Responses in plants

Question 1

What are auxins?

Answer 1

Plant growth hormones

Question 2

What do auxins do?

Answer 2

1) They control the growth at the tips of shoots and roots.
2) They move through the plant in a solution.
3) Auxin is produced at the tips and diffuses backwards to stimulate the cell elongation process.
4) Promotes the growth of shoots, but inhibits the growth of roots.

Question 3

What are auxins involved in?

Answer 3

Growth responses of plants to light (phototropism) and gravity (geotropism).

Question 4

Shoots are positively geotropic (grow towards light)

Answer 4

1) When a shoot tip is exposed to light, it accumulates more auxin on the side that’s in the shade than the side that’s in the light.
2) This makes the cells elongate faster on the shaded side.
3) Therefore, the shoot bends towards the light

Question 5

Shoots are negatively geotropic (grow away from gravity)

Answer 5

1) When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side.
2) This causes the lower side to elongate faster, bending the shoot upwards.

Question 6

Roots are positively geotropic (grow towards gravity)

Answer 6

1) A root growing sideways will have more auxin on its lower side.
2) But in a root the extra auxin inhibits growth.
3) This means the cells on top elongate faster, and the roots bend downwards.

Question 7

Roots are negatively phototropic (grow away from light)

Answer 7

1) Auxin is produced on the shaded side of a root when it is exposed to light.
2) This auxin inhibits cell elongation on the shaded side, so the root bends downwards, back into the ground.