Fill in the blanks.
12. _________are the basic units of structure and function in living things
13. A(n)__________is a group of similar cells that perform a specific function in an organism.
14. __________are nerve cells that carry response information to muscles and organs.
15. Carbon dioxide and________ are outputs of cellular respiration.
16. __________is essential to living things because many of the chemical reactions that occur in living things require it.
17. scientists did not discover the cell until the__________ was invented because cells are too small to see without one.