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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.
