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WalesBiologyQuick questions
Unit 1: Cells and exchange
Quick questions on Digestive enzymes and food tests - WJEC GCSE Biology (Unit 1)
5short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is temperature?Show answer
As temperature rises from low values, the enzyme and substrate gain kinetic energy and collide more often, so the rate increases up to the optimum temperature (around 37 degrees Celsius for human enzymes). Above the optimum, the heat breaks bonds holding the enzyme in shape, so the active site changes shape, the substrate no longer fits, and the enzyme is denatured. Denaturing is permanent, and the rate falls sharply.
What is pH?Show answer
Each enzyme has an optimum pH. Protease in the stomach works best in acidic conditions (about pH 2), while enzymes in the small intestine work best in slightly alkaline conditions. If the pH is too far from the optimum, the active site changes shape and the enzyme denatures.
What is starch test?Show answer
Add a few drops of orange-brown iodine solution; it turns blue-black if starch is present.
What is protein test?Show answer
Add biuret solution (or sodium hydroxide followed by copper sulfate). It changes from blue to purple if protein is present.
What is lipid test?Show answer
Mix the sample with ethanol, then pour into water. A cloudy white emulsion forms if lipid is present.
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