Across
1
Substance with pH above 7
4
Element found in all living things
5
Precious yellow metallic element
7
Center of an atom or cell
8
Our home planet
10
Mass per unit volume
Down
2
Force that attracts objects together
3
Gas essential for breathing
6
Magnetic metallic element
9
Icy body with a tail near the sun
11
Ball of burning gas in space
12
Group of similar cells