B4 Plant Growth

Question 1

What are auxins?

Answer 1

Plant hormones which control and coordinate growth at the tips of shoots and roots.

Question 2

How do auxins move through the plant?

Answer 2

In solution (dissolved in water)

Question 3

Where is auxin produced?

Answer 3

At the tips of shoots and roots.

In the tips and they diffuse backwards to stimulate the cells to elongate (grow), which happens just behind the tips.

Question 4

How does auxin affect:

Roots

Shoots

Answer 4

Roots - inhibits growth

Shoots - promotes growth

Question 5

What do auxins respond to?

Answer 5

Light and gravity

Question 6

What is the growth repose to light called?

Answer 6

Phototropism

Question 7

What is the growth response to gravity called?

Answer 7

Gravitropism

Question 8

How does light change the direction of growth in shoots?

Answer 8

When a shoot tip is exposed to light, it accumulates more auxin on the side that’s in the shade than the side that’s in the light.

This makes the cells grow faster on the shaded side so the shoot bends towards the light.

Question 9

How does gravity change the direction of growth in shoots?

Answer 9

When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side.

This causes the lower side to grow faster, bending the shoot upwards.

Question 10

What is the phrase that tells us that shoots grow towards the light?

Answer 10

Shoots are positively phototropism.

Question 11

What is the phrase that tells us shoots grow away from gravity?

Answer 11

Shoots are negatively gravitrophic

Question 12

What is the phrase that tells us roots grow towards gravity?

Answer 12

Roots are positively gravitrophic

Question 13

What is the phrase that tells us roots grow away from light?

Answer 13

Roots are negatively phototophic

Question 14

How does gravity change the direction of growth in roots?

Answer 14

A root growing sideways will also have more auxin on its lower side.

In a root auxin inhibits growth, this means the cells on top elongate faster and the roots bend downwards.

Question 15

How does light change the direction of growth in roots?

Answer 15

If a root starts being exposed to some light, more auxin accumulates on the more shaded side.

The auxin inhibits cell elongation on the shaded side, so the root bends downwards back into the ground.

Question 16

What is the purpose of phototropism and gravitropism?

Answer 16

To increase a plants chance of survival.

Eg. by growing towards the light, a plant shoot is able to absorb more light for photosynthesis

Eg. by growing downwards a plant root is more likely to anchor itself into the soil and find water and minerals.

Question 17

What is a cutting?

Answer 17

A part of a plant that has been cut off it (end of a branch with a few leaves).

Question 18

Why does rooting powder help cuttings grow?

Answer 18

Rooting powder contains auxins, to encourage the plant to produce roots rapidly and start growing as new plants.

Question 19

What is the benefit of using rooting powder to grow cuttings?

Answer 19

It enables growers to produce lots of clones of a really good plant very quickly.

Question 20

What is a clone?

Answer 20

An exact copy

Question 21

What are gibberellins?

Answer 21

Plant hormones that break the dormancy and low seeds to germinate.

Question 22

Why do seeds need gibberellins?

Answer 22

Seeds won’t germinate until they’ve been through certain conditions (eg, a period of cold or of dryness). This is called dormancy.

Gibberellins break the dormancy and allow seeds to germinate.

Question 23

Why do commercial growers use gibberellins?

Answer 23

To make seeds germinate at times of year they wouldn’t normally germinate.

It make sure all the seeds in a batch germinate at the same time.

Question 24

What response to a cold spell or lack of water do gibberellins trigger?

Answer 24

Bolting.

Question 25

What is bolting?

Answer 25

A response triggered by gibberellins in response to a cold spell of lack of water.

The plant produces lots of flowers in an attempt to reproduce before it dies.

Question 26

How do commercial growers use gibberellins to make plants flower?

Answer 26

Commercial growers use gibberellins to make plants flower earlier than they usually would, or under conditions in which they wouldn’t normally flower (bolting)

Question 27

What part of the plant produce ethane?

Answer 27

Ageing leaves.

Question 28

Why do ageing leaves produce ethane?

Answer 28

To cause the leaf to fall off the plant.

Question 29

How does ethane cause ageing leaves to fall of the plants?

Answer 29

Ethane stimulates cells that connect the leaf to the rest of the plant to expand, this breaks the cell walls and causes the leaf to fall off the plant.

Question 30

Why do commercial growers use ethane?

Answer 30

To remove leaves from a crop before it is harvested, to make it easier to collect seeds or fruits.

Question 31

How is fruit affected by ethane?

Answer 31

It stimulates enzymes that cause fruit to ripen.

Question 32

How is ethane used to ripen fruits commercially?

Answer 32

Ethene can be used to control the ripening of fruits either while they are still on the plant or during transport to the shops.

The fruit can be picked whilst it’s still unripe and ethene has. Then added so the fruit ripens on its way to the supermarket, to reach the shelves in perfect condition.

Question 33

Why is fruit picked when unripe?

Answer 33

Because it is firmer and less easily damaged.

Question 34

Give two ways in which gibberellin affects the natural growth and development of plants. (2 marks)

Answer 34

Stimulates seed growth (1 mark)

Stimulates bolting/flowering (1 mark)