Across
1
Form of thermal energy
3
Particle of light
4
Substance with pH below 7
5
Natural satellite of Earth
6
Biological catalyst
7
Element found in all living things
11
Force that attracts objects together
12
The Red Planet
Down
1
Second lightest element
2
Compound containing oxygen
3
Tectonic landmass section
8
Mass per unit volume
9
Molten rock beneath Earth surface
10
Group of similar cells
13
Unit of energy