Chapter 20, Problem 46P

Interpretation Introduction

(a)

Interpretation:

The data were most likely to be generated by the C₄ plant and C₃ plant should be determined.

Concept introduction:

When O₂content is high in the atmosphere, the Rubisco enzyme(carbon-fixing enzyme of Calvin cycle) binds with O₂ instead of CO₂. The O₂binding initiates oxygenase reaction rather than carboxylase reaction. This process is called photorespiration.

Interpretation Introduction

(b)

Interpretation:

Possible explanations for the decrease in photosynthetic activity at higher temperature should be determined.

Concept introduction:

Multiple factors affect enzyme activity such as temperature, pH, enzyme concentration, substrate concentration, and inhibitors or activators.

Interpretation Introduction

(c)

Interpretation:

Why C₄ plants thrive at CO₂ concentrations that do not support the growth of C₃ plants should be explained.

Concept introduction:

C₃ plants have no specific adaptations to minimize photorespiration. But C₄ plants have a mechanism to reduce photorespiration. In C_4, cells light-dependent reactions and Calvin cycles occur in two different types of cell

Interpretation Introduction

(d)

Interpretation:

A possible explanation of why C₃ plants continue to increase photosynthetic activity at higher CO₂ concentrations, whereas C₄ plants reach a plateau should be suggested.

Concept introduction:

In C₄ plants, atmospheric CO₂ is first fixed in one type of cell as oxaloacetate and then converted to malate. Malate is then broken down to produce CO₂ in another type of cells. This CO₂ is then fixed to produce glucose via the Calvin cycle like C₃ plants.