What defines a tissue in the context of biology?

A tissue is defined in biology as a group of cells that work together to perform a specific function. This definition is crucial because it highlights the collaborative nature of cells within a tissue, indicating that they share a common purpose and structure to fulfill particular roles in an organism.

For instance, muscle tissue is composed of muscle cells that contract to produce movement, while epithelial tissue forms protective layers on surfaces, serving both as a barrier and as a point of absorption or secretion. The organization of cells into tissues allows for the specialization and division of labor, contributing to the overall efficiency and functionality of multicellular organisms.

This understanding contrasts with the other choices. For example, while organs are indeed made of tissues, defining a tissue solely as cells that form organs misses the important aspect of function. An assembly of organ systems involves a higher level of organization and complexity than what defines a tissue. Lastly, individual cells with unique functions do not collectively categorize as a tissue; rather, a tissue is about the collective effort of multiple cells working together, rather than isolated functions.