The Cell Membrane Flashcards
What does the cell membrane do?
The cell membrane controls the exchange of substances between the internal and external environments of the cell.
What does it mean when the cell membrane is referred to as “selectively permeable?”
It only allows certain molecules or ions in and out of the cell.
How does the fluid mosaic model describe the membrane?
A double layer of lipids.
Why do hydrophilic molecules have difficulty penetrating a membrane?
Water-soluble (hydrophilic) molecules have difficulty penetrating a membrane, whereas lipid-soluble molecules do not. This is due to the phospholipid bilayer structure of the cell membrane. The lipid ‘tails’ impede the progress of hydrophilic molecules and enhance the movement of lipid-soluble molecules such as urea and ethanol.
How does water easily move throught the membrane although it is not lipid-soluble?
It moves through these special tiny hydrophillic pores in the membrane called aquaporins through osmosis
What is diffusion?
Diffusion is the net movement of any molecules from a region of high concentration to a region of low concentration of that substance, until equilibrium is reached. Equilibrium is reached when the there is no net movement of molecules in either direction – the molecules move equally in each
direction. This process does not require an energy input.
