1. Photosynthesis

2. Well most of it anyway……
Photosynthesis
Where does the energy come from that sustains all life?
The Sun!!
Well most of it anyway……

3. Respiration vs. Photosynthesis
Photosynthesis and respiration as complementary processes in the living world.
Photosynthesis uses the energy of sunlight to produce sugars and other organic
molecules. These molecules in turn serve as food. Respiration is a process that uses
O2 and forms CO2 from the same carbon atoms that had been taken up as CO2 and
converted into sugars by photosynthesis. In respiration, organisms obtain the energy
that they need to survive. Photosynthesis preceded respiration on the earth for probably
billions of years before enough O2 was released to create an atmosphere rich in oxygen.
(The earth's atmosphere presently contains 20% O2.)

4. Cellular Respiration -vs- Photosynthesis

5. Overview of Photosynthesis
6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O DG = kcal/mol
Photosynthesis, like cellular respiration, is a series of redox reactions!
What is being oxidized and what is being reduced in the summarizing equation above?

6. Historical perspective
Early thinking: O2 released came from the CO2
CO2  C + O2
sugar
C + H2O  CH2O
Water was added to the carbon to make sugar
van Neil’s experiments with the sulfur bacteria showed that the bacteria used CO2 but did NOT release O2 ...he suggested that plants split water as a source of e- and H+
Scientists used radioactive isotopes to test this idea

7. 18Oxygen (Heavy Oxygen) Isotope Experiment…
CO2
CO2
C18O2
C18O2
CO2
C18O2
CO2
CO2
C18O2
CO2
C18O2
CO2
C18O2
C18O2
H218O
H2O

8. 18O Isotope Experiment C18O2 H218O
Hypothesis: If CO2 is being oxidized
C18O2
H218O
6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O
6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O
18O
18O
Can you predict where the heavy oxygen will end up in each case?

9. 18O Isotope Experiment C18O2 H218O
Hypothesis: If H2O is being oxidized
C18O2
H218O
6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O
6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O
18O
18O
Can you predict where the heavy oxygen will end up in each case?

10. The Actual Results!! C18O2 H218O
6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O
6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O
18O
18O
So..it’s the water that’s being oxidized!

11. Tracking Atoms in Photosynthesis…
Reactants
6 CO2
12 H2O
Products
C6H12O6 6H2O 6O2

12. What does this suggest about photosynthesis?
The sugars that result from photosynthesis are produced by adding the hydrogen ions and electrons from water to carbon dioxide, NOT by splitting CO2 and adding water!
oxidized
H+ and e-
6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O
reduced

13. Plant Photosynthesis internal leaf structure chloroplasts
Figure: 06-01
Title:
An overview of photosynthetic structures.
Caption:
outer membrane
inner membrane
thylakoid

14. The stages of photosynthesis…
Light Dependent Reactions
Occurs along the thylakoid membrane
this is where H2O is oxidized.
chemiosmotic production of ATP!
electron carrier (NADPH) is synthesized

15. The stages of photosynthesis…
Light Independent Reactions
Occurs in the stroma of the chloroplast.
Where CO2 is “fixed” into sugars!

16. How plants harness energy from sunlight…
Photosynthetic pigments
Chlorophylls a – the “main” photosynthetic pigment
Accessory pigments..
Chlorophyll b
Carotenoids

17. Photosynthetic pigments are arranged as “photosystems”

18. What wavelengths of light do you think plants use the least in photosynthesis?

19. Photosystems use some wavelengths of light but reflect others…

20. Photosystem
From the Photosystem, e- are passed along an Electron Transport Chain.. The Photosynthetic Electron Transport Chain (PETC)
Photon
Reaction Center
Light Harvesting Pigments

21. Photosystem
Photon
PETC

22. Photosynthetic Electron Transfer Chain (PETC)
series of electron carriers which take electrons from photosystem, and..
ultimately carry electrons to NADP+

23. Photosystems
Experiments in the 1940’s suggested that light photons are absorbed at 2 different points along the same PETC.…
In fact, there are two Photosystems in operation

24. This powerpoint was kindly donated to www.worldofteaching.com
is home to over a thousand powerpoints submitted by teachers. This is a completely free site and requires no registration. Please visit and I hope it will help in your teaching.