This is an explanation of the Calvin Benson cycle and photosynthesis starting from the meaning, function, stages, processes, schemes, and results. What is the Calvin Cycle? We know that plants are the source of life for all living things on earth. Useful plants produce oxygen or O2 that humans and animals need to breathe. In addition, plants are also useful as producers that are used by consumers who are above them. Plants can make their own food through photosynthesis with the help of leaf green substances and sunlight.
In carrying out the process of photosynthesis, plants must go through two stages. The plant must go through the light reaction as well as the dark reaction. When in the light reaction, chlorophyll captures light and converts it into energy compounds that will later be used in the dark reactions. This dark reaction is known as the Calvin cycle.
In the following, we will invite you to learn more about the Calvin cycle including understanding, stages, the process of the Calvin cycle, and so on.
What is the Calvin Cycle?
The Calvin cycle is a series of chemical reactions that occur in plants without the need for light. However, this cycle does not mean the process occurs in the dark. The term dark reaction is the term used when the reaction does not use energy from light. Of course, this is very different from the dark reaction, the process of which requires the help of light energy.
The place where the Calvin cycle occurs is in the stroma, which is located inside the chloroplast. The Calvin cycle of photosynthesis works by converting CO2 into a three-carbon sugar. When the process of making three-carbon sugar, the cycle requires NADPH2 and requires a lot of energy in the form of ATP to be able to add electrons when you want to reduce power. Then, the sugar will be converted into nucleotides, amino acids, and starch (a more complete/complex sugar).
Calvin Cycle Functions
Simply put, the Calvin cycle works to make carbon sugars. Then the carbon sugar will be used to form other sugars such as starch, glucose, and cellulose which will then be used by plants for structural building materials.
The Calvin cycle will directly take carbon molecules from the air and also directly convert them into plant matter. This is what makes this cycle a very important role for the existence of most ecosystems. Without this cycle, plants would not be able to store energy in a form that herbivores could digest. As a result, carnivores cannot have access to energy that comes from herbivores.
Difference Between Dark Reaction and Light Reaction
As we have already explained that both dark reactions and light reactions occur during the process of photosynthesis. The dark reactions will utilize the energy that comes from the light reactions. There are several things that distinguish between dark reactions and light reactions, namely:
- The light reactions require light energy and the dark reactions do not
- The process that occurs in the light reaction: ADP + NADP + Phosphate + Light energy + Water → ATP + NADH + Oxygen. Meanwhile, the Calvin cycle process: NADPH + ATP + RuDP + Carbon dioxide → PGAL + NADP
- The light reactions require sunlight as an energy source. While the dark reactions require energy that comes from the light reactions
- The light reactions produce oxygen and the dark reactions produce simple carbohydrates or sugars
Calvin Cycle Stages
As you can see that the Calvin cycle picture above represents the stages. You can see information about the Calvin cycle chart below.
1. Carbon Fiction
The first scheme of the Calvin cycle begins with the fiction of carbon. CO2 or carbon dioxide will be bound to RuBP or five-carbon sugar. RuBP or ribulose bisphosphate works with the help of the enzyme Rubisco. Later, this process produces 6 unstable carbon molecules. As a result, the molecule will split into 6 PGA molecules which have 3 carbon atoms.
The second stage of the Calvin cycle is called reduction. At this stage the process of converting 3-phosphoglycerate into glyceraldehyde 3-phosphate will take place and will later be required for ATP and NADPH2. Then there are 6 molecules of 3 PGA (phosphoglycerate) which have 3 carbon atoms that were previously formed in phase 1. They will each get 6 molecules of phosphate from ATP which will then form 1,3-diphosphoglycerate or PGAP of 6 molecules.
This NADPH will reduce 6 molecules of 1,3 PGAP so that there will be the release of 1 phosphate which will produce PGAL, namely glyceraldehyde 3 phosphate, totaling 6 molecules.
The third stage is regeneration. This step is derived from 6 molecules of 3 PGAL which have been obtained from the reduction phase. After that, 5 molecules will be taken to be used in the regeneration of 1,5 RuBP or biphosphate which will form 3 RuBP molecules obtained through phosphate from ATP for carbon dioxide fixation and 1 molecule which is used as raw material in the manufacture of glucose.
Through these 3 CO2 molecules, 1 molecule of glyceraldehyde 3-phosphate will be produced. In carrying out the synthesis, each molecule of glyceraldehyde 3-phosphate requires 6 molecules of NAPDH2 and 9 molecules of ATP. In regenerating ATP and NAPDH2, the Calvin cycle requires the help of light reactions.
Calvin Cycle Results
Other information that is no less important is related to the results of the Calvin cycle.
- Each turn that occurs in this cycle will fix one carbon molecule. This carbon molecule will later be used as a sugar maker
- There are at least three turns of the Calvin cycle to make one molecule of glyceraldehyde-3 phosphate
- After six rounds, it will form two molecules of glyceraldehyde-3 phosphate which will later be combined to form a glucose molecule
You need to remember that each cycle of this cycle uses 2 NADPH and 3 ATP in the process of adding electrons to 3-phosphoglyceric acid to get glyceraldehyde-3 phosphate. There is also regeneration of RuBP which makes it able to accept new carbon atoms derived from carbon dioxide from the air. In other words, to produce 1 molecule of glucose, 12 NADPH and 18 ATP are needed.
The Role of the Calvin Cycle
For higher plants as well as algae, a single primary carboxylation mechanism occurs. This mechanism then results in the synthesis of carbon compounds, namely the pentose phosphate pathway. This cycle is the only path that must be passed by autotrophic organisms , both chemosynthesis and photosynthesis, which will potentially lead to the incorporation of inorganic materials in living things.
The products produced by these cycles have great benefits for the biosphere. This is because the resulting covalent bonds will represent the amount of energy obtained from the light of photosynthetic organisms. Organisms belonging to the autotroph type will release most of their energy through cellular respiration and glycolysis.
This energy will later be useful for maintaining growth, development, and reproduction. Most of the plants will later be consumed by heterotrophs that cannot synthesize themselves but only depend on autotrophs for their energy needs.