Final answer:
Junctional complexes facilitate paracellular transport, which allows substances to move between cells passively along their concentration gradient, rather than through transcellular pathways involving the cell membrane.
Step-by-step explanation:
Junctional complexes allow for paracellular transport. This type of transport refers to the movement of substances through the tiny spaces between cells, rather than directly through the cell membranes (transcellular transport). Junctional complexes are structures in the cell membrane that seal cells together in a tissue, forming a barrier but still allowing small molecules and ions to passively move along their concentration gradients between the cells.
It is distinct from other forms of transport such as active transport, where substances move across a cell membrane against their concentration gradient with the use of energy, and facilitated diffusion, which involves the use of carrier proteins in the cell membrane to move substances down their concentration gradients.
In summary, paracellular transport facilitated by junctional complexes is a critical aspect of cellular functioning that allows for selective movement of substances between cells in a tissue.