Question

Beginning with carbon fixation, arrange the steps of the Calvin cycle in the correct order.

Answer 1

By starting with carbon fixation, we should consider the moment where carbon dioxide enters the cycle and the enzyme RuBisCo plays an important role in this fixation. So, the cycle starts by the
- formation of an unstable 6-carbon compound,
and continues through the following steps in the presented order:
- formation of a stable 3-carbon compound
- use of ATP to form a high-energy 3-carbon compound
- formation of glucose, which leaves the chloroplast
- use of enzyme and ATP to form 5-carbon compound
- carbon dioxide reacts with a 5-carbon compound

Answer 2

Answer: The correct order of steps in the Calvin cycle is as follows-

1) Carbon dioxide reacts with five carbon compound.

2) Formation of an unstable 6-carbon compound.

3) Formation of a stable 3-carbon compound.

4) Use of ATP to form a high energy 3-carbon compound.

5) Formation of glucose, which leaves the chloroplast.

6) Use of enzyme and ATP to form 5-carbon compound.

Calvin cycle ( also called dark reacton or light independent reaction) is the second phase of photosynthesis that utilizes chemical energy from light dependent phase that is ATP and NADPH and fixes carbon from CO₂ into 3-carbon sugar, which is used for the formation of glucose.

It is primarily divided into 4 steps-

Carbon fixation - CO₂ binds to RuBP ( 5 carbon molecule) in presence of RuBisCO enzyme and forms an unstable 6 carbon molecule that splits into stable 2 molecules of 3 carbon that is PGA ( phosphoglyceric acid).

Reduction- PGA is reduced to G3P ( glyceraldehyde 3- phosphate) ATP and NADPH.

Carbohydrate formation- G3P is turned into carbohydrate ( like glucose) and one G3P is utilized for RuBP regeneration.

Regeneration- Using ATP from light dependent phase, RuBP is regenerated with the help of G3P.