The symbol used to measure energy inside a cell is Δ G, which represents the change in Gibbs free energy. Gibbs free energy is crucial in biological systems because it indicates the spontaneity of a reaction and the energy available to do work within the cell. A negative Δ G indicates that a reaction can occur spontaneously and is often associated with exergonic reactions, which release energy.
In cellular processes, such as metabolism, Δ G helps determine whether the reactions will proceed in the forward direction or reach equilibrium. Understanding Δ G allows biologists to predict how cells will respond to changes in conditions such as temperature, pH, and concentration of reactants and products, reflecting the cell's energy status and facilitating cellular decision-making in terms of resource allocation and regulation.
Other options reflect different aspects of thermodynamics but are not specifically used to measure energy available for cellular work. For instance, Δ H represents the change in enthalpy or heat content, Δ E denotes the total energy change in a system, and Δ S refers to the change in entropy or disorder. While these concepts are interconnected in the context of thermodynamics, Δ G is the most pertinent when considering energy measurement related directly to cellular functions.