Plants show two types of movements - tropic movements which are directional responses to stimuli and involve growth, and nastic movements which are non-directional and do not involve growth. Tropic movements include phototropism, hydrotropism, chemotropism, geotropism, and thigmotropism in response to light, water, chemicals, gravity, and touch respectively. Plant growth and development is regulated by plant hormones such as auxins, gibberellins, cytokinins, ethylene, and abscisic acid which promote or inhibit growth. Auxins promote cell elongation, rooting, flowering, and fruit development while inhibiting leaf and fruit abscission. Gib

1. CLASS 10 CBSE
SCIENCE
CHAPTER-7
CONTROL AND COORDINATION
PART-1
CHEMICAL COORDINATION IN PLANTS
Presented by,
SARANYA D
SECONDARY SCHOOL TEACHER
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2. Plants show two different movements
Plant Movements
Tropic movements
-Growth dependent movement
-Directional movement (towards or away
from the stimuli)
-Cell division occurs
-Slow response (since, growth is involved)
Eg., growth of stem towards light-
Phototropic movement
Nastic movements
-Growth independent movement
-Non directional movement
-No cell division occurs
-Rapid movement (response is fast)
Eg., immediate response to touch-
thigmonastic movement by Mimosa
pudika (touch me not plant)
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3. Points to remember
 Stimuli- a detectable change in the internal and external
environment
 Coordination- process through which two or more organs interact
and complement the functions of one another
 Curvature movement- curving or bending of a plant in response to
any stimuli ( a type of trophic movement)
eg., curving of the stem tip towards light (due to auxin)
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4. TROPIC MOVEMENTS IN PLANTS4
Positive tropism
Growth of plant
towards the
stimuli
Negative tropism
Growth of plant
away from the
stimuli

5. Phototropic movement –stimuli light
Growth of stem towards light (positive tropism)
Growth of root away from the light (negative tropism)
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6. Hydrotropic movement- stimuli water
Growth of root towards water (positive tropism)
Growth of root away from the water, seen in mangrove
trees for getting oxygen (negative tropism)
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7. Chemotropic movement- stimuli chemical
Growth of pollen towards ovary (positive tropism)
Growth of root away from the toxic chemicals (negative
tropism)
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8. Geotropic movement- stimuli gravity8
Growth of root towards gravity (positive tropism)
Growth of stem away from gravity (negative tropism)

9. Thigmotropic movement- stimuli touch
 Growth of tendril towards the support
eg., Pea plant
Auxin is diffused in the part of the tendril away from the
object
This causes the tendril to circle around the object and thus
cling to it
When tendril come in contact with any support, the part of the
tendril in contact with the object does not grow as rapidly as
the part of the tendril away from the object
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10. Nastic movement
 Thigmonastic or seismonastic – stimuli touch Drooping of leaves
by the movement of water.
 Nictinastic- stimuli darkness sleeping movement of plants in night
time
 Photonastic- stimuli light Many flowers open with the increasing
illumination of the day and close up with the dawn of the day
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11. Plant hormones
Growth promoters Growth inhibitors
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Auxin
Gibberellin
Cytokinin
Ethylene
Abscisic acid

12. Auxin
Cell elongation and cell differentiation
initiate rooting in stem cuttings,
an application widely used for plant propagation.
Auxins promote flowering e.g. in pineapples.
They help to prevent fruit and leaf drop at early stages but
promote the abscission of older mature leaves and fruits.
In most higher plants, the growing apical bud inhibits the
growth of the lateral (axillary) buds, a phenomenon called
apical dominance.
Auxins also induce parthenocarpy, e.g., in tomatoes.
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13. Gibberellins
 Elongation of stem
 ability to cause an increase in length of axis is used to increase the
length of grapes stalks.
 Gibberellins, cause fruits like apple to elongate and improve its
shape. They also delay senescence.
 Thus, the fruits can be left on the tree longer so as to extend the
market period.
 GA3 is used to speed up the malting process in brewing industry.
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14. Cytokinins
 Cell division
helps to produce new leaves, chloroplasts in leaves, lateral
shoot growth and adventitious shoot formation.
Cytokinins help overcome the apical dominance.
They promote nutrient mobilisation which helps in the
delay of leaf senescence.
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15. Ethylene (gaseous hormone)
Ripening of fruit
 Ethylene promotes senescence and abscission of plant
organs especially of leaves and flowers.
Ethephon hastens fruit ripening in tomatoes and apples
and accelerates abscission in flowers and fruits (thinning
of cotton, cherry, walnut).
 It promotes female flowers in cucumbers thereby
increasing the yield.
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16. Abscisic acid (stress hormone)
regulating abscission and dormancy
inhibits seed germination
 stimulates the closure of stomata in the epidermis and
increases the tolerance of plants to various kinds of
stresses.
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