Across
1
Mass per unit volume
4
Tissue that contracts for movement
8
Unit of energy
10
The Red Planet
11
Substance with pH below 7
13
Smallest unit of an element
Down
2
Our home planet
3
Chemical element in table salt
5
Positive particle in nucleus
6
Ball of burning gas in space
7
Disturbance that transfers energy
9
Center of an atom or cell
12
Substance with pH above 7