Friday, June 13, 2008

Form 5 Chapter 3 Biology-> Coordination and Response

What is an external stimuli?
-Changes that occur outside the body of an organism.
-For instance, light,sound,smell,taste,touch and temperature plus pressure also.

What about an internal stimuli?
-Changes that occur inside the body of an organism.
-For example, sugar level in the blood and osmotic pressure of blood.

State the necessity for living organs to respond to internal stimuli.
-To maintain a constant environment within our body which is a process called homeostasis.

What is tropism?
-It occur only in plants...
-It is defined as the directional growth of a plant part in response to an external stimulus.
-Growth towards the stimulus is known as positive tropism,while growth away from the stimulus is known as negative tropism.

eg: phototropism->response of plant to light
geotropism->response of plant to earth's gravitational pull
hydrotropism=>response of plant to water

Nastic movement->movement of parts of plant in response to external stimuli.

What is a receptor?
Receptor are cells or group of cells specialised in detecting a particular stimulus and initiating transmission of nerve impulses through the sensory organs.For instance,eyes,ears,nose and skin all have specialised receptor cells to respond to particular stimuli.