PAG6: Chromatography or Electrophoresis

Use the centre’s approved leaf-extraction and chromatography procedure, with the specified solvent and handling arrangements. Compare suitable leaves and apply comparable extracts to a marked origin, allowing appropriately concentrated small applications rather than a large spreading patch.

The origin must begin above the solvent level so the applied extract is not simply washed into the reservoir. Use a suitable pencil mark rather than soluble ink. Keep the same stationary material, solvent system and development conditions across samples; these affect separation and the resulting pattern.

As solvent moves, pigment molecules partition differently between the stationary phase and moving phase. Differences in solubility and attraction lead components to travel different distances. A separated colour band is evidence of a component under those conditions, not automatically proof of its identity.

Mark the solvent front promptly and measure from the origin to the centre of the pigment band and from the origin to the solvent front. Rf is the first distance divided by the second, so it has no unit. A valid band cannot have travelled farther than the recorded solvent front in the same run.

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Compare band position and colour with suitable known references under matching conditions. Similar Rf values alone do not prove that two compounds are identical. Diffuse or overlapping bands make centres and component counts uncertain, while different extract concentrations can alter band intensity.

Differences between shade-tolerant and other leaves may suggest different pigment complements or relative amounts, but chromatography alone does not directly measure photosynthetic rate. Control leaf source, extraction efficiency and loading before attributing a darker band only to greater biological pigment abundance. Use independent samples and record limitations.

DNA’s phosphate backbone gives it a negative charge, so fragments move toward the positive electrode in an appropriately set up gel. Under comparable agarose conditions, smaller fragments generally migrate farther than larger ones. A reference ladder contains known fragment sizes; compare it on the same gel rather than assigning a size from distance alone.

Use the laboratory’s approved loading, electrical and staining arrangements. A tracking dye is not necessarily a DNA band. Gel composition, voltage, run time and detection affect the pattern, and equal band positions do not uniquely prove identity. A suitable multi-locus comparison and other evidence are needed for a strong identification claim.

Pigment chromatography depends on relative interactions with stationary and mobile phases. DNA electrophoresis uses charge-driven movement through a matrix. Both separate components, but a chromatography Rf value is not a universal DNA fragment-size conversion. Electrophoretic size estimates often use a local relation between log fragment size and migration distance when that calibration is justified.

This group permits chromatography or electrophoresis. The examples explain both so you can identify the method needed for an unfamiliar question; the centre maps the actual chosen activities to required technique evidence.

Try each question before opening the worked response. Use precise biological terms, connect each cause to its effect, and check units and assumptions when interpreting data.