*The Mystery Story: The Secret of the Missing Oxygen** During gym class, Sami suddenly felt dizzy. He wasn’t sick—but he couldn’t stand properly. He closed his eyes… And when he opened them, he was inside an air tunnel. A sign in front of him read: Respiratory System – Emergency Situation ✦✦✦ ? The Mystery Begins A transparent figure greeted him. — I’m Dr. Oxygen. We have a problem: oxygen is entering—but it’s not being used. Sami walked through the trachea. He noticed it was supported by rings of cartilage. — So it doesn’t collapse, — the doctor explained. They reached the lungs. — The right lung is larger, — Sami observed. — Because the heart occupies part of the left side, — replied the doctor. ✦✦✦ ? The Clues: The Alveoli They entered an area filled with tiny bubble-like structures. — These are the alveoli, — said the doctor. — Their walls are extremely thin. Sami saw blood capillaries surrounding them. — This is where gas exchange happens: oxygen enters the blood, and carbon dioxide leaves it. But something was wrong. — The alveoli aren’t fully expanding! ✦✦✦ ? The Smart Connection Sami thought carefully. — If breathing is fast and shallow, the alveoli won’t fill properly. The doctor smiled. — Exactly. The child was anxious and breathing too quickly. The doctor said: — Try slow, deep breathing. The alveoli filled completely… And the blood became rich with oxygen again. ✦✦✦ ?️ Mystery Solved Sami found himself back in the schoolyard. He was breathing deeply—no dizziness at all. He