Across
1
Curved glass that refracts light
4
Mass per unit volume
5
Smallest unit of an element
6
Compound containing oxygen
10
Unit of heredity
12
Solid with repeating atomic pattern
13
Form of thermal energy
Down
2
Second lightest element
3
Tissue that contracts for movement
7
Ball of burning gas in space
8
Nerve cell in the brain
9
Biological catalyst
11
Tectonic landmass section