AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
Students should be able to interpret information relating to examples of…
Full specification wording
Principles of homeostasis and negative feedback (A-level only): Students should be able to interpret information relating to examples of negative and positive feedback.
You will be given a trace, a flow diagram or a passage about an unfamiliar system and asked which kind of feedback it shows.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 6 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
You will be given a trace, a flow diagram or a passage about an unfamiliar system and asked which kind of feedback it shows. Work it out rather than recall it. Identify the variable that changes, identify the response, then ask whether the response moves the variable back towards its starting value or further away from it. Negative feedback appears as oscillation around a steady level: the variable rises, a correction follows and it falls back. Positive feedback appears as an accelerating departure from the starting value, usually ending only when something else intervenes. On a graph, look for a return to the original value after a disturbance, which is negative, or a rise that becomes steeper, which is positive. Then justify the answer with the data: quote values, times and the direction of change, and name the receptor or effector if the information allows it.
What earns the marks
- A classification that carries its justification, naming the feedback as negative or positive together with the reason read from the information, since the name on its own is not the mark point.
- Using data from the figure, quoting values or times, to show the direction of the change.
- Stating whether the response opposes the change and returns the variable to its original level, or amplifies it.
- Naming the receptor, coordinator or effector identified from the information provided.
- Explaining the biological benefit or the consequence of the feedback described.
Common mistakes and how to put them right
Naming the type of feedback but giving no data, when the justification carries the marks.
Quoting data without saying what it shows about the direction of the response.
Assuming that every physiological example must be negative feedback.
Reading a variable that stays high as negative feedback, when nothing has returned it to the set point.
Treating a correlation in the data as proof of a causal control mechanism.
Exam tips
- The bare word negative or positive is usually worth nothing; the explanation carries the marks.
- Quote at least one pair of figures with units when you justify a conclusion from a graph.
- Check whether the trace returns to its starting value, because that is the clearest signature of negative feedback.
Try the lesson
The start of the Principles of homeostasis and negative feedback (A-level only): Students should be able to interpret information relating to examples of negative and positive feedback. lesson, made from checked teaching notes for this specification point.
Have a go first
During an action potential, the opening of voltage-gated sodium ion channels causes sodium ions to diffuse into the axon. This depolarises the membrane, which causes more voltage-gated sodium ion channels to open. Which statement correctly interprets this mechanism?
Listen
You will be given a trace, a flow diagram or a passage about an unfamiliar system and asked which kind of feedback it shows. Work it out rather than recall it. Identify the variable that changes, identify the response, then ask whether the response moves the variable back towards its starting value or further away from it. Negative feedback appears as oscillation around a steady level: the variable rises, a correction follows and it falls back. Positive feedback appears as an accelerating departure from the starting value, usually ending only when something else intervenes. On a graph, look for a return to the original value after a disturbance, which is negative, or a rise that becomes steeper, which is positive. Then justify the answer with the data: quote values, times and the direction of change, and name the receptor or effector if the information allows it. A strong answer earns marks for these points. a classification that carries its justification, naming the feedback as negative or positive together with the reason read from the information, since the name on its own is not the mark point. using data from the figure, quoting values or times, to show the direction of the change. stating whether the response opposes the change and returns the variable to its original level, or amplifies it. naming the receptor, coordinator or effector identified from the information provided. Exam tip: The bare word negative or positive is usually worth nothing; the explanation carries the marks.
Key words
Say what each word means before you turn the card.
interpreting data
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oscillation around a set point
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amplification of a change
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justifying with figures
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See every definition
- interpreting data
- Reading a trace, flow diagram or passage about an unfamiliar system and working out which kind of feedback it shows rather than recalling it.
- oscillation around a set point
- The pattern of negative feedback in which the variable rises, a correction follows and it falls back around a steady level.
- amplification of a change
- An accelerating departure from the starting value, usually ending only when something else intervenes, which is how positive feedback appears.
- justifying with figures
- Quoting values, times and the direction of change from the data to support a conclusion, since the name on its own is not the mark point.
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