Featured in PASCO’s Advanced Biology through Inquiry Teacher Guide
This manual features 22 challenging, standards-based, inquiry lab activities for AP, IB, and honors programs.
Students analyze spinach pigments and chloroplasts using paper chromatography, a colorimeter, and a spectrometer to understand how plants capture light for photosynthesis.
Students extract pigments from spinach leaves for analysis using chromatography and colorimetry. Paper chromatography separates the pigments present in the extract so they can be identified. Analysis of the extract with a colorimeter allows students to determine the relative absorbance of four different colors of light (blue, green, orange, and red). They relate the chromatography results to the colorimeter measurements to refine their understanding of how plants capture light for photosynthesis. If available, a spectrometer allows students to view the full absorbance spectrum for spinach leaves.
The colorimeter is used again in Part 2 to measure photosynthesis using DPIP (2,6-dichloropheno-lindophenol), an electron acceptor that experiences a color change if photosynthesis is occurring. For student-designed experiments, students can analyze factors such as the effect of different light sources, distance from a light source, and comparison of pigments in the leaves of different plants using chromatography, DPIP analysis, or both.
A large number of chromatograms need to be created to have sufficient quantities of isolated pigments for analysis. (This is one of the suggested inquiry options.) One option is to have all students contribute their chromatograms to this purpose after they record their observations in the Initial Investigation. Students should cut carefully along the border lines between pigments to cut strips of chromatography paper that have only one pigment per strip. Discard the sections of paper that do not contain pigments. Place all of the chlorophyll a strips into a beaker with ethanol or chromatography solvent. Place all of the chlorophyll b strips into a different beaker, and do the same for the carotenoids and xanothophylls. Over time, the pigments will dissolve out of the paper and into the solvent. Cutting the strips into smaller pieces, or crumpling the strips, can accelerate the process.
This experiment may require software and an interface for data collection.