Across
1
Curved glass that refracts light
3
Force that attracts objects together
5
Center of an atom or cell
6
Nerve cell in the brain
9
Second lightest element
10
Tissue that contracts for movement
11
Unit of energy
13
Compound containing oxygen
Down
2
Our home planet
4
Element found in all living things
7
Chemical element in table salt
8
Absolute temperature scale unit
12
Natural satellite of Earth