Photosynthesis:  Carbon Metabolism

Readings for Chapter 10:

Goals and Objectives:
  1. Be able to describe why the C3 pathway is said to be autocatalytic and why it is considered beneficial to the plant.
  2. Be able to relate the C3 pathway mechanics to photorespiration.  Explain why a proper balance of CO2 and O2 is required by the plant.  In so doing, realize the importance of controlling transpiration at the same time.
  3. Be able to discuss the ecological importance of photorespiration.
  4. Be able to relate the importance of leaf structure in the C4 plant to the function of C4 metabolism.  Relate this to photorespiration.
  5. Be able to compare and contrast C3 and C4 metabolism.
  6. Be able to describe the significant way in which CAM differs from C4 metabolism.

Study Questions:

The Photosynthetic Carbon Reduction (PCR) Cycle

  1. Review the process behind C3 metabolism.  Pay particular attention to RuBisCo  (pages 189-195)
Activation and Regulation of the PCR Cycle (pages 195-197)
  1. Why is it important to regulate the pool of intermediates in PCR?
  2. How do light, pH, Mg2+, and CO2 control Rubisco activity?
  3. How does Rubisco activase function in controlling Rubisco activity?
  4. There are four other light activated enzymes in PCR.  What mechanism for regulation is used with these four enzymes?
  1. Review the process of photorespiration.  Familiarize yourself with the process, the organelles, the intermediates, and the enzymes involved.  (pages 197-199
  2. Why does photorespiration occur?
  3. Compare/contrast the problems that a C3 plant would have balancing transpiration, CO2, and O2 in a leaf.
C4 Metabolism
  1. Review the processes involved in C4 metabolism and the structure of the C4 leaf (pages 200-203)
  2. Compare/contrast C3 and C4 metabolism processes for the following (pages 204-205
  1. Review the process of CAM (pages 206-207)
  2. What are the differences/similarities between C4 and CAM (pages 207)
  3. Describe why CAM plants are well adapted to dry environments (pages 207)
Regulation of C4 and CAM
  1. How is PEPcase different in C4 and CAM plants?
  2. How is PEPcase activated in the C4 plant?
  3. How is activation of PEPcase accomplished in CAM plants?