Name of the process when plants respire at night?

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The process by which plants respire at night is called respiration. This process also takes place during the day time (it's just that we do not concentrate on it during the daytime). In fact, respiration is a continuous process. During the daytime, plants convert the light energy of sun into chemical energy (along with generation of oxygen and consumption of carbon dioxide) through the process of photosynthesis. The organic molecules formed during this process are consumed during the process of respiration, in which plants consume oxygen and produce carbon dioxide and water, along with energy (in the form of ATP molecules). Energy is required for the plant's growth, maintenance and other activities and is a constant necessity. Hence, respiration is a constant process, irrespective of light availability. It is only that during the daytime, photosynthesis ensures that plants are net producers of oxygen (produces more oxygen than respiration can consume), while at night, the absence of photosynthesis means that plants are net producers of carbon dioxide. This is why we focus on the respiration of plants at night.

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How do plants respire at night?

Plants have a series of light-dependent and light-independent reactions to respire. In the absence of light (at night), plants must rely on their light-independent reactions to respire.

The light-independent reactions involve carbon fixation and the Calvin cycle.

The light-independent reactions take place in the stroma of the chloroplasts. The first reaction involves a five-carbon sugar called ribulose biphosphate (RuBP). RuBp is also a product of this reaction. Therefore, this reaction is a cycle: the Calvin Cycle.

Carbon dioxide enters the stroma of chloroplast by diffusion. In the stroma, it combines with RuBP in a carboxylation reaction, which is catalyzed by the enzyme ribulose biphosphate carboxylase, or rubisco. The product of the reaction is a six carbon compound which then splits to form two molecules of glycerate 3-phosphate, the first product of carbon fixation.

While one out of every six glycerate 3-phosphates are used to regenerate RuBP for the Calvin Cycle again, the remaining 5/6 glycerate 3-phosphates are reduced using energy from ATP and hydrogen ions from NADPH (which are produced by light-dependent reactions and stored). The glycerate 3-phosphates, through the reduction reaction, are reduced to a three-carbon sugar, triose phosphate, which link together to produce glucose phosphate, which forms starch (the storage form of energy as carbohydrates in plants) in the stroma by condensation.

Through these light-independent reactions, plants respire and generate energy when in the absence of light.

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