1. iGCSE Biology Section 2 lesson 8

2. Structures and functions in living organisms
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

3. Lesson 8 Content 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.
Lesson 8
j) Coordination and response

4. Lesson 8 Content 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.
Lesson 8
j) Coordination and response

5. Lesson 8 Content 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.
Lesson 8
j) Coordination and response

6. The Central Nervous System

7. The Central Nervous System
Brain

8. The Central Nervous System
Brain
Spinal cord

9. The Central Nervous System
Brain
Spinal cord
Spinal nerves

10. The Central Nervous System
Brain
Spinal cord
Spinal nerves
Cell body
Motor neurone
Direction of impulse

11. The Central Nervous System
Brain
Spinal cord
Spinal nerves
Sensory neurone
Cell body
Direction of impulse

12. The Central Nervous System
Brain
Spinal cord
Spinal nerves
Relay neurone
Cell body

13. Nerve cell (neurone)
Neurones are specially adapted cells that can carry impulses (electrical signals)

14. 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

15. 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

16. 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
The cell body has many connections, so enabling communication with other neurones

17. Myelin (fatty) sheath)
Nerve cell (neurone)
Dendrites
Cell body
Myelin (fatty) sheath)
Axon endings

18. Eg. removing the hand from a hot object.
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.

19. The Reflex Action

20. Stimulus, eg. a hot object
The Reflex Action
Stimulus, eg. a hot object

21. The Reflex Action
Receptor eg. in the skin

22. The Reflex Action
Sensory neurone

23. The Reflex Action
Relay neurone

24. The Reflex Action
Motor neurone

25. The Reflex Action
Effector, eg. muscle

26. 1. The receptor is stimulated by the hot object
The Reflex Action 1
1. The receptor is stimulated by the hot object

27. The Reflex Action 2. This causes an impulse to pass along.1
1. The receptor is stimulated by the hot object

28. The Reflex Action 2. This causes an impulse to pass along.
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

29. The Reflex Action 2. This causes an impulse to pass along.
3. The spinal cord (or brain) co-ordinates response without conscious thought.
2. This causes an impulse to pass along.
4. An impulse is transmitted along a motor neurone 3 2 4 1
1. The receptor is stimulated by the hot object

30. The Reflex Action 2. This causes an impulse to pass along.
3. The spinal cord (or brain) co-ordinates response without conscious thought.
2. This causes an impulse to pass along.
4. An impulse is transmitted along a motor neurone 3 2 4 5 1
1. The receptor is stimulated by the hot object
5. The muscle contracts in response to the stimulus

31. 1. Receptors in your foot detect a stone in your shoe
The Conscious Action
1. Receptors in your foot detect a stone in your shoe 1

32. The Conscious Action 2. An impulse is sent along a sensory neurone
1. Receptors in your foot detect a stone in your shoe 2

33. The Conscious Action 2. An impulse is sent along a sensory neurone 3
3. In the spinal cord another sensory neurone takes the impulse to the brain
2. An impulse is sent along a sensory neurone 3
1. Receptors in your foot detect a stone in your shoe

34. The Conscious Action 4. The brain co-oordinates the input and output 4
3. In the spinal cord another sensory neurone takes the impulse to the brain 4
2. An impulse is sent along a sensory neurone
1. Receptors in your foot detect a stone in your shoe

35. The Conscious Action 4. The brain co-oordinates the input and output
3. In the spinal cord another sensory neurone takes the impulse to the brain
5. An impulse is sent along a motor neurone in the CNS 5
2. An impulse is sent along a sensory neurone
1. Receptors in your foot detect a stone in your shoe

36. The Conscious Action 4. The brain co-oordinates the input and output
3. In the spinal cord another sensory neurone takes the impulse to the brain
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 6

37. The Conscious Action 4. The brain co-oordinates the input and output
3. In the spinal cord another sensory neurone takes the impulse to the brain
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

38. 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

39. 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

40. The Eye

41. The Eye

42. The Eye Structure Function 1. Cornea 2. Iris 3. Lens 4. Ciliary muscle
5. Retina
6. Optic nerve

43. Front of the eye, helps to focus the light
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

44. The Eye Structure Function Front of the eye, helps to focus the light
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

45. The Eye Structure Function Front of the eye, helps to focus the light
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

46. The Eye Structure Function Front of the eye, helps to focus the light
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

47. The Eye Structure Function Front of the eye, helps to focus the light
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

48. The Eye Structure Function Front of the eye, helps to focus the light
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.

49. The Eye

50. Focusing on near and distant objects
suspensory ligaments pull tight
ciliary muscles relax
lens is pulled thinner and so light isn’t bent as much.

51. 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.

52. 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

53. 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

54. 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)

55. 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)

56. Lesson 8 Content 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.
Lesson 8
j) Coordination and response

57. 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