Organisms contain different levels of organization within their bodies. Arachnoidiscus ehrenbergi, pictured below, is a single-celled organism that is part of the group of algae known as diatoms. A microscopic image of Arachnoidiscus ehrenbergi.
Photo by Gordon T. Taylor, courtesy of the NOAA

Which level of organization is seen in both Arachnoidiscus ehrenbergi and the human stomach?
cell
tissue
organ
organ system