What is defined as a collection of tissues that carry out a specialized function of the body?

The correct choice identifies an organ as a collection of tissues that carry out specialized functions within the body. Organs are complex structures composed of different types of tissues working together to perform specific roles vital to the body's functioning. For example, the heart is an organ that consists of muscle tissue, connective tissue, and nerve tissue, all contributing to its function of pumping blood.

In contrast, a cell is the basic unit of life and is much smaller than an organ, unable to perform specialized functions on its own without forming tissues. A tissue is a group of similar cells that work together to perform a particular task, but it does not represent the higher level of organization that an organ does. A system is an even broader concept, representing a group of organs that collaborate to carry out complex functions, like the circulatory system or respiratory system. Therefore, the term that accurately describes a collection of tissues operating together for a specific function is indeed an organ.