Which types of cell junctions are needed in a mucosal membrane, such as the digestive tract, to keep the digestive enzymes, juices, and bacteria from leaking out?

The plasma membrane of the adjoining cells is generally distinguished by the extracellular fluids, which permit conduction of wastes and nutrients to and from the bloodstream. However, in some kind of tissues, the membranes of the adjoining cells may combine and form a junction.  

Tight junctions are found in the cells lining of the digestive tract, where the materials are needed to go through the cells (rather than the intercellular spaces) to infiltrate the bloodstream, these junctions entirely envelopes each cell, inhibiting the movement of substances amid the cells.  

d. organisms have cells with different shapes and functions.