Why is it necessary for a plant to convert the energy of the sun into energy it can use?

Plants are autotrophs, meaning they have to make their own food. Plants rely on the conversion of solar energy into chemical energy to obtain the food they need. This process is called photosynthesis. Plants must take in carbon dioxide and water. They use energy from the sun to convert carbon dioxide and water into glucose and oxygen. Plants release oxygen as a waste product. They can then use and store the glucose as their food source. Glucose can be converted into starch (long-term storage). Glucose and starch can then be converted into other substances such as cellulose (for cell walls) and proteins (for growth and repair). For photosynthesis to happen, it must be light out. Photosynthesis cannot happen in the dark. Humans rely on plants because we breathe in the oxygen they release. With that oxygen, we in turn do cellular respiration.