Topic 5.6: Photosynthetic pigments (Ed B)

This lesson describes the meaning of absorption and action spectra and explains why plants contain several photosynthetic pigments. The PowerPoint and accompanying resources have been designed to cover both specification points in topic 5.6 of the Edexcel A-level biology B specification and includes key information to prepare the students for the photosynthesis lessons in topic 5.7.

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 and name the ion which is deficient in the soil, drawing on their knowledge from topic 1. The lesson has been intricately planned to build on their limited knowledge of photosynthesis from GCSE, and to introduce key details such as the location of chlorophyll in the photosystems 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 the students are presented with a spectra, they 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, before the correlation between the two spectra is considered.