AP BIOLOGY

Detailed explanation-1: -What Do Membranes Do? Cell membranes serve as barriers and gatekeepers. They are semi-permeable, which means that some molecules can diffuse across the lipid bilayer but others cannot. Small hydrophobic molecules and gases like oxygen and carbon dioxide cross membranes rapidly.

Detailed explanation-2: -The cell membrane is like a security guard, because the cell membrane controls what goes in and out of a cell like a security guard controls who goes in and out of the gate.

Detailed explanation-3: -Answer and Explanation: An analogy for the endoplasmic reticulum is that the endoplasmic reticulum is like a tunnel connecting different areas within a city, almost like a subway system. The endoplasmic reticulum is a tube network located near the nucleus.