During respiration, a seed metabolizes sugars. what is the source of the sugar metabolized by the seed?

The source of the sugar metabolized by the seed is photosynthesis.  

The procedure used by plants to transform light energy into a chemical form of energy is known as photosynthesis. The chemical energy can afterward be discharged to fuel the plants to perform their activities.  

During photosynthesis, carbon dioxide and water can be combined in the existence of chlorophyll and sunlight to generate oxygen and glucose (carbohydrates). However, the prime component generated in the procedure is glucose (sugar) that is the molecule, which generates energy to mediate the activities of the cell.  

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