Question

How many molecules of water are needed by a green plant to produce one molecule of hexose/reduce 6 molecules of $C{O}_2$?

• A. 6
• B. 12
• C. 24
• D. 1

Answer 1

Answer: (B)

12

Fixation of six carbon dioxide molecules to generate a molecule of hexose is accompanied by the release of six moles of oxygen. The released oxygen comes from water not from carbon dioxide. During photosynthesis, water is oxidized to release oxygen and carbon dioxide is reduced to form sugar. The twelve molecules of water release six molecules of oxygen along with the formation of one molecule of hexose.