response to light.

Are plant shoots positively or negatively phototropic? How does this affect shoot growth?

● Plant shoots are positively phototropic.
● Plant shoots grow towards the light.

Are plant roots positively or negatively phototropic? How does this affect root growth?

● Plant roots are negatively phototropic.
● Plant roots grow away from the light.

Define gravitropism

A plant's growth in response to gravity.

Are plant roots positively or negatively gravitropic? How does this affect root growth?

● Plant roots are positively gravitropic.
● Plant roots grow downwards, towards gravity.

Are plant shoots positively or negatively gravitropic? How does this affect shoot growth?

● Plant shoots are negatively gravitropic.
● Plant shoots grow upwards, away from gravity.

What are auxins?

● A group of plant hormones involved in plant tropisms.

● They control growth in plant roots and shoot tips.

Where are auxins produced?

Root and shoot tips.

How do auxins affect plant shoots?

They stimulate growth in plant shoots.

How do auxins affect plant roots?

They inhibit growth in plant roots.

Explain how plant tropisms increase the chance of survival.

● They enable plants to respond to their environment.

● Shoot growth towards the light maximises light absorption.

● Root growth downwards increases the uptake of water and minerals from the soil and enables anchorage of the plant body to the ground.