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Photosynthesis is a process in which plants produce the energy required for their survival with the help of sunlight, carbon dioxide, water, and chlorophyll. A dark phase of photosynthesis also occurs in the plants called a dark reaction. It is a type of cycle in which photosynthesis is performed in the absence of sunlight. The production of carbohydrates from carbon dioxide occurs during this stage. This type of production of food in the dark can be found in two types of plants. They are
C3 plants
C4 plants
C3 Plants
Definition: C3 plants are a type of plants in which the first result of carbon dioxide assimilated through photosynthesis is 3-phosphoglycerate. 3-phosphoglycerate is composed of three carbon atoms. Direct CO2 fixation is a feature of C3 plants. Rubisco is the enzyme that plays a key role in catalysing carbon fixation. C3 plants, on the other hand, need to be in locations with high CO2 concentrations, moderate light intensity, moderate temperature, and plenty of groundwater. This is because in hot climates, the stomata close to prevent water loss. However, it causes an increase in O2 levels. When this happens, rubisco reacts with O2 instead of CO2, which in turn results in photorespiration and wasteful CO2 loss in C3 plants.
C3 Cycle: The C3 cycle can popularly be called the Calvin cycle. The C3 photosynthesis occurs as a chemical reaction in which hydrogen-carrying elements and carbon dioxide is converted to produce glucose. The region at which this reaction occurs is the stroma. Stroma is a part of the chloroplast that is filled with fluids and present outside the thylakoid membrane. The products like ATP and NADPH formed during light-dependent reactions are used by this cycle to proceed with its chemical reactions. ATP provides chemical energy and NADPH serves with reducing the power that helps in sugar formation.
Examples: Some of the commonly found C3 plants are rice, oats, barley, wheat, tobacco, spinach, soybeans, sugarbeets, oats, peanuts, cotton, sunflower, etc.
C4 Plants
Definition: C4 plants are a type of plant that uses the C4 carbon fixation pathway. In this pathway, the C4 cycle occurs with CO2 present bound to phosphoenolpyruvate in the mesophyll cell. This results in the formation of a four-carbon compound called oxaloacetate. Oxaloacetate is then shuttled to the bundle sheath cell, where it is decarboxylated to liberate CO2 for use in the C3 pathway. PEP carboxylase, PPDK (pyruvate phosphate dikinase), and a C4 acid-decarboxylation enzyme are the enzymes involved in this process. C4 plants get their name from the first product of CO2 fixation which is the oxaloacetate.
C4 Cycle: The C4 cycle is familiarly called C4 carbon fixation or the Hatch–Slack pathway. It is a development or addition of the C3 cycle. The enzyme PEP carboxylase is used to add Carbon dioxide to phosphoenolpyruvate which results in the formation of a four-carbon compound. This formation initially occurs in the mesophyll and is later transported to the bundle sheath cells. This reaction will lead to the release of Carbon dioxide by the Calvin cycle.
Examples: Some of the commonly found C4 plants are corn, switchgrass, sorghum, millet, sugarcane, hair sedges, dwarf umbrella sedge, castor, calva, golden cleome, African cabbage, upload, dahlia, practice, etc.
C3 and C4 Plants: Difference
Conclusion
Dark reactions linked with the photosynthesis of plants and microbes are facilitated by C3 and C4 pathways. They play a vital role in the production of food in plants. The dark reactions utilise the products produced or released during light reactions. These pathways play a key role in converting the Carbon dioxides to carbohydrates which serve as the basis of life for all plants and other organisms dispensing on plants. They serve as the producers of the primary source of energy for plants. They act as the driving cycle for the growth and development of plants. They also play a key role in carbon dioxide recycling and turn to protect the environment.
