Question

The first step in dark reaction of photosynthesis is

• A. formation of ATP
• B. ionization of water
• C. attachment of $CO_2$ to a pentose sugar
• D. excitement of electron of chlorophyll by a photon of light

Answer 1

Answer: (C)

attachment of $CO_2$ to a pentose sugar

Answer 2

The dark phase of photosynthesis involves fixation of $CO_2$ by the enzyme ribulose bisphosphate carboxylase [RUBISCO]. The two substrates are $CO_2$ and 1,5- bisphosphate (RuBP) and the product is the 3 - carbon compound, 3 - PGA (3 - phosphoglyceric acid). RuBP is a 5 - C sugar.