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AQA GCSE Biology (triple) notes Chapter 2-10
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AQA GCSE Biology notes Topic 5 – Homeostasis and response
Topic 5 – Homeostasis and response
Table of Content
5.1 Homeostasis ..................................................................... 2
5.2 The human nervous system .............................................. 2
5.2.1 Structure and function ................................................................................................2
5.2.2 The brain (biology only) ..............................................................................................4
5.2.3 The eye (biology only) .................................................................................................4
5.2.4 Control of body temperature (biology only) ...............................................................6
5.3 Hormonal coordination in humans ................................... 6
5.3.1 Human endocrine system ...........................................................................................6
5.3.2 Control of blood glucose concentration .....................................................................7
5.3.3 Maintaining water and nitrogen balance in the body (biology only) ..........................8
5.3.4 Hormones in human reproduction ...........................................................................10
5.3.5 Contraception ...........................................................................................................11
5.3.6 The use of hormones to treat infertility (HT only) ....................................................12
5.3.7 Negative feedback (HT only) .....................................................................................13
5.4 Plant hormones (biology only) ........................................ 13
5.4.1 Control and coordination ..........................................................................................13
5.4.2 Use of plant hormones (HT only) ..............................................................................15
1
, AQA GCSE Biology notes Topic 5 – Homeostasis and response
5.1 Homeostasis
What is homeostasis?
• Regulation of internal conditions of a cell or organism to maintain optimal conditions
Why is homeostasis important in body? (1)
• Maintain optimal conditions for enzymes action & all cell functions
In human body, these include control of:
• Blood glucose con
• Body temp
• Water levels
These automatic control systems may involve nervous or chemical responses
All control systems include:
• Receptors - cells which detect stimuli (changes in environment)
• Coordination centres eg brain, spinal cord & pancreas - receive & process info from receptors
• Effectors, muscles or glands - restore optimum levels
5.2 The human nervous system
5.2.1 Structure and function
Central nervous • Brain & spinal cord
system (CNS) • Coordinates response of effectors eg muscles contracting / glands secreting
hormones
Describe the function of receptors. (2) Describe the function of effectors. (2)
• Detect changes in surroundings • Convert impulse to an action
• Convert stimulus to impulse • Eg muscle / gland
Reflex action
• Automatic & rapid
• Over short period of time
• Don't involve conscious part of brain
• Involves nerve cells & impulses
• Affects only one part of body
2
, AQA GCSE Biology notes Topic 5 – Homeostasis and response
Structure in a reflex action
Type of effector Response effector makes
muscle contraction
gland Produce chemical /
enzyme
Describe the stages that happened in a reflex action. (6)
Stimulus → receptor → sensory neurone (in peripheral) → synapse → relay neurone (in CNS) → synapse →
motor neurone (in peripheral) → effector → response
1. Stimulus detected by receptor
2. Receptor sends electrical impulses along sensory neurons and reaches synapse
3. Chemical releases from sensory neurons
4. Chemical diffuses across synapse and attaches to relay neurone to stimulate electrical impulse
5. Impulse passes along relay neurone and reaches synapse
6. Chemical release from relay neurone
7. Chemical diffuses across synapse and attaches to motor neurone to stimulate electrical impulse
8. Impulse passes along motor neurone to an effector
9. Effector causes a response
How can you tell that it's not a conscious action? (1)
• Not connected to brain
• Coordinated only by spinal cord
Reflex actions like this are useful. Explain why. (2)
• Rapid response protects body from damage or pain
Reflex action times investigation
1. Student A sits with his elbow resting on the edge of a table.
2. Student B holds a ruler with the bottom of the ruler level with the thumb of Student A.
3. Student B drops the ruler.
4. Student A catches the ruler and records the distance.
5. Steps 1 to 4 are then repeated.
Give two variables the students controlled in their investigation. (2)
• Drop ruler from same height
• Use same weight of ruler
What improvement could the students make to the method so the results are more valid? (1)
• Carry out more repeats
Give a conclusion about the effect of caffeine on reflex actions & reaction time. (1)
• Caffeine speeds up reflex actions & decreases reaction time
3
, AQA GCSE Biology notes Topic 5 – Homeostasis and response
5.2.2 The brain (biology only)
Functions
Cerebral cortex - consciousness, intelligence, memory & language
Cerebellum - coordination of muscular activity & balance
Medulla - unconscious activities eg heartbeat & breathing
Methods of finding out how much the brain is damaged
Neuroscientists map regions of brain to particular functions by…
1. Studying patients with brain damage
2. Electrode stimulaton - electrically stimulating different parts of brain
3. MRI scan
Name the technique a doctor would use to find out if the man's brain has been damaged. (1)
• MRI scan
Difficulties of brain investigation
Explain why it is difficult to treat brain damage. (1)
• High risk of causing more damage to brain
• It's complex & delicate
• Difficult to treat brain disorders
5.2.3 The eye (biology only)
Eye - a sense organ containing receptors sensitive to light intensity & colour
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