Topic 2 - Responding To Change: Plant Growth Hormones

Question 1

What make a plant shoot grow towards the light?

Answer 1

When a shoot tip is exposed to light, more auxin accumulates on the side that’s in the shade than the side that’s in the light. This makes the cells grow (elongate) faster on the shaded side, so the shoot bends towards the light. This is called phototropism.

Question 2

Why are the plant hormones used to control the ripening of fruit?

Answer 2

It allows fruit to be picked while it’s still unripe. Ripening hormone can then be added so the fruit will be perfect just as it reaches the shop.

Question 3

Name a plant growth hormone other than auxin.

Answer 3

Gibberellin.

Question 4

How are seedless fruit produced?

Answer 4

Growth hormones are added to unpollinated flowers. This makes the fruit grow without seeds.

Question 5

Describe an experiment that would show that plant shoots are positively phototrophic.

Answer 5

E.g. Put 10 cress seeds into three different Petri dishes, each lined with moist filter paper. Shine a light onto one of the dishes from above and two of the dishes from different directions. After several days the seedlings in each dish will have grown towards the light.

Question 6

What is gravitropism? What hormone controls it?

Answer 6

Gravitropism (or geotropism) is the growth of a plant in response to gravity. It’s controlled by the hormone auxin.

Question 7

Why do weed killers containing plant growth hormones work?

Answer 7

Selective weedkillers containing plant growth hormones can be used to kill weeds. They disrupt the normal growth patterns of broad-leaved plants (often weeds), leaving grasses and cereal crops untouched.

Question 8

What effect does gravitropism have on the roots of a plant?

Answer 8

It causes the plant roots to grow downwards.