Crossword

12345678
Across
  1. 5. Gas we breath out
  2. 7. Number of lungs we have
  3. 8. What we produce when we exercise
Down
  1. 1. Gas we breath in
  2. 2. What are our lungs used for
  3. 3. Source of Oxygen
  4. 4. What pumps blood around the body
  5. 6. What happens to our heart rate during exercise