Across
1
Gas essential for breathing
5
Path of a planet around the sun
6
Basic unit of life
7
Chemical element in table salt
8
Hottest planet in solar system
9
Nerve cell in the brain
11
Group of similar cells
Down
2
Force that attracts objects together
3
Blocking of light by a celestial body
4
Positive particle in nucleus
10
Fourth state of matter
12
Our home planet