Across
1
Particle of light
4
Mass per unit volume
6
Second lightest element
7
Amplified beam of light
8
Biological catalyst
13
Nerve cell in the brain
Down
2
Curved glass that refracts light
3
Unit of energy
5
Center of an atom or cell
9
Reddish electrical conductor
10
Absolute temperature scale unit
11
Tissue that contracts for movement
12
Fourth state of matter