Question

. Why is the dark reaction called a cycle?

The products of the dark reaction are the reactants of cellular respiration.
ATP is used at multiple steps during the chemical reactions.
RuBP made during the dark reaction is used to start the reaction again. Glucose produced during the dark reaction is a ring-shaped molecule.

Answer 1

RuBP made during the dark reaction is used to start the reaction again

Answer 2

RuBP made during the dark reaction is used to start the reaction again.

Step-by-step explanation:

Dark reactions start with carboxylation of RuBP (ribulose 1,5 bisphosphate) in presence of enzyme RuBisCo. The regeneration phase of dark reactions forms the RuBP again which then enter the next round of dark reactions. Since the initial substance (RuBP) is reformed during dark reactions, they form a cyclic pathway.