2.  Electromagnetic energy › Solar energy or radiation which travels in space a rhythmic waves and can be measured in photons  Wavelength › The distance between crests of adjacent waves such as those of the electromagnetic spectrum  Visible Light › The radiation our eyes see as different colors

3. UV Fig. 10-6 Visible light Infrared Micro- waves Radio waves X-rays Gamma rays 10 3 m 1 m (10 9 nm) 10 6 nm 10 3 nm 1 nm 10 –3 nm 10 –5 nm 380 450 500 550 600 650 700 750 nm Longer wavelength Lower energyHigher energy Shorter wavelength

4.  Pigments › Substances that absorb some wavelengths of light and reflect others › Different pigments absorb/reflect different wavelengths  Photon › A fixed quantity of light energy › The shorter the wavelength of light the greater the energy of a photon

5. Fig. 10-7 Reflected light Absorbed light Light Chloroplast Transmitted light Granum

6.  Which wavelengths are absorbed most? › Primarily blue and red  Why do plants appear green? › They reflect green light  What is the role of accessory pigments? › They allow the plant to absorb energy from more the visible light spectrum – making the plant more efficient.

7. Fig. 10-9 Wavelength of light (nm) (b) Action spectrum (a) Absorption spectra (c) Engelmann’s experiment Aerobic bacteria RESULTS Rate of photosynthesis (measured by O 2 release) Absorption of light by chloroplast pigments Filament of alga Chloro- phyll a Chlorophyll b Carotenoids 500 400 600700 600 500 400

8.  When a pigment absorbs light, it goes from a ground state to an excited state, which is unstable  When excited electrons fall back to the ground state, photons are given off, an afterglow called fluorescence  If illuminated, an isolated solution of chlorophyll will fluoresce, giving off light and heat

9.  Photosystem (1 st part) › Light harvesting complexes  pigment molecules bounded by proteins; absorb  transfer energy to chlorophyll a of reaction center

10.  Photosystem (2 nd part) › Reaction Center  Chlorophyll a and a primary electron acceptor  Chlorophyll a uses energy from light harvesting complexes to pass a pair of electrons to the primary electron acceptor