5. INTRODUCTION
PLANTS EXHIBIT MOVEMENTS
MOVEMENTS ARE DUE TO CERTAIN EXTERNAL
STIMULI.
EXTERNAL STIMULI ARE
LIGHT,WATER,CHEMICALS, GRAVITY,
TOUCH,ETC.
6. PHOTOTROPISM
Plants are very sensitive
to light.
Shoots tend to grow
towards light while the
roots grow away from
light.
Shoots are positively
phototrophic .
Roots are negatively
phototrophic.
7. GEOTROPISM
Plants are grow in response
to gravity.
The roots are positively
geotropic.
The shoots are negatively
geotropic.
It is also known as
gravitropism
8. HYDROTROPISM
The plants are grow in
response to water.
The roots are grow
towards water.
The roots show positive
hydrotropism.
9. CHEMOTROPISM
Chemicals are
responsible for the
direction of growth
of the roots.
Chemicals produced
by the ovary
influences the
direction growth of
pollen tube.
10. HAPTOTROPISM
Some creepers climb
around supporting
plants.
The stimulus of
touch(tactile
stimulus)influences the
climbing movement
These movements are
stimulated by touch.
11. NASTIC MOVEMENTS
The stimulus of touch
does not influence
the direction of
movement.
Touch any part of the
plant, the leaves
droop downwards.
Eg: Touch-me-not
plant
12. CONCLUSION
Tropism is a biological
phenomenon.
It indicating growth or turning
movement.
It is due to environmental
stimulus.
Eg: growth of stem, turning of
climbers around the supports,
growth of roots etc.
