OxfordAQA International A Level Biology
OxfordAQA International A Level Biology 3.4.1 Control Systems Involve Stimulus and Response Exam Questions
Free OxfordAQA International A Level Biology revision for 3.4.1 Control Systems Involve Stimulus and Response: what you need to know, common mistakes and exam-style questions with answers. Covers stimuli and responses, simple reflex arcs with three neurones, the importance of reflexes, and taxes and kineses in simple organisms.
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About OxfordAQA International A Level Biology 3.4.1 Control Systems Involve Stimulus and Response
This short topic opens Unit 4, Control. You need to explain how organisms detect stimuli and respond to them, describe a simple reflex arc involving three neurones (sensory, relay and motor), and explain why reflexes are important in avoiding damage. You also need to describe taxes and kineses as simple responses that keep mobile organisms in a favourable environment. It sets up the work on receptors, nerve impulses, synapses and effectors that follows, and links to plant tropisms in 3.4.5. Questions often ask you to explain the results of choice chamber experiments with woodlice or maggots.
What you need to know
- Stimulus and response A stimulus is a detectable change in the environment. Receptors detect it, a coordinator processes the information and effectors such as muscles or glands bring about a response.
- Reflex arc A simple reflex arc has three neurones: a sensory neurone carries impulses from the receptor, a relay neurone in the spinal cord passes them on, and a motor neurone carries them to the effector.
- Importance of reflexes Reflexes are rapid and involuntary, so they protect the body from damage, such as withdrawing a hand from a hot object. They do not need to be learned.
- Taxes A taxis is a directional response towards or away from a stimulus, for example woodlice moving away from light.
- Kineses A kinesis is a non-directional response where the speed of movement or the rate of turning changes with the intensity of the stimulus, for example woodlice moving faster and turning less in dry conditions.
Common mistakes in 3.4.1 Control Systems Involve Stimulus and Response
- Saying reflexes involve the brain making a decision. Simple reflexes are coordinated in the spinal cord and are involuntary.
- Confusing taxis and kinesis. A taxis has a direction relative to the stimulus; a kinesis changes speed or turning rate.
- Calling the receptor the effector. Receptors detect stimuli; effectors produce the response.
- Leaving out the relay neurone in a three-neurone reflex arc.
Try three 3.4.1 Control Systems Involve Stimulus and Response exam-style questions
1. Describe the pathway of a reflex arc that moves a hand away from a hot object. (3 marks)
Show the mark scheme answer
Receptor in the skin detects heat and sends impulses along a sensory neurone; relay neurone in the spinal cord; motor neurone carries impulses to the effector muscle, which contracts.
2. Woodlice move faster and turn less often in dry air. Explain the advantage of this. (2 marks)
Show the mark scheme answer
This is a kinesis; it makes them more likely to reach a moist area where they lose less water / do not dry out.
3. Explain why reflexes are important for survival. (2 marks)
Show the mark scheme answer
They are rapid / involuntary; so they protect the body from damage before the brain has processed the information.
3.4.1 Control Systems Involve Stimulus and Response FAQs
What does OxfordAQA International A Level Biology 3.4.1 Control Systems Involve Stimulus and Response cover?
It covers stimuli and responses, simple reflex arcs with three neurones, the importance of reflexes, and taxes and kineses in simple organisms.
Which unit is 3.4.1 Control Systems Involve Stimulus and Response examined in?
It is part of Unit 4, Control, which is an International A2 paper. The Unit 5 synoptic paper can also draw on this content.
How do I tell a taxis from a kinesis in a question?
If the organism moves towards or away from the source of the stimulus, it is a taxis. If it changes how fast it moves or how often it turns, without a direction, it is a kinesis.
