Final answer:
Tissues are a group of cells that share a common origin and work together to perform specific functions in the body. They are found in more complex organisms and are absent in simpler organisms like protists.
Step-by-step explanation:
The term tissue is used to describe a group of cells found together in the body.
The cells within a tissue share a common embryonic origin.
Microscopic observation reveals that the cells in a tissue share morphological features and are arranged in an orderly pattern that achieves the tissue's functions.
From the evolutionary perspective, tissues appear in more complex organisms.
For example, multicellular protists, ancient eukaryotes, do not have cells organized into tissues.