Light and Pigments

Properties of Light Electromagnetic energy/radiation Travels in waves Photon Light travels as a wave, behaves as particle Fixed nrg quantity Wavelength (λ) Distance between waves Determines NRG NRG inversely related to wavelength Shorter wavelength (λ) = ______ energy. Higher

Light and Matter 3 types of interactions Reflected Light bounces off matter Transmitted Passes through matter Absorbed Light disappears from spectrum . . . sorta Substances absorb light = pigments

Spectrophotometer discussion only Detects absorption spectrum of pigments Uses light of different λ through a sample Measures light transmitted Generates light absorption vs. λ

Photosynthesis Pigments Chlorophylls Chlorophyll a Absorbs violet blue and red Transmits green Chlorophyll b Absorbs Blue light Accessory Pigments Carotenoids Photoprotection Transmits yellow and orange

Action Spectrum Not all colors are best for photosynthesis Red and Blue light- absorbed and used in photosynthesis Identified by measuring O2 release under different λ of light Question: Why is this graph different then that of chlorophyll a or b absorbance?

Excited Chlorophyll! Yipee! When a molecule absorbs a photon 1 of its e- will jump from its ground state (low NRG) to an excited state (high NRG). Excited state Energy of election Heat Photon (fluorescence) Chlorophyll molecule Ground e– Figure 10.11 A

Excitation of Chlorophyll by Light When pigment absorbs light Goes from a ground state  excited state = unstable Molecule can absorb photons only if there NRG matches the NRG difference between the ground state and excited stare of e- A particular compound absorbs only photons corresponding to specific λ. Excited state Energy of election Heat Photon (fluorescence) Chlorophyll molecule Ground e– Figure 10.11 A

Fluorescence If an isolated solution of chlorophyll is illuminated It will fluoresce, giving off light and heat Figure 10.11 B