Question

the respiratory and circulatory systems tutorial
improve the students model of gas exchange by drawing the missing component.
gas exchange
oxygen (o₂)
carbon dioxide (co₂)
red blood cells

Explanation:

The missing component in the gas exchange model is the capillaries (tiny blood vessels surrounding lung alveoli). This is where the key gas exchange occurs: oxygen from the lungs moves into the capillaries to bind with red blood cells, and carbon dioxide from red blood cells moves out of the capillaries into the lungs to be exhaled. The model currently shows the lungs and red blood cells but lacks the capillary interface that connects these two for gas transfer.

Answer:

The missing component to add is capillaries (tiny blood vessels between the lungs and red blood cells), drawn as a network surrounding the lung structure, linking the lung's gas intake/output to the red blood cells for oxygen and carbon dioxide exchange.