Plant Responses

PLANT RESPONSES How plants move and communicate

TROPISMS Tropisms are the growth of a plant toward

or away from a stimulus, including: Phototropism: in response to light Gravitropism (geotropism): in response to

gravity Thigmotropism: in response to touch

Auxins are plant growth hormones that promote elongation of cells

TROPISMS: CELL ELONGATION In general,

tropisms involve cell elongation or suppression of cell elongation on one side of a plant, causing the plant to grow in a particular direction.

PHOTOTROPISM Look at the sprouts in the bottom picture

and the explanatory diagram at the top.

GRAVITROPISM In this plant, shoots

grow upwards and roots grow downwards in response to gravity.

On which side of the shoot and root do you think auxins are more concentrated?

GRAVITROPISM IN ROOTS

In roots, however, auxin concentration on the lower side of the root suppresses cell elongation.

The upper side of the root continues to grow, causing the roots to bend downward.

THIGMOTROPISM In some plants,

vining stems or tendrils will grow in response to touch.