11 SolubilityMaterials that are soluble in lipids can pass through the cell membrane easily
12 Crossing the membrane. Molecules cross the membrane in several ways. Some methods require the cell to expend energy, some do not.How a particular molecule crosses the membrane depends on the molecules size, polarity, and concentration inside versus outside the cell.Small non-polar molecules easily pass through the membrane.Small polar molecules are transported via proteins.Large molecules are moved in vesicles.
13 Chemical signals are transmitted across the cell membrane A receptor is a protein that detects a signal molecule and performs an action in response.It recognizes and binds to only certain molecules, which ensures that the right cell gets the right signal at the right time.When receptors are activated (they combine with a hormone or neurotransmitter), they change shape.This relays information to the cell.