Across
1
Substance with pH above 7
3
Hottest planet in solar system
4
Ball of burning gas in space
6
Icy body with a tail near the sun
8
Nerve cell in the brain
9
Biological catalyst
Down
2
Element found in all living things
3
Infectious microscopic agent
5
Tissue that contracts for movement
7
Group of similar cells
10
Preserved remains of ancient life
11
The Red Planet
12
Positive particle in nucleus