M5 CH16 plant hormones

Question 1

state where auxins are produced, and their role in plants.

Answer 1

produced in the tip of meristems
- stimulate cell elongation
- maintain apical dominance by promoting apical shoot growth

Question 2

explain the action of auxin in causing cell elongation (6)

Answer 2

1. auxin diffuses down the shoot from the tip
2. binds to receptors in cell membrane
3. H ions move into the cell wall from the cytoplasm
4. this causes the PH to fall
5. enzymes break down cellulose, making it more stretchy
6. water moves into cells, causing swelling and elongation

Question 3

explain, referring to auxin, why the lateral shoots near the top of a plant are shorter than the lateral shoots at the bottom.

Answer 3

because auxins favour growth of the apical shoot, but inhibit lateral shoot growth
therefore, the highest concentration of auxin is found in the tip (at the top) and so the growth of the lateral shoots near the top is inhibited- shorter

Question 4

what processes do auxins inhibit, and what is the name of the hormone that counteracts auxin in these processes?

Answer 4

inhibits fruit ripening and abscission
ETHENE counteracts this, promoting fruit ripening and abscission

Question 5

outline the commercial uses of auxins (3)

Answer 5

• hormone rooting powder: causes C. elongation
• production of seedless fruit
• creation of herbicides- selective weed killer

Question 6

outline the role of gibberellins in plants. (2)

Answer 6

promotes germination
cause cell elongation: increasing internodes

Question 7

explain how gibberellins provide plants with glucose for respiration, to increase growth. (3)

Answer 7

1. switch on genes that code for enzymes: proteases and amylase
2. amylase catalyses the hydrolysis of starch into maltose
3. maltose is then converted to glucose in respiration

Question 8

state and explain experimental evidence for the role of gibberellins in germination.

Answer 8

1. gibberellin inhibitors: applied to plant- seeds didn’t germinate
2. GM seeds: genes that code for gibberellin synthesis were removed, and the seeds didn’t germinate

Question 9

outline the commercial uses of gibberellins.

Answer 9

• delated ripening of fruit
• production of larger fruit (due to stem elongation)

Question 10

explain the meaning of phototropism

Answer 10

the growth of a plant in response to light stimulus

Question 11

are shoots positively or negatively phototrophic?
why?

Answer 11

shoots are positively phototrophic
they grow towards the light (upwards)

Question 12

are shoots positively or negatively geotropic?
why?

Answer 12

negatively geotropic
shoots grow against the pull of gravity (upwards)

Question 13

are roots positively or negatively phototrophic?
Why?

Answer 13

negatively phototrophic
they grow away from light, down into soil

Question 14

are roots positively or negatively geotropic?
why?

Answer 14

positively geotropic
they grow with the pull of gravity (downwards)

Question 15

explain the role of auxin in geotropism

Answer 15

• auxin is produced in the root tip
• causes elongation of one side, downwards with pull of gravity
• roots are positively geotropic