2.10.3 Response to Stimuli: Plants

Question 1

Plants need to be able to grow in response to certain stimuli, for example. (give 2 examples)

Answer 1

1. plants need to be able to grow in response to light, to ensure their leaves can absorb light for photosynthesis

Question 2

What is the directional growth responses made by plants in response to light and gravity known as?

Answer 2

tropisms

Question 3

A response to light is what?

Answer 3

phototropism

Question 4

A response to gravity is what?

Answer 4

geotropism (or gravitropism)

Question 5

If the growth is towards the stimulus, the tropism is, what?

Answer 5

positive

Question 6

If the growth is away from the stimulus the tropism is, what?

Answer 6

negative

Question 7

As shoots grow upwards, away from gravity and towards the light (so that leaves are able to absorb sunlight), shoots show, what?

Answer 7

show a positive phototropic response and a negative geotropic response

Question 8

As roots grow downwards into the soil, away from light and towards gravity (in order to anchor the plant and absorb water and minerals from the soil), roots show, what?

Answer 8

a negative phototropic response and a positive geotropic response

Question 9

Plants produce plant growth regulators (similar to hormones in animals) called, what?

Answer 9

auxins

Question 10

What do auxins do?

Answer 10

coordinate and control directional growth responses such as phototropisms and geotropisms

Question 11

Where are auxins produced

Answer 11

in the tips of the shoots and the roots; they diffuse to the cells below the tips and have the following effects

Question 12

In the shoots, auxins promote, what?

Answer 12

cell elongation (growth); more auxin = more cell elongation = more growth

Question 13

In the roots, auxins inhibit, what?

Answer 13

cell elongation (growth); more auxin = less cell elongation = less growth

Question 14

The distribution of auxin in the shoots is affected by, what?

Answer 14

by light and gravity

Question 15

The distribution of auxin in the roots is primarily affected by, what?

Answer 15

by gravity alone

Question 16

If a shoot or root is placed on its side, what will auxins do?

Answer 16

auxins will accumulate along the lower side as a result of gravity; so the uppermost side has a lower auxin concentration

Question 17

In the shoots, what grows faster, the lower side or upper side

Answer 17

the lower side grows faster than upper side (more auxin = more cell elongation), so the shoot grows upwards

Question 18

In the roots, what grows faster, the lower side or upper side

Answer 18

In the roots, the lower side grows slower than the upper side (as auxin inhibits cell elongation and growth in roots), so the root grows downwards

Question 19

Unequal distributions of auxin causes what?

Answer 19

unequal growth rates in plant roots and shoots