1. Active Transport: Moving molecules across a cell membrane against their concentration gradient. This means moving molecules from an area of low concentration to an area of high concentration, which requires energy to overcome the natural tendency for molecules to move from high to low concentration. Think of it like pushing a ball uphill – you need to put in work (energy) to move it against gravity.

2. Muscle Contraction: The shortening of muscle fibers, which allows for movement. This process involves the interaction of proteins (actin and myosin) that require energy to slide past each other, causing the muscle to contract.

3. Protein Synthesis: The creation of new proteins from amino acids. This complex process involves reading genetic information (DNA) and using that information to assemble the correct sequence of amino acids into a functional protein. This requires energy to create the bonds between amino acids and to maintain the intricate machinery of protein synthesis.