During muscle contraction, which molecule stores energy that is used to power the myosin heads?

Correct Answer: A

Rationale: ATP (adenosine triphosphate) provides the energy for muscle contraction by binding to myosin heads, allowing them to detach from actin and re-cock for another pull. Glucose is a fuel source, oxygen supports aerobic respiration, and lactic acid is a byproduct, making 'ATP' the correct answer.

Correct Answer: B

Rationale: Carpals and tarsals are short bones, roughly equal in length and width, providing stability and flexibility in wrist and ankle joints. They are not irregularly shaped (like vertebrae) but are classified as short, making 'Short bone' the correct answer despite the question’s phrasing.

Correct Answer: B

Rationale: In the sliding filament theory, ATP binds to myosin heads, causing them to detach from actin after a power stroke. This allows the cycle to repeat. Calcium initiates binding, acetylcholine triggers the process indirectly, and sodium is unrelated, making 'ATP' the correct answer.

Correct Answer: A

Rationale: Joints are classified by movement: immovable (e.g., skull sutures), slightly movable (e.g., vertebrae), and freely movable (synovial). Hinge joints (e.g., elbow) allow bending in one plane, and ball-and-socket joints (e.g., shoulder) permit multi-directional movement—both are correct per the document. Fixed joints don’t move, cartilage joints are slightly movable, and tendon joints aren’t a category, making 'hinge joints' a correct choice (noting ball-and-socket is also valid).

Correct Answer: A

Rationale: Flat bones, such as the scapula and cranial bones, are thin, broad, and plate-like, offering protection (e.g., skull) and muscle attachment surfaces. Irregular bones are complex, long bones are cylindrical, and short bones are cube-like, making 'flat' the correct answer.