16.1 Plant Hormones & Growth In Plants

Question 1

What’s the the four plant hormones to know

Answer 1

Auxins
Gibberellin
Ethene
ABA

Question 2

What are roles of auxins

Answer 2

Control cell elongation
Prevent leaf fall
Maintain apical dominance

Question 3

What are roles of gibberellins

Answer 3

Trigger mobilisation of food stores in seed germination

Cause stem elongation

Question 4

What are the roles of ethene

Answer 4

Cause fruit ripening

Promote abscission in deciduous trees

Question 5

What are the roles of ABA

Answer 5

Maintain dormancy of seeds and buds
Stimulate cold protective responses like antifreeze
Stimulate stomatal closing

Question 6

What must be the first thing to happen for a plant to grow

Answer 6

The seed must germinate

Question 7

What are the first steps of a seed germinating

Answer 7

The seed absorbs water and this activates the embryo and gibberellins begin to be produced

Question 8

What happens when gibberelins start to be produced in seed germination

Answer 8

The gibberellins stimulate the production of enzymes that break down food stores in the seed
These food stores are used to produce ATP to build materials to grow

Question 9

What enzymes do gibberellins switch on the genes for in germination of a seed

Answer 9

Amylase and protease

Digestive enzymes

Question 10

What are some of the experimental evidence for gibberellins

Answer 10

Mutant varies of seeds that have been bred to not have the gene for gibberellins are seeds that don’t germinate
If you add gibberellins biosynthesis inhibitors to seeds they won’t germinate as gibberellins aren’t made

Question 11

Where are auxins made

Answer 11

In the tips of roots and shoots

Question 12

How do auxins stimulate growth of main apical shoots

Answer 12

Auxins bind to specific receptor sites causing a fall in pH to 5
This is the opt pH for enzymes needed to keep walls flexible
As cell matures auxin is destroyed and pH rises again so the enzymes become inactive and the walls become rigid abs fixed in shape

Question 13

What is apical dominance

Answer 13

The main shoot dominates/ inhibits the outgrowth of other shoots

Question 14

How do auxins cayse apical dominance in roots

Answer 14

High concentration of auxins in apical shoots suppress teh growth of lateral shoots

Question 15

What does high concentrations of auxins in roots mean

Answer 15

Inhibit roots growth

Shaded roots contain more auxin and so grow less

Question 16

What is the evidence for auxins working on stem growth

Answer 16

If the apical shoot is removed then the auxin producing cells are removed and so there is no auxin - the lateral shoots are then freed from dominance and the apical shoot grows faster

Question 17

What is the eve induce for auxin being produced in root tops and auxin reaching roots in low concentrations from growing shoots

Answer 17

If apical shoots are removed then the amount of auxin getting to roots is reduced and root growth slows

Question 18

What are internodes

Answer 18

The regions between leaves on a stem

Question 19

What do gibberellins have to do with seed elongation

Answer 19

They effect the length of the internodes

Without gibberellins the plant stems are much shorter makes them less vulnerable to damage by weather and reduces waste

Question 20

What is synergism

Answer 20

When different hormones work together and give a greater response than on there own

Question 21

What is antagonism

Answer 21

When hormones have oppsosite effects to one another

Question 22

What practical investigation can be used to see the effect of hormones on plant growth

Answer 22

Grow seedlings hydrophonically (in nutrient solution) in serial solutions of different hormones

Apply different concentration of hormones to cut ends of stems and roots