Across
1
Force that attracts objects together
3
Particle of light
4
Compound containing oxygen
7
Preserved remains of ancient life
9
Center of an atom or cell
Down
1
Precious yellow metallic element
2
Mass per unit volume
5
Tissue that contracts for movement
6
Gas essential for breathing
8
Group of similar cells
10
Hottest planet in solar system
11
Substance with pH below 7