PHOTOSYNTHESIS

The development of ideas Hales 1727 Plants took their nourishment in part from the atmosphere Light energy participated in this process. Preistly 1771 Green plants “renewed” air was made “bad” by breathing animals or burning candles “Renewed” air = Oxygen “Bad” air = Carbon Dioxide © 2010 Paul Billiet ODWSODWS

The composition of the atmosphere O 2 Scheele 1773 and Preistly 1774 CO 2 Black 1777 N 2 Rutherford 1772 The composition of air Lavoisier 1774 © 2010 Paul Billiet ODWSODWS

Ingenhousz 1779 Light is necessary for the production of O 2 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 CO 2 absorbed – Mass of O 2 released The difference was attributed to water © 2010 Paul Billiet ODWSODWS

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 © 2010 Paul Billiet ODWSODWS

By the end of C19 th Sunlight CO 2 + H 2 O (CH 2 O) + O 2  Carbohydrate © 2010 Paul Billiet ODWSODWS

Light, Chlorophyll and Photosynthesis Engelmann 1894 Experiment 1 Using Cladophora, a filamentous alga, and motile oxygen sensitive bacteria Image Credit: CladophoraCladophora © 2010 Paul Billiet ODWSODWS

Visible spectrum Cladophora cells Motile bacteria Chloroplasts which practically fill each cell Red Orange Yellow Green Blue Indigo Violet © 2010 Paul Billiet ODWSODWS

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 © 2010 Paul Billiet ODWSODWS

Experiment 2 Using Spirogyra, a filamentous alga + motile oxygen sensitive bacteria © 2010 Paul Billiet ODWSODWS

WHITE LIGHTWHITE LIGHT Oxygen sensitive bacteria Chloroplast © 2010 Paul Billiet ODWSODWS

Observation The bacteria accumulate in the regions nearest the chloroplasts Conclusion O 2 is produced by the chloroplast This is the site of photosynthesis © 2010 Paul Billiet ODWSODWS

Light Intensity v Temperature Blackman 1920s Experiment 1 T°C Rate of photosynthesis Light intensity T + 10°C © 2010 Paul Billiet ODWSODWS

Observations At low light intensities – when light is a limiting factor – temperature has no effect upon photosynthesis. Therefore Q 10 = 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 Q 10 = 2 T°C Rate of photosynthesis Light intensity T + 10°C © 2010 Paul Billiet ODWSODWS

Conclusion Photosynthesis consists of two reactions I The Light Dependent Reaction Photochemical and unaffected by the temperature (Q 10 = 1) II The Light Independent Reaction Enzyme controlled as it has a Q 10  2 © 2010 Paul Billiet ODWSODWS

Experiment 2: Light Intensity and CO 2 Concentration 0.03% CO 2 Rate of photosynthesis Light intensity 0.13% CO 2 © 2010 Paul Billiet ODWSODWS

Carbon fixation is light independent Observation CO 2 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 © 2010 Paul Billiet ODWSODWS