18 5A.5 Simple experiments on enzymes (aim, method, expected result)
- Catalase in potato or liver. Aim: show that an enzyme speeds up decomposition of hydrogen peroxide (2H₂O₂ → 2H₂O + O₂). Method: put hydrogen peroxide solution into three test tubes; add (a) a small piece of fresh liver, (b) a piece of boiled liver, (c) sand (control). Result: vigorous bubbling of oxygen with fresh liver; no bubbling with boiled liver (enzyme denatured) or sand. Conclusion: catalase is a protein catalyst, destroyed by heat; a glowing splint relights in the gas.
- Effect of temperature on amylase. Method: mix starch solution and saliva (or amylase) at 0 °C, 37 °C and 70 °C; after 10 minutes test samples with iodine. Result: the 37 °C sample no longer turns blue-black (starch digested); the 0 °C one stays blue-black (slow); the 70 °C one stays blue-black (enzyme denatured). Conclusion: the optimum temperature is near 37 °C.
- Osmosis in a cell (see Module 4, potato strips) to show how water enters and leaves cells.
✍️ Worked examples
Worked example 9.
- Problem. Enzyme activity (product in mg per minute) at different substrate concentrations: 0.1 mol/L: 2; 0.2: 4; 0.4: 7; 0.8: 9; 1.6: 9.5; 3.2: 9.6.
- Describe the pattern and explain it.
- Solution. At low substrate concentration the rate increases almost in proportion (more substrate molecules meet more active sites).
- From about 0.8 mol/L the rate levels out near 9.6 mg/min because all the enzyme's active sites are occupied (saturation); adding more substrate cannot increase the rate; only more enzyme can.