Across
1
Mass per unit volume
4
Basic unit of life
5
Nerve cell in the brain
8
Glass that splits light into spectrum
10
Particle of light
Down
2
Unit of force
3
Gas essential for breathing
6
The Red Planet
7
Our home planet
9
Element found in all living things
11
Ball of burning gas in space
12
Second lightest element
13
Measure of matter in an object