photo_4.htm [cam and c4 plants]

Notes: Exceptions: CAM and C₄

CAM Plants (crassulacean acid metabolism)

C₄ Plants

CAM is a mode of C fixing in which stages of C₄ occur in one cell but at different hours of the day

@night when cool: stomata open, take in CO₂, incorporate it into organic acids and store those acids in vacuoles until daylight

@day when light: light powers regeneration of ATP and NADPH to supply the Calvin Cycle and the release of CO₂ from organic acids into the Calvin Cycle

e.g., cacti, pineapple

Calvin cycle is in bundle-sheath cells in the mesophyll near vascular tissue

CO₂+ PEP (phosphoenol pyruvate) + carboxylase (enzyme)OxaloacetateMalatethrough plasmodesmata to bundle-sheath cell4 C compounds are oxidized to carbon dioxide (to Calvin cycle) and pyruvate (to replace PEP)

e.g., sugarcane, corn

Q:Why do they do this?
A:Photorespiration

Q:What's photorespiration?
A:It's when rubisco accepts oxygen instead of carbon dioxide when carbon dioxide concentrations are low. Rubisco accepts oxygen because it has an "archaic" affinity for the compound.

In Very Dry Heat
Rubisco PEP carboxylase

accepts O2 instead of CO2 when ratio is favorable;
therefore rubisco is inefficient has much higher affinity for CO2 than rubisco;
therefore PEPco is efficient

**In Very Dry Heat**
Rubisco	PEP carboxylase
accepts O2 instead of CO2 when ratio is favorable; therefore rubisco is inefficient	has much higher affinity for CO2 than rubisco; therefore PEPco is efficient

Next: "Bacterial Replication."