b22

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Across
  1. 2. Nutrient usage
  2. 6. Oxygen-free
  3. 8. Waste elimination
  4. 12. Light-based food making
  5. 14. Plant-eating animal
  6. 16. Meat-eating animal
  7. 18. Growth-restricting
  8. 19. Dead-matter feeder
  9. 20. Trophic structure
Down
  1. 1. Light-absorbing compound
  2. 3. Oxygen-using
  3. 4. Decaying material
  4. 5. Nutrient uptake
  5. 7. Survival necessity
  6. 9. Mixed diet animal
  7. 10. Cellular energy release
  8. 11. Anaerobic energy process
  9. 13. Energy transfer path
  10. 15. Undigested waste removal
  11. 17. Total living mass