Trace each arrow and name what moves. Air travels in airways, while blood travels in blood vessels. At lung air sacs oxygen enters blood and carbon dioxide leaves blood. Follow the blood loop: lungs, left heart side, body, right heart side, lungs. The heart boxes show parts of one organ, not two hearts.
Worked example
If a label says blood returning from the body goes straight to the outside air, it needs repair. Blood goes through the right heart side to the lungs; carbon dioxide then crosses into the air sacs and is breathed out.
Four cards, one connected route
A class has four cards: lungs, left heart side, body, and right heart side. A student draws arrows from lungs to left heart side, then to body, then to right heart side, and back to lungs. Another student claims the two heart cards mean two separate hearts. Check each claim using functions and directions, not card color. This is a paper model, not a health test. Do not hold your breath or collect personal measurements.