Which structures cover body organs or line body cavities?

• A. Cells
• B. Tissues
• C. Eyes
• D. Membranes

Answer: (D)

Membranes are thin tissue layers that cover organs or line body cavities, providing protection, lubrication, and a boundary between areas. They come in several types: epithelial membranes include the cutaneous membrane (the skin) that covers the body, mucous membranes that line cavities open to the outside (like the mouth and airways), and serous membranes that line closed cavities (such as the chest and abdominal spaces, with layers like visceral and parietal membranes). There are also connective tissue membranes, such as synovial membranes that line joints. This is why membranes are the structures described as covering organs or lining cavities.

Think of cells as the tiny building blocks, and tissues as groups of those blocks forming a layer or structure. They don’t by themselves serve as the covering or lining for organs or cavities the way membranes do. Eyes are organs, not coverings, so they don’t fit the description either.