With the understanding that arteries take blood away from the heart, veins bring blood back to the heart, and capillaries are the juncture vessels through which blood-borne substances can diffuse, challenge the students to answer the questions:
- “What is the main destination of the blood that flows through arteries away from the right ventricle and the left ventricle of the heart?”
- “What is the main origin of the blood that flows through veins and enters the right ventricle and the left ventricle of the heart?”
The entire class should review a diagram of the circulatory system. Make special note of the diagram’s coloring of the blood filed vessels. Vessels colored in red contain oxygenated (oxygen-carrying) blood, while vessels colored in blue are deoxygenated. Ask the students to answer the following question:
- “What is blood composed of?”
By making a list of all of the things that they believe to constitute blood, students should eventually organize their answers on the front board into the main two components of blood:
- Cellular component: RBCs (Red Blood Cells), WBCs (White Blood Cells) and Platelets
- Non-cellular component: Nutrients (including water), oxygen, carbon dioxide, plasma proteins, other wastes like urea, hormones, electrolytes, etc.
Review the importance of oxygen, asking the students:
- “Why is oxygen so important to the body?” and/or
- “What does the body do with the oxygen that you inhale?”
Allow the students’ answers to reveal that oxygen is needed by all body cells for a special process (cellular respiration), which produces most of the body’s energy.
Assist the students to understand that oxygen is obtained by red blood cells at the capillaries of the lungs and then carried to the capillaries of all organs/body parts so that it can be delivered to all cells. Additionally, review that carbon dioxide is a by-product gas that is produced by all cells, but toxic to the body if not removed through the lungs.