Biology crossword

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Across
  1. 3. 21% of the air is made up of this gas
  2. 5. offers structure to the cell
  3. 6. a layer of cells that work together to perform a specific function
  4. 7. where respiration takes place
  5. 10. a group of organs that work together to perform a certain function
  6. 11. what we are 18% of
  7. 12. site of protein synthesis
  8. 14. protects our body from infection
  9. 16. a place inside the cell which is empty of cytoplasm
  10. 17. produces energy through photosynthesis
  11. 19. the smallest unit that can live on its own
Down
  1. 1. where most of the chemical reactions take place
  2. 2. carries oxygen to the rest of our bodies
  3. 3. a collection of tissues with a specific function
  4. 4. something which has many parts that function together as a whole
  5. 8. transmits signals to the brain
  6. 9. what controls the cell
  7. 13. a subcellular structure with a specific job in the cell
  8. 15. the liquid that circulates in the arteries and veins
  9. 18. provides surface area for chemical reactions to take place