A2E Today: 1. Introduction to Photosynthesis 2. Lunch 3. Guest Speaker (noon; Green Room)

? PHOTOSYNTHESIS! Brainstorm: 4 Things We Know About Photosynthesis 4 Questions About Photosynthesis Why is Photosynthesis important?? ?

A Quick Introduction to the Carbon Cycle What does it mean to be a carbon source? A carbon sink? Examples?

6CO2 + 6H2O + Light Energy  C6H12O6 + 6O2 PHOTOSYNTHESIS Photosynthesis is an enzyme-mediated, metabolic process performed by photoautotrophs 6CO2 + 6H2O + Light Energy  C6H12O6 + 6O2 or CO2 + H2O  CH2O + O2

Overview of Leaf and Chloroplast Anatomy Note the interplay of Form and Function!

Overview of Photosynthesis

The LIGHT Reactions

LIGHT used in Photosynthesis ?

LIGHT used in Photosynthesis

Engelmann figured out the ACTION SPECTRUM in 1883!!

When PHOTONS hit a Chlorophyll Molecule they EXCITE ELECTRONS

When PHOTONS hit a Chlorophyll Molecule they EXCITE ELECTRONS

EXCITED ELECTRONS are passed from molecule to molecule until they reach the REACTION CENTER

Noncyclic electron flow generates ATP and NADPH

What is NADPH? I carry electrons!

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

CHEMIOSMOTIC synthesis of ATP

Overview of Photosynthesis

The Light-Independent Reactions

RUBISCO

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

O2 H2O CO2

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

The Pitfall…

Why is this enzyme so sloppy?? RUBISCO 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

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:

What Can You Do If You Understand Photosynthesis?? Feed a growing human population?? Maybe! Maybe not!