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
UV Fig 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 nm Longer wavelength Lower energyHigher energy Shorter wavelength
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
Fig Reflected light Absorbed light Light Chloroplast Transmitted light Granum
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.
Fig 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
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
Photosystem (1 st part) › Light harvesting complexes pigment molecules bounded by proteins; absorb transfer energy to chlorophyll a of reaction center
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