Coordination and Response in plants

What are auxin?

• Auxins are plant hormones which control growth at the tips of roots and shoots

• Auxin is produced in the tips and diffuses backwards to stimulate the cell elongation process

• Auxin promotes growth in the shoot, but actually inhibits growth in the root

What does positively phototrophic mean?

• When a shoot tip is exposed to light, it accumulates more auxin on the side that’s in the shade than the side thats in the light

• This makes the cell grow faster on the shaded side, so the shoot bends towards the light

What does negatively geotropic mean?

• When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side

• This causes the lower side to grow faster, bending the shoot upwards

What does positively geotropic mean?

• A root growing sideways will also have more auxin on its lower side

• But in a root the extra auxin inhibits growth. This means the cells on top elongate faster, and the root bends downwards

What does negatively phototrophic mean?

• If a root stars being exposed to some light, more auxin accumulates on the more shaded side

• The auxin inhibits cell elongation on the shaded side, so the root bends downwards, back info the ground

What is a clinostat?

• A device which uses rotation to negate the effects of gravitational pull on plant growth and development