Question

The first step of the Calvin cycle is the incorporation of ______ into ______.

A) O2… G3P
B) RuBP… O2
C) CO2… RuBP
D) G3P… RuBP

Answer 1

The first step of the Calvin cycle is the incorporation of CO2 into RuBP, which is catalyzed by RuBisCO, resulting in the formation of 3-PGA and leading to the production of carbohydrate molecules.

C is correct

Step-by-step explanation:

The first step of the Calvin cycle is the incorporation of carbon dioxide (CO2) into ribulose bisphosphate (RuBP). Therefore, the correct answer to the given question is C) CO2… RuBP. This step is catalyzed by the enzyme RuBisCO, which facilitates the combination of CO2 with RuBP, resulting in a 6-carbon intermediate that immediately splits into two molecules of 3-phosphoglycerate (3-PGA).

The Calvin cycle is a part of the light-independent reactions of photosynthesis, contributing to the production of carbohydrate molecules from G3P after several turns of the cycle. The Calvin cycle must be completed multiple times to eventually produce a molecule of glucose (C6H12O6).

Answer 2

The correct answer is: C) CO2… RuBP

Calvin cycle is the second phase of photosynthesis also called light-independent reactions (no light required for this step). This process occurs in in the stroma (the inner space of chloroplasts) and during it three-carbon sugars are produced from CO2. Calvin cycle can be divided into three steps:

1. Carbon fixation where CO2 from the air is “apsorbed” by plants and combined with a five-carbon acceptor molecule, ribulose-1,5-bisphosphate (RuBP). Formed molecule with 6 C atoms is then split into two 3-phosphoglyceric acid (3-PGA) molecules by the enzyme rubisco.

2. Reduction refers to conversion of 3-PGA to glyceraldehyde-3-phosphate (G3P), sugar that can be used in further steps of photosynthesis.

3. Regeneration refers to recycle of some G3P in order to regenerate the RuBP acceptor for the carbon fixation.