| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Biology |
| Lesson Topic: describe and use chromatography to separate and identify chloroplast pigments (reference should be made to Rf values in identification of chloroplast pigments) |
Learning Objective/s:
- Describe the principle of paper chromatography and how it separates chloroplast pigments.
- Calculate and interpret Rf values to identify individual pigments.
- Explain the role of each pigment in the photosynthetic energy‑transfer process.
- Analyse experimental results, recognise sources of error and suggest improvements.
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Materials Needed:
- Whatman No. 1 chromatography paper (or equivalent)
- Solvent mixture (petroleum ether : acetone 90:10 v/v)
- Fresh spinach leaves for pigment extraction
- Mortar and pestle, 80 % acetone
- Capillary tubes or micropipettes
- Pencil, ruler, and sealed chromatography chamber
- Gloves, goggles, and access to a fume cupboard
- Worksheet for recording measurements and reflections
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Introduction:
Begin with a striking image of a leaf after chromatography, asking students what the coloured bands represent. Recall that pigments absorb specific wavelengths and that previous lessons covered the light reactions of photosynthesis. Explain that today they will separate these pigments using paper chromatography and use Rf values to identify each one, with success measured by accurate calculations and clear explanations.
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Lesson Structure:
- Do‑now (5'): Students label a diagram of a chloroplast pigment spectrum and predict absorption colours (quick check).
- Mini‑lecture (10'): Review chromatography principle, solvent front, and Rf calculation with board examples.
- Practical set‑up (15'): Prepare pigment extracts, spot chromatography strips, and place them in the solvent chamber while the teacher circulates.
- Development & observation (10'): Allow solvent to rise, then remove strips, mark solvent front, and let dry safely.
- Data collection (10'): Measure distances, calculate Rf values, record results on worksheets, and compare with reference tables.
- Analysis discussion (10'): In pairs, interpret pigment identities, discuss their photosynthetic roles, and identify any experimental errors.
- Extension/Reflection (5'): Exit ticket – one improvement for future runs and how pigment composition relates to plant adaptation.
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Conclusion:
Summarise how the separation pattern and calculated Rf values allowed identification of chlorophylls and carotenoids and their function in energy transfer. Ask students to complete an exit ticket stating one pigment’s role and one source of error they observed. Assign homework to read a short article on how pigment composition varies with light intensity and prepare a brief summary.
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