What is a collection of similar cells that perform a specialized function called?

A collection of similar cells that perform a specialized function is known as tissue. In biological terms, tissues are groups of cells that are similar in structure and work together to carry out specific tasks essential to the body. There are four primary types of tissues in animals: epithelial, connective, muscle, and nervous tissue. Each of these tissues has distinct roles that contribute to the overall functioning of the organism.

For instance, muscle tissue is responsible for movement, connective tissue supports and binds other tissues, epithelial tissue covers body surfaces and lines cavities, and nervous tissue facilitates communication through nerve impulses. This classification is fundamental in biology since it helps to organize and understand the complex structures and functions of living organisms.

The other options refer to different levels of biological organization: organs are made up of tissues working together for specific functions, systems comprise groups of organs that perform related tasks, and aggregates typically refer to a collection of cells or particles that may not have a functional specialization. Thus, tissue is the correct term for a collection of similar cells performing a specialized function.