Which law states energy can't be created or destroyed, only changed into another form?

• A. Second Law of Thermodynamics
• B. Entropy
• C. First Law of Thermodynamics
• D. Metabolism

Answer: (C)

Energy cannot be created or destroyed; it can only be transformed from one form to another. This principle, the law of energy conservation, is the idea being tested. In biological systems, energy flows and changes form all the time: light from the sun is captured and stored as chemical energy in plants during photosynthesis, then that chemical energy is transferred through food chains as organisms eat, or metabolize, it, and some energy is eventually released as work or heat. The total amount of energy remains the same even as its form changes.

This is different from ideas about entropy, which describe how energy becomes more spread out or less available to do work over time. Entropy is a measure tied to disorder and the direction of processes, not a statement about whether energy can be created or destroyed. Metabolism describes the actual chemical reactions that cells use to move energy around and build or break down molecules; it’s about processes, not the universal accounting rule of energy conservation.