SAT Subject Biology Practice Question 191: Answer and Explanation
1. The diagram shows the muscles involved in extending the arm. Which actions result in this movement?
A. Muscle 1 relaxes while muscle 2 contracts.
B. Muscle 1 contracts while muscle 2 relaxes.
C. Muscle 1 contracts, and then both muscles relax.
D. Muscle 1 and muscle 2 both relax the same time.
E. Muscle 1 and muscle 2 both contract at the same time.
Correct Answer: A
Voluntary muscle movements are carried out by the contraction and relaxation of opposing muscles. To carry out the movement shown, the triceps muscle (2) must contract while the biceps (1) relaxes.