Summary Edexcel iGCSE Biology Revision notes on Section 6 of the CGP
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Course
Biology
Institution
GCSE
I used this document in my GCSE revision and it helped me to achieve a Grade 8 in my final biology GCSE exam (edexcel igcse board). These notes are made based on the CGP GCSE guide.
THE NERVOUS SYSTEM AND RESPONDING TO STIMULI
Animals increase their chance of survival by : Stimulus : a change in the internal of
responding to changes in their external environment external environment of an organism
↳ e g
. .
by avoiding places that are too hot/cold
responding to changes in their internal environment censuring conditions are optimum for your
metabolism)
plants increase their chance of survival by responding to changes in their environment
Receptors detect Stimuli Receptors in Sense organs (eyes , ears etc
.) are groups of
Care cells) that bring
Effectors cells that detect external stimuli
about a response to a stimuli e .
g .
rod and come cells detect changes in light
·
Effectors include muscle cells and cells found in glands (e g
.
. the pancreas) .
↳ respond in different ways -
muscle cells contract
glands secrete mormones
-
The Central Nervous System (CNS) Coordinates information
The nervous system is made up of all the neurones/ nerve cells in your body
neurotransmitters
released
-menon synapse
a 1 .
the connection/space between two neurones is a
. the Merve
2 signal is transmitted by Neurotransmitters (chemicals) that
diffuse across the gap to the next neurone
. the neurotransmitters set off an electrical impluse
3 in the next neurone
REFLEXES
1. Reflexes are automatic responses to certain Stimuli (which reduces the chance of
injury
↳ e g . . if a , your pupils automatically get
bright light is in your face smaller so
less light gets into the eyes to prevent damage
. if you get a shock , adrenaline is released
g ↳ e .
Reflex arc the route taken by the information in
: a reflex
(receptor >
-
effectors
*
Neurones in the spinal cord go through the spinal cord or an unconscious part of the
bravin
*
The stages of a reflex arc :
I . A stimulus is detected by a receptor , causing an implse to be sent along the
sensory neurone to the CNS
. Im
2 the CNS ,
the sensory neurone passes on the message to the relay neurone
.
3 Relay Neurones relay the implse to a motor neurone
. The
4 impulse then travels along the motor neurone to the effector (e .
g . a muscle or
gland)
5
. The muscle then contracts causing you to move (if the effector is a gland mormones
,
, EYE
Conjunctiva 1) Conjunctiva : lubricates and protects the surface of
ciciary the eye
mine
muscles
2) Sclera : the tough outer layer that protects the
(whole) eye
ligaments
a
↳ it has no blood vessels to With
supply it
Oxygen
-
Oxygen diffuses in from the outer
surface
4) Iris controls the diameter of
:
Optic the pupil and how much light
nerve
enters
(white
3) Pupil : the opening in the center of the
6) Lens : focuses light onto the retina
7) Retina : light-sensitive part of the eye covered in light receptors called rods and
cones
↳ 8) Rods :
more sensitive in , does not detect/sense colour
dim light
↳ lots found at the fored
↳ 9) Comes sensitive to colour
:
,
mot good in dim light
↳ found all over the retina
8) Suspensory ligaments :
puls the lens right , making it go thin or slackens and
makes the lens become more curved depending on the ciliary muscles
9) Ciliary muscles : relax or contract to help focus light on the retina by changing the
Shape of the lens (accomodation
10) Optic nerve : carries impulses from the receptors to the brain
Accomodation :
to look at distant objects : to look at mean objects :
ciliary muscles relax ciliary muscles contract
allows the suspensory ligaments suspensory ligaments slacken
to pull right lens becomes more curved, the
the lens goes thin and light is amount of light recracted increases
refracted by a smaller amount
Iris reflex :
↳ bright light can reflect the retina so there is a reflex to protect it
↳ bright light triggers a reflex that makes the pupil smaller
↳ circular muscle contracts pupil gets smaller ,
↳ dim light also triggers a reflex that makes the pupil bigger
↳ radial muscles contract bigger
, pupil gets
Long / short-sighted
·
short-sighted : ·
Long-sighted :
) unable to
↳
focus on distant objects ↳ unable to nearby objects
focus on
↳ because the cornea or lens bends light Cornea or lens doesn't bend light
↳
too Much or the eye is too long enough Or is too short
↳ images arebrought into focus in front ↳ images are brought into focus
of the eye behind the reting
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