9. (a) (i) Cardiac muscle may be described as a **contractile** tissue - Leaving Cert Biology - Question 9 - 2004

The left ventricle has the greatest amount of muscle in its wall. This is because it must generate a substantial amount of force to pump oxygenated blood to the entire body, unlike the other chambers which pump blood only to nearby structures.

To dissect a mammalian heart, first, identify the anterior and posterior sides. Begin by placing the heart on a cutting board with the ventral side facing up. Use scissors to make an incision along the atria and ventricle walls to observe the internal structure. Be sure to maintain safety procedures by wearing gloves and goggles throughout the dissection.

A clear diagram should be drawn to depict the four chambers of the heart, indicating the bicuspid valve located between the left atrium and left ventricle, as well as the tricuspid valve situated between the right atrium and right ventricle. Ensure both valves are clearly labelled for identification.

To expose a semilunar valve, first cut the aorta or the pulmonary artery. This incision allows for easy access to the base of the heart where these valves are located. Be cautious to follow anatomical landmarks during this procedure.

The function of a semilunar valve is to prevent the backflow of blood into the ventricles after it has been pumped into the aorta or pulmonary artery. This ensures that blood flows in one direction, maintaining efficient circulation.

In the dissection, the origin of the coronary artery was found at the base of the aorta, near the semilunar valves. This location is crucial as the coronary arteries supply blood to the heart muscle itself.