Testing for biological molecules — OCR GCSE Biology
Test yourself on Testing for biological molecules with OCR GCSE practice questions.
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Testing for biological molecules explained
Carrying out the Benedict's test for reducing sugars requires heating reaction mixtures to at least 75 to 80 °C, or placing them in a boiling water bath for approximately 5 minutes.
Read the full explanation
Safe heating demands an electrically heated, thermostatically controlled water bath or a beaker of water supported on a tripod and wire gauze over a Bunsen burner set to a blue heating flame. Test tubes must be secured in a test tube rack within the water bath or held using wooden test tube tongs, with the tube mouth angled away from all persons to prevent injury from sudden boiling or bumping. Personal protective equipment, including safety goggles and heat-resistant gloves, prevents scalds and chemical splash injuries.
Your focus
- Set up and operate water baths safely using Bunsen burners or electric heaters to reach required temperatures.
- Apply safety protocols including protective eyewear and tube orientation to manage boiling and chemical hazards.
- Explain why reducing sugar testing requires controlled water bath heating rather than direct naked flame application.
Testing for biological molecules exam tips
Marking Points
- Heat the test mixture with an equal volume of Benedict's reagent in a water bath maintained at 75 to 80 °C or boiling water for 5 minutes.
- Use a thermostatically controlled electric water bath or a beaker of water over a Bunsen burner on a tripod and gauze rather than direct flame heating.
- Secure boiling tubes with test tube holders or a test tube rack and point tube openings away from people to avoid bumping hazards.
- Wear eye protection and handle hot glassware with tongs or heat-resistant gloves to prevent scalding.
Examiner Tips
- 💡In exam questions about food tests, state that Benedict's test specifically requires heating in a water bath, whereas iodine and Biuret tests do not.
- 💡When asked to improve safety in heating experiments, suggest an electric water bath to avoid open flames and provide precise temperature control.
Common Mistakes
- Heating the test tube directly over a naked Bunsen flame, causing the liquid to boil violently and eject corrosive contents.
- Failing to reach the required temperature of at least 75 °C, resulting in a false-negative result for reducing sugars.
- Leaving a Bunsen burner on an invisible roaring blue flame unattended rather than switching to a yellow safety flame.