Lesson Plan

• Describe the chemical principles behind Benedict’s, iodine, emulsion, and Biuret tests.
• Perform each qualitative test safely and accurately, recording observations.
• Interpret colour changes to identify reducing sugars, starch, lipids, and proteins.
• Compare the sensitivity and limitations of the four tests.
• Apply the tests to design a simple experiment for unknown plant extracts.

• Benedict’s reagent, test tubes, boiling water bath, gloves.
• Iodine solution (I₂/KI), white tile or test tubes, gloves.
• Ethanol, distilled water, test tubes, shaker or vortex, gloves.
• Biuret reagent (CuSO₄ in NaOH), test tubes, gloves, eye protection.
• Micropipettes or droppers, waste disposal container, lab notebook.
• Projector and slides for demonstration.

Begin with a quick question: “How can we tell which macromolecules are present in a fruit extract?” Students recall previous work on carbohydrate and protein tests. They will know they must correctly carry out four standard qualitative assays and explain the observed colour changes.

1. Do‑now (5'): List the four major biomolecule classes and the classic test associated with each.
2. Mini‑lecture (10'): Explain the chemical basis of each test using slides and short animations.
3. Teacher demonstration (20'): Perform Benedict’s, iodine, emulsion, and Biuret tests while students record observations.
4. Guided practice (15'): In small groups, students repeat the tests with provided unknown samples.
5. Check for understanding (5'): Rapid Kahoot quiz on colour‑change interpretation.
6. Summary discussion (5'): Consolidate results, link observations to underlying reactions.

Review the key colour changes and what they reveal about each macromolecule. Students complete an exit ticket stating one practical tip for each test. For homework, they prepare a brief report predicting the results of the four tests on a chosen food item.