Responding to Changes in the Environment

gcse revision notes- module 1b and 1a

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  • Created on: 22-05-09 23:53
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Responding to Changes in the Environment
All organisms respond to chnges in their environment and this section explores some of the
ways in which they do this. The human eye is studied as an example of a receptor organ.
Stimuli: Changes in external or internal environment which cause a response
Receptor: Cells in the body which detect stimuli
Effector: Part of the body which responds to stimuli
Central Nervous System
1. Brain
2. Spinal Chord
Nerves: a bundle of nerve cells. A nerve cell is called a neurone.
1. Senesory Neurone: Carries impulses from the receptor to the central nervous system
2. Motor Neurone: Carries impulses from teh central nervous system to the effectors
3. Realy neurone: connects the sensory neurone to the motor neurone.
Motor Neurone
Myelin Sheath: Is fatty and insulates electricity inside the axon.
Dendrites: Recieve nerve impulses from sensory cells.
Reflex Action, Involuntary/Voluntary
Reflex arc is the path taken by an impulse in a reflect arc
Stimulus>Receptor>Sensory neurone>Relay neurone>Motor Neurone>
Spinal Chord (Reflex arc only concerned with stimulus from the skin)

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Stimulus (sharp object) > Sensory neurone (through dorsal route in white matter) >
(synaps in grey matter) > realy neurone > (synaps) > motor neurone (in white matter)
> muscle effector (move hand)
The Eye
Know the structure of the eye. Will put image here someday.
How we see
Light rays from objects are refracted by the cornea and focussed by the lengs. This
forms an upside down image on the retina.…read more

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Auxn is a chemical growth regulating substance, which is produced at the tip of shoots when
exposed to light.
Auxin diffuses down the shoot, on the side which is shaded
o it causes cells in zone of cell elongation to grow faster
o therefore one side is long/bigger than the other, so the plant bends towards the
light.…read more


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