Across
1
Natural satellite of Earth
3
Path of a planet around the sun
4
Substance with pH below 7
6
Our home planet
8
Disturbance that transfers energy
10
Biological catalyst
12
Second lightest element
Down
2
Element found in all living things
5
Fourth state of matter
7
Unit of force
9
Amplified beam of light
11
Nerve cell in the brain
13
Basic unit of life