Page 1 - 2.4-Lesson Notes-Coordination in Plants-(i)

SAI International School

Std -X, Subject- BIOLOGY
Chapter- Control and Coordination
Sub Topic- Coordination in Plants- Immediate response to
stimulus, Movement due to Growth (tendrils)
Module- 16
Lesson Notes

Plants response towards stimuli
• Plants cannot move as animals do. Plants do not have a nervous system or a
muscle system.
• Despite not having sense organs plants can also sense things and respond to
them. Plants respond to things like light, gravity, touch, water etc. These are
environmental stimuli for a plant.
• They respond to the stimuli very slowly because they have no nervous
system.
• Plants coordinate their behaviour by using their hormones (phytohormones)
and respond to the environmental changes.

What is a Stimulus?
• The changes in the environment to which the organisms respond are known
as stimuli.
• Living organism responds when an external stimulus acts on it.
• Plants do move from their place but change their growth patterns. That is why
plants of the same species have different body forms. This change in the
growth pattern in response to a stimulus is known as tropism.

The movement in plants are of two types:-
(i) Growth dependent movement
(ii) Growth independent movement

Immediate Response to Stimulus
Immediate response to stimulus is independent of growth.
• The non-directional movements of the plant in response to external
stimuli are called nastic movement.
• E.g. When we touch the leaves of a chhui-mui (the ‘sensitive’ or ‘touch-me-not’
plant of the Mimosa family), they begin to fold up and droop.
• Where exactly the plant is touched, and what part of the plant actually moves,
it is apparent that movement happens at a point different from the point of
touch.
• So, information that a touch has occurred must be communicated.
• The plants also use electrical-chemical means to convey this information from
cell to cell, but unlike in animals, there is no specialised tissue in plants for the
conduction of information.
• In animals, some cells must change shape in order for movement to happen.
• Instead of the specialised proteins found in animal muscle cells, plant cells
change shape by changing the amount of water in them, resulting in swelling
or shrinking, and therefore in changing shapes.