respiration in organism

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Across
  1. 2. Tiny air sacs in lungs where gas exchange happens (8 letters)
  2. 4. Organism that breathes through skin (9 letters)
  3. 5. Gas produced during respiration (13 letters)
  4. 7. Gas taken in by humans during breathing (6 letters)
Down
  1. 1. Process of breaking down food to release energy (11 letters)
  2. 3. Organ in humans responsible for gas exchange (4 letters)
  3. 6. A gas which we use to breathe (6 letters)