B1.12 - Plant growth

Question 1

Do plants respond to stimuli in the environment?

Answer 1

Yes

Question 2

What do plant hormones/ plant growth substances do?

Answer 2

They control and coordinate:

• The growth of shoots and roots
• Flowering
• Ripening of fruits

Question 3

What direction would plants grow when on a window sill?

Answer 3

Plants would grow towards the light source. (If you want them to grow straight, you have to keep turning them.)

Question 4

What is tropism?

Answer 4

Tropism is a plants response to a stimulus.

Question 5

What is phototropism?

Answer 5

Phototropism is when plants respond to the stimulus of light and grow towards the light.

Question 6

How does a positively phototropic plant (responds to a light stimulus) grow towards light?

Answer 6

• A plant hormone called auxin is made which moves through the plant in a solution form.
• When light strikes one side of the shoot tip, more auxin builds up on the other side of the shoot tip (furthest from the light).
• This causes the shoot to Ben Dover towards the light.

Question 7

How does auxin make the shoot bend?

Answer 7

Auxin is made in the shoot tip and is unevenly distributed when the shoot is exposed to light from one side. This auxin moves down the stem and causes cells on the side of the shoot furthest away from the light to elongate more than those nearest the light. This causes it to bend towards the light.

Question 8

What is Geotropism?

Answer 8

Geotropism is the response of a plant to gravity. Roots grow downwards in response to gravity. Auxins may be involved in this response but other chemicals that inhibit growth may also be involved.

Question 9

How are plant hormones used in agriculture?

Answer 9

Plant hormones can be applied to plants to either slow down or speed up their growth.

Question 10

Name four commercial uses of auxins?

Answer 10

• Weedkillers
• Rooting powder
• Fruit ripening
• Control of dormacy