The phenomenon described by the conservation of energy is known as the first law of thermodynamics. This principle states that energy cannot be created or destroyed, only transformed from one form to another. In a closed system, the total energy remains constant over time, which is foundational in various fields, including physics and chemistry. It underscores the principle that energy transformations, such as during metabolic processes in living organisms or physical changes in the environment, adhere to this law, illustrating the interconnectivity of energy flow in nature.