B1.12 Controlling Plant Growth

Question 1

What chemicals do plants make, and what do they control?

Answer 1

Plant hormones
Control the:
- growth of shoots and roots
- flowering
-ripening of fruits

Question 2

What is a plants response to a stimuli called?

Answer 2

Tropism

Question 3

What is it called when plant shoots grow towards light? How does this work?

Answer 3

Positively phototropic

• make plant hormone - auxin- moves through the plant in solution
• when light strikes one side of the shoot tip, more auxin builds up on other side
• causes the shoot to bend over, towards the light
• increases the plants chance of survival because it needs light to photosynthesise and make food.

Question 4

How does auxin make the bend?

Answer 4

The auxin moves down the stem and causes cells on the side of the shoot furthest from the light to elongate more than those nearest the light

Question 5

What is geotropism?

Answer 5

Is the repsonse of a plant to gravity. Roots grow downwards in response to the pull of gravity. Auxins and also other chemicals involves

Question 6

Weedkillers?

Answer 6

Auxins used as selective weedkillers

Question 7

Rooting powder?

Answer 7

Cuttings are dipped into auxin powder, helping the cuttings make new roots, so cuttings can anchor in the soil and take up water and minerals

Question 8

Fruit ripening?

Answer 8

Auxin sprayed onto fruit trees to prevent ripe fruit from dropping. Can be harvested at the same time - fruit is not bruised from falling

Question 9

Control of dormancy?

Answer 9

• seeds usually dormant when fhey shed from parent plant
• stops them from germinating
• but if growers want to germinate seeds in greenhouses in winter, they apply auxin that can break the dormancy.