Download iGCSE Biology Section 2 lesson 8

IGCSE BIOLOGY
SECTION 2 LESSON 8
Content
Section 2
Structures
and
functions
in living
organisms
a) Levels of organisation
b) Cell structure
c) Biological molecules
d) Movement of substances
into and out of cells
e) Nutrition
f) Respiration
g) Gas exchange
h) Transport
i) Excretion
j) Coordination and response
Content
Lesson 8
j) Coordination
and
response
j) Coordination and response
2.77 understand that organisms are able to respond to changes in their
environment
2.78 understand that homeostasis is the maintenance of a constant internal
environment and that body water content and body temperature are both
examples of homeostasis
2.79 understand that a coordinated response requires a stimulus, a receptor and
an effector
Flowering plants
2.80 understand that plants respond to stimuli
2.81 describe the geotropic responses of roots and stems
2.82 describe positive phototropism of stems
Humans
2.83 describe how responses can be controlled by nervous or by hormonal
communication and understand the differences between the two systems
2.84 understand that the central nervous system consists of the brain and spinal cord
and is linked to sense organs by nerves
2.85 understand that stimulation of receptors in the sense organs sends electrical
impulses along nerves into and out of the central nervous system, resulting in rapid
responses
2.86 describe the structure and functioning of a simple reflex arc illustrated by the
withdrawal of a finger from a hot object
2.87 describe the structure and function of the eye as a receptor
2.88 understand the function of the eye in focusing near and distant objects, and in
responding to changes in light intensity
2.89 describe the role of the skin in temperature regulation, with reference to
sweating, vasoconstriction and vasodilation
2.90 understand the sources, roles and effects of the following hormones: ADH,
adrenaline, insulin, testosterone, progesterone and oestrogen.
Content
Lesson 8
j) Coordination
and
response
j) Coordination and response
2.77 understand that organisms are able to respond to changes in their
environment
2.78 understand that homeostasis is the maintenance of a constant internal
environment and that body water content and body temperature are both
examples of homeostasis
2.79 understand that a coordinated response requires a stimulus, a receptor and
an effector
Flowering plants
2.80 understand that plants respond to stimuli
2.81 describe the geotropic responses of roots and stems
2.82 describe positive phototropism of stems
Humans
2.83 describe how responses can be controlled by nervous or by hormonal
communication and understand the differences between the two systems
2.84 understand that the central nervous system consists of the brain and spinal cord
and is linked to sense organs by nerves
2.85 understand that stimulation of receptors in the sense organs sends electrical
impulses along nerves into and out of the central nervous system, resulting in rapid
responses
2.86 describe the structure and functioning of a simple reflex arc illustrated by the
withdrawal of a finger from a hot object
2.87 describe the structure and function of the eye as a receptor
2.88 understand the function of the eye in focusing near and distant objects, and in
responding to changes in light intensity
2.89 describe the role of the skin in temperature regulation, with reference to
sweating, vasoconstriction and vasodilation
2.90 understand the sources, roles and effects of the following hormones: ADH,
adrenaline, insulin, testosterone, progesterone and oestrogen.
Content
Lesson 8
j) Coordination
and
response
j) Coordination and response
2.77 understand that organisms are able to respond to changes in their
environment
2.78 understand that homeostasis is the maintenance of a constant internal
environment and that body water content and body temperature are both
examples of homeostasis
2.79 understand that a coordinated response requires a stimulus, a receptor and
an effector
Flowering plants
2.80 understand that plants respond to stimuli
2.81 describe the geotropic responses of roots and stems
2.82 describe positive phototropism of stems
Humans
2.83 describe how responses can be controlled by nervous or by hormonal
communication and understand the differences between the two systems
2.84 understand that the central nervous system consists of the brain and spinal cord
and is linked to sense organs by nerves
2.85 understand that stimulation of receptors in the sense organs sends electrical
impulses along nerves into and out of the central nervous system, resulting in rapid
responses
2.86 describe the structure and functioning of a simple reflex arc illustrated by the
withdrawal of a finger from a hot object
2.87 describe the structure and function of the eye as a receptor
2.88 understand the function of the eye in focusing near and distant objects, and in
responding to changes in light intensity
2.89 describe the role of the skin in temperature regulation, with reference to
sweating, vasoconstriction and vasodilation
2.90 understand the sources, roles and effects of the following hormones: ADH,
adrenaline, insulin, testosterone, progesterone and oestrogen.
The Central Nervous System
The Central Nervous System
Brain
The Central Nervous System
Brain
Spinal cord
The Central Nervous System
Brain
Spinal cord
Spinal nerves
The Central Nervous System
Brain
Spinal cord
Spinal nerves
Cell
body
Motor neurone
Direction of impulse
The Central Nervous System
Brain
Spinal cord
Spinal nerves
Cell
body
Sensory neurone
Direction of impulse
The Central Nervous System
Brain
Spinal cord
Spinal nerves
Cell
body
Relay neurone
Nerve cell (neurone)
Neurones are specially
adapted cells that can carry
impulses (electrical signals)
Nerve cell (neurone)
Neurones are specially
adapted cells that can carry
impulses (electrical signals)
They are very long
(elongated) and connect
parts of the body
Nerve cell (neurone)
Neurones are specially
adapted cells that can carry
impulses (electrical signals)
They are very long
(elongated) and connect
parts of the body
They have branched
endings to allow a
single neurone to
link to may muscle
fibres
Nerve cell (neurone)
Neurones are specially
adapted cells that can carry
impulses (electrical signals)
They are very long
(elongated) and connect
parts of the body
The cell body has many
connections, so enabling
communication with other
neurones
They have branched
endings to allow a
single neurone to
link to may muscle
fibres
Nerve cell (neurone)
Dendrites
Cell body
Myelin (fatty) sheath)
Axon endings
The Reflex Action
A reflex action is a rapid, unlearned response to
a stimulus. It has a high survival value.
When specific receptors are stimulated they
cause a very fast, automatic response to the
presence of danger. Co-ordination between the
sensory and motor neurones takes place without
the need for conscious thought.
Eg. removing the hand from a hot object.
The Reflex Action
The Reflex Action
Stimulus, eg.
a hot object
The Reflex Action
Receptor
eg. in the
skin
The Reflex Action
Sensory
neurone
The Reflex Action
Relay neurone
The Reflex Action
Motor neurone
The Reflex Action
Effector, eg.
muscle
The Reflex Action
1
1. The receptor
is stimulated by
the hot object
The Reflex Action
2. This
causes an
impulse to
pass along.
2
1
1. The receptor
is stimulated by
the hot object
The Reflex Action
3. The spinal cord (or brain) co-ordinates
response without conscious thought.
2. This
causes an
impulse to
pass along.
3
2
1
1. The receptor
is stimulated by
the hot object
The Reflex Action
3. The spinal cord (or brain) co-ordinates
response without conscious thought.
2. This
causes an
impulse to
pass along.
3
2
4
1
1. The receptor
is stimulated by
the hot object
4. An
impulse is
transmitted
along a
motor
neurone
The Reflex Action
3. The spinal cord (or brain) co-ordinates
response without conscious thought.
2. This
causes an
impulse to
pass along.
3
2
4
1
1. The receptor
is stimulated by
the hot object
4. An
impulse is
transmitted
along a
motor
neurone
5
5. The muscle
contracts in
response to the
stimulus
The Conscious Action
1. Receptors in
your foot detect a
stone in your shoe
1
The Conscious Action
2. An impulse is
sent along a sensory
neurone
1. Receptors in
your foot detect a
stone in your shoe
2
The Conscious Action
3. In the spinal cord
another sensory
neurone takes the
impulse to the brain
2. An impulse is
sent along a sensory
neurone
1. Receptors in
your foot detect a
stone in your shoe
3
The Conscious Action
3. In the spinal cord
another sensory
neurone takes the
impulse to the brain
2. An impulse is
sent along a sensory
neurone
1. Receptors in
your foot detect a
stone in your shoe
4. The brain
co-oordinates the
input and output
4
The Conscious Action
3. In the spinal cord
another sensory
neurone takes the
impulse to the brain
2. An impulse is
sent along a sensory
neurone
1. Receptors in
your foot detect a
stone in your shoe
4. The brain
co-oordinates the
input and output
5
5. An impulse is
sent along a motor
neurone in the CNS
The Conscious Action
3. In the spinal cord
another sensory
neurone takes the
impulse to the brain
4. The brain
co-oordinates the
input and output
2. An impulse is
sent along a sensory
neurone
1. Receptors in
your foot detect a
stone in your shoe
5. An impulse is
sent along a motor
neurone in the CNS
6. The impulse leaves
the CNS via another
motor neurone
6
The Conscious Action
3. In the spinal cord
another sensory
neurone takes the
impulse to the brain
4. The brain
co-oordinates the
input and output
5. An impulse is
sent along a motor
neurone in the CNS
2. An impulse is
sent along a sensory
neurone
6. The impulse leaves
the CNS via another
motor neurone
1. Receptors in
your foot detect a
stone in your shoe
7. Muscles (the
effectors) lift the
foot out of the shoe
7
Responding to our environment
LIGHT
receptors in
the EYES
TASTE
receptors in
the TONGUE
SOUND
receptors in
the EARS
SMELL
receptors in
the NOSE
CHANGE OF
POSITION
receptors in
the EARS
(balance)
TOUCH,
PRESSURE and
TEMPERATURE
receptors in
the SKIN
Responding to our environment
LIGHT
receptors in
the EYES
TASTE
receptors in
the TONGUE
SOUND
receptors in
the EARS
SMELL
receptors in
the NOSE
CHANGE OF
POSITION
receptors in
the EARS
(balance)
TOUCH,
PRESSURE and
TEMPERATURE
receptors in
the SKIN
The Eye
The Eye
The Eye
Structure
1. Cornea
2. Iris
3. Lens
4. Ciliary
muscle
5. Retina
6. Optic
nerve
Function
The Eye
Structure
Function
1. Cornea
Front of the eye, helps to focus the
light
2. Iris
3. Lens
4. Ciliary
muscle
5. Retina
6. Optic
nerve
The Eye
Structure
Function
1. Cornea
Front of the eye, helps to focus the
light
2. Iris
Controls the amount of light reaching
the back of the eye.
3. Lens
4. Ciliary
muscle
5. Retina
6. Optic
nerve
The Eye
Structure
Function
1. Cornea
Front of the eye, helps to focus the
light
2. Iris
Controls the amount of light reaching
the back of the eye.
3. Lens
Focuses the light rays on the retina
4. Ciliary
muscle
5. Retina
6. Optic
nerve
The Eye
Structure
Function
1. Cornea
Front of the eye, helps to focus the
light
2. Iris
Controls the amount of light reaching
the back of the eye.
3. Lens
Focuses the light rays on the retina
4. Ciliary
muscle
Alters the shape of the lens so it can
focus on near and distant objects.
5. Retina
6. Optic
nerve
The Eye
Structure
Function
1. Cornea
Front of the eye, helps to focus the
light
2. Iris
Controls the amount of light reaching
the back of the eye.
3. Lens
Focuses the light rays on the retina
4. Ciliary
muscle
Alters the shape of the lens so it can
focus on near and distant objects.
5. Retina
Contains the light sensitive receptor
cells
6. Optic
nerve
The Eye
Structure
Function
1. Cornea
Front of the eye, helps to focus the
light
2. Iris
Controls the amount of light reaching
the back of the eye.
3. Lens
Focuses the light rays on the retina
4. Ciliary
muscle
Alters the shape of the lens so it can
focus on near and distant objects.
5. Retina
Contains the light sensitive receptor
cells
6. Optic
nerve
Sends impulses from the retina to the
brain.
The Eye
Focusing on near and distant
objects
DISTANT OBJECT
• suspensory ligaments
pull tight
• ciliary muscles relax
• lens is pulled thinner
and so light isn’t bent as
much.
Focusing on near and distant
objects
NEAR OBJECT
• suspensory ligaments
relax and go slack
• ciliary muscles
contract
• lens becomes fatter
and so light is bent
much more.
Responding to changes in light
intensity
The IRIS is the
coloured part, and
made of muscle.
The PUPIL is made
bigger or smaller
by the iris
Responding to changes in light
intensity
In brighter light the pupil is
made smaller by the iris, so
limiting the amount of light
hitting the retina
In dim light the pupil is made
larger by the iris, so allowing
as much light as possible to
hit the retina
The skin and temperature control
• In cold conditions, the
erector muscles contract,
pulling the hairs away
from the skin (the ‘wet
suit’ effect).
• The sweat glands stop
producing sweat.
• Capillaries near the skin
surface are closed,
preventing excessive heat
loss from the skin ( =
vasoconstriction)
The skin and temperature control
• In hotter conditions, the
erector muscles relax, the
hairs lie closer to the skin
surface.
• The sweat glands produce
sweat.
• Capillaries near the skin
surface are opened,
allowing excessive heat to
be lost from the skin ( =
vasodilation)
Content
Lesson 8
j) Coordination
and
response
j) Coordination and response
2.77 understand that organisms are able to respond to changes in their
environment
2.78 understand that homeostasis is the maintenance of a constant internal
environment and that body water content and body temperature are both
examples of homeostasis
2.79 understand that a coordinated response requires a stimulus, a receptor and
an effector
Flowering plants
2.80 understand that plants respond to stimuli
2.81 describe the geotropic responses of roots and stems
2.82 describe positive phototropism of stems
Humans
2.83 describe how responses can be controlled by nervous or by hormonal
communication and understand the differences between the two systems
2.84 understand that the central nervous system consists of the brain and spinal cord
and is linked to sense organs by nerves
2.85 understand that stimulation of receptors in the sense organs sends electrical
impulses along nerves into and out of the central nervous system, resulting in rapid
responses
2.86 describe the structure and functioning of a simple reflex arc illustrated by the
withdrawal of a finger from a hot object
2.87 describe the structure and function of the eye as a receptor
2.88 understand the function of the eye in focusing near and distant objects, and in
responding to changes in light intensity
2.89 describe the role of the skin in temperature regulation, with reference to
sweating, vasoconstriction and vasodilation
2.90 understand the sources, roles and effects of the following hormones: ADH,
adrenaline, insulin, testosterone, progesterone and oestrogen.
End of Section 2 Lesson 8
In this lesson we have covered:
The Central Nervous System
Nerve cells (neurones)
The Reflex Action
The Conscious Action
Structure and Function of the Eye
The Skin and Temperature Control