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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.