1. Light which strikes a leaf may be :- Reflected Transmitted – pass straight through Absorbed White light is a mixture of wavelengths which show up as different colours when light is passed through a prism Reflected Transmitted Absorbed Light striking a leaf

2. When white light is passed through leaf pigments certain colours are absorbed and disappear from the light spectrum. This gives rise to the absorption spectrum -see Handout 1 750 350 400 450 500 550 600650 700 Beam of white light. eg. daylight Components of light emerge to form a pattern of colours called a spectrum Wavelength of light (nm )

3. Solvent Front Spot Line Concentrated Chlorophyll Spot Carotene ( Orange ) Xanthophyll ( Yellow ) Chlorophyll a ( Blue-green ) Chlorophyll b ( Dark green ) Leaves contain a mixture of pigments :-

4. A detailed absorption spectrum can be produced for each pigment

5. Chlorophyll a and b absorb in the blue and red end Carotenoids such as xanthophyll and carotene absorb light in other regions e.g. green Accessory pigments such as the carotenoids absorb some light from other regions of the spectrum and pass the energy on to the chlorophyll. A range of pigments are desirable as this increases the total quantity of light absorbed by a plant. Another type of spectrum can be done, where the rate of photosynthesis is measured at different wavelengths. This is called an Action Spectrum 400 440 480 520 560 600640 680720 Wavelength of illumination (nm ) Amount of Photosynthesis (arbitrary units)

6. Comparison of Absorption and Action Spectrum OHP/Handout  The absorption spectrum shows that light is absorbed in blue and red ends of the spectrum by chlorophyll  The action spectrum shows that light absorbed by chlorophyll is used for photosynthesis  The absorption spectrum shows that light is absorbed in green areas of spectrum by carotenoids ( X )  The action spectrum shows that the light absorbed by carotenoids in not used directly for photosynthesis Wavelength of light (nm ) 400 440 480 520 560 600640 680720 Relative absorption of light (arbitrary units) Relative rate of Photosynthesis (arbitrary units) X

7. Leaf pigments are found in the grana of chloroplasts Double Membrane Lamella – part of inner membrane Starch Grain Granum – contains chlorophyll Stroma

8. Features of a chloroplast Smooth outer membrane Highly folded inner membrane which forms layers Layers contain areas where the membranes are far apart and full of chlorophyll, these are called grana. The fluid filled interior is called stroma.