Across
1
Natural satellite of Earth
4
Ball of burning gas in space
5
Push or pull on an object
7
Center of an atom or cell
8
Compound containing oxygen
10
Nerve cell in the brain
Down
2
Element found in all living things
3
Gas essential for breathing
6
Tissue that contracts for movement
7
Unit of force
9
Particle of light
11
Preserved remains of ancient life
12
Positive particle in nucleus
13
Substance with pH below 7