Question

which of these cell junctions form a barrier to the passage of materials?
plasmodesmata
tight junctions
keratin fibers
desmosomes (anchoring junctions)
gap (communicating) junctions

Explanation:

Tight junctions seal adjacent epithelial cells together, preventing the passage of materials between them. Plasmodesmata are channels in plant cells for communication. Keratin fibers are structural proteins, not cell - junctions for material - barrier. Desmosomes are for cell - cell adhesion. Gap junctions allow the passage of small molecules between cells.

Answer:

B. tight junctions