What is the most important barrier protecting the inner contents of an animal cell?

The cell membrane. (It also could be cytoplasm because it supports the organelles. But I think it is the cell membrane because it says barrier, and the cell membrane is the cell's barrier between it and the outside of the cell.)

The cell membrane is the outer most layer of the animal cell. It is selectively permeable, so it lets good things in and keeps bad things out. It also helps larger things that the cell needs to get in such as glucose by the process of endocytosis.

Ifound this information on google “yes. they have a mouth and brain at one end and an anus at the opposite end. what characteristics distinguish an annelid from other worms? annelids have segmented bodies and a coelem which is a tube filled with fluid and contains most of the organs.“ i hope it you