Photosynthesis Conversion of light energy into chemical energy by green plants, algae, and cyanobacteria I.Some history II.The light reactions (chapter 7) III. The carbon reactions (chapter 8) IV.Ecophysiology of photosynthesis (chapter 9)

Thought that water was the source of plant mass. WRONG! Von Helmont,

Joseph Priestly ( ) found that air contains something vital to mice and candles

Priestly: green plants can replenish air for candles and mice.

Jan Ingenhousz ( ) Experiments upon Vegetables only the green parts of plants can revitalize stale air and they do so only in the presence of sunlight gas produced in the dark does not revitalize air sun’s light, not heat, is necessary for photosynthesis Ingenhousz proved that the solid matter of plants came from the air, not the soil. Julius von Sachs ( ) suggested that starch is a product of carbon dioxide. also argued in 1865 that, in the presence of light, chlorophyll catalyzes photosynthetic reactions discovered the chlorophyll-containing chloroplasts

Traditional summary equation for photosynthesis 6CO 2 + 6H 2 O ---> C 6 H 12 O 6 + 6O 2 The two sets of photosynthetic reactions. 1) Light reactions light H 2 O ---> O 2 + ATP + NADPH 2 2) “Dark” or Carbon reactions CO 2 + ATP + NADPH ---> carbohydrates

II. The light reactions of photosynthesis Objectives are to understand: 1)Variation in energy of different forms of light 2)Light absorption by photosynthetic pigments 3)Energy transduction - conversion of light energy to chemical energy as ATP and NADPH

The wave properties of light Fig. 7.1 Frequency,  is the number of peaks passing per second. Units are s -1. Wavelength has units of distance, m, nm, µm

Wavelength  (nm) and frequency  (s  ) are inversely related, and their product equal to the speed of light, C. C =  and  C = 3 x 10 8 m s -1 Visible light & light used in photosynthesis span the 400 to 700 nm (10 -9 m) wavelength range. PAR is Photosynthetically Active Radiation Fig 7.2 The electromagnetic radiation (EMR) spectrum PAR

Photosynthesis derives energy from the particle nature of light. EMR consists of particles called photons. The energy of a photon, “quantum”, increases with frequency,. E = h  h = x J s Energy = Planck’s constant x frequency

E = h  Joule/photon) h = x J s  is frequency, s -1  C  E/ photon  E/mol  nm   m Blue x x x 10 5 Red x x x 10 5 Compare the energy of a red and blue photon