Respiratory System - Crossword

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