1. PHOTOSYNTHESIS
© 2016 Paul Billiet ODWS

2. 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

3. 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
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4. The composition of the atmosphere
O2 Scheele 1773 and Priestly 1774 CO2 Black 1777 N2 Rutherford 1772 The composition of air Lavoisier 1774
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5. 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

6. 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.
The First Book of Farming CHARLES L. GOODRICH 1905
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7. By the end of C19th Sunlight CO2 + H2O Carbohydrate (CH2O) + O2 
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8. Light, Chlorophyll and Photosynthesis
Engelmann 1894
Experiment 1 Using Cladophora, a filamentous alga, and motile oxygen sensitive bacteria
Cladophora
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9. 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
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10. 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

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

12. WHITE LIGHT Oxygen sensitive bacteria Chloroplast
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13. 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

14. Light Intensity v Temperature
Blackman 1920s Experiment 1
T°C
Rate of photosynthesis
Light intensity
T + 10°C
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15. 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

16. 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
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17. Experiment 2: Light Intensity and CO2 Concentration
Rate of photosynthesis
Light intensity
0.13% CO2
0.03% CO2
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18. 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