Cell-to-cell communication (gap junctions, plasmodesmata) Transitional Reasoning Practice

Questions

1. 1.

   A researcher microinjects a small fluorescent tracer with a molecular mass of 400 Da into a single animal epithelial cell and a single plant mesophyll cell, observing rapid diffusion of the dye into immediately adjacent cells in both tissue types. Subsequent ultrastructural examination confirms that the channels mediating this intercellular transport in the plant tissue feature continuous plasma membranes and an internal tubular endomembrane strand, which are absent in the animal channels. Based on this investigation, which statement accurately contrasts the functional architecture of these direct cell-to-cell communication channels?

   • A) Both junction systems are composed of concentric rings of connexin proteins that physically fuse the outer lipid leaflets of adjacent plasma membranes into a shared bilayer.
   • B) While both junctions permit the passage of small cytosolic molecules, plasmodesmata uniquely maintain plasma membrane continuity and contain an internal desmotubule, unlike protein-lined animal gap junctions.
   • C) Gap junctions facilitate the unrestricted exchange of large cytosolic proteins and organelles, whereas plasmodesmata are rigidly limited to the transport of monovalent inorganic ions.
   • D) Plasmodesmata connect adjacent protoplasts across fluid extracellular spaces without traversing a cell wall, preventing any physiological regulation of their pore aperture.

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