Name: Kranz Anatomy - The Ring of Cells
Uploaded: 2019-07-19
Duration: 5 min 1 s
Description: Let's learn about the characteristic features of certain plants responsible for the process of photosynthesis and photorespiration.

Question

The Calvin cycle consists of three phases. What are they? Explain the significance of each of them.

Accepted Answer

The Calvin cycle consists of three phases, and their significances are following:
1. Carbon fixation:
An atmospheric CO₂ molecule combines with a five-carbon acceptor molecule called ribulose-1,5-bisphosphate (RuBP) and results in an unstable six-carbon compound. The 6C-containing molecule splits into two molecules of the three-carbon compound, 3-phosphoglyceric acid (3-PGA). The reaction occurs in the presence of the enzyme RuBP carboxylase-oxygenase (RuBisCO).

2. Reduction:
The 3-PGA molecules created through carbon fixation converts into simple sugar — glyceraldehyde-3 phosphate (G3P) by using ATP and NADPH synthesized in the light-dependent reactions. In this way, the Calvin cycle becomes how plants convert energy from the sunlight into long-term storage molecules, such as sugars. The energy stored in the ATP and NADPH gets fixed into the sugar molecules.
This step involves electron transfer from NADPH to the 3-phosphoglyceric acid molecules to create glyceraldehyde-3 phosphate (GAP), hence called reduction.

3. Regeneration:
Few glyceraldehyde-3 phosphate molecules continue reactions to synthesize glucose while remaining are recycled to regenerate the five-carbon RuBP compound used to accept new carbon molecules. The regeneration process requires ATP. It is a complex process involving many steps. Because it takes six-carbon molecules to make single glucose, this cycle must be repeated six times to make a single molecule of glucose.
To accomplish this equation, five out of six glyceraldehyde-3 phosphates (GAP) molecules created through the Calvin cycle are regenerated to form RuBP molecules. The sixth or last molecule exits the cycle and involves the synthesis of one-half of a glucose molecule.

The Calvin cycle consists of three phases. What are they? Explain the significance of each of them.

Important Questions on Photosynthesis in Higher Plants

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