B11: Plant Hormones and Response

Question 1

What is phototropism?

Answer 1

A plants response to light

Question 2

What is geotropism

Answer 2

A plants response to gravity

Question 3

Where is auxin produced?

Answer 3

In the tips of plant shoots and roots

Question 4

Which part of the shoot is more sensitive to light?

The upper or lower part?

Answer 4

The upper part

Question 5

How do shoots use auxin to grow towards light?

Answer 5

Auxin is produced in the tips of the shoots, light causes auxin to concentrate on the darker side of the shoot tip. Auxin now spreads down the shoot, so cells on the darker side grow faster than the cells on the lighter side, causing the shoot to grow towards the light.

Question 6

What is the effect of Auxin in the shoots?

Answer 6

Auxin triggers growth in the shoots

Question 7

How does Auxin affect the roots of a plant?

Answer 7

Auxin is produced in the root, but gravity causes auxin to concentrate on the lower side. As auxin inhibits growth in the roots, the lower side now grows more slowly than the upper side, causing the roots to grow towards the force of gravity.

Question 8

What does Auxin do in roots

Answer 8

It inhibits growth

Question 9

How are Giberellins useful for plants?

Answer 9

They are important in starting seed germination

Question 10

How is Ethene important for plants?

Answer 10

They are important in controlling cell division and the ripening of fruit

Question 11

Describe the 3 main uses of Auxins

Answer 11

• Weedkillers in gardens
• Rooting powders
• Promoting growth in tissue culture

Question 12

Describe uses of Giberellins

Answer 12

• Can be used to end seed dormancy (force a seed to germinate early)
• Trigger plants to flower
• Make fruits grow larger

Question 13

Describe the use of Ethene in the food industry

Answer 13

Foods (e.g. bananas) are usually harvested before they’re ripe, and are then transported long distances and stored.

• Ethene is used to trigger the bananas to ripen just before they’re sold

Question 14

What is a tropism?

Answer 14

The response of a plant to a specific stimulus

Question 15

Explain the results for the “Plant response to light intensity” practical

Answer 15

The height of the seedlings are similar for full and partial sunlight, as chlorophyll is very efficient at absorbing light energy, so plants don’t need full sunlight to grow. Plants grow towards the light due to phototropism. The seedlings in the dark have grown the tallest as seeds usually germinate underground, and grow rapidly to reach the light. Keeping seedlings in the dark causes them to grow rapidly to reach light. Also, the leaves left in the dark are small and yellow as a result of using up all energy stores, and can’t carry out photosynthesis in the dark