CONTROL AND COORDINATION
STIMULUS- The changes in the environment to which the organisms respond and react are
called stimulus. Light, heat, cold, sound, water, gravity etc. are some stimuli.
RESPONSE- The reaction of an organism to a stimulus is called response. Animals respond to
stimulus in many ways because they have nervous system and endocrine system
(hormones).The plants react to stimuli very slowly by growing, because they don’t have nervous
system they use only hormones to respond to stimulus.
COORDINATION-The working together of various organs of an organism in a systematic way so
as to produce a proper response to the stimulus is called coordination.
CONTROL AND COORDINATION IN PLANTS
The growth of a plant can be divided into three stages: cell division, cell enlargement and cell
differentiation, and these have particular location in a plant. These three stages of growth as
well as promotion of dormancy, breaking of dormancy, stomata control, falling of leaves, fruit
growth, ripening or growth and ageing in plants are controlled by various plant hormones.
DORMANCY- A resting, inactive condition in which metabolism almost stops is called dormancy.
A seed is inactive or dormant. It must get conditions like water, warmth, air and hormones to
break dormancy. Another part that shows dormancy is the bud, on breaking dormancy it can
form a branch, a flower or a leaf depending upon its position in the plant.]
The control and coordination in plants is done by plants hormones also called phytohormones.
There are four major hormones:
1. Auxins-
• Promote cell enlargement and cell differentiation.
• Controls plants response to light and gravity.
• Auxins moves away from sunlight and towards gravity.
• It has opposite effect on growth of stem and roots. It speeds up growth in stem but slows
down growth in roots.
• It is made by cells at the tip of stems and roots.
Action of Auxin on stem-*When sunlight comes from above, then Auxin hormone present in tip
of stem spreads evenly and both the sides of the stem grows equally and the stem grows
straight up.
* when light falls on right side of the stem then Auxin collects in the left side of the
stem(because Auxin prefers to stay in shade), due to this left side grows faster and becomes
longer than the right side. Therefore the stem bends towards the right.
Action of Auxin on roots-
*The side of a root away from light will have all Auxin concentrated in it. Due to this the root
away from light will grow slower than the other side and makes root bend away from light.
2. Gibberellins-
• Promote cell enlargement and cell differentiation in the presence of Auxin.
• Helps in breaking dormancy in seeds and buds.
STIMULUS- The changes in the environment to which the organisms respond and react are
called stimulus. Light, heat, cold, sound, water, gravity etc. are some stimuli.
RESPONSE- The reaction of an organism to a stimulus is called response. Animals respond to
stimulus in many ways because they have nervous system and endocrine system
(hormones).The plants react to stimuli very slowly by growing, because they don’t have nervous
system they use only hormones to respond to stimulus.
COORDINATION-The working together of various organs of an organism in a systematic way so
as to produce a proper response to the stimulus is called coordination.
CONTROL AND COORDINATION IN PLANTS
The growth of a plant can be divided into three stages: cell division, cell enlargement and cell
differentiation, and these have particular location in a plant. These three stages of growth as
well as promotion of dormancy, breaking of dormancy, stomata control, falling of leaves, fruit
growth, ripening or growth and ageing in plants are controlled by various plant hormones.
DORMANCY- A resting, inactive condition in which metabolism almost stops is called dormancy.
A seed is inactive or dormant. It must get conditions like water, warmth, air and hormones to
break dormancy. Another part that shows dormancy is the bud, on breaking dormancy it can
form a branch, a flower or a leaf depending upon its position in the plant.]
The control and coordination in plants is done by plants hormones also called phytohormones.
There are four major hormones:
1. Auxins-
• Promote cell enlargement and cell differentiation.
• Controls plants response to light and gravity.
• Auxins moves away from sunlight and towards gravity.
• It has opposite effect on growth of stem and roots. It speeds up growth in stem but slows
down growth in roots.
• It is made by cells at the tip of stems and roots.
Action of Auxin on stem-*When sunlight comes from above, then Auxin hormone present in tip
of stem spreads evenly and both the sides of the stem grows equally and the stem grows
straight up.
* when light falls on right side of the stem then Auxin collects in the left side of the
stem(because Auxin prefers to stay in shade), due to this left side grows faster and becomes
longer than the right side. Therefore the stem bends towards the right.
Action of Auxin on roots-
*The side of a root away from light will have all Auxin concentrated in it. Due to this the root
away from light will grow slower than the other side and makes root bend away from light.
2. Gibberellins-
• Promote cell enlargement and cell differentiation in the presence of Auxin.
• Helps in breaking dormancy in seeds and buds.
