What is the Primary Function of the Calvin Cycle [Expert Answer]

What is the Primary Function of the Calvin Cycle [Expert Answer]
What is the Primary Function of the Calvin Cycle [Expert Answer]

What is the primary function of the Calvin Cycle? The process where plants or algae take in carbon dioxide and transform them into their food is called the Calvin cycle.

Since we were children, we all were taught that trees give us oxygen to breathe in and take in carbon dioxide. As kids, we wondered, we have a nose, so we breathe in oxygen, but how do trees take carbon dioxide? Do trees have a nose too?

As we grew up, we definitely understood that trees in no shape or form have a nose. Then again, the question remains the same, how do trees take in carbon dioxide then? And what do they do with it?

Well, in this article we will discuss it all. Before that, let me give you a spoiler.  Now let’s learn more about the Calvin cycle and find the answer of what is the primary function of the Calvin cycle?

Calvin Cycle Definition

The Calvin cycle is a series of chemical reactions performed by plants and algae. It occurs as a part of the dark reaction of photosynthesis. Through these reactions, carbon dioxides are turned into sugar and other products that the plants need to grow. Plants and algae depend on the Calvin cycle for energy and food.

Purpose of the Calvin Cycle

Calvin cycle’s purpose is to produce organic products that a plant needs. To do so, a plant converts carbon dioxide and water into glucose or sugar. It additionally produces some proteins and lipids.

Overview of the Calvin Cycle

The Calvin cycle takes place in the stroma of the chloroplast. Carbon dioxide enters the interior of leaves through the stroma. If simply put, the Calvin cycle has three stages.

First of all, in this stage, carbon dioxide fixation happens. The plant takes CO2 from the atmosphere and forms a stable organic compound called  PGA (Phosphoglyceric acid). This entire process occurs with the help of an enzyme called RuBisCO.

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In the next stage, the reduction of carbon dioxide occurs. With the help of different components, the process of the formation of sugar starts.

Lastly, sugar formation happens. Due to the constant requirement of carbon dioxide for fixation, regeneration of RuBP happens parallelly.

What is the Primary Function Of the Calvin Cycle | Step by Step

We described the Calvin cycle function in the simplest way possible in just three steps. However, if you dig a little deeper into the detailed process, you should know there are more to the Calvin Cycle steps.

Below we have discussed the three steps of the Calvin cycle. So, keep on reading to know further.

1. Carbon Fixation

The first stage of the Calvin cycle is called carbon fixation. Plants absorb carbon dioxide from the atmosphere. The pores of the leaves are called stomata, through which CO2 enters the mesophyll layer. Then it gets diffused into mesophyll cells and into the stroma of chloroplast, where the Calvin cycle takes place.

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Firstly, rubisco (RuBP carboxylase-oxygenase), an enzyme catalyzes in producing ribulose bisphosphate (RuBP) from CO2, which is a 5-carbon sugar. The resulting 6-carbon molecule is unstable, and later it splits into two 3-carbon sugars. They are called  3-phosphoglycerate (3-PGA). From each CO2, two 3-phosphoglycerate is produced.

2. Reduction Phase

The reduction stage requires two things to function, ATP and NADPH. The 3-PGA from the previous stage gets converted into 3-carbon sugar in this stage. The reduction phase consists of two major steps.

In the first step, ATP provides a phosphate group to the 3-PGA.  Then it turns into a molecule named 1,3-bisphosphoglycerate. This step leaves ADP as a by-product.

Next, the 1,3-bisphosphoglycerate molecules get reduced by gaining electrons. It turns into 3-carbon sugar called glyceraldehyde 3-phosphate (G3P) by receiving two electrons from NADPH and losing one from its phosphate groups.

The ATP and NADPH used in this reduction phase are light-dependant, meaning they are created in the presence of solar energy. After the reduction phase, the resulting molecules (ADP and NADPH+) are also needed for further light-dependant reactions.

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3. Regeneration Phase

Lastly, some of the G3P molecules make glucose, and the rest are again used to create RuBP acceptor. Some complex reactions take place in this regeneration phase with the presence of ATP.

Three atoms are needed from CO2 molecules for G3P to exit the cycle and go towards glucose synthesis. With these three CO2 molecules, six G3P molecules are made. Among these six, only one goes to become glucose while the other five is again used for RuBP acceptor.

Products of the Calvin Cycle

To create one G3P, three Calvin cycle is needed. The final products from the Calvin cycle are G3P, ADP, and NADPH+. The G3P is later used for making glucose, while the other two are recycled for another Calvin cycle.

The chemical equation for Calvin cycle is,

3 CO2 + 6 NADPH + 5 H2O + 9 ATP → glyceraldehyde-3-phosphate (G3P) + 2 H+ + 6 NADP+ + 9 ADP + 8 Pi

*(Pi = inorganic phosphate)

The products from the three phases of Calvin cycle are mentioned in a summeried way below.

  • 3 CO2 combined with 3 RuBP acceptors creates six molecules of glyceraldehyde-3-phosphate (G3P).
  • 1 G3P goes to produce glucose.
  • 5 G3P are recycled and regenerated to become RuBP acceptors.
  • During the fixation phase, 6 ATP is converted into 6 ADP.
  • During the reduction phase, 6 NADPH is converted into 6 NADPH+.
  • During regeneration phase 3 ATP is converted into 3 ADP.

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Commonly Asked Questions About Calvin Cycle

Here we answered some commonly asked questions related to the Calvin cycle for better understanding.

Question-01: What is the Primary Function of the Calvin Cycle?

The primary function of the Calvin cycle is to form sugar. Through this cycle, plants make 3-carbon sugar, which can become other types of sugars, such as glucose, starch, and cellulose. The plants then use these sugars for development.

Question-02: What is the Primary Function of Photosynthesis?

Photosynthesis is the process in which plants convert solar energy into chemical energy. Afterward, they store the chemical energy for future use. These energies are the source of living for plants in most cases.

Question-03: What is the Primary Product of the Calvin Cycle?

There are three primary products that come from the Calvin cycle. They are 2 glyceraldehyde-3-phosphate (G3P) molecules, 3 ADP, and 2 NADP+. (ADP and NADP+. Though they are not always considered products as they later turn into other forms of carbohydrates.

Question-04: What is the Primary Function of Light Reactions?

The light reaction in photosynthesis captures solar energy and converts it into chemical energy for later use. The chemical energy is stored in molecules of NADPH and ATP. While this reaction occurs, waste oxygens are released that humans and other animals breathe in.

Question-05: Why is the Calvin Cycle Referred to as a Dark Reaction?

The Calvin cycle is also referred to as the dark reactions or light-independent phase because it does not require sunlight. However, the ATP and NADPH that the Calvin cycle needs are produced in the presence of sunlight.

Question-06: Is the Calvin Cycle Light Independent?

Yes. The Calvin cycle is also known as light-independent reactions as it does not require sunlight to perform.

Question-07: How do the Light Reactions Help the Calvin Cycle?

Light reactions take solar energy and produce components or molecules, including ATP and NADPH. These two are used in the Calvin cycle to produce glucose.

Question-08: What Does Rubisco Do in the Calvin Cycle?

Rubisco (RuBP carboxylase-oxygenase), in short RuBP, catalyzes carbon fixation in the Calvin cycle. It reacts with CO2 and creates a 6-carbon compound that later breaks into two 3-carbon compounds. Again, with ATP and NADPH, the 3-carbon molecules are converted into one G3P, and 5 RuBP acceptors are created.

Question-09: What is the End Result of the Calvin Cycle?

As the end result, from one Calvin cycle, one glyceraldehyde-3-phosphate (G3P) is produced. The rest are recycled and reused to perform Calvin cycles once again.

To Conclude

Hopefully, now you have got a clear idea of how the Calvin cycle works and how plants produce G3P to make glucose. Later, the glucose that is made is stored or used as food for plants or algae.

Now you should know the answer to the question – what is the primary function of the Calvin cycle? If you haven’t understand, we recommend to read the entire article again. This time read it with more concentration on each terms we have discussed so far.

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