The study of large and easily observable structures in an organism is called gross anatomy, also known as macroscopic anatomy.

Here's a breakdown:

* Gross: Refers to large-scale, visible structures.

* Anatomy: The study of the structure of living organisms.

So, gross anatomy is the branch of anatomy that deals with the study of structures that are visible to the naked eye, such as organs, muscles, bones, and tissues.

It contrasts with microscopic anatomy, which focuses on structures that require a microscope to be seen, like cells and tissues at a cellular level.