SCIENCE PROJECT

1.3 STIMULI AND
RESPONSES IN PLANTS

TABLE OF 01 THE STIMULI AND RESPONSES
CONTENTS IN PLANTS
Tropism and Nastic Movement

02 TROPISM

Phototropism, Geotropism, Hydrotropism
and Thigmotropism

03 NASTIC MOVEMENT

Photonastic, Seismonastic, Thermonastic

01

THE STIMULI AND
RESPONSES IN PLANTS

Tropism and Nastic Movement

RESPONSES OF PLANTS

TO STIMULI

● Plants can detect stimuli and
respond to them

● Response only involve movement of
parts of plant

● The stimuli that can be detected by
plants include light, water, gravity
and touch

● Two types of responses :
A) Tropisms and B) Nastic Movement

Responses of plants Tropism
Nastic Movement

02

TROPISM

Phototropism, Geotropism, Hydrotropism
and Thigmotropism

TROPISM

● Tropism is a directional response of plants
to stimuli such as light, water, gravity and
touch coming from a certain direction

● A certain part of a plant will grow towards
or move away from the detected stimulus

● Occur slowly and less significantly
● Parts of plant grow towards stimulus

Positive tropism

● Parts of plant grow away from stimulus

Negative tropism

1. phototropism 2. geotropism 3. hydrotropism 4. thigmotropism

1. PHOTOTROPISM

Response of plants towards light (Enable the plant to get
sunlight to carry out photosynthesis)

Shoots of plants show
Positive Phototropism
(grow towards light)

Roots of plants show
Negative Phototropism
(grow away from light)

2. GEOTROPISM

Response of plants to gravity (Roots can grow deep into the ground
to grip and stabilise the position of the plant in the ground)

Roots show Shoots show
Positive Geotropism Negative Geotropism

(grow towards (grow away from
gravity) gravity)

3. HYDROTROPISM

Response of plants to water (Enable the roots to get
water for living process)

Shoots show
Negative Hydrotropism
(grow away from water)

Roots show
Positive Hydrotropism
(grow towards the water)

4. THIGMOTROPISM

Response of plants to touch (Enable the plant to
climb to on other structures for support)

Tendrils or twining Roots show Negative
stems show Thigmotropism
Positive Thigmotropism
since they avoid
when they cling on any object that
whatever objects or obstructs their
other plants come search for water
into contact with any
support structures

03

NASTIC MOVEMENT

Photonastic, Seismonastic, Thermonastic

NASTIC MOVEMENT

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

● Nastic movement occurs more rapidly than
tropism

● Three types of nastic movements : Photonastic,
Seismonastic, Thermonastic

NASTIC MOVEMENT

Photonastic Seismonastic Thermonastic

PHOTONASTIC

Response to light by flowers

EXAMPLE :

Morning glory flowers and sunflowers bloom
in sunlight

SEISMONASTIC

Response to touch

EXAMPLE :

Mimosa pudica quickly fold its leaves when touch
Venus fly trap closes and trap insect

THERMONASTIC

Response of plant to temperature

EXAMPLE :

Tulip flowers bloom at high temperature in spring

THANK YOU !