2.10.4 The Role of Auxin in Phototropism

Question 1

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

Answer 1

auxins

Question 2

What do auxins do?

Answer 2

coordinate and control directional growth responses such as phototropisms and geotropism

Question 3

Where are auxins mostly made

Answer 3

in the tips of growing shoots and then diffuses down to the region where cell division occurs (just below the tip)

• This is an important point – only the region behind the tip of a shoot is able to contribute to growth by cell division and cell elongation

Question 4

Auxin stimulates the cells in this region to do what?

Answer 4

to elongate (get larger); the more auxin there is, the faster they will elongate and grow

Question 5

If light shines all around the tip, what does the auxin do?

Answer 5

auxin is distributed evenly throughout and the cells in the shoot grow at the same rate – this is what normally happens with plants growing outside

Question 6

When light shines on the shoot predominantly from one side, what does the auxin do?

Answer 6

the auxin produced in the tip concentrates on the shaded side, making the cells on that side elongate and grow faster than the cells on the sunny side

Question 7

unequal growth on either side of the shoot causes the shoot to, do what?

Answer 7

to bend and grow in the direction of the light