7.5 Products of Photosynthesis
Christelle Sabatier
Learning Objectives
By the end of this section, you will be able to do the following:
- Describe the two major metabolic roles of the Calvin Cycle product, G3P
- Identify the form of carbohydrate transported throughout the plant body
The G3P produced by the Calvin Cycle has several possible fates. When photosynthetic rates are at their highest, G3P builds up in the chloroplast stroma and is converted into glucose and starch that is stored in the chloroplast until photosynthetic rates decrease (at night) at which point the starch is hydrolyzed to ensure plant tissues continue to receive carbohydrates day and night.
Most of the G3P is transported out of the chloroplast into the mesophyll cell cytoplasm where it is converted into glucose or fructose through the action of various enzymes:
2xG3P → C6H12O6
Glucose and fructose are isomers of each other and both have the molecular structure C6H12O6. When combined together into a disaccharide, they form sucrose.
glucose + fructose → sucrose
Sucrose is the form of carbohydrate that is transported throughout the plant body. We will discuss this in detail in Chapter 8.
Video 7.5.1. Photosynthesis: Part 7: Biosynthesis | HHMI BioInteractive Video by biointeractive
Practice Questions
Glossary
fructose
a 6-carbon simple sugar (monosaccharide) integral to metabolic processes
glucose
a 6-carbon simple sugar (monosaccharide) most involved in eukaryotic energy production
starch
complex carbohydrate and the primary source of energy for plants
sucrose
a disaccharide composed of glucose and fructose serving as an energy source
glyceraldehyde-3-phosphate (G3P)
a 3-carbon sugar phosphate that is the net product from the Calvin Cycle, which can be used to synthesize other organic molecules like glucose, starch, and sucrose
calvin cycle
the metabolic pathway that uses the chemical energy (ATP and NADPH) generated during the light-dependent reactions of photosynthesis to fix atmospheric carbon dioxide (CO2) into G3P
a 3-carbon sugar phosphate that is the net product from the Calvin Cycle, which can be used to synthesize other organic molecules like glucose, starch, and sucrose
