Structures and Functions in Living Organisms · 9 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 16% of your exam marks.
Enzymes in digestion and the role of digestive structures appear regularly across both papers.
Four standard food tests detect the four major nutrient groups. Each works by adding a reagent to a food sample and watching for a specific colour change.
For solid food, before testing:
| Test for | Reagent | Method | Positive result |
|---|---|---|---|
| Glucose (reducing sugar) | Benedict's solution | Add a few drops; heat in a water bath for 5 minutes | Blue → brick-red (orange/yellow if less glucose) |
| Starch | Iodine solution | Add a few drops at room temperature | Yellow-brown → blue-black |
| Protein | Biuret solution | Add a few drops at room temperature | Blue → violet (lilac/purple) |
| Lipids | Ethanol (then water) | Mix the sample with ethanol, then add an equal volume of cold water | Clear → cloudy white emulsion |