CLASS: X-SCIENCE-CHAPTER: CONTROL AND COORDINATION-NOTES

CLASS: X-SCIENCE

CHAPTER: CONTROL AND COORDINATION-NOTES

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.