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.
The answer is the apoplast, the symplast, and the transmembrane pathway.
1. The apoplast pathway occurs through cell walls and space between cells. So, water does not cross any cell membrane as it travels this pathway.
2. The symplast pathway occurs through the continuum of cytoplasm. So, water travels through plasmodesmata which connect cells.
3. The transmembrane pathway occurs across cell membranes. So, water enters the cell on one side of the membrane and exits on the other.
