Plant responses Module 5

Question 1

3 examples of plants increasing their chances of surviving by responding to changes in their environment?

Answer 1

Sense the direction of light and grow towards it
Can sense gravity, so their roots and shoots grow in the right direction
Climbing plants have a sense of touch so can find things to climb and reach the sunlight

Question 2

2 examples of plants having chemical defences against herbivory?

Answer 2

Produce alkaloids which are chemicals which produce bitter tastes or poisonous

Produce tannins - Taste bitter, and can bind to proteins in the gut to make them hard to digest

Question 3

2 exampes of plants releasing pheromones in reponse to herbivory?

Answer 3

Release alarm pheremones, in response to herbivore grazing nearby plants can detect these and start making chemical defences

Question 4

Some plants are able to roll up to protect themselves in response to being?

Answer 4

Touched

Question 5

How do some plants respond to extreme cold?

Answer 5

Producing their own anti-freeze, the proteins bind to ice crystals and lower the temperature water freezes at

Question 6

What is tropism?

Answer 6

The response of a plant to a directional stimulus

Positive tropism = growth towards the stimulus
Negative tropism = growth away from the stimulus

Question 7

What is phototropism?

Answer 7

The growth of a plant is response to light

Shoots are positively phototropic so grow towards light
Roots are negatively phototropic, so grow away from light

Question 8

What is geotropism?

Answer 8

Growth a plant is response to gravity

Shoots are negatively geotropic so grow upwards

Roots are positvely geotropic so grow downwards

Question 9

What’s hydrotropism, thermotropism, and thigmotropism?

Answer 9

Plant growth in response to water
Plant growth in response to temperature
Plant growth in response to touch

Question 10

In plants where are growth hormones produced?

Answer 10

In the growing regions of the plant eg shoot tips and leaves

Question 11

What does the growth hormone gibberellin stimulate?

Answer 11

Seed germination
Stem elongation
Side shoot formation
Flowering

Question 12

What does the growth hormone auxin do generally?

Answer 12

Stimulate growth of shoots via cell elongation

High concentrations inhibit growth in roots

Question 13

Describe what the important auxin (IAA) does?

Answer 13

It stimulates cell elongation, and is move around the cell via diffusion, active transport and via the phloem for long distances

IAA moves to the more shaded parts of shoots and roots, stimulates cell elongation in cells so causes them to grow towards the light. Inhibts growth in roots, causing them to grow away from the light

Moves to the underside of shoots and roots, causing cell elongation in shoots so makes them grow upwards. Inhibits growth in roots so causes them to grow downwards

Question 14

What’s the shoot tip at the top of a flowering plant called?

Answer 14

Apical bud

Question 15

How do auxins cause apical dominance?

Answer 15

Auxin stimulate the growth of the apical bud, and inhibit the growth of side shoots from lateral buds - this is apical dominance

This saves energy and prevents side shoots from competing with the shoot tip for light

So plant will grow taller faster to outcompete other plants for light

Question 16

What happens if you remove the apical bud?

Answer 16

The side shoots will start growing by cell division and cell elongation

Question 17

How do gibberelins stimulate seed germination?

Answer 17

Triggering the breakdown of starch into glucose in the seed

The plant embryo in the seed can then use the glucose to respire a release the energy it needs to grow

Question 18

What chemical inhibits gibberellins and therfore seed germination?

Answer 18

The hormone abscisic acid

Question 19

Gibberellins and auxins are often synergetic what does this mean?

Answer 19

They work together to have a big effect eg. both make a plant grow very tall

Question 20

Gibberellins and auxins are sometimes antagonistic what does this mean?

Answer 20

They oppose each others actions, eg gibberlins stimulate side root growth, whilst auxins inhibit side shoot growth

Question 21

What are deciduous plants?

Answer 21

Plants that lose their leaves in winter, to preserve water as difficult to uptake from soil, and there’s not much sun for photosynthesis anyway

Question 22

Describe how leave loss is controlled by hormones?

Answer 22

Auxins inhibit leave loss, and are produced by young leaves so as they get older are more likely to fall off

Ethene stimulates leaf loss, and is produced by ageing leaves, as the leaf gets older more ethene is produced, causing layer of cells called the abscission layer to form at the bottom of the leaf stalk.

This separates the leaf from the rest of the plant, the abscission layer expands breaking cell walls, and causes the leaf to fall off

Question 23

Explain how plant hormones are involved in stomatal closure?

Answer 23

Need to be able to close stomata to reduce water loss

This is done using guard cells found each side of the stomatal pore

When they are filled with water, they are turgid and the pore is forced open, when they lose water they become flaccid and the pore is closed

Absisic acid (ABA) triggers stomatal closure by binding to receptors on the guard cell membranes which causes specific ion channels to open, this allows Ca2+ ions in, this increase then causes K+ ion channels to open so they leave the cell, raising the water potential of the cells, so water then leaves the guard cells via osmosis

So the guard cells become flaccid and the stomata close

Question 24

Give examples of plant hormones in commercial use?

Answer 24

Ethene to ripen fruit at perfect time

Auxins to kill weeds as makes them produce long stems instead of lots of leaves so can’t get enough water or nutrients and they die

Auxins can be used as rooting powders, so make a cut stem grow roots

Question 25

How does Ethene make fruit ripen?

Answer 25

Stimulates hormones, that break down cell walls and chlorphyll, and convert starch into sugars