Unit 2: Metabolic Processes History SBI4U – Ms. Richardson

History 1600’s: J.B. Van Helmont Compared soil mass to that of a growing willow tree Demonstrated that soil nutrients were not responsible for growth of plants Concluded water absorption was responsible

History 1771, Joseph Priestly Discovered gases play a role in photosynthesis “injured air” hypothesis: Placed lit candle in bell jar candle goes out (injured air) Placed live mint plant + lit candle in bell jar after 10 days, plant “restores” air and candle burns again

History 1796, Jan Ingenhousz Confirmed Priestley’s findings Demonstrated that light was essential to photosynthesis Defined “injured air” as CO2 Proposed O2 is produced from splitting of CO2

History 1882, T.W Engelmann Used Spirogyra alga to determine which colours of visible light were most effective in photosynthesis Demonstrated that chloroplasts respond to red and blue light

History 1905, F.F Blackman Measured effect of change in light intensity and temperature on CO2 concentrations Demonstrated: At low light intensity: Rate of photosynthesis can be increased by increasing light intensity but not temperature At high light intensity: Rate of photosynthesis can be increased by increasing temperature but not light intensity Concluded there are 2 stages of photosynthesis: Light dependent (photochemical) Light independent (biochemical)

History 1930’s, C.B. Van Niel 1938, S.M Ruben, M. Kamen Used purple sulfur bacteria to demonstrate O2 is produced by splitting water, not CO2 Proposed the following: CO2 + 2H2S + light  carbohydrate + H2O + 2S 1938, S.M Ruben, M. Kamen Used radioactivity to confirm Van Niel’s findings