Advanced Placement (AP) Biology Practice Exam

What type of cellular work involves muscle contractions?

1. Transport work

2. Chemical work

3. Mechanical work

4. Thermal work

The correct answer is: Mechanical work

Muscle contractions are a prime example of mechanical work. This type of work is associated with movement and physical change in position or configuration, which is precisely what occurs when muscles contract. When muscle fibers are activated, they generate force that results in the movement of bones and, ultimately, the entire body. This mechanical action is governed by the interaction of proteins such as actin and myosin within the muscle cells, utilizing energy derived from ATP (adenosine triphosphate) to facilitate this contraction. Transport work, on the other hand, involves the movement of substances across membranes, such as the transport of ions or molecules in and out of cells. Chemical work typically refers to processes that involve the transformation of substances and the synthesis of macromolecules, rather than physical movement. Thermal work relates to heat generation and energy transfer, which is not directly associated with muscle contractions. Understanding this distinction highlights why mechanical work is the most accurate representation of the energy involved during muscle contractions.