Based on this illustration, match the right description with the left numbered muscle.

In order for a muscle contraction to occur, cross-bridges must form between which one of the following structures within a myofibril?

Which one of the following statements correctly describes the activities of muscles? 

The movement of actin and myosin fibers in a muscle contraction contains all of the following steps EXCEPT

Most digestion in humans occurs in the first 25 centimeters of the 6-meter length of the small intestine called the ________.

Each nephron of the kidney consists of a long tubule and associated small blood vessels. Blood cells and plasma proteins are too large to enter with the glomerular filtrate. What is the correct path for the filtrate to follow through the nephron in the production of urine?

The ____________ valve guards the opening between the pulmonary artery and the right ventricle.

Which of the following statements regarding gas exchange is true?

The large number of alveoli in lungs improve gas exchange by ________.

The ____________ valve guards the opening between the left atrium and left ventricle.