PHOTOSYNTHESIS © 2016 Paul Billiet ODWS

The development of ideas Hales 1727 Plants took their nourishment in part from the atmosphere Light energy participated in this process. Priestly 1771 Green plants “renewed” air that was made “bad” by breathing animals or burning candles “Renewed” air = Oxygen “Bad” air = Carbon Dioxide © 2016 Paul Billiet ODWS

Joseph Priestley’s Experiment He put a bunch of mint under the jar He allowed a few days to pass The candle could be relit and remain lit for a while Lens © 2016 Paul Billiet ODWS

The composition of the atmosphere O2 Scheele 1773 and Priestly 1774 CO2 Black 1777 N2 Rutherford 1772 The composition of air Lavoisier 1774 © 2016 Paul Billiet ODWS

Ingenhousz 1779 Light is necessary for the production of O2 by plants Senebier 1782 Plants breathe like animals in the dark De Saussure 1804 Quantitative measurements of photosynthesis. Mass gain by plants through growth > Mass of CO2 absorbed – Mass of O2 released The difference was attributed to water © 2016 Paul Billiet ODWS

Observed the growth of starch grains in illuminated chloroplasts Sachs 1864 Observed the growth of starch grains in illuminated chloroplasts Classic experiment: Leaf exposed to light with certain parts covered In the exposed parts starch is produced In the covered parts starch is absent. http://science.marshall.edu/murraye/alpha_amylase.htm The First Book of Farming CHARLES L. GOODRICH 1905 © 2016 Paul Billiet ODWS

By the end of C19th Sunlight CO2 + H2O Carbohydrate (CH2O) + O2  © 2016 Paul Billiet ODWS

Light, Chlorophyll and Photosynthesis Engelmann 1894 Experiment 1 Using Cladophora, a filamentous alga, and motile oxygen sensitive bacteria Cladophora © 2016 Paul Billiet ODWS

Chloroplasts which practically fill each cell Visible spectrum Red Orange Yellow Green Blue Indigo Violet Cladophora cells Chloroplasts which practically fill each cell Visible spectrum Motile bacteria © 2016 Paul Billiet ODWS

Observation Motile bacteria sensitive to oxygen accumulate in the areas illuminated by red and blue light Conclusion Photosynthesis, which produces oxygen, takes place in the parts illuminated by red and blue light This is the action spectrum of photosynthesis. © 2016 Paul Billiet ODWS

Experiment 2 Using Spirogyra, a filamentous alga + motile oxygen sensitive bacteria Spirogyra © P Billiet © 2016 Paul Billiet ODWS

WHITE LIGHT Oxygen sensitive bacteria Chloroplast © 2016 Paul Billiet ODWS

The bacteria accumulate in the regions nearest the chloroplasts Observation The bacteria accumulate in the regions nearest the chloroplasts Conclusion O2 is produced by the chloroplast This is the site of photosynthesis. © 2016 Paul Billiet ODWS

Light Intensity v Temperature Blackman 1920s Experiment 1 T°C Rate of photosynthesis Light intensity T + 10°C © 2016 Paul Billiet ODWS

Rate of photosynthesis Observations At low light intensities – when light is a limiting factor – temperature has no effect upon photosynthesis. Therefore Q10 = 1 At high light intensities – when light is not limiting – temperature has an effect upon photosynthesis. The rate doubles for every 10°C rise in temperature Therefore Q10 = 2 T°C Rate of photosynthesis Light intensity T + 10°C © 2016 Paul Billiet ODWS

Conclusion Photosynthesis consists of two reactions I The Light Dependent Reaction Photochemical and unaffected by the temperature (Q10 = 1) II The Light Independent Reaction Enzyme controlled as it has a Q10  2 © 2016 Paul Billiet ODWS

Experiment 2: Light Intensity and CO2 Concentration Rate of photosynthesis Light intensity 0.13% CO2 0.03% CO2 © 2016 Paul Billiet ODWS

Carbon fixation is light independent Observation CO2 limits the rate of photosynthesis at high light intensities i.e. when light is not a limiting factor Conclusion Carbon fixation takes place in the Light Independent Reaction It is an enzyme controlled process © 2016 Paul Billiet ODWS