Final answer:
Epithelial tissue cells are bound by tight junctions, which are watertight seals formed by proteins, allowing them to cover body surfaces and line internal organs, preventing leakage of materials between cells.
Step-by-step explanation:
The animal cell type bound by tight junctions and forming sheets that cover body surfaces and line internal organs is the epithelial tissue. These specialized cells are held tightly together by proteins, which include claudins and occludins, to form watertight seals known as tight junctions. This structure is crucial as it prevents the leakage of materials between cells. For instance, tight junctions in the epithelial cells of the urinary bladder ensure that urine does not leak into the extracellular space. Similarly, epithelial tissues with tight junctions line the gut, preventing the leakage of food materials into the body.