NEM 10V Lecture Notes - Lecture 14: Ion Channel, Phospholipid, Osmosis
Nematology
Cell Membrane:
• Molecules dissolved in a solution are in constant random motion due to kinetic energy. In
diffusion molecules move from areas of their higher concentration to areas of their lower
concentration. Water molecules move in response to their own concentration gradient.
The higher the water concentration, the lower the solute concentration. Water will move
across a selectively permeable membrane to the side where concentration is lowest.
Osmosis is the movement of water across a selectively permeable membrane, down its
concentration gradient. Tonicity is the relative concentration of solutes in two fluids. The
fluid with the lower concentration of solutes is hypotonic. The fluid with the higher
concentration of solutes is hypertonic Two fluids with the same concentration of
solutes are isotonic. Water diffuses from a hypertonic to a hypotonic solution.
• The fluid mosaic model describes a cell membrane as a two-dimensional liquid consisting
of a phospholipid bilayer embedded with freely moving molecules, including steroids and
proteins. The cell membrane is a phospholipid bilayer meaning it is composed of 2
molecules of phospholipid. The lipid molecules of the membrane naturally assemble in a
double layer because their tails repel water and their heads attract it. Cell membranes are
selectively permeable meaning that some substances can diffuse through a cell membrane
while others cannot. Passive transport is the flow of ions or molecules through a cell
membrane. Phospholipids and protein channels control which molecules can cross the
membrane. Substances move from areas of high concentration to areas of low
concentration. There are three types of passive transport that occur as a result of
diffusion: simple diffusion, facilitated diffusion, and osmosis. Simple Diffusion is the
process by which molecules diffuse across the phospholipid bilayer at any location.
Facilitated diffusion requires a substance to cross the membrane through a protein
channel or with the help of a carrier protein. In facilitated diffusion either channel
proteins or carrier proteins facilitate the crossing of a cellular membrane by water soluble
substances that cannot typically diffuse through the phospholipid bilayer.
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Document Summary
Cell membrane: molecules dissolved in a solution are in constant random motion due to kinetic energy. In diffusion molecules move from areas of their higher concentration to areas of their lower concentration. Water molecules move in response to their own concentration gradient. The higher the water concentration, the lower the solute concentration. Water will move across a selectively permeable membrane to the side where concentration is lowest. Osmosis is the movement of water across a selectively permeable membrane, down its concentration gradient. Tonicity is the relative concentration of solutes in two fluids. The fluid with the lower concentration of solutes is hypotonic. The fluid with the higher concentration of solutes is hypertonic two fluids with the same concentration of solutes are isotonic. Water diffuses from a hypertonic to a hypotonic solution: the fluid mosaic model describes a cell membrane as a two-dimensional liquid consisting of a phospholipid bilayer embedded with freely moving molecules, including steroids and proteins.
