F3 Science 1.3 Stimuli and responses in plants

1.3 STIMULI

AND RESPONSE

IN PLANTS

Prepared by
Ms. Lee Tzyy Ling
Mdm. Wong Choy Wan
SMK Buntong, Ipoh, Perak.

CONTENT STANDARD : 1.3 THE STIMULI AND RESPONSES IN PLANTS

LEARNING STANDARD:

1.3.1 Describe the parts of a plant that are sensitive towards stimuli.
1.3.2 Justify how responses in plants ensure their sustainability and
survival.
1.3.3 Carry out experiments to study responses in plants towards
various stimuli.

LEARNING OBJECTIVE:

At the end of this module, students are able

1. To explain the part of the plant that respond to the stimulus

2. To write at least two importance of the response in plants towards
stimuli

3. To write the response of the plants based on the activities shown in
module.

Let’s us reflect what we have learnt from 1.2.

We know human being are using their five sensory organs on to detect
different stimulus around us.

This happen is to ensure our body to carry out to correct action to
respond towards the stimuli to ensure we are save and not being harm.

What about plants? Does plant respond to stimuli?
If the plants are able to respond to the stimuli, then what are the stimuli?

And how they respond?

So, let’s us check out what
are the stimuli that plants
will respond to.

Look at the plant!

The plant is bending towards the light!

The light is stimulate
the plant to bend
towards it.

Yes, light is one of the stimulus for
plants. Can you think of other stimuli?

What are the stimuli for plants?

The stimuli for plants are
a. Light
b. Water
c. Gravity
d. Touch



The parts of plants that respond towards stimuli are the shoot or
the root of the plant

shoot

root

Let’s check out what are the
responses of plants!



A. Tropism

What is tropism?

Tropism is plant-directed response to
stimulus. The action is slow.

There are 4 types of tropisim

1. Phototropism - the response to light
2. Hydrotropism - the response to water
3. Geotropism - the response to gravity
4. Thigmotropism - the response to touch

What is
Phototropism?

Phototropism is where the plants respond
towards light.

The shoot

grows * As we observe the pictures that shown. The
towards the
light shoot in diagram A dan B shows positive

A phototropism because the shoot is
growing towards the light.

The shoot
bends
towards the
light

B

Does the root of plant grow toward the light?

No. The root of the plant does not respond to the
light. Therefore, we say that the root shows negative
phototropism.

Phototropism

Positive phototropism
• The shoots grow towards

the light

Negative phototropism
• The roots grow away from

light

What is
hydrotropism?

Hydrotropism is where the plants
respond towards water.

• Base on what we observed from the diagram A and B, the root in
diagram A grows straight in the moist soil. The root of the plant in
diagram B is bending towards the moist soil.

• The root of the plant show positive hydrotropism because it growing
towards to water.

• However, the shoot of the plant is growing upwards. The shoot of the
plant shows negative hydrotropism.

What is geotropism?

Geotropism is where the plants respond
towards gravity.

The root of The shoot of the
the plant is plant is growing

growing upwards, and
toward the away from the

gravity gravity

When the vase of the plant is placing vertically, we can see the
root of the plant is growing towards the gravity. The root shows
positive geotropism.

The shoot of the plant is growing away from gravity. The shoot
shows negative geotropism.

What is thigmotropism?

Thigmotropism is where the plants respond
towards touch.

The stem of plants is attached to any object or
plant in contact with it.

● Positive thigmotropism
• The stems of the plants attached to the support such as

fence, wooden sticks or plants to grow upwards.

● Negative thigmotropism
• The roots is not showing any respond towards the stimulus.

Soft stem of morning glory is twinning
around to get support from
surrounding to grow upwards.

Tendrils from the stem of cucumber
plant is twinning around on wooden
stick to get support.

Scan the QR code
to watch video

The importance of tropism of the
plants

Phototropism Hydrotropism

• To help the plants to get light for • To help the roots get water and

photosynthesis mineral salts from the soil

Geotropism Thigmotropism

• To help the roots penetrate the soil to • To help plants grow upward to get

get water and light for photosynthesis

• the roots can anchor on the ground • To help the plant to get support.

strongly

B. Nastic
Movement

What is nastic movement?

Nastic movement is the reactions of
the plants do not depend on the
direction of the stimulus. The action
is fast.

The stimulus for nastic movement
can be light, heat or touch.

Example of nastic movement

The leaves of the Venus flytrap close
when the insects settle on it.

Mimosa pudica plants are closed when
touched.

The importance of nastic movement
of the plants

• To protect plants from injury
• To help the plant to get food.

Scan the QR code
to watch video

Venus flytrap and nastic movement

Test yourself

Self-assessment TP1

Match the responses to the correct stimulus.

Thigmotropisme Water

Hydrotropisme Light

Geotropisme touch
Phototropisme Gravity

Structure questions

1. The picture shows an experiment a. State the stimulus in this
conducted by a students to
study the plant's response to a experiment.(1m) TP 2
stimulus.
a. State the meaning of positive

tropism. (1m) TP 1

b. Based on the diagram, draw the

condition of the green plant after 5

days.(1m) TP 2

c. Name the reaction that is shown by
the shoots of the plant in the
diagram. (1m)

TP 2

2. Aaron has conducted

experiments to study

the response of the

roots of a plant

towards water. The

diagram shows Aaron’s

observation.

TP4

a. Based on the diagram, explain the response of the roots of seedling

towards water. (1m) TP 2

b. State the importance of this response to the seedling. (1m) TP 2

c. State the reaction shown by the shoots of the seedling in this

experiment. TP 2

d. Explain why plant shoots do not show the same response the root.(2m)

TP 2

A PICTURE IS
WORTH THAN

THOUSAND
WORDS

THANKS!

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