The mechanism of a plant response to light (i.e. mechanism of phototropism)

Question 1

What do auxins do to cell walls?

Answer 1

Auxin loosens cell walls,

Question 2

Auxins loosen cell walls, what does this allow for the cell walls to then do?

Answer 2

Auxin loosens cell walls, which allows them to expand.

Question 3

What is essential for normal growth and tropisms?

Answer 3

Cell elongation is essential for normal growth and tropisms.

Question 4

Outline the 4 steps of the role of auxin (IAA) in phototropism (4)

Answer 4

Role of auxin (IAA) in phototropism

1. IAA is produced in the growth tips (meristems) of the stem.
2. If the stem is exposed to light from one side IAA will diffuse down the shaded side (ie. the side furthest from the light source).
3. The concentration of IAA present in the shaded cells causes them to elongate more than the cells on the bright side of the stem.
4. As a result of the uneven elongation, the stem bends towards the light (phototropism will result)

Question 5

Where is IAA produced specifically?

Answer 5

IAA is produced in the growth tips (meristems) of the stem.

Question 6

What happens when a stem is exposed to light from one side? (in terms of IAA)

Answer 6

If the stem is exposed to light from one side IAA will diffuse down the shaded side (ie. the side furthest from the light source).

Question 7

What causes cells to elongate in a plant?

Answer 7

The concentration of IAA present in the shaded cells causes them to elongate more than the cells on the bright side of the stem.

Question 8

what is the result of uneven elongation in a plant?

Answer 8

As a result of the uneven elongation, the stem bends towards the light (phototropism will result)