Across
1
Particle of light
3
Substance with pH below 7
6
Infectious microscopic agent
7
Second lightest element
8
Our home planet
11
Unit of heredity
13
Smallest unit of an element
Down
2
Preserved remains of ancient life
4
Element found in all living things
5
The Red Planet
9
Reddish electrical conductor
10
Unit of force
12
Path of a planet around the sun