IAA

Question 1

What is IAA?

Answer 1

Indoleacetic acid is the growth factor involved in phototropism and gravitropism responses

Question 2

What is IAA made and released by in the shoots and root cells?

Answer 2

Apical meristem

Question 3

How does IAA cause cell elongation?

Answer 3

It increases the stretchiness of the cell wall when water enters by osmosis

Question 4

How does IAA cause a positive phototropism response in shoot tips?

Answer 4

1. Cells of the shoot tip make and release IAA which diffuses down the chute through cells.
2. Light causes IAA to move via active transport from the lit side to the shaded side of the shoot, so a greater concentration of IAA builds up in the cells on the shaded side.
3. IAA causes shoots cells to elongate so the cells on the shared side lengthen more than the cells on the lit side.
4. Due to this, the shaded side of the shoot grows faster causing the shoot to bend TOWARDS the light source.

Question 5

How does IAA cause the negative gravitropism response in root tips?

Answer 5

1. IAA gathers in the lower cells of the shoot tissue.
2. This stimulates cell elongation.
3. So lower shoot cells lengthen at a faster rate than the upper cells.
4. This causes the shoot to grow UPWARDS.

Question 6

How does IAA cause the positive gravitropism response in root tips?

Answer 6

1. IAA gathers in the lower cells of the root tissue.
2. This inhibits cell elongation.
3. So the lower cells lengthen at a slower rate than the upper cells.
4. This causes the root to grow DOWNWARDS.