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 necessary to generate the high pressure required to pump oxygenated blood throughout the body.

To dissect a mammalian heart, I first identified the dorsal and ventral sides, ensuring the ventral side was facing up. I placed the heart on a board, using a scalpel to carefully cut through the pericardial sac and opened the heart to view the internal structure. I ensured to wear safety goggles and gloves for protection throughout the dissection.

The diagram should illustrate both the bicuspid valve located between the left atrium and left ventricle, as well as the tricuspid valve between the right atrium and right ventricle. Each valve should be properly labelled to highlight their structures.

To expose the semilunar valve, I either cut the aorta or the pulmonary artery at their base, allowing visibility of the valve structure beneath.

The function of a semilunar valve is to prevent the backflow of blood into the ventricles. It allows blood to flow from the ventricles into either the aorta or the pulmonary artery during contraction and closes to keep blood from returning during relaxation.

In the dissection, I found the origin of the coronary artery at the aorta, near the semilunar valve, where it branches off to supply blood to the heart muscle itself.