What is the main carbohydrate produced during photosynthesis?

• A. Fructose
• B. Lactose
• C. Sucrose
• D. Glucose

Answer: (D)

The key idea is that the Calvin cycle in photosynthesis ends up producing a form of sugar that can be used immediately or stored: glucose. In the process, carbon dioxide is fixed and reduced to three-carbon sugars, which are then converted into glucose (and related forms that can be turned into starch for storage in chloroplasts). Glucose is the primary carbohydrate made during photosynthesis and serves as the building block for more complex carbohydrates; plants often store energy as starch, which is essentially glucose polymers. Fructose and sucrose are also present in plant metabolism—sucrose is a transportable sugar, and fructose is derived from glucose in various pathways—but they are not the main carbohydrate produced directly by photosynthesis. Lactose is a milk sugar and is not produced by plants.