Control and Coordination

 Control and Coordination

Systematic working of the various organs of an organism (plants or animals) producing a proper response to the stimulus is called co-ordination.
Coordination in Plants
Not so elaborate, controlled by phytohormones and external stimulus.
Phytohormones
•   Control and coordination in plants is done by phytohormones.
•   They are naturally occurring chemical substances which control one or other aspect of growth.
•   Auxin – Cell enlargement and differentiation.
•   Gibberellins – In presence of auxin, promotes cell enlargement and differentiation.
•   Cytokinins – Promotes cell division, opening of stomata, etc.
•   Abscisic acid – Closing of stomata, wilting and falling of leaves, etc.
Tropic Movements
•   Directional plant growth movement in response to an external stimulus.
•   Growth of a plant may be towards the stimulus (positive tropism) or away from it (negative tropism).
•   Phototropism – movement in response to light.
•   Chemotropism – in response to chemicals.
•   Hydrotropism – in response to water.
•   Geotropism – in response to gravity.
Nastic Movements
•   Non-directional movement of a plant part in response to an external stimulus.
•   May or may not be a growth movement.
•   All parts of the organ of a plant are affected equally irrespective of the direction of the stimulus.
•   Thigmonasty – Nastic movement in response to touch of an object.
•   Photonasty – Nastic movement in response to light.
Coordination in Animals
Elaborate, very complex and is controlled by neuroendocrine system.
Endocrine (chemical) Coordination
•   Consists of hormones (chemical messengers) regulating biological processes and secreted by endocrine glands.
•   Homeostasis is maintained by hormones by their integrated action and feed back control.
Nervous Coordination
•   Neuron forms the fundamental unit.
•   Sensory neurons in sense organs receive stimulus and transmit impulses to CNS.
•   Motor neurons transmit impulses from CNS to effectors.
•   Relay or connector neurons serve as links between sensory and motor neurons.
Nervous System (Human)
•   CNS – Consists of brain and spinal cord.
      Brain – Controls various voluntary (walking, riding, running, etc.) and involuntary actions (sneezing, coughing, etc). Also controls thinking, reasoning, and intelligence.
      Spinal Cord – Controls reflex action.
•   PNS – Consists of cranial nerves (12 pairs) and spinal nerves (31 pairs).
•   ANS – Two set of nerves (parasympathetic and sympathetic) supplying visceral organs which are antagonistic to each other.

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