Topic 5c- Plant hormones

Question 1

What does auxin do?

Answer 1

Controls growth near the tips of shoots and roots

Question 2

What does auxin control?

Answer 2

• phototropism
• gravitropism

Question 3

What is phototropism?

Answer 3

Plant growth in response to light

Question 4

What is gravitropism?

Answer 4

Plant growth in response to gravity

Question 5

What does auxin stimulate / inhibit ?

Answer 5

The elongation of cells in the tips of plants but inhibits growth in the root

Question 6

What happens when a shoot tip is exposed to light (in reference to pllant hormones)

Answer 6

• 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

Question 7

What effect does gravity have on a shoot tip (in relation to plant hormones)

Answer 7

• Gravity produces an unequal distribution of auxin at the tip
• More auxin is produced on the lower side
• This causes the lower side to grow faster and the shoot grows upwards

Question 8

What effect does gravity have on a root (in relation to plant hormones)

Answer 8

• More auxin will accumulate on the lower side of the root
• Auxin has the opposite effect in roots as in shoots and therefore the cells where the auxin has accumulated (on the lower side) have inhibited growth
• This results in the cells on the upper side of the root (which has less auxin) growing faster and therefore bending the root downwards

Question 9

What are the uses of auxin

Answer 9

1. Killing weeds
2. Growing from cuttings with rooting powder
3. Growing cells in tissue culture

Question 10

How can auxin be used to kill weeds?

Answer 10

• Most weeds growing in fields of crops are broad-leaved in contrast to grasses or cereals
• Selective weedkillers have been developed to only affect broad-leaved plants.
• They totally disrupt the normal growth patterns, which soon kills them, whilst leaving the grass and crops untouched

Question 11

What do gibberellins do?

Answer 11

Gibberellins stimulate:

• seed germination
• stem growth
• flowering

Question 12

What is dormancy (relating to seeds)

Answer 12

Certain conditions that lots of seeds must go through before germination (e.g. a period of cold or dryness)

Question 13

How can gibberellins be used to control dormancy of seeds?

Answer 13

Gibberellins alter dormancy and can make seeds germinate at times of the year that they wouldn’t normally. It also helps to ensure that all the seeds in a batch germinate at the same time.

Question 14

How can gibberellins induce flowering?

Answer 14

Some plants require certain conditons to flower (e.g. longer days) but if these plants are grown with gibberellins, they will flower without any change in environment and can be used to grow larger flower

Question 15

How can gibberellins grow larger fruits?

Answer 15

Seedless varieties of fruits tend to not grow as much as seeded however gibberellins will help seedless grow to match the normal types

Question 16

Where is ethene produced in a plant?

Answer 16

In the aging parts of a plant

Question 17

What does ethene do in plants?

Answer 17

• influences the growth of a plant by controlling cell division
• stimulates enzymes that cause the fruits to ripen

Question 18

How can ethene be used comercially to ripen fruits / prevent them from ripening

Answer 18

• it can be used to speed up the ripening of fruits while still growing on the plant
• can be used to ripen fruit while being transported to shops → fruit can be picked while unripe (therefore firmer and less easily damaged) before becoming ripe at the shops
• ripening can be delayed while fruits are in storage by using chemicals that block or reduce the amount of ethene that the fruit produces