The branch of science that deals with the study of groups of tissues is histology.

Here's a breakdown:

* Histology is the microscopic study of the structure, composition, and function of tissues.

* Tissues are groups of similar cells that work together to perform a specific function.

* Cells are the basic building blocks of all living things.

So, in essence, histology bridges the gap between the microscopic world of cells and the macroscopic world of organs and organ systems.