Which is a buffer zone between the outside world and most of the cells of the body?

Some tools have graduations to show multiple measurements. for example, a ruler may have graduations for both millimeters and centimeters. when measuring the length of an earthworm, which graduations would allow for the most accurate measurement? millimeters centimeters decimeters meters

This is the interaction of two organisms where one is and the other is neither nor harmed.

Produce proteins by following coded instructions that come from the nucleus of the cell.