Calvin Cycle And Photorespiration

Calvin Cycle and Photorespiration

Calvin Cycle • • • • • •

Where does the Calvin Cycle occur? In the stroma What goes into the Calvin Cycle? ATP, NADPH, Carbon Dioxide What comes out of the Calvin Cycle? Sugar, ADP, NADP+

The G3P made in the Calvin Cycle is involved in the biosynthesis of other organic molecules

Rate of Photosynthesis • What is a rate? • It is the activity per unit time. • What factors can affect the photosynthetic rate?

The Effect of Light Intensity on Photosynthetic Rate

The Effect of Temperature on Photosynthetic Rate

The Effect of Light Intensity and Temperature on Photosynthetic Rate

Which is the limiting factor here; light intensity or temp.?

Oxygen Concentration

What would a graph for increasing levels of CO2 look like?

Why Does Oxygen Effect Photosynthetic Rate? • What is the role of rubisco? • Rubisco incorporates carbon dioxide into the RuBP during the Calvin cycle. • Rubisco, however, has an active site that accommodates both oxygen and carbon dioxide. • What happens when rubisco incorporates oxygen into the RuBP molecule?

Photorespiration • The overall rate of photosynthesis decreases. • Both photorespiration and photosynthesis occur at the same time

Conditions for Photorespiration • What conditions will lead to a lot of photorespiration? • Hot • Dry • Sunny • What happens to stomates under such conditions? • They close.

Evolution • Why does rubisco bind both oxygen and carbon dioxide? • When Calvin Cycle evolved there was little oxygen in the atmosphere.

Solutions • What solutions have some plants found for this problem? • C4 Pathway. • Sugarcane, corn, crabgrass have all evolved a different structure that minimizes photorespiration.

What is the new structure?

The bundle sheath cells!

How do the bundle sheath cells minimize photorespiration?

C3 vs. C4 plants • When do C4 plants outcompete C3 plants? • Under the hot, dry, sunny conditions that favor photorespiration. • C4 plants have evolved in these hot, warm climates. • What happens to acid levels in a C4 plant, as compared to a C3 plant during the day?

CAM Plants • At night, stomata open, take in CO2, incorporate it into organic acids and store those acids in vacuoles until daylight • during the day, stomates close • The organic acids stored at night, break down, release CO2 and rubisco incorporates it into sugar.

• C4 plants use a new structure to solve the photorespiration problem. • CAM plants use time to solve the photorespiration problem.