Law would be the correct answer to fill in the blank. Law is correct because scientific law explains behaviors of natural phenomenons since it's based on repeated experiments.
In this question in which is the major source then of free oxygen in the earth's Proterozoic atmosphere is being produce by the evaporation of the ocean water. Hope this answer would be of big help to this assignment then.
Organ is an organism that is a collection of tissues and it perform a specific functions.It is found in the higher biological systems like plants, animals, and human beings. While the organelle is a part of a cell that specialized units and capable of performing a specific function for the cell. It is a very small subunits inside a cell.
