biology

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Across
  1. 2. light
  2. 8. species largely depend on
  3. 10. relating to earth
  4. 12. no sunlight
  5. 14. cold
  6. 16. harmful effect
  7. 17. warming hot earth
  8. 18. species invade
  9. 19. classified
  10. 20. salt freshwater
Down
  1. 1. group of people
  2. 3. harmful substance
  3. 4. species' first colonizers
  4. 5. trees
  5. 6. combined food chains
  6. 7. species nowhere else
  7. 9. too many people
  8. 11. symbiotic relationship
  9. 13. variety
  10. 15. biome water