Question

Which one of the following is represented by the Calvin cycle?
A. Reductive carboxylation
B. Oxidative carboxylation
C. Photophosphorylation
D. Oxidative phosphorylation

Answer 1

Hint: There are two stages of photosynthesis, light-dependent reaction - as the name suggests, these require light and occur mainly during the day. Reactions are independent of light - also known as dark reactions or the Calvin cycle or C3 cycle. This reaction occurs both in the presence and without sunlight.

Complete answer: The Calvin cycle refers to the light-free reaction in photosynthesis that takes place in three key steps. Although the Calvin cycle is not directly dependent on light, it is indirectly dependent on light, because the required energy carriers (ATP and NADPH) are the products of light-dependent reactions.

The Calvin cycle is classified into three phases.
1. The first phase is carboxylation, in which RuBP is converted into two 3-carbon compounds.
2. The next phase is a reduction, the 3-PGA molecule, made by fixing carbon, is converted into a regular sugar molecule – glucose.
3. The final stage is regeneration, a complex process requiring ATP. At this stage, some G3P molecules are used to make glucose while others are recycled to regenerate RuBP acceptors. So, the first two phases represent the reductive carboxylation.
Thus, option (A) is correct.

Note: RuBP is one of the organic substances that occurs in photosynthesis. Photosynthesis is a biochemical process that occurs in all green plants or autotrophs that produce organic molecules of carbon dioxide. This organic molecule contains a lot of carbon-hydrogen (C-H) bonds and is greatly reduced compared to carbon dioxide.