This lesson describes the meaning of the absorption and action spectrum and explains how to interpret these graphs. The PowerPoint and accompanying resources have been designed to cover point 5.6 of the Edexcel International A-level biology specification and includes descriptions of the roles of the photosynthetic pigments to link to content covered in the earlier lessons in topic 5.
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 topics 4 and 5. The lesson has been intricately planned to build on the previous lessons on the structure of the chloroplast and the reactions of photosynthesis, and the students are reminded that chlorophyll is located 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.
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