Crossword Puzzle

1. vertical columns in the periodic table of elements that signify the number of valence electrons in an element's atom
5. the characteristic of bulging outwards
7. the characteristic of curving inwards
10. the bending of light rays as they pass through a different medium
12. a group of cells that function together to perform a function
14. horizontal rows of the periodic table of elements that signify the total number of electron shells in an element's atom
16. cell division resulting in 2 daughter cells
17. average weather conditions of a region over long periods of time
18. the basic unit of life that makes up all living organisms

2. system a group of organs that function together to perform one or more function
3. one or two letter codes that abbreviate elements of the periodic table of elements
4. environmental conditions of a certain place at a certain time
6. a pure substance that cannot be broken down into simpler substances
8. large geographical region with a defined climate
9. thin layer of Earth that has conditions to support life
11. layer of gases that extend approximately 300 km from Earth's surface
13. number number used to identify an element and represents the number of protons and electrons an element's atom has
15. the reproduction of an object produced by an optical device
19. transparent substance for the purpose of diverging or converging light rays