Today: -Photosynthesis! -Lunch -Lab 3

Setting the Stage…

An Overview of Photosynthesis

LIGHT used in Photosynthesis ?

LIGHT used in Photosynthesis

Check Out the Structure of Chlorophyll:

When PHOTONS hit a Chlorophyll Molecule they EXCITE ELECTRONS

ELECTRON TRANSPORT CHAINS The Gain and Loss of Electrons through REDOX reactions allows for ELECTRON TRANSPORT CHAINS

Noncyclic electron flow generates ATP and NADPH

of NONCYCLIC ELECTRON FLOW Cartoon Schematic of NONCYCLIC ELECTRON FLOW in the LIGHT REACTIONS

ELECTRON FLOW may also by CYCLIC Cyclic Electron Flow allows cells to “catch up” on the production of ATP!

CHEMIOSMOTIC synthesis of ATP

What Should We Do With the ATP and Electrons (NADPH)??

The Light-Independent Reactions The Calvin Cycle The Light-Independent Reactions

Uh Oh… RUBISCO

THE DOWNSIDE: Plants must open their STOMATA to acquire CO2 and release O2. Open Stomata allow for Transpiration (the evaporative loss of water)!

How could plants minimize this evaporative loss of water (transpiration)??

Why is this enzyme so sloppy?? The Pitfall… Why is this enzyme so sloppy??

Photorespiration generates no ATP, NADPH, or glucose! Photorespiration is a major limiting factor in the production levels of C3 PLANTS Photorespiration generates no ATP, NADPH, or glucose! Rice Up to 50% of the yield of many important agricultural crops like rice, soybeans, and wheat may be lost to photorespiration. Soybeans

Alternate Strategy #1: the C4 PATHWAY Carbon fixation and the Calvin Cycle are separated. Fixation occurs in the MESOPHYLL CELLS while the Calvin Cycle occurs in the BUNDLE-SHEATH CELLS. corn This separation allows the plants to minimize photorespiration and maximize sugar production. sugarcane

Results in a SPATIAL SEPARATION of CO2 acquisition and fixation! An Overview of the C4 Pathway: Results in a SPATIAL SEPARATION of CO2 acquisition and fixation!

Alternate Strategy #2: CAM CAM plants open their STOMATA at night to acquire CO2. This CO2 is used during the day for fixation in the Calvin Cycle. (Temporal separation!)

C4 and CAM Strategies Summarized:

Final Key Point: Metabolic Processes are Connected! During periods of light, which cycle must be faster, the Calvin Cycle or the Citric Acid Cycle? Why??