Endothermic reactions are chemical processes that absorb heat from their surroundings. This means that the temperature of the environment decreases as the reaction occurs. Common examples include the dissolution of ammonium nitrate in water and the process of photosynthesis in plants, where sunlight is absorbed to convert carbon dioxide and water into glucose and oxygen. In these reactions, energy is required to break bonds in the reactants, leading to a net intake of energy. The absorbed heat is often measured in calories or joules, and understanding endothermic reactions is essential in fields like chemistry and thermodynamics.