Explain glucose test strips and biosensors
Relate glucose oxidase and peroxidase reactions to glucose measurements in blood or urine.
A Level; Cambridge International Biology 9700, 2028–2030. Written answers are self-checked; this is not a practical skills certification.
Before you begin
- A control system detects a change, communicates information and changes an effector response.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does calibration connect in a glucose test?
What you will learn
- Explain the principle of glucose test strips
- Explain how enzyme biosensors convert glucose reaction into a measurable signal
From glucose reaction to concentration
| Feature | Meaning |
|---|---|
| Enzyme | Glucose oxidase recognises glucose |
| Readout | Indicator colour or electrical response |
| Calibration | Reference response estimates concentration |
Build the explanation
In an enzyme test strip, glucose oxidase catalyses oxidation of glucose and transfers electrons to an indicator system. A colour change can be compared with a calibrated scale. In a biosensor, the enzyme reaction produces an electrical signal related to glucose concentration. Some systems use peroxidase in a coupled reaction: hydrogen peroxide produced by glucose oxidase is used to oxidise a colourless indicator. Calibration converts colour intensity or current into an estimated concentration.
Apply the limits
A strip or biosensor measures a sample; it does not itself regulate blood glucose or diagnose every condition. The signal depends on calibration, sample handling and the specific device design. Distinguish the enzyme that recognises glucose from the indicator or electrical readout.
Pause and explain
A biosensor gives an electrical current, but the calibration curve is not supplied. What can be concluded from the current alone?
Worked example
What role does glucose oxidase play in a glucose strip?
Show the worked solution
- It catalyses a reaction involving glucose.
- The resulting indicator change is compared with a calibrated scale.
Answer Glucose oxidase initiates the glucose-dependent reaction that leads to a measurable colour or electrical signal.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain how a glucose-oxidase test strip can estimate glucose concentration.
Give me a hint
Name the relevant structure or signal, then state its effect.
Compare my reasoning
- Glucose oxidase catalyses a glucose-dependent reaction.
- The indicator signal is compared with a calibrated reference.
Glucose oxidase catalyses a reaction involving glucose. The resulting colour change is compared with a calibrated scale to estimate glucose concentration.
Look for these in your work
- Correct mechanism
- Direction of response explained
In a coupled color test, what is the role of peroxidase after glucose oxidase acts?
Give me a hint
Separate the observed change from the body's response.
Compare my reasoning
- Glucose oxidase produces hydrogen peroxide in the coupled reaction.
- Peroxidase uses it to oxidise the colour indicator.
Peroxidase catalyses oxidation of the colour indicator using hydrogen peroxide produced in the glucose-oxidase reaction, so colour can indicate glucose-dependent activity.
Look for these in your work
- Evidence interpreted
- Control step identified
A biosensor gives an electrical current, but the calibration curve is not supplied. What can be concluded from the current alone?
Give me a hint
Apply the mechanism to the new context without claiming more than the evidence shows.
Compare my reasoning
- It is a measured signal from the sensor.
- Without calibration, it cannot be converted reliably into a glucose concentration.
The current shows a sensor response, but without an appropriate calibration it cannot be interpreted as a reliable glucose concentration.
Look for these in your work
- New context applied
- Limits preserved
Common mistakes
- Calling glucose oxidase the colour indicator
- Treating a measurement as a homeostatic response
What can you explain now?
What does calibration connect in a glucose test?
Compare with the explanation
A measured colour or electrical signal to glucose concentration
A reference scale relates instrument response to concentration.
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Make it stick
How do enzyme specificity, an indicator signal and calibration work together?
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