Plants produce glucose through the process of photosynthesis. In this process, green plants consume carbon dioxide and water, and in the presence of sunlight, produce glucose and oxygen. The relevant chemical equation can be written as:
`6CO_2 + 6H_2O + sunlight -> C_6H_12O_6 + 6O_2`
This is the primary process for the production of glucose (C6H12O6). Since sunlight is used up in this process, we can also state that plants convert light energy into chemical energy by photosynthesis. This process can only take place during the sunlight hours.
Some of the glucose generated here is broken down in the presence of oxygen into carbon dioxide and water in the process of cellular respiration. The breakdown of glucose is accompanied by the generation of ATP molecules, which are energy molecules.
Most organisms are dependent on plants, and therefore the process of photosynthesis, for food and oxygen.
Hope this helps.