Respiratory System - Crossword

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Across
  1. 3. Main organ of the respiratory system
  2. 4. Tiny sacs within the lungs where gaseous exchange occurs
  3. 6. Allows air to enter and leave the body
  4. 9. Muscle located under the lung
  5. 11. Tubes which leads from windpipe to each lung
Down
  1. 1. Letting air out of the lungs
  2. 2. Taking air into the lungs
  3. 5. The process of producing energy using sugar and oxygen
  4. 7. Bone structure which protects the heart and lungs
  5. 8. Filters the air we inhale and branches into the air tubes
  6. 10. A substance that moistens the air as well as trapping foreign substances