IP Biology Notes: Biological Molecules (Upper Sec 03)
Free IP Biology notes on carbohydrates, fats, proteins, enzymes, and food tests for Sec 3 to Sec 4.
Use this as a free IP Biology notes chapter on biological molecules for Year 3 to Year 4. It keeps the IP pacing while reinforcing the 6093 biology foundations most schools test through DBQs, diagrams, and practical explanations.
Status: SEAB O-Level Biology 6093 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for this note.
The core idea is simple: Biological molecules are tested through roles, enzymes, and food tests.
Use it as a working check: Learn what carbohydrates, fats, and proteins do, then link each food test to its reagent, condition, and positive result.
Then go one layer deeper: Example: Benedict's test needs heating in a water bath. A brick-red precipitate means reducing sugar is present, not simply that the sample turned red.
What you must know
- Carbohydrates (C, H, O): glucose, sucrose, starch, glycogen; energy source/storage. Fats (C, H, O): energy storage, insulation; formed from glycerol + fatty acids. Proteins (C, H, O, N sometimes S): structure and enzymes.
- Food tests: iodine for starch (blue-black), Benedict for reducing sugars (brick-red ppt on heating), biuret for protein (violet), ethanol emulsion for fats (white emulsion).
- Enzymes: specific active site; lock-and-key/induced fit; lower activation energy; affected by temperature (optimum then denaturation) and pH (active site charges disrupted).
Decision map - identifying an unknown food sample
Use separate portions of the same sample so one reagent does not contaminate the next test. Start with the test that needs no heating, then run the heated Benedict test in a water bath.
| Step | Test | Positive result | What you can conclude |
| 1 | Add iodine solution. | blue-black colour | starch is present |
| 2 | Add Benedict's solution, then heat in a water bath. |
