The effects of plant hormones

Question 1

What is apical dominance?

Answer 1

When auxins stimulate apical bud growth,

but inhibits growth of side shoots from lateral buds

Question 2

What happens when the apical bud is removed?

Answer 2

Auxins stops being produced, and the side shoot formation is no longer inhibited.

Question 3

What are the control variables for apical dominance practical?

Answer 3

light intensity, temperature, water

you leave all the plants to grow for 6 days

Question 4

What do gibberellins do? (4 things)

Answer 4

Stimulate

1) seed germination
2) stem elongation
3) side shoot formation
4) Flowering

Question 5

How do gibberellins stimulate seed germination?

Answer 5

They trigger the break down of starch into glucose

The glucose is then used to respire and release energy it needs to grow

Question 6

What inhibits gibberellins ?

Answer 6

Abscisic acid.

Question 7

For the apical dominance practical :

Answer 7

30 plants total

10 with removed tip and auxin paste

10 with removed tip and without auxin paste

10 with no change ( “control” to compare)

Question 8

Gibbering stem elongation practical:

Answer 8

40 plants in total

• 20 plants leave normal, water the normally and keep conditions same
• The other 20 plants, leave them to grow normally, BUT
  water them with a dilute solution of gibberellin
• Results suggest that gibberellins stimulate stem elongation

^ the ones watered with gibberellins have longer stems

(LET PLANTS GORW FOR 28 DAYS)

Question 9

Are auxins and gibberellins synergistic or antagonistic?

Answer 9

BOTH

Question 10

What does synergistic mean?

Answer 10

It means the auxins and gibberellins can work together and have a really big effect.

Question 11

What does antagonistic mean?

Answer 11

Means that auxins and gibberellins can sometimes oppose each others actions.

E.g. Gibberellins stimulate side shoot formation, but auxins inhibit side shoot formation.

Question 12

What are deciduous plants?

Answer 12

Plants that lose their leaves

Question 13

Why do plants lose their leaves?

Answer 13

To conserve water during cold parts of the year

• where, it is a lot harder to absorb water from the frozen soil
• there is also less sunlight available for photosynthesis

Question 14

What hormones control leaf loss?

Answer 14

Auxins and ethene

Question 15

How do auxins control leaf loss?

Answer 15

Auxin inhibits leaf loss

However as a leaf gets older less auxin is produced, so there is more leaf loss.

Question 16

How does ethene control leaf loss?

Answer 16

A layer of cells called the abscission layer develops at the bottom of the leaf stalk.

• The abscission layer separates the leaves from the rest of the plant.

ETHENE CAUSES the abscission layer to expand, breaking the cell walls causing LEAF LOSS.

Question 17

What hormone triggers the stomata to close?

Answer 17

Abscisic acid ( ABA)

Question 18

How does abscisic acid trigger “stomatal closure” ?

Answer 18

ABA binds to the receptors on the membrane of the guard cells.

• This causes ion channels to open which allows calcium ions to move from the vacuole into the cytosol.
• High concentration of calcium ions int he cytosol causes other ion channels to open.
• It is this that causes things like potassium ions to leave the guard cells through ion channels increasing the water potential of the guard cells
• WATER LEAVES the guard cells by osmosis, guard cells become flaccid and the stomata closes.

Question 19

How can ethene be used commercially ( fruit industry)

Answer 19

• Ethene stimulates BREAK DOWN of cell walls, chlorophyll and converts starch into sugars.
• This makes fruit soft and ripe and ready to eat.

Question 20

How can auxins be used commercially ( farmers and gardeners)

2 ways

Answer 20

1) Used in selective weed kills ( herbicides)

2) Used as rooting hormone in rooting powder

Question 21

How is auxin used in weed killers?

Answer 21

Auxins make weeds produce long stems, so weeds grow tall, so they can’t manage to get enough water or nutrients SO THEY DIE

Question 22

How is auxin used in rooting powder?

Answer 22

• auxins make a cutting grow roots
• The cutting can be planted and grown into a new plant.
• Many cuttings can be taken from one plant, and can be treated with rooting hormones, so lots of the same plant can be grown quickly and cheaply from one plant.