IP Biology Notes: Biological Molecules (Upper Sec 03)

For Integrated Programme students: Your current school materials, teacher instructions, and assessment scope take precedence because IP topic sequence and depth vary by school. This is an Eclat IP guide, not the O-Level / SEC G3 exam-track guide.

How this chapter applies

• Eclat core: carbohydrates, fats, proteins, food tests, synthesis from smaller units, enzyme specificity, activation energy, temperature, and pH form the main route.
• School-sensitive extension: DCPIP and vitamin C work, molecular structures, induced-fit comparisons, and quantitative enzyme modelling should be used only where the current school teaches them.
• 2027 national comparison: K325 Topic B3 covers elements, biological roles, four food tests, synthesis of large molecules, lock-and-key enzyme action, activation energy, temperature, and pH.
• Check your school: reagent concentrations, heating methods, observation wording, and the molecular depth expected in enzyme explanations can differ.
• Exam-track route: use the separate O-Level and SEC G3 Biology notes for K325 topic ownership.

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.