Which of the following best describes connective tissue?

Connective tissue is primarily defined by its structure, which includes a sparse population of cells surrounded by a substantial nonliving extracellular matrix. This matrix comprises various proteins and fibers, like collagen and elastin, that provide strength, elasticity, and support to the tissue. The cells present in connective tissue, such as fibroblasts, adipocytes, and macrophages, are usually fewer in number compared to cells in other tissue types like epithelial tissue.

This characteristic of having a significant extracellular matrix is fundamental to the role of connective tissue in the body. It not only supports and binds other tissues together but also plays a critical role in nutrient transport, immune response, and tissue repair. The other descriptions provided in the answer choices do not accurately reflect the defining features of connective tissue, with mischaracterizations of vascularity, insulation, and function related to lining surfaces and cavities. These aspects relate more closely to other tissue types, such as epithelial or nervous tissue, rather than to connective tissue itself.