• The Chapter 31 and 32 homework is due on April 7 at 11:59 pm. (Chapter 32 only includes pages 641-653.)

• The Chapter 31 and 32 Test will be on April 8th.

Chapter 31Auxin

You Must Know

• The role of auxins in plants. (This is the only plant hormone you will be expected to remember.)

• How phototropism use changes in the environment to modify plant growth and behavior.

Cell 1

Cell 2

Basal endof cell

25 m

Auxin

Light

Cell elongation

Figure 31.5a

CELL WALL

Cell wall-loosening enzymes cleave cross-linkingpolysaccharides.

CYTOPLASM

H

Plasma membraneATP

Acidityincreases.

Low pHactivatesexpansins.

Protonpumpactivityincreases.

1

2

H

H

H

H

H

H

H

H

3

4

Figure 31.5b

Plasmamembrane

Cellwall

H2O

Vacuole

Sliding cellulose microfibrilsallow cell to elongate.

5

• Auxin also alters gene expression and stimulates a sustained growth response