A-level set practicals – TLC of plant photosynthetic pigments

This new resource supports the use of practicals across various new 2015 A-level biology specifications (OCR, AQA, Edexcel and Eduqas).

Students conduct Thin Layer Chromatography (TLC) individually or in pairs to separate and identify the photosynthetic pigments from plant material within half an hour. This simple method has been designed to produce good separation of photosynthetic pigments using solvents that are suitable for use in a school biology laboratory. By using grass from a school lawn or playing field, students can see the variety of different molecules that can be separated from a plant they know.

These resources and this practical allow students to develop their understanding of photosynthetic pigments and how chromatography separates molecules. By taking simple distance measurements from the chromatogram for calculating Rf values, this practical provides a good opportunity to introduce the concept of percentage error. It provides students with the opportunity to develop (and demonstrate) their skills of taking quantitative measurements. It also encourages their ability to consider variables that need to be controlled.

Through the suggested questioning in the teacher support materials (or the student worksheet) students can be encouraged to explore the molecular properties of the pigments and how this relates to their separation by chromatography. Students could also explore the occurrence of pigments in different plant (or animal) material either by designing their own experiments or through research online.

Materials include:

• Tested materials to support the A-level practical endorsement (CPAC)
• Support materials for teachers and technicians
• Student worksheet to help provide evidence for meeting the practical skills requirements
• Student revision materials to help prepare for exams

Support materials for other key practicals in A-level specifications can be found on the A-level set practicals main page.