Responses in Plants

Question 1

How do plants respond to stimuli?

Answer 1

Tropisms

Question 2

What is a tropism?

Answer 2

The response of a plant to a directional stimulus (a stimulus coming from a particular direction).

Question 3

How do plants respond to stimuli using tropisms?

Answer 3

By regulating their growth

Question 4

What can tropisms be?

Answer 4

• Positive

* Negative

Question 5

What is a positive tropism?

Answer 5

A growth towards the stimulus.

Question 6

What is a negative tropism?

Answer 6

A growth away from the stimulus.

Question 7

What are the types of tropism?

Answer 7

• Phototropism

* Gravitropism

Question 8

What is a phototropism?

Answer 8

A growth in response to light.

Question 9

How do plants do phototropisms?

Answer 9

• Shoots are positively phototropic (and grow towards light).
• Roots are negatively phototropic (and grow away from light).

Question 10

What is a gravitropism?

Answer 10

A growth in response to gravity.

Question 11

How do plants do gravitropisms?

Answer 11

• Shoots are negatively phototropic (and grow upwards, against gravity).
• Roots are positively phototropic (and grow downwards, with gravity).

Question 12

How do plants do these tropisms?

Answer 12

Using specific growth factors.

Question 13

What are growth factors?

Answer 13

Hormone-like chemicals that speed up or slow down plant growth.

Question 14

Where are growth factors produced?

Answer 14

In the growing regions of the plants (e.g. shoots and roots).

Question 15

What do growth factors do in response to stimuli?

Answer 15

They move to where they are needed in the plant.

Question 16

What is an example of a growth factor used in plants?

Answer 16

Auxins

Question 17

Where are auxins produced?

Answer 17

In the tips of shoots.

Question 18

What do auxins do?

Answer 18

They diffuse backwards from the tips of shoots to stimulate the cell just behind the tips to elongate.

Question 19

How do cells elongate because of auxin?

Answer 19

The cell walls become loose and stretchy, so the cell gets longer.

Question 20

What happens if the tip of a shoot is removed?

Answer 20

No auxin will be available so the shoot stops growing.

Question 21

What does auxin do (not just in shoots)?

Answer 21

It stimulates the growth in shoots, but high concentrations inhibit the growth in roots.

Question 22

What is an example of an auxin?

Answer 22

Indoleacetic acid (IAA)

Question 23

Where is IAA produced?

Answer 23

In the tips of shoots and roots in flowering plants.

Question 24

What does IAA do?

Answer 24

It moves around the plant to control tropisms.

Question 25

How does IAA move over short distances?

Answer 25

Via diffusion and active transport over short distances.

Question 26

How does IAA move over long distances?

Answer 26

Via the phloem over long distances.

Question 27

What does IAA moving over short and long distances via different methods mean?

Answer 27

That different parts of the plant have different concentrations of IAA, this uneven distribution causes uneven growth of the plant.

Question 28

How does IAA aid phototropisms?

Answer 28

* IAA concentration increases on the shaded side of the shoot, so cells elongate and bend towards the other side (towards the light). * IAA concentration increases on the shaded side of the root, growth is inhibited so the roots bend away from the light.

Question 29

How does IAA aid gravitropisms?

Answer 29

* IAA concentration increases on the lower side of the shoot, so cells elongate upwards (away from gravity). * IAA concentration increases on the lower side of the root, growth is inhibited so the roots grow downwards (with gravity).

Question 30

How does IAA cause uneven growth?

Answer 30

* IAA moves to the more shaded side of the shoots and roots. | * IAA moves to the lower side of the shoots and roots.

Question 31

If IAA (or any auxin) is on the right hand side of the tip of the shoot in the dark, what happens?

Answer 31

Cells elongate on that side causing the shoot to grow towards the left.

Question 32

If IAA (or any auxin) is on the right hand side of the tip of the shoot in the light, what happens?

Answer 32

IAA will accumulate on the shaded side no matter where the IAA is placed initially, so cells will elongate on the shaded side, causing the shoot to grow towards the light.