Multiple choice

The first step in the dark reaction of photosynthesis is

  1. formation of ATP

  2. ionisation of water

  3. attachment of CO2 to a pentose sugar

  4. excitement of an electron of chlorophyll by a photon of light

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The first step in the dark reaction of photosynthesis is carboxylation in which one molecule of CO2 combines with one molecule of ribulose 1, 5-biphosphate (RuBP) to form unstable six carbon compounds. Carboxylation of RuBP is catalysed by the enzyme RuBP carboxylase or Rubisco.