Across
1
Biological catalyst
4
Center of an atom or cell
5
Gas form of a liquid
6
Infectious microscopic agent
11
Icy body with a tail near the sun
12
Substance with pH below 7
13
Path of a planet around the sun
14
Element found in all living things
Down
2
Nerve cell in the brain
3
Disturbance that transfers energy
7
Preserved remains of ancient life
8
Force that attracts objects together
9
Ball of burning gas in space
10
Solid with repeating atomic pattern
15
Unit of energy