6 Chapter 5 Teacher Copy F5 BI

Jisrun Najaah Fi Ilmi Al Insan Chapter 5: Response in Plants

CHAPTER 5

RESPONSE
IN

PLANT

Dan perumpamaan orang-orang yang
membelanjakan hartanya karena mencari
keredhaan Allah dan untuk keteguhan jiwa
mereka, seperti sebuah kebun yang terletak di
dataran tinggi yang disiram oleh hujan lebat,
maka kebun itu menghasilkan buahnya dua

kali ganda. Jika hujan lebat tidak
menyiraminya, maka hujan gerimis (pun
memadai). Dan Allah Maha Melihat apa yang

kamu perbuat
Surah QS AL BAQARAH:265

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Jisrun Najaah Fi Ilmi Al Insan Chapter 5: Response in Plants

5.1 TYPES OF RESPONSES

1. Two types of responses
Tropism responses
Nastic responses.

Tropism Responses

1. Responses of certain parts of a plant such as roots and shoots towards or away from a
stimulus

characteristic

Characteristics of Tropism

1. The response is permanent and influenced by plant hormones.
2. The response is slow and not apparent.
3. The response direction is dependent on the direction of the stimulus.
4. Positive tropism - Growth towards direction of stimulus
5. Negative tropism – Growth away from stimulus

Type of Tropism

Tropism Plant Response To Examples
Thigmotropism Touch
Tendrils exhibit positive thigmotropism
Geotropism Gravity Coiling around an object such as a wooden
Hydrotropism Water stake
Phototropism Light For support
Chemotropism Chemical Shoots show negative geotropism.
Roots show positive geotropism.
Roots show positive hydrotropism
Grow towards water
Shoots show positive phototropism
Grow towards light
Roots show positive chemotropism when
o Grow towards mineral salts
Roots show negative chemotropism
o Grow away from chemical substances

such as poison

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Jisrun Najaah Fi Ilmi Al Insan Chapter 5: Response in Plants

Nastic Responses

Characteristics of Nastic Responses

1. Not all nastic responses are growth responses
2. This response is quicker and more apparent compared to tropism response
3. Some nastic responses are intended for survival

Types of Nastic Responses

Nastic Plant Response To Examples
Photonasty Light Plant petal open when receive maximum
Seismonasty sunlight
Mechanical stimulus Plant petal close at night
Nyctinasty Example; Can be seen on leaves, stigma and stamens
Thermonasty o Touch Mimosa plant leaf close when touched
Thigmonasty o Shock
o Wind River tamarind closes its leaves at night
o Raindrop Unfurls them during daytime
Darkness Tulips open when there is an increase in
temperature
Temperature Close when the temperature drops
Vibration stimulus causes Venus flytrap to
Vibration clamp its leaves
Shut and trap the insect inside it

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Jisrun Najaah Fi Ilmi Al Insan Chapter 5: Response in Plants

Comparison Between Tropism and Nastic Responses

Similarities
Both responses caused by external stimulus
Both processes produce respond in plant.

Differences

Aspect Tropism Nastic
Immediately
Time of action Slow
Turgor pressure
Reason for action Cell division Independent of the direction of
Depend on the direction of stimulus

Direction of respond Reversible
stimulus

Action of respond Irreversible

Response occurs All plant Few specialised plant
Involve Not involve
Hormone
involvement

5.2 PHYTOHORMONE

1. Phytohormones or plant hormones are chemical substances
2. Stimulate and coordinate responses in plants at low concentrations.
3. Synthesised in a certain plant organ and transported to a target organ
4. Through the phloem.

The Functions of Phytohormones

Types of Function
phytohormone
Ethylene Stimulates ripening in fruits
Stimulates senescence process in plants
Stimulates abscission of leaves and fruit

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Jisrun Najaah Fi Ilmi Al Insan Chapter 5: Response in Plants

Types of Function
phytohormone
Auxin Functional in phototropism and geotropism
Stimulates development of the apical dominance in
Gibberellin shoots and roots
Cytokinin Stimulates growth and elongation in root and shoot cells
Stimulates development of adventitious roots at the end
Abscisic acid of stem cuttings
Stimulates cell division in cambium during secondary
growth
Inhibits abscission of fruits and young leaves
Inhibits growth of lateral buds

Stimulates growth and elongation in the stem cell
Stimulates development of leaves, flowers and fruits
Stimulates development and germination of seeds
Causes growth of flowers in dwarf plants
Inhibits development of roots

Stimulates division and elongation of root and stem cells
when auxin is present
Stimulates seed germination
Inhibits development of apical dominance
Delays leaf senescence
Stimulates growth of lateral buds

Inhibits growth of plants
Stimulates abscission of mature fruits, leaves and
flowers
Induces seed dormancy
Induces stomatal closing during drought season
Inhibits growth of buds and seed germination

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Jisrun Najaah Fi Ilmi Al Insan Chapter 5: Response in Plants

Effects of Auxin on Growth Response

1. Plants respond to stimulus in the form of growth. Coleoptile Light
2. Controlled by the auxin Shade
3. Auxin synthesised at the coleoptile tips stimulate side Bright
side
cell elongation A B
4. Auxin distribution influences the direction of the

shoot growth

5. Auxin will move away from the light when the AB
shoots are exposed to the light from only one
direction

6. The auxin concentration is higher on the shaded
side.

7. The concentration of auxin becomes uneven on
the shoots

8. The cells in the shaded side elongate more than
the cells in the bright side.

9. Shoots bend towards the light
10. Show positive phototropism

Auxin Experiment During experiment Result
Before experiment

Light

• colleoptiles is removed • No growth because auxin
is not produced

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Jisrun Najaah Fi Ilmi Al Insan Chapter 5: Response in Plants
Before experiment
During experiment Result

Light Agar
block

• Block of agar is put between • Shoot bend toward light

coleoptiles and shoot • Auxin can diffuse across

the agar block to shade

area at elongation zone

• Stimulate cell division

Light Mica
plate

• Plate of mica is inserted • No growth because auxin

between the coleoptiles and can’t diffuse across mica
shoot plate to elongation zone

• Inhibit cell division at the

elongation zone

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Jisrun Najaah Fi Ilmi Al Insan Chapter 5: Response in Plants
Before experiment
During experiment Result

Light Mica
plate

• Half plate of mica is inserted • Shoot bend toward sunlight

between the coleoptiles and • Auxin accumulate at shade

shoot area in coleoptiles

• Diffuse to elongation zone

to stimulate cell division

Agar
block

• Half of agar block is inserted • No growth because auxin

between the coleoptiles and can’t diffuse to elongation

shoot zone

• Inhibit cell division at the

elongation zone

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Jisrun Najaah Fi Ilmi Al Insan Chapter 5: Response in Plants
Before experiment
During experiment Result

Light Black cap

• Auxin produced by

• The coleoptiles is covered by coleptiles diffuse into

black cap elongation zone

• It evenly distributed

• Cell division at elongation

zone is even

Graph of Effect of Concentration of Auxins to Cell Elongation at Shoot and Root

Stimulation At Shoot
1. Increase concentration of auxin will
Shoot
stimulate cell division
Growth Root 2. Shoot bend towards sunlight
response 3. Show positive phototropism

Inhibition Molar concentration
of auxin (mgl-1)

At Root

4. Increasing concentration of auxin will inhibit cell division
5. Root bend toward soil
6. Show positive geotropism

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Jisrun Najaah Fi Ilmi Al Insan Chapter 5: Response in Plants

The Role of Auxin in Geotropism

1. Auxin controls plant response to gravity
2. Seeds germinate horizontally in the soil.
3. Roots grow downwards following the pull of gravity
4. Exhibiting positive geotropism.
5. Shoots grow upwards against the pull of gravity
6. Exhibiting negative geotropism.

At Shoot At Root

1. Auxins are produced by Shoot Root 1. Auxins are produced by root
coleoptiles A C tip

2. Diffuse into elongation zone B D 2. Diffuse into elongation zone
at the shoot at the root
Gravity
3. Auxin pools at the bottom Gravity 3. Auxin pools at the bottom
side of the shoot(B) side of the root(D)

4. Due to the pull of gravity 4. Due to the pull of gravity

5. High auxin concentrations A 5. High auxin concentrations
at the bottom of the shoot B at the bottom of the root
tip (B) stimulates cell tip(D) inhibit cell elongation
elongation
6. Cells at the bottom (D) grow
6. Cells at the bottom (B) grow C slower than cells on the
faster than cells on the
upper side of the shoot (A) upper side of the root (C)
D 7. The root will bend towards
7. The shoot will bend
towards the light the soil
8. Showing positive
8. Showing negative
geotropism. geotropism

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Jisrun Najaah Fi Ilmi Al Insan Chapter 5: Response in Plants

5.3 APPLICATION OF PHYTOHORMONES IN AGRICULTURE

Hormone Explanation
Auxin
Encourages growth in crops
Gibberellin Promotes root growth (asexual reproduction) on woody
Cytokinin plant stems for horticultural crops (adventitious root)
Abscisic acid Produces fruit without seeds via parthenocarpy
Ethylene o Flowers are sprayed with auxin
o Auxin stimulate ovary to develop into fruit
o Without fertilisation occurs
o Produce seedless fruits
Used as weed killer
Induces dormancy in potatoes during storage or
distribution
Promotes growth of low-lying and lush plants

Treats mutated dwarf plants to grow to normal heights
Promotes rapid elongation of flower stems
Used to produce larger grapes
Promotes germination of seeds such oats during low
temperatures and low light intensity

Tissue culture technique
o Promote division and differentiation of cells
o Used together with auxin to form plant organs such

as roots and stems
Used to delay leaf senescence in newly cut flowers

Inhibits germination and growth

Used commercially to promote maturation of fruit quickly
and evenly
Promotes simultaneous flowering in plants in the field

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Jisrun Najaah Fi Ilmi Al Insan Chapter 5: Response in Plants
Adventitious Root

Adventitious root

Fruits Formation

Before auxin sprayed After auxin sprayed
Parthenocarpy

Fruits without auxin spray Fruits with auxin spray
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Jisrun Najaah Fi Ilmi Al Insan Chapter 5: Response in Plants
Weeds killers

Dicot plant with auxin spray Monocot plant with auxin spray

Traditional Practice to Speed Up the Ripening of Fruits

Cover

Rice
Unripe chiku

1. Chiku is put inside a rice in a closed container
2. Ethylene hormone is released during ripening process of chiku
3. Ethylene hormone is trapped by rice and not released to surrounding
4. High concentration of ethylene hormone stimulates the chiku ripe faster

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