The correct option is (c).
Explanation
Epithelial tissue (epithelium) forms the covering or lining of both external and internal body surfaces. It acts as a fundamental interface between the body and the external environment, as well as between different internal compartments. Its primary function is to serve as a selective barrier.
Statement 1 is Incorrect:
Epithelial tissue does not prevent any exchange of materials; rather, it facilitates and controls it. While it acts as a protective barrier against pathogens and mechanical injury, it is also the primary site for absorption (e.g., in the intestines) and secretion (e.g., in glands). If it prevented all exchange, essential processes like nutrient absorption and gas exchange could not occur.
Statement 2 is Correct:
The permeability of the cells of various epithelia plays a pivotal role in regulating the exchange of materials. Depending on the location and type of epithelium (e.g., simple squamous in alveoli vs. stratified squamous in skin), the tissue regulates what enters or leaves the body and what moves between different body compartments.
Statement 3 is Correct:
Since epithelial tissue covers the entire body surface (skin) and lines all internal cavities and organs (such as the digestive and respiratory tracts), any substance entering the body from the external environment must cross at least one layer of epithelial cells. For example, oxygen entering the blood must cross the alveolar epithelium, and nutrients must cross the intestinal epithelium.
Key Takeaway:
Epithelial tissue is not an impermeable wall but a selectively permeable barrier that regulates the movement of substances into and out of the body.