5.6 Plant responses

Question 1

Why do plants respond to stimuli?

Answer 1

In order to survive.

Question 2

What is abiotic stress?

Answer 2

Anything that’s potentially harmful to a plant that’s natural but not living
eg drought.

Question 3

What is herbivory?

Answer 3

When plants are being eaten by animals.

Question 4

What do plants do to limit herbivory?

Answer 4

•Produce chemicals like alkaloids and tannins to make them taste bitter and deter animals.
•Release pheromes (chemical signallers) to get other plants nearby to respond.
•Nastic movements -Fold up in response to touch. (eg mimosa pudica)

Question 5

What is a tropism? Positive vs negative?

Answer 5

The response of a plant to a directional stimulus.

A positive is growth towards a stimulus.
A negative is growth away from the stimulus.

Question 6

What is Phototropism? What are shoots and roots like?

Answer 6

The growth of a plant in response to light.
Shoots are positively phototropic and grow towards the light but roots are negatively phototropic and grow away from the light.

Question 7

What is Geotropism? What are roots and shoots?

Answer 7

Geotropism is the growth of a plant in response to gravity.

Shoots = negatively geotropic as grow up and against gravity
Roots = positively geotropic as grow down and with gravity

Question 8

What are the other tropisms other than phototropism and geotropism?

Answer 8

Hydrotropism
Thermotropism
Thigmotropism

Question 9

Practical to investigate phototropism

Answer 9

• Cover shoot tips in foil and some without
  ones with should grow straight up
  ones without should grow towards light (bend)

Question 10

What are the two growth hormones?

Answer 10

Gibberellins and Auxins

Question 11

What is auxin ? What does it do?

Answer 11

• A plant hormone produced in apical meristems of shoots that causes cell elongation behind the tip on the shaded side.
• It inhibits growth of lateral buds (apical dominance)
• Inhibits leaf fall
• High concs inhibit growth in roots
• Cell elongation.

Question 12

What is IAA and where is it found?

Answer 12

Indoleacetic acid an auxin found in tips of roots and shoots of flowering plants

Question 13

How do auxins move?

Answer 13

By diffusion and active transport over short distances and phloem over long distances

Question 14

What happens if tip of shoot is removed?

Answer 14

No auxin will be produced so plant won’t grow any taller

Question 15

What is apical dominance?

Answer 15

it’s where auxins stimulate growth of the apical bud and inhibit growth of side shoots from lateral buds.
- The apical bud is dominant over the lateral bud

Question 16

Why is apical dominance a good thing for plants ?

Answer 16

As it allows the plant to grow up and not out so it isn’t bushy. This means that no leaves are shaded so there’s a higher primary productivity.

Question 17

What are gibberellins? what do they do?

Answer 17

Hormones produced in young leaves and seeds.

Stimulate
•elongation between internodes
•stimulate seed germination
•side shoot formation
•Flowering

Question 18

What don’t gibberellins do?

Answer 18

Don’t inhibit growth in any way.

Question 19

What hormone inhibits gibberellins and what does this cause?

Answer 19

abscidic acid and this causes seed germination to be prevented

Question 20

What is synergistic?

Answer 20

Where the hormones work together

Question 21

What is an example of plant hormones being synergistic?

Answer 21

Auxins and Gibberellins working together to help plants grown tall

Question 22

What is antagonistic?

Answer 22

Where the hormones work against each other and oppose each others actions.

Question 23

What is an example of antagonistic hormones in plants?

Answer 23

Auxins and Gibberellins as auxins inhibit side shoot growth but gibberellins stimulate side shoot growth.

Question 24

What are the dominant alleles for gibberellins? what do dwarf plants have?

Answer 24

Le is dominant (has GA)
le is recessive (doesn’t have GA)

dwarf plants have le le and are recessive so have no GA

Question 25

What hormones control leaf abscission?

Answer 25

• Auxins inhibit leaf loss
• Ethene stimulates leaf loss

Question 26

How does a decrease in auxin production affect leaf loss?

Answer 26

Increases leaf loss when there is less auxin concentrations

Question 27

What does an increase in ethene levels do and why?

Answer 27

Causes more leaf loss as the production of cellulase that breaks down cell walls in the abscission layer increase. This causes the leaves to fall

Question 28

What hormone triggers stomatal closure and how?

Answer 28

Abscisic acid (IAA)

As it binds to receptors on guard cell membranes which cause ion channels to open and more calcium ions enter so this lowers the water potential and causes water to enter by osmosis.

Question 29

What are the commercial uses of ethene and how does this work?

Answer 29

Used to ripen fruits like bananas.
Fruit picked before ripe and exposed to ethene on arrival to prevent damage.

Works because ethene stimulates enzymes that break down cell walls.

Question 30

How are auxins used commercially?
How does this work?

Answer 30

• As weed killers
• In rooting powder

Weed killers works as auxins cause plants to produce long stems and no leaves which causes them to die

Rooting powder as it allows cuttings to grow roots and be grown into new plant