Investigating Leaf Pigments Using

Chromatography

Photosynthesis depends on more than just chlorophyll. Leaves contain a mixture of pigments that absorb different wavelengths of light. Using chromatography, students can separate these pigments and see the hidden colours that power photosynthesis.

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The Experiment

Students grind up a fresh green leaf with a small amount of ethanol or propanone to extract the pigments. A strip of chromatography paper is dipped into the solution, ensuring the pigment spot stays above the solvent level. As the solvent travels up the paper, it carries the pigments at different speeds, separating them into distinct bands.

Typical pigments seen include:

• Chlorophyll a – blue-green

• Chlorophyll b – yellow-green

• Xanthophylls – yellow

• Carotenes – orange

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The Science

Each pigment has a different solubility in the solvent and a different attraction to the paper. The more soluble pigments travel further, while less soluble ones remain near the baseline. This demonstrates the principle of separation by differential solubility.

Students can measure the Rf value for each pigment using:

$$Rf = \frac{\text{distance moved by pigment}}{\text{distance moved by solvent front}}$$

These values help identify unknown pigments and link to photosynthetic efficiency under different light conditions.

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Skills Highlight

• Applying chromatography to biological molecules

• Measuring and comparing Rf values

• Understanding pigment roles in light absorption

• Linking results to plant adaptation and light capture

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Why It Works in Teaching

Chromatography makes an invisible process visible. Students not only see that leaves contain more than one pigment but also learn how separation techniques reveal the complexity of photosynthesis. It is a simple, colourful experiment that connects molecular biology with plant physiology.