When you eat food, glucose gets absorbed from your intestines and distributed by the bloodstream to all of the cells in your body. Your body tries to keep a constant supply of glucose for your cells by maintaining a constant glucose concentration in your blood -- otherwise, your cells would have more than enough glucose right after a meal and starve in between meals and overnight. So, when you have an oversupply of glucose, your body stores the excess in the liver and muscles by making glycogen , long chains of glucose. When glucose is in short supply, your body mobilizes glucose from stored glycogen and/or stimulates you to eat food. The key is to maintain a constant blood-glucose level.
The energy source of photosynthesis is the sun, the unique and central star of our solar system. In photosynthesis, solar energy is transformed into chemical energy, the energy of the chemical bonds of the produced glucose molecules (and of the molecular oxygen released). The energy of glucose is then stored as starch (a glucose polymer) or it is used in the cellular respiration process and transferred to ATP molecules. ATP is consumed during metabolic processes that require energy (for example, in active transport across membranes).