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All plant species rely on this process to produce their source of energy.

Photosynthesis is a complex pathway which is used by plants to fix carbon, present in the atmosphere, into sugar. All plant species rely on this process to produce their source of energy.

A typical plant on the earth that uses photosynthesis is a C3 plant. Photosynthesis is the process when carbon dioxide enters a plant through its stomata, and the enzyme Rubisco fixes carbon into sugar using the Calvin cycle. It fuels plant growth. This fixation of carbon dioxide by rubisco is the first step of the Calvin cycle. The plants that use this mechanism of carbon fixation are called C3 plants. Approx 95% of plants on the earth are C3 plants. They are also known as temperate plants. The photosynthesis process can take place only when the micropores (stomata) on leaves are open. The leaves of C3 plants do not show kranz anatomy. C3 plants exhibit the C3 pathway. It is the three-carbon compound (3-PGA). Here the first carbon compound produced has three carbon atoms. The Calvin cycle is useful to convert CO2 into carbon. It eliminates greenhouse gas (CO2) from the atmosphere efficiently. Calvin cycle helps plants to store energy for a more extended period. C3 plants are highly rich in proteins. They can be annual perennial. Some of the C3 plant examples are wheat, rye, oats, orchard grass.

C4 plants possess a particular type of leaf anatomy. They use Phosphoenolpyruvate carboxylase (PEP enzyme) instead of photorespiration to enter the Calvin cycle. Enzymes of C4 metabolism are regulated by light. PEP enzyme is more attracted to CO2 molecules and reacts less with O2 molecules. PEP carboxylase does not tend to bind oxygen. This process takes place in the mesophyll cells (spongy cells in the middle of the leaf) instead of the stomata where CO2 and O2 enter the plant. The light-dependent reaction occurs in mesophyll cells, and the Calvin cycle occurs in bundle-sheath cells around the leaf veins. Carbon dioxide present in the atmosphere is fixed in the mesophyll cells to form a pure 4-carbon organic acid (oxaloacetate) by the non-rubisco enzyme. The 4-carbon organic acid is then converted to a similar molecule, called malate, that can be transported into the bundle-sheath cells. Inside the bundle-sheath cells, malate breaks down and releases a molecule of CO2. Enzymes of C4 metabolism – PEP enzyme (Image to be added soon) Then the rubisco fixes the carbon through the Calvin cycle, the same as by C3 plants in photosynthesis. C4 plants exhibit the C4 pathway. Examples are maize, sorghum, and sugarcane. The leaves possess kranz anatomy. Approx 5% of plants on earth are C4 plants. C4 plants examples are pineapple, corn, sugar cane, etc. C4 photosynthesis is capable of increasing the crop yields. Researchers are focusing on understanding the evolution of C4 plants metabolism better, in an attempt to engineer important crops with more energy and water efficiency because they use less water and can grow in conditions of drought too. A Diagram showing C3 and C4 photosynthesis (Image to be added soon) Let’s explain more to understand the similarities and differences between C3 and C4 plants.

The Systematic Comparison of C3 and C4 Plants can be made through Metabolic Network.

Yes, there are the following similarities in C 3  and C 4  plants:

C 3  Plant and C 4  Plants both are productive, but C 4  plants are more productive and efficient. C 4  plants examples are corn, sorghum, sugarcane, millet, and Panicum virgatum switchgrass. C 3  plants fix the carbon dioxide with the help of Rubisco through a process called photorespiration. O 2  can bind to Rubisco instead of CO 2 . In this way, O 2  reduces C 3  plant photosynthetic efficiency and water use efficiency. As a result, C 4  plants are more productive than C 3  plants, even in high-temperature environments. So it can be undoubtedly said that the C 4  pathway is more efficient than the C 3  pathway in the sense of carbon fixation.

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Photosynthesis occurs in mesophyll tissues.

Photosynthesis occurs in both mesophyll cells and bundle sheath cells.

Via both C3 and C4 cycles. C4 in the mesophyll cells then C3 in the bundle sheath cells.

Tropical or semi-tropical, high temperature, low rainfall conditions, high light intensity

The CO2 acceptor is PEP carboxylase

The 1st Stable compound is 3C compound.

The 1st Stable compound is 4-carbon organic acid called oxaloacetate.

The optimum temperature is 20-25oC.

Photorespiratory does not take place.