GCSE BIOLOGY AQA
Paper 2
Topics 5-7
1. Homeostasis and response
2. Inheritance, variation and evolution
3. Ecology
1hour 45 minutes
100 marks
50% of GCSE
,TOPIC 5: HOMEOSTASIS AND RESPONSE
HOMEOSTASIS
Homeostasis is the regulation of internal conditions of a cell or organism in response to internal and
external changes.
Homeostasis maintains optimal conditions for enzyme action and all cell functions.
Homeostasis consists of automatic control systems. These automatic control systems may involve nervous
responses or chemical responses.
In the human body, there are three main automatic control systems:
1. Blood glucose concentration
2. Body temperature
3. Water levels.
All control systems are made up of components which work
together to maintain a steady condition.
• Stimuli = changes in the environment
• Receptor cells = detect stimuli
• Coordination centres (brain/spinal cord/pancreas) = receive and process information from the receptor
cells. Organises a response.
• Effectors (muscles/glands) = produce a response which counteracts the change and restores optimum
levels.
,THE NERVOUS SYSTEM
A key part of homeostasis is the nervous system.
The nervous system enables humans to react to their surroundings and coordinate a response.
Neurone = nerve cells.
1) Receptors detect a stimulus
2) Sensory neurones carry electrical impulses from the receptors to the CNS
3) Central Nervous System (CNS): the brain and spinal cord = coordination centre
4) Motor neurones carry electrical impulses from the CNS to effectors
5) Effectors are usually a muscle which contracts or a gland which secretes a hormone
Synapses
The connection between two neurones is called a synapse.
When the electrical impulse reaches the end of the neurone, it stimulates the release of a chemical. The
chemical diffuses across the synapse to activate an electrical impulse in the next neurone.
o Impulses travel along a sensory neurone
o Impulses are passed along a relay neurone via a synapse
o Impulses travel along a motor neurone via a synapse
Reflex arcs
Passage of information from receptor to effector = reflex arc
Reflex actions do not involve the conscious part of the brain. This makes them automatic and rapid.
Reflexes help to protect us from danger.
e.g. if a bright line is shone in your eyes, the pupil automatically gets smaller to stop it from getting
damaged
, THE BRAIN
The brain plays a critical role in the central nervous system.
The brain controls complex behaviour.
It is made of billions of interconnected neurones.
Different parts of the brain carry out different functions.
o Cerebral Cortex: highly folded, outer part of the brain.
Responsible for consciousness, intelligence, memory,
and language.
o Cerebellum: controls our balance and co-ordinates our
movements.
o Medulla: controls unconscious activities like our heart
rate and our breathing rate.
It is difficult to treat brain damage or brain diseases:
• The brain is protected by the skull, so it is difficult to access
• The structures are extremely complex
• The brain is extremely delicate and easy to damage
Three ways in which neuroscientists investigate the brain:
1) They can study patients with brain damage to work out what the damaged part of the brain does
2) We can electrically stimulate different parts of the brain to look at the effects on the person’s
behaviour
3) Use MRI scanning techniques to identify which parts of the brain are most active during different
activities
Paper 2
Topics 5-7
1. Homeostasis and response
2. Inheritance, variation and evolution
3. Ecology
1hour 45 minutes
100 marks
50% of GCSE
,TOPIC 5: HOMEOSTASIS AND RESPONSE
HOMEOSTASIS
Homeostasis is the regulation of internal conditions of a cell or organism in response to internal and
external changes.
Homeostasis maintains optimal conditions for enzyme action and all cell functions.
Homeostasis consists of automatic control systems. These automatic control systems may involve nervous
responses or chemical responses.
In the human body, there are three main automatic control systems:
1. Blood glucose concentration
2. Body temperature
3. Water levels.
All control systems are made up of components which work
together to maintain a steady condition.
• Stimuli = changes in the environment
• Receptor cells = detect stimuli
• Coordination centres (brain/spinal cord/pancreas) = receive and process information from the receptor
cells. Organises a response.
• Effectors (muscles/glands) = produce a response which counteracts the change and restores optimum
levels.
,THE NERVOUS SYSTEM
A key part of homeostasis is the nervous system.
The nervous system enables humans to react to their surroundings and coordinate a response.
Neurone = nerve cells.
1) Receptors detect a stimulus
2) Sensory neurones carry electrical impulses from the receptors to the CNS
3) Central Nervous System (CNS): the brain and spinal cord = coordination centre
4) Motor neurones carry electrical impulses from the CNS to effectors
5) Effectors are usually a muscle which contracts or a gland which secretes a hormone
Synapses
The connection between two neurones is called a synapse.
When the electrical impulse reaches the end of the neurone, it stimulates the release of a chemical. The
chemical diffuses across the synapse to activate an electrical impulse in the next neurone.
o Impulses travel along a sensory neurone
o Impulses are passed along a relay neurone via a synapse
o Impulses travel along a motor neurone via a synapse
Reflex arcs
Passage of information from receptor to effector = reflex arc
Reflex actions do not involve the conscious part of the brain. This makes them automatic and rapid.
Reflexes help to protect us from danger.
e.g. if a bright line is shone in your eyes, the pupil automatically gets smaller to stop it from getting
damaged
, THE BRAIN
The brain plays a critical role in the central nervous system.
The brain controls complex behaviour.
It is made of billions of interconnected neurones.
Different parts of the brain carry out different functions.
o Cerebral Cortex: highly folded, outer part of the brain.
Responsible for consciousness, intelligence, memory,
and language.
o Cerebellum: controls our balance and co-ordinates our
movements.
o Medulla: controls unconscious activities like our heart
rate and our breathing rate.
It is difficult to treat brain damage or brain diseases:
• The brain is protected by the skull, so it is difficult to access
• The structures are extremely complex
• The brain is extremely delicate and easy to damage
Three ways in which neuroscientists investigate the brain:
1) They can study patients with brain damage to work out what the damaged part of the brain does
2) We can electrically stimulate different parts of the brain to look at the effects on the person’s
behaviour
3) Use MRI scanning techniques to identify which parts of the brain are most active during different
activities
