Plant response, taxes and kineses

Example of an auxin

IAA (indoleacitic acid)

How does IAA move around the plant

By diffusion and active transport from cell to cell, and in the phloem for long distances

Where is IAA synthesised

In the growing tips of the roots and shoots

How does IAA influence root growth

• IAA moves to the lower side of the root cell, setting up an IAA gradient across the root

• In roots, IAA inhibits cell elongation, so the cells on the lower side of the root will grow more slowly than those on the upper side

• So the root will grow downwards, towards gravity (positive gravitropism) 

How does IAA influence growth in shoots

• IAA moves to the shaded side of the shoot, setting up an IAA gradient across the shoot

• In the shoot, IAA causes cell elongation, so the cells on the shaded side elongate faster than those on the light side

• This causes the cells to bend towards the light

What are kineses 

Non-directional responses to stimuli 

Description of flatworm photokinesis

They show photokinesis - when they are exposed to light (unfavourable conditions) they move faster and change direction more often, so that they are more likely to move from the unfavourable conditions into favourable ones.

What are taxes

Directional responses to a stimulus - involves moving towards (positive) or away from (negative) the stimulus.