PHOTOSYNTHESIS

1. PHOTOSYNTHESIS

2. 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 ODWS

3. The composition of the atmosphere O2 Scheele 1773 and Preistly 1774 CO2 Black 1777 N2 Rutherford 1772 The composition of air Lavoisier 1774 © 2010 Paul Billiet ODWS

4. 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 © 2010 Paul Billiet ODWS

5. 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 producedIn the covered parts starch is absent © 2010 Paul Billiet ODWS

6. By the end of C19th Sunlight CO2 + H2O (CH2O) + O2 Carbohydrate © 2010 Paul Billiet ODWS

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

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

9. 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 ODWS

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

11. WHITE • LIGHT Oxygen sensitive bacteria Chloroplast © 2010 Paul Billiet ODWS

12. Observation The bacteria accumulate in the regions nearest the chloroplasts Conclusion O2 is produced by the chloroplast This is the site of photosynthesis © 2010 Paul Billiet ODWS

13. Rate of photosynthesis T + 10°C T°C Light intensity Light Intensity v Temperature Blackman 1920sExperiment 1 © 2010 Paul Billiet ODWS

14. 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 Rate of photosynthesis T + 10°C T°C Light intensity © 2010 Paul Billiet ODWS

15. 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 © 2010 Paul Billiet ODWS

16. Rate of photosynthesis Light intensity Experiment 2:Light Intensity and CO2 Concentration 0.13% CO2 0.03% CO2 © 2010 Paul Billiet ODWS

17. 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 © 2010 Paul Billiet ODWS