Across
1
Tissue that contracts for movement
3
Element found in all living things
6
Icy body with a tail near the sun
7
Force that attracts objects together
8
Chemical element in table salt
12
Unit of heredity
14
Unit of energy
15
Our home planet
Down
2
Substance with pH above 7
4
Mass per unit volume
5
Ball of burning gas in space
9
Preserved remains of ancient life
10
Naturally occurring inorganic solid
11
Nerve cell in the brain
13
Center of an atom or cell