Chapter 2. Carbon Metabolism: Rate of Photosynthesis

General Purpose

This pre-lab will present some of the general concepts related to the measurement of the rate of photosynthesis.

Learning Objectives

General Purpose

Background Information

The light-absorbing reactions you studied in the previous lab are just a part of the process of photosynthesis. The energy from absorbed light is initially used to synthesize ATP and NADPH (Figure 8-1).

Figure 8-1. Summary of photosynthesis.

Oxygen is generated and released as a by-product of this process when water is split during the light reactions. Oxygen is also used during aerobic respiration by many organisms, including plants. The ATP and NADPH from the light reaction are used, at least in part, to chemically reduce carbon from CO₂ to produce sugar during the Calvin cycle. Since plants can produce oxygen during photosynthesis and use oxygen during respiration it is difficult to use changes in oxygen level to directly measure rates of photosynthesis. In addition, the small changes in oxygen that may result from these combined processes are difficult to detect in an atmosphere that contains approximately 21% oxygen. Similarly, since plants use carbon dioxide during the Calvin cycle and produce it during respiration it is also difficult to use changes in CO₂ levels to measure photosynthesis rates. However, since the level of CO₂ in the atmosphere is much lower, there is less difficulty detecting changes in the CO₂ levels.

Pre-Lab Quiz

Proceed to the Pre-Lab Quiz