Summary Plant Responses and Hormones

Plant Responses and Hormones:
 Plant responses are important to increase their chance of
survival by:
o Responding to changes in their environment. E.g. shoots
growing towards light, roots growing with gravity &
climbing plants having a sense of touch to grab on to
things.
o Responding to the presence of herbivores. E.g. producing
toxic chemicals (like alkaloids or tannins), producing
pheromones (which can attract predators of the
herbivore or signal other plants to start producing toxins),
& mechanical responses (like folding leaves).
o Responding to abiotic stress. E.g. carrots produce
antifreeze proteins at low temperatures.


 Tropisms – growth responses to directional stimuli.
 Positive tropism = growth towards a stimuli.
 Negative tropism = growth away from a stimuli.


STIMULUS NAME OF RESPONSE OF RESPONSE OF
RESPONSE SHOOTS ROOTS
Positive Most have no
LIGHT Phototropism. (grows response.
towards light). Some have
negative.
GRAVITY Geotropism. Negative Positive
(grows away (grows with
from gravity). force of
gravity).