Final answer:
The pulmonary valve prevents backflow of deoxygenated blood into the right ventricle and is composed of three pocket-like cusps without the chordae tendineae or papillary muscles.
Step-by-step explanation:
The pulmonary valve prevents backflow of deoxygenated blood into the right ventricle when the heart is relaxed. This valve, located at the base of the pulmonary trunk emerging from the right ventricle, is made up of three semilunar cusps, which are essentially pocket-like flaps that close when filled with blood during ventricular relaxation. The closure prevents the oxygen-poor blood that's on its way to the lungs from re-entering the heart chamber.
Contrastingly, the sound generally associated with heart valves closing is not from the pulmonary valve but from the atrioventricular valves (such as the tricuspid and mitral valves) during the first heart sound. Also, the pulmonary valve does not have chordae tendineae or papillary muscles, which are structures present in the atrioventricular valves. These are important distinctions because chordae tendineae are tendon-like fibres that anchor the leaflets of the atrioventricular valves to the heart muscles to prevent them from inverting, while the semilunar valves naturally close due to pressure differences without the need for these cords.