Photosynthesis c3 and c4 pathways

Plants manufacture glucose by the use of carbon dioxide from the atmosphere and water in the presence of sunshine during this process. Consequently, oxygen is released into the atmosphere as a by-product, which contributes to global warming.

In general, the photosynthesis process can be divided into two major phases: the photochemical phase and the biosynthetic phase. The C3 and C4 routes, which are the subject of this article, are two different types of biosynthetic pathways. Plants use water and carbon dioxide to synthesise carbohydrates, which is known as the biosynthetic process.

C3 Pathway (Calvin Cycle)

The majority of plants make a 3-carbon acid known as 3-phosphoglyceric acid (PGA) as a first product of carbon dioxide fixation, which is known as the first product. The C3 route, which is often referred to as the Calvin cycle, is a type of metabolic process.

The Calvin Cycle includes the three steps:

• carboxylation – Carboxylation is the first step in the Calvin cycle, and it is the most important. This is the point at which inorganic carbon first enters the biosphere and becomes bioavailable. The products of the carboxylation step of the Calvin cycle are the source of nearly all organic molecules found on the surface of the planet. This reaction converts one five-carbon molecule (RUBP) into two three-carbon molecules (two 3-PGAs) as a result of the carboxylation reaction.

• reduction – The next step in the Calvin cycle is the phosphorylation and reduction of 3 phosphoglycerate, which results in the formation of a triose phosphate. Dihydroxyacetone phosphate and glyceraldehyde 3 phosphate are both triose phosphates that can be converted into each other. Plant cells use triose phosphates as a form of currency to exchange carbon. Among the functions of the chloroplast are the production of starch, the synthesis of fatty acids, and the production of RUBP. Triose phosphates are also transported from the chloroplast to the cytosol, where they are utilised in the synthesis of sucrose and the breakdown of glycogen.

• regeneration – It is possible that the Calvin cycle would be stopped if all of the triose phosphates produced by the first two parts of the Calvin cycle were used for the synthesis of sucrose and fatty acids. However, this is unlikely to happen because the stroma contains an abundance of RUBP that can be used as a substrate. In order to avoid this, the majority of the triose phosphates produced by the first two steps are subjected to a series of reactions that result in the formation of RUBP.

The enzyme RuBP carboxylase is responsible for the production of the first two molecules of 3-phosphoglyceric acid (PGA) in the first phase of the reaction. Later on, in the second and third phases, the ATP and NADPH phosphorylate the 3-PGA, which finally results in the production of sugar. After that, the cycle is restarted by the regeneration of RuBP.

Plants that follow the C3 route include beans, rice, wheat, and potatoes, to name a few examples.

C4 Pathway (Hatch and Slack Pathway)

The Calvin cycle is followed by every photosynthetic plant, although in some plants, there is a basic stage to the Calvin Cycle known as the C4 pathway that is present. The C4 pathway is frequently used by plants in tropical desert environments. The first product of carbon fixation is a 4-carbon molecule known as oxaloacetic acid (OAA), which is produced in this case. Such plants are unique, and they have adapted to their environment in various ways.

It all starts with a 3-carbon compound known as phosphoenolpyruvate (PEP), which serves as the starting point for the C4 pathway. This is the principal CO₂ acceptor, and the carboxylation process is carried out with the assistance of an enzyme known as PEP carboxylase (PEP for short). They result in the formation of a 4-C molecule known as oxaloacetic acid (OAA).

Malic acid is a 4-carbon molecule that is eventually transformed into another 4-carbon compound known as acetic acid. Later on, they are transported from mesophyll cells to bundle sheath cells, where they remain until they die. As a result of this reaction, OAA is broken down into carbon dioxide and a 3-C molecule.

The CO₂ that is produced is used in the Calvin cycle, whereas the 3-C molecule is returned to mesophyll cells for the purpose of regenerating phospholipid peroxide.

Plants that follow the C4 pathway include corn, sugarcane, and a few bushes, to name a few examples. Calvin pathway is a common pathway in both C3 and C4 plants; however, it is only found in the mesophyll cells of C3 plants and not in the mesophyll cells of C4 plants.

The distinction between the C3 and C4 pathways

Some of the most significant distinctions between these two routes are as follows:

I. The very first stable compound

It is a 3-carbon molecule known as 3-phosphoglyceric acid that is the first compound to be created in a C3 cycle. The predominant stable component in C4 routes, on the other hand, is a 4-carbon compound known as oxaloacetate acid, which is produced in large quantities.

II. The presence of the substance in plants

Every plant has a C3 cycle, which is found in every cell. However, the C4 pathway diagram can only be found in plants that grow in tropical climates.

III. Fundamental carbon dioxide acceptor.

In the case of C3, the compound is Ribulose Bi Phosphate (RBP) (RUBP). Phosphoenolpyruvate is the compound responsible for C4 (PEP).

IV. Carboxylase enzyme.

PEP carboxylase and rubisco are the enzymes found in C4 plants. In the case of C3, on the other hand, it is merely rubisco.

V. Carbon fixation

A C3 cycle has only one instance of carbon fixation. Double carbon fixation takes place during the C4 cycle.

VI. Photorespiration

The rate of photorespiration in C3 is extremely high. With regard to C4, there is no evidence of photorespiration.

The C3 and C4 pathways are two phases in the photosynthesis process that are very necessary. In addition, you will be able to participate in all of the live classes with our subject experts and students from all across the United States.

Conclusion

It is the biological process by which all green plants, photosynthetic bacteria, and other autotrophs transform light energy into chemical energy, which is known as photosynthesis. Carbon dioxide and water are converted into glucose in the presence of sunshine, which is the final step in the process. The process of photosynthesis also results in the release into the atmosphere of dissolved oxygen gas as a by-product.

During the process of photosynthesis, plants utilise this light energy to prepare chemical energy for use by other organisms. Photographic photosynthesis occurs in two phases: the photochemical phase and the biosynthetic phase, which are intertwined.

The photochemical phase is the first stage in which ATP and NADPH are synthesised in preparation for the biosynthetic phase. The biosynthetic step is responsible for the production of the final product, glucose.