Across
1
Gas essential for breathing
4
Magnetic metallic element
6
Element found in all living things
7
Smallest unit of an element
11
Unit of energy
Down
2
Nerve cell in the brain
3
Substance with pH above 7
5
Force that attracts objects together
6
Basic unit of life
8
The Red Planet
9
Icy body with a tail near the sun
10
Unit of heredity
12
Our home planet