Usable chemical energy on earth begins as light energy, usually solar energy. plants and other autotrophs convert solar energy to chemical energy via the process of photosynthesis. carbon dioxide and water, in the presence of light, are transformed into glucose. the chemical energy is stored in the chemical bonds of glucose and is released during the process of cellular respiration. cellular respiration releases the chemical energy stored in food molecules to produce high-energy atp molecules. macromolecules such as carbohydrates and fats can be used as fuels for the production of atp. all foods contain chemical energy, but the amount of chemical energy is dependent of the type of food. the larger the compound, the more chemical bonds present and the greater amount of available chemical energy. we can rank molecule size, from smallest to largest, as sugar, starch, fat. we refer to the stored chemical energy in foods as calories. a calorie is the amount of energy required to raise the temperature of 1 gram of water 1 degree celsius. when we refer to the calories in food, we are really talking about kilocalories or 1000 calories. biology students “burned” 2 grams of food to heat water in a calorimeter in order