Supramolecular Chemistry, UAF, 2005
PhotosynthesisPhotosynthesis
Supramolecular Chemistry, UAF, 2005
PhotosynthesisPhotosynthesis
Where does the energy come from that sustains all life?
The Sun!!Well most of it anyway……
Supramolecular Chemistry, UAF, 2005
Respiration vs. PhotosynthesisRespiration 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.)
Supramolecular Chemistry, UAF, 2005
Cellular Respiration -vs- Cellular Respiration -vs- PhotosynthesisPhotosynthesis
Exergonic and endergonicreactions of metabolism…Exergonic:
C6H12O6 + 6O2 6CO2 + 6H2O G = -686 kcal/mole
Cellular respiration!
Endergonic:
6CO2 + 6H2O C6H12O6 + 6O2 G = +686 kcal/mole
Photosynthesis!
Provides the energy to run cell processes
Allows plants to make energy rich sugars fromenergy poor molecules
Supramolecular Chemistry, UAF, 2005
Overview of PhotosynthesisOverview of Photosynthesis
6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O G = + 686 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?
Supramolecular Chemistry, UAF, 2005
Early thinking: O2 released came from the CO2
CO2 C + O2
C + H2O CH2O
sugar
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+
Historical perspectiveHistorical perspective
Scientists used radioactive isotopes to test this idea
Supramolecular Chemistry, UAF, 2005
Experiment #1
H218O
CO2CO2
CO2
CO2
CO2
CO2
CO2
H2O
C18O2
C18O2
C18O2 C18O2C18O2
C18O2
C18O2
Experiment #2
1818Oxygen (Heavy Oxygen) Isotope Oxygen (Heavy Oxygen) Isotope Experiment…Experiment…
Supramolecular Chemistry, UAF, 2005
1818O Isotope ExperimentO Isotope Experiment
6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O
C18O2
Hypothesis: If CO2 is being oxidized
H218O
18OCan you predict where the heavy oxygen will end up in each case?
6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O
18O
Supramolecular Chemistry, UAF, 2005
6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O
C18O2
Hypothesis: If H2O is being oxidized
H218O
18OCan you predict where the heavy oxygen will end up in each case?
6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O
18O
1818O Isotope ExperimentO Isotope Experiment
Supramolecular Chemistry, UAF, 2005
6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O
C18O2
H218O
18O
6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O
18O
The Actual Results!!The Actual Results!!
So..it’s the water that’s being oxidized!
Supramolecular Chemistry, UAF, 2005
6 CO2 12 H2OReactants
Products C6H12O6 6H2O 6O2
Tracking Atoms in Photosynthesis…Tracking Atoms in Photosynthesis…
Supramolecular Chemistry, UAF, 2005
What does this suggest about What does this suggest about photosynthesis?photosynthesis?
6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O
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
reduced
H+ and e-
Supramolecular Chemistry, UAF, 2005
internal leaf structure
chloroplastsouter membrane
inner membrane
thylakoid
Plant PhotosynthesisPlant Photosynthesis
Supramolecular Chemistry, UAF, 2005
The stages of photosynthesis…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
Supramolecular Chemistry, UAF, 2005
Light Independent Reactions
• Occurs in the stroma of the chloroplast.
• Where CO2 is “fixed” into sugars!
The stages of photosynthesis…The stages of photosynthesis…
Supramolecular Chemistry, UAF, 2005
How plants harness energy from sunlight…How plants harness energy from sunlight…
Photosynthetic pigments
Chlorophylls a – the “main” photosynthetic pigment
Chlorophyll b
Accessory pigments..
Carotenoids
Supramolecular Chemistry, UAF, 2005
Photosynthetic pigments are arranged as Photosynthetic pigments are arranged as “photosystems”“photosystems”
Supramolecular Chemistry, UAF, 2005
What wavelengths of light do you think plants use the least in photosynthesis?
Supramolecular Chemistry, UAF, 2005
Photosystems use some wavelengths of Photosystems use some wavelengths of light but reflect others…light but reflect others…
Supramolecular Chemistry, UAF, 2005
Light Harvesting Pigments
Reaction Center
Photon
PhotosystemPhotosystem
From the Photosystem, e- are passed along an Electron Transport Chain..
The Photosynthetic Electron Transport Chain (PETC)
Supramolecular Chemistry, UAF, 2005
PETCPhoton
PhotosystemPhotosystem
Supramolecular Chemistry, UAF, 2005
Photosynthetic Electron Transfer Chain Photosynthetic Electron Transfer Chain (PETC)(PETC)
• series of electron carriers which take electrons from photosystem, and..
• ultimately carry electrons to NADP+
Supramolecular Chemistry, UAF, 2005
PhotosystemsPhotosystems
• 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
Supramolecular Chemistry, UAF, 2005
This powerpoint was kindly donated to www.worldofteaching.com
http://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.