Across
1
Force that attracts objects together
3
Basic unit of life
4
Center of an atom or cell
8
Magnetic metallic element
11
Natural satellite of Earth
12
Compound containing oxygen
Down
2
Nerve cell in the brain
5
Biological catalyst
6
Reddish electrical conductor
7
Chemical element in table salt
9
Icy body with a tail near the sun
10
Positive particle in nucleus
13
Preserved remains of ancient life