Final answer:
A group of similar cells that work together is referred to as a tissue, which is essential for the functioning of complex organisms.
Step-by-step explanation:
When several cells are selected together, they're referred to as a cell tissue. A tissue is a group of similar cells working together to perform a shared function. This organization is essential for complex organisms, where cells must communicate and coordinate their actions, resembling a team working together on a project. The ability for cellular communication is fundamental for the functioning of tissues, which then combine to form organs and organ systems, eventually constituting an entire organism.