Chloroplast pigments (CIE A-level bio)

This lesson describes the role of the chlorophylls, carotene and xanthophyll and explains how to interpret absorption and action spectra. The PowerPoint and accompanying resources have been designed to cover points 4 and 5 in topic 13.1 of the CIE A-level biology specification.

The students are presented with a picture of a leaf with chlorosis at the start of the lesson and are challenged to explain the appearance by drawing on any knowledge from GCSE. The lesson has been intricately planned to build on the previous lesson on the structure of the chloroplast, and the students are reminded that chlorophyll is located in the thylakoids. The students will learn that there are two forms of chlorophyll a as well as a chlorophyll b, and a quick quiz round is used to reveal the values of 680 and 700. The absorption spectrum for chlorophyll a and b are displayed and when they are presented with a spectra, the students will discover that there are more chloroplast pigments. The carotenoids are introduced and the students have to interpret the spectra to reveal more details about these pigments. The meaning of an action spectrum is provided and the students are challenged to draw a sketch graph to show how the rate of photosynthesis differs for different wavelengths.