What is the growth response of a plant to light called?

phototropism. Photo means light.

In which direction do roots grow?

downwards, towards gravity. This takes them to water.

Where is auxin made in a shoot?

in the tip. It then moves down the shoot.

On which side of a shoot lit from one side does auxin collect?

the shaded side. The shaded side then grows faster.

What does auxin do to the cells of a shoot?

makes them elongate. Longer cells on one side make the shoot bend.

Plant responses · Edexcel IGCSE Biology 4BI1 revision

In plain words

Plants can't walk towards the light, but they can grow towards it. A seedling on a windowsill bends to the glass; a seed planted upside down still sends its root down. Plants steer by growing faster on one side, and the growth is controlled by a hormone called auxin.

Three things to know

A tropism is a growth response to a stimulus that comes from one direction. Phototropism is a response to light; gravitropism (geotropism) is a response to gravity.
Shoots grow towards light and away from gravity. Roots grow down, towards gravity.
Auxin is made in the tip of a shoot and moves down. It collects on the shaded side, where it makes the cells get longer. The shaded side grows faster, so the shoot bends towards the light.

Tips and tricks

Auxin makes shoot cells elongate (get longer). It doesn't make more cells.
More auxin on the shaded side, more growth on the shaded side, shoot bends towards the light. Say all three steps.

5 questions, about 2 minutes.

It lands in your notebook with its questions as flashcards.

Plant responses: 5 questions and answers

These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.

What is the growth response of a plant to light called?
- gravitropism
- phototropism (the answer)
- photosynthesis
- transpiration
Photo means light.
In which direction do roots grow?
- towards light
- downwards, towards gravity (the answer)
- upwards
- sideways only
This takes them to water.
Where is auxin made in a shoot?
- in the tip (the answer)
- in the roots
- in the leaves only
- in the flowers
It then moves down the shoot.
On which side of a shoot lit from one side does auxin collect?
- the lit side
- the shaded side (the answer)
- both sides equally
- neither
The shaded side then grows faster.
What does auxin do to the cells of a shoot?
- kills them
- makes them divide only
- makes them elongate (the answer)
- makes them photosynthesise
Longer cells on one side make the shoot bend.

5 questions

Tap an answer and you’ll see straight away whether it’s right, and why.

Worksheet

3 questions, 8 marks. Write your answers on paper, then check them.

Plant responses

Edexcel International GCSE Biology 4BI1 · 8 marks · papermunch.org

Name ______________________________ Date ______________

State what is meant by phototropism and by gravitropism.[2]
Show answerHide answer
Phototropism is a growth response to the direction of light. Gravitropism is a growth response to gravity.
I got this one
Explain how a shoot bends towards light coming from one side.[4]
Show answerHide answer
Auxin is made in the shoot tip and moves down the shoot. More of it collects on the shaded side. Auxin stimulates the cells there to elongate, so the shaded side grows faster and the shoot bends towards the light.
I got this one
Explain the advantage to a plant of its roots growing downwards.[2]
Show answerHide answer
They reach water and mineral ions in the soil, and they anchor the plant.
I got this one

Answers: Plant responses

1. Phototropism is a growth response to the direction of light. Gravitropism is a growth response to gravity.
2. Auxin is made in the shoot tip and moves down the shoot. More of it collects on the shaded side. Auxin stimulates the cells there to elongate, so the shaded side grows faster and the shoot bends towards the light.
3. They reach water and mineral ions in the soil, and they anchor the plant.