Science Fair Crossword Puzzle!

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Across
  1. 2. This force is always acting upon us...
  2. 4. A system of the environment and its organisms
  3. 6. Atomic mass of 108
  4. 8. From solid to liquid
  5. 9. Organ of the digestive system that produces enzymes
  6. 12. Measurement of the length of a wave
  7. 15. Low on the pH scale
  8. 16. An apple fell on his head
  9. 18. Negative charges in an atom
  10. 19. Atomic number of 20
Down
  1. 1. The process of cell division
  2. 3. Unit of measurement for temperature (SI)
  3. 5. The powerhouse of the cell!
  4. 7. What happens when too equal charges get near each other
  5. 10. Coldest planet in the solar system
  6. 11. The ability to reflect sunlight
  7. 13. Device to measure current in a circuit
  8. 14. Living organisms
  9. 17. The unit of energy