Single Molecule Glucose by Photosynthesis

Sunlight provides the energy that produces a glucose molecule by photosynthesis.

In photosynthesis, the production of a single six-carbon sugar requires many steps. The first steps require light energy. The final steps can take place in the dark.

The Light Reaction

Chlorophyll in plants absorb energy from sunlight. This energy decomposes water to form hydrogen and the waste product oxygen. The hydrogen then becomes part of two compound called nicotinamide adenine dinucleotide phosphate (NADPH). Adenine triphosphate (ATP) is also produced in the light reaction. These compounds are reservoirs of energy that the plant uses when needed

Calvin-Benson Cycle

Most plants make glucose molecules by the Calvin-Benson cycle. Ribulose diphosphate, a five-carbon sugar molecule with two phosphate groups attached, takes a carbon dioxide molecule from the air, undergoes several transformations and finally assumes its original form once more. This happens six times. The six carbon dioxide molecules taken from the air eventually convert into glucose. The reactions of the Calvin-Benson cycle use the energy produced in the light reaction. Enzymes also help.

C4 Photosynthesis

Plants such as sugar cane make glucose molecules by C4 Photosynthesis, also called the Hatch and Slack Pathway. Here a three-carbon molecule takes a carbon dioxide molecule out of the air six times, each time passing it on to a ribulose diphosphate molecule. The rest of the reaction resembles the Calvin-Benson cycle.

References

• "Excel HSC Biology"; Diane Alford and Jennifer Hill; 2000
• Clinton Community College: Photosynthesis
• "Botany: An Ecological Approach"; William A. Jensen and Frank B. Salisbury; 1972
• The Community College of Baltimore County: The C4 Pathway
• Auburn University: C4 Photosynthesis