Question:

The primary acceptor, during CO2 fixation in C3 plants, is

Updated On: Aug 3, 2024
  • phosphoenolpyruvate (PEP)
  • ribulose 1, 5-diphosphate (RuDP)
  • phosphoglyceric acid (PGA)
  • ribulose monophosphate (RMP).
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The Correct Option is B

Solution and Explanation

The Calvin cycle is also known as C3 cycle because CO2, reduction is cyclic process and first stable product in this cycle is a 3-C compound (i.e., 3-phosphoglyceric acid or 3-PGA). In this cycle, CO2 acceptor molecule is RuBP or RuDP (i.e., Ribulose 1, 5-biphosphate or Ribulose 1, 5-diphosphate). There occurs covalent bonding of CO2, to RuBP and the enzyme catalyzing this reaction is RuBP-carboxylase/oxygenase (RuBisCO).
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Concepts Used:

Calvin Cycle

The Calvin cycle is a process that plants and algae use to turn carbon dioxide from the air into sugar, the food autotrophs need to grow.

Every living thing on Earth depends on the Calvin cycle. Plants depend on the Calvin cycle for energy and food. Other organisms, including herbivores, also depend on it indirectly because they depend on plants for food. Even organisms that eat other organisms, such as carnivores, depend on the Calvin cycle. Without it, they wouldn't have the food, energy, and nutrients they need to survive.

Stages of C3 Cycle:

It is divided into three main stages:

Carbon fixation

In this stage the carbon dioxide combines with RuBP, to be reduced and attached to an organic molecule. It forms 2 molecules of 3-PGA (3-phosphoglyceric acid). The enzyme which is used in this process to catalyse the reaction is ribulose bisphosphate carboxylase/oxygenase. The enzyme works rather slowly and processes only 3 molecules of RuBP per second. The process is called carbon fixation because carbon dioxide is fixed from an inorganic form to organic molecules.

Reduction

In this step, 3-PGA (3-phosphoglyceric acid) is converted into simple sugar- G3P (Glyceraldehyde-3 phosphate). ATP and NADPH is utilized in this stage as energy sources and the energy is transferred to sugar molecules for long storage purposes.

Regeneration

It is the third stage of the Calvin cycle and is a complex process that requires ATP. In this stage, some of the G3P molecules are used to produce glucose, while others are recycled to regenerate the RuBP acceptor.