Across
1
Basic unit of life
3
Gas essential for breathing
4
Mass per unit volume
7
The Red Planet
9
Ball of burning gas in space
Down
2
Preserved remains of ancient life
5
Substance with pH above 7
6
Substance with pH below 7
8
Nerve cell in the brain
10
Biological catalyst
11
Amplified beam of light
12
Group of similar cells
13
Gas form of a liquid