AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Temperature must be controlled by use of a water bath or electric heater.
Full specification wording
The human digestive system: Temperature must be controlled by use of a water bath or electric heater.
Enzymes are sensitive to temperature, so temperature must be kept constant during the starch–amylase practical.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 24 of 25
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Enzymes are sensitive to temperature, so temperature must be kept constant during the starch–amylase practical. A water bath or electric heater maintains a steady temperature, such as 37 °C, which is close to human body temperature. If temperature changes during the investigation, enzyme activity changes too, so the time taken for starch to be digested would not be a fair comparison between pH values. You should allow the starch, amylase and buffer solutions to reach the set temperature before mixing them, and keep the reaction tube in the water bath throughout. Temperature is therefore a control variable, while pH is the independent variable. A thermometer can be used to check that the water bath is at the required temperature.
What earns the marks
- State that temperature affects enzyme activity and must be kept constant.
- Describe using a water bath or electric heater to maintain a steady temperature.
- Explain that all solutions should be allowed to reach the set temperature before mixing.
- Identify temperature as a control variable while pH is the independent variable.
- Explain that a change in temperature would change the rate of digestion and make results invalid for comparing pH.
- Use a thermometer to check the temperature of the water bath.
Common mistakes and how to put them right
Leaving the reaction tube out of the water bath during sampling.
Put it right by returning the tube to the water bath between samples.
Mixing solutions before they have reached the set temperature.
Put it right by allowing them to equilibrate in the water bath first.
Treating temperature as the independent variable.
Put it right by identifying pH as the independent variable and temperature as a control variable.
Exam tips
- Name the control variable as temperature and state the value used, such as 37 °C.
- Explain the consequence of not controlling temperature: enzyme activity would change, so the pH comparison would not be valid.
- Describe the method step of allowing solutions to reach the set temperature before mixing.
Try the lesson
The start of the The human digestive system: Temperature must be controlled by use of a water bath or electric heater. lesson, made from checked teaching notes for this specification point.
Have a go first
In the starch digestion practical, why is the mixture of starch and amylase kept in a water bath at a set temperature?
Listen
Enzymes are sensitive to temperature, so temperature must be kept constant during the starch–amylase practical. A water bath or electric heater maintains a steady temperature, such as 37 °C, which is close to human body temperature. If temperature changes during the investigation, enzyme activity changes too, so the time taken for starch to be digested would not be a fair comparison between pH values. You should allow the starch, amylase and buffer solutions to reach the set temperature before mixing them, and keep the reaction tube in the water bath throughout. Temperature is therefore a control variable, while pH is the independent variable. A thermometer can be used to check that the water bath is at the required temperature. A strong answer earns marks for these points. State that temperature affects enzyme activity and must be kept constant. Describe using a water bath or electric heater to maintain a steady temperature. Explain that all solutions should be allowed to reach the set temperature before mixing. Identify temperature as a control variable while pH is the independent variable. A common slip: Leaving the reaction tube out of the water bath during sampling. Instead, returning the tube to the water bath between samples. Exam tip: Name the control variable as temperature and state the value used, such as 37 °C.
Key words
Say what each word means before you turn the card.
Enzyme activity and temperature
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Control variables in investigations
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Fair testing and validity
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Use of water baths in practical work
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See every definition
- Enzyme activity and temperature
- Enzymes are sensitive to temperature, so if temperature changes during the investigation, enzyme activity changes too.
- Control variables in investigations
- Temperature is a control variable, while pH is the independent variable.
- Fair testing and validity
- If temperature changes, the time taken for starch to be digested would not be a fair comparison between pH values.
- Use of water baths in practical work
- A water bath or electric heater maintains a steady temperature, such as 37 °C, which is close to human body temperature.
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