Across
1
Tectonic landmass section
4
Unit of force
7
Basic unit of life
8
Substance with pH below 7
9
Center of an atom or cell
12
Infectious microscopic agent
Down
2
Path of a planet around the sun
3
Second lightest element
5
Biological catalyst
6
Blocking of light by a celestial body
7
Element found in all living things
10
Magnetic metallic element
11
Gas essential for breathing