Across
1
Ball of burning gas in space
2
Biological catalyst
3
Preserved remains of ancient life
5
Compound containing oxygen
7
Chemical element in table salt
11
Center of an atom or cell
12
Fourth state of matter
Down
2
Blocking of light by a celestial body
4
Measure of matter in an object
6
Gas form of a liquid
8
Group of similar cells
9
Basic unit of life
10
Tissue that contracts for movement
13
Gas essential for breathing