1.3 STIMULI AND RESPONSES IN PLANTS

STIMULI AND
RESPONSES
IN PLANTS

Name: Chea Jing Rou
Class: 33

THE STIMULI AND RESPONSES IN
PLANTS

Plants respond to stimuli

Responses only involve movement of parts of plant
Respond to: light, gravity, water, touch, temperature,

chemicals

TWO TYPES OF RESPONSES

TROPISMS NASTIC MOVEMENT

WHAT IS TROPISM? ? ?

Tropism is a directional response of
plants to stimuli such as light, water,

gravity, and touch coming from a
certain direction.

Parts of plant grow towards stimulus Positive tropism

Parts of plant grow away from stimulus Negative tropism

Phototropism Geotropism

Response of plants to Response of plants
light (enable the plant to gravity (roots
to get sunlight to can grow deep to
carry out hold soil firmly)
photosynthesis)

4 TYPES OF
TROPISM

Hydrotropism Thigmotropism

Response of plants to Response of plants to
water (enable the touch (enable the
roots to get water for plant to climb on
living process
other structures for
support

PHOTOTROPISM GEOTROPISM

HYDROTROPISM THIGMOTROPISM

NASTIC MOVEMENT

Nastic movement is the response towards a stimulus
such as touch but does not depend on the direction of


the stimulus.

Why is nastic movement not a type of tropism???

It is because nastic movement occurs more rapidly than
tropism.

3 TYPES OF NASTIC MOVEMENT

PHOTONASTIC SEISMONASTIC THERMONASTIC

Response to Response Response of
light by to touch plant to
flowers
temperature

Example of photonastic, seismonastic
and thermonastic

PHOTONASTIC SEISMONASTIC THERMONASTIC

Morning glory Mimosa pudica Tulip flowers
flowers bloom in quickly fold its leaves bloom at high
sunlight when touch temperature in
Sunflower blooms spring
in sunlight Venus fly trap
closes and trap
insect