Typical setup: Unknown solutions X, Y, Z tested for reducing sugars, starch, protein, and fat.
| Test | Reagent | Positive Observation (Expected Answer) | |------|---------|----------------------------------------| | Reducing sugar | Benedict’s solution | Blue → Brick-red/orange precipitate upon heating | | Starch | Iodine solution | Brown/yellow → Blue-black | | Protein (biuret) | Biuret test (NaOH + CuSO₄) | Blue → Lilac/violet | | Fat (lipid) | Ethanol emulsion | Clear → Milky white emulsion | o level biology practical 2020 answers
Marking point: “Precipitate” is accepted, but “color change to brick-red” scores higher. For starch, “blue-black” is required (not just “blue”). Typical setup: Unknown solutions X, Y, Z tested
A classic planning question appeared: "Plan an experiment to investigate the effect of light intensity on the rate of photosynthesis of Canadian pondweed (Elodea)." A classic planning question appeared: "Plan an experiment
Answer: 0.4 M sucrose (isotonic point – water potential equal inside and outside cells).