Final answer:
Among the given options, the Proximal Convoluted Tubule (PCT) of the kidney is considered a transport epithelium, which is made up of simple cuboidal cells that actively transport solutes. So, the correct answer is option c.
Step-by-step explanation:
The question seeks to identify which option represents a transport epithelium. Transport epithelia are specialized cells that facilitate the selective movement of substances from one side to another. For example, they may be involved in the absorption of nutrients or the secretion of waste products.
Proximal Convoluted Tubule (PCT) of the kidney is the best example of transport epithelium among the given options. The PCT is composed of simple cuboidal cells with prominent microvilli that increase the surface area for absorption and secretion. These cells actively transport solutes, such as sodium (Na+), chloride (Cl-), and glucose, across their membranes and thus require a high concentration of mitochondria to produce ATP for energy.
On the other hand, the other options like the porocytes of a sponge, the longitudinal muscles of the digestive tract, and the myenteric plexus do not fit the definition of transport epithelium. Porocytes are involved in water flow, not solute transport; the longitudinal muscles facilitate movement, and the myenteric plexus is a part of the nervous system regulating digestive tract motility.