DEFINITIONS+OF++INTERACTION+FUNCTION

=STIMULUS. Any change which can be perceived by an organism and cause an effect in it.= =RECEPTORS are the parts of an organism that make it possible for the living thing to perceive stimuli.= =EFFECTORS are the parts of an organism that carry out responses to stimuli.= ||  || =NEURON. A specialised cell which transmits information. The basic unit of the nervous system.= =NERVOUS SYSTEM. System which captures signals from the sense organs, interprets them and= =triggers a coordinated response in the effector organs.= =ENDOCRINE GLAND. A group of cells which produce hormones.= =HORMONE. A substance which travels through the blood and provokes responses in certain effectors.= ||  || =MUSCLE. An organ made up of cells, called muscle fibres, that produce movements when they contract= =SECRETION. A substance that glands produce and release to the exterior environment when they receive a stimulus.= ||  || =THIGMOTROPISM. A type of permanent tropism which responds to contact.= =PHOTONASTY. A type of temporary movement which occurs when the stimulus is light.= ||  ||
 * =PAGE -34-=
 * =PAGE 41=
 * =PAGE 42=
 * =PAGE 46.=
 * Stimuli can be: Internal (when they come from inside the organism. e.g. hunger or thirst) or external (when they come from the environment) Sun rays that cause sunflowers to face the Sun or the presence of a predator that causes its prey to run.
 * Stimuli can be: Internal (when they come from inside the organism. e.g. hunger or thirst) or external (when they come from the environment) Sun rays that cause sunflowers to face the Sun or the presence of a predator that causes its prey to run.

=ACTIVITY:= =Identify whether the following stimuli are internal or external:= =a) A loud noise.....= =b) Feeling hungry.......= =c) The smell of food.......= =d) An itch.....= =e) Reaching very cold temperatures....= =f) A bright light.....= ||  || =PAGE 34. QUESTION 3= = = =STIMULI>PERCEPTION OF INFORMATION->RECEPTORS>PROCESSING AND COORDINATION>EFFECTORS>EXECUTION OF RESPONSES=