Responses in plants

Question 1

define tropism`

Answer 1

growth response of a plant in response to a directional stimuli

Question 2

positive tropism

Answer 2

growth towards a stimulus

Question 3

negative tropism

Answer 3

growth away from a stimulus

Question 4

gravitropism

Answer 4

growth of a plant in response to gravity

Question 5

negative gravitropism

Answer 5

grow upwards (against gravity) e.g shoots

Question 6

positive gravitropism

Answer 6

grow downwards (towards gravity) e.g roots

Question 7

What do plants use to respond to directional stimuli?

Answer 7

Specific growth factors; these are hormone-like chemicals that speed up or slow down plan growth

Question 8

Where are plant growth factors produced and where do they move to?

Answer 8

Produced in the growing regions of the plant, for example, shoot and root tips, and they move to where they’re needed in the other parts of the plant

Question 9

What are the growth of shoots and roots controlled by?

Answer 9

Auxins

Question 10

What causes a plant to produce auxins?

Answer 10

Environmental stimuli like gravity, light and water.

Question 11

What happens when auxins are produced in the shoots, how do they move and why?

Answer 11

Growth factors called auxins are produced in the tips of the shoots and stimulate the cell just behind the tips to elongate; this is where cell walls become loose and stretchy, so the cells get longer.

Question 12

What happens if the tip of a shoot is removed?

Answer 12

No auxin will be available and the shoots stop growing.

Question 13

What happens if there is a high concentration of auxins in shoots?

Answer 13

Auxins stimulate growth in shoots but high concentrations inhibit growth in roots.

Question 14

Why does IAA move and how?

Answer 14

by diffusion and active transport over short distances, and via the phloem over long distances.

Question 15

What does distribution of IAA cause?

Answer 15

Different parts of the plant having different concentrations of IAA -means there’s an uneven growth of the plant.

Question 16

Give an example of phototropism

Answer 16

IAA moves to the more shaded parts of the shoots and roots so there’s uneven growth.
Shoots: IAA concentration increases on the shaded side , cells elongate and the shoot bends towards the light.
Roots: IAA concentration increases on the shaded side , growth is inhibited so the root bends way from the light.
Example: gravitropism
IAA moves to the underside of shoots and roots , so there’s uneven growth.
Shoots: IAA concentration increases on the lower side , cells elongate so the shoot grows upwards.
Roots: IAA concentration increases on the lower side, growth is inhibited so the root grows downwards.