This exam tips covers Exam Tips within Enzymes in Digestion for GCSE Biology. Enzyme structure and function, digestive enzymes, factors affecting enzyme activity, lock and key model, and practical investigations It is section 19 of 19 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Topic position
Section 19 of 19
Practice
20 questions
Recall
25 flashcards
Exam Tips
Know Your Enzyme Locations
Pepsin works in the stomach only. Amylase works in the mouth AND is secreted by the pancreas into the small intestine. Trypsin and lipase are pancreatic enzymes released into the small intestine. Memorise where each enzyme is produced and where it acts.
Bile is Not an Enzyme
Bile does not break chemical bonds — it physically breaks large fat droplets into smaller ones (emulsification). This increases the surface area for lipase to work on. Bile is produced by the liver, stored in the gall bladder, and released into the duodenum. It also neutralises stomach acid, creating the alkaline conditions trypsin and lipase need.
Denaturation vs Slowing Down
At low temperatures, enzymes slow down but are not denatured — warming them up restores activity. At high temperatures above the optimum, enzymes denature permanently. Always use the word "denature" not "killed" in the exam.
Graph Skills
Practise drawing enzyme activity graphs for temperature and pH. The curve rises to a peak at the optimum, then drops sharply. For temperature, explain the rise (more kinetic energy, more collisions) and the fall (denaturation of active site). For pH, explain that the wrong pH alters the shape of the active site.
Food Tests — Colours to Learn
Benedict's: blue to brick red (reducing sugars). Iodine: orange to blue-black (starch). Biuret: blue to purple (proteins). Emulsion: clear to white cloudy (lipids). Learn the reagent, method, and both the positive and negative results for each test.
Calculations
Rate = amount of product ÷ time. Also know: rate = 1/time (useful when measuring how long a reaction takes). For initial rate from a graph, draw a tangent to the curve at time zero and calculate gradient = rise ÷ run. Always include units.