Now carrying oxygenated blood students enter the Left Atrium and are ready to begin the circulatory cycle again. Once everyone seems to have the idea, tell the students they are going to have a relay race to see which group can complete the relay in the shortest amount of time. Explain that from the moment the heart begins beating until it stops, the heart works tirelessly, without ever pausing to rest. The average heart muscle will contract and relax about 70 to 80 times a minute. It takes one blood cell approximately 20 seconds to complete the journey through the circulatory system.
Blood cells go exactly where they are needed most in the body without ever stopping.
Students should be prepared to take on the role of a blood cell and know exactly where to travel in the circulatory system. Have one group of 5 students demonstrate. One student must go through the entire circulatory system before the next blood cell may continue. Begin timing with a stop watch with the first student starting from the left ventricle, and end timing when the last student reenters the left atrium from the heart. If each blood cell only takes 20 seconds to complete the circuit a group should be able to complete the process in about 1 minute and 20 seconds.