Plant Hormones and Growth

Question 1

What are the 3 ways hormones travel?

Answer 1

-diffusion, active transport and mass flow in xylem and phloem

Question 2

What are the 5 main growth hormones?

Answer 2

-auxins, cytokinins, gibberllins, abscisic acid and ethene

Question 3

How do hormones travel in a plant?

Answer 3

-diffusion, active transport and mass flow in xylem and phloem

Question 4

What are the 5 growth hormones?

Answer 4

-auxins, cytokinins, gibberellins, abscisic acid and ethene

Question 5

What are auxins?

Answer 5

-cause elongation in stems and inhibits growth in roots
-prevents leaves from dropping

Question 6

What is ethene?

Answer 6

-gas causing fruit to ripen

Question 7

What is gibberellin?

Answer 7

-stimulates seed germination, elongation and pollen tube growth in fertilisation

Question 8

What is abscisic acid?

Answer 8

-stimulates stomatal closing and maintains dormancy of seeds
-promotes leaf fall
-high auxin in shoot keeps ABA levels high

Question 9

What are cytokinins?

Answer 9

-promote growth
-directly applying to buds can override apical dominance
-high levels of auxin make shoot apex a sink for cytokinins produced in roots

Question 10

What is apical dominance?

Answer 10

-inhibition of lateral bud growth due to chemicals produced by apical bud

Question 11

What are terminal buds?

Answer 11

-on top

Question 12

What are axillary/lateral buds?

Answer 12

-on sides

Question 13

How do growth hormones work?

Answer 13

-act on target cells
-bind to specific complementary receptors on cell surface memb of target cells
-hormones sped up or slow growth
-hormones more through plant

Question 14

What will happen if you cut off the shoot tip (apex) of a plant?

Answer 14

-it will grow side branches from lateral buds that were previously dormant
-auxins from apical bud prevent lateral buds from growing
-when tip removed. auxin levels drop = buds

Question 15

What experimental evidence is there to test auxin growth?

Answer 15

-they showed that
1. if you cut of the apex - more lateral buds grow
2. then do the same bud add auxin to the cut off shoot - no buds

Question 16

What are some problems with experimental manipulation of plants?

Answer 16

-unexpected effects like exposure to oxygen, cells on the cut end could have produced a hormone that promoted lateral growth
-scientists added ring of auxin transport inhibit below apex of shoot

Question 17

How is seed germination promoted by gibberellin?

Answer 17

1. water diffuses into embryo
2. embryo releases gibberellin
3. gibberellin promotes amylase production
4. amylase converts starch into glucose
5. glucose can be used for respiration or protein synthesis

Question 18

What evidence is there for germination?

Answer 18

-mutant varieties = no germination
but when artificial gel applied = germinate

-if G biosynthetic inhibitors were applied to no G seeds - if inhibitors removed and G applied = germination

Question 19

Explain why plants need to be able to respond to their environment

Answer 19

-to cope with changing conditions
-avoid abiotic stress
-maximise photosynthesis