The Cell Membrane Cell Membrane – boundary that separates cells from their environment and controls what moves in and out of the cell.

Selective Permeability  Only certain substances are allowed to pass through the membrane.

 Simple Model showing hydrophillic (water “loving”) head and hydrophobic (water “fearing”) tails.  Complex model showing atom arrangement:

 The phosphate heads are attracted to water and point toward the outside of the cell.  The fatty acid tails are not attracted to water and point toward the inside (toward each other).

 The two layers of phospholipids form a lipid bilayer.

 The phospholipids are not locked into one spot, but are able to “float around”.  This fluidity allows molecules to pass through and proteins to move around.

 Floating around in the cell membrane are different kinds of proteins.  These proteins help move molecules from one side of the cell membrane to the other.

There are two different types of transport  Passive (Does not require energy) - Moves substances down the concentration gradient (like sliding down a slide)

There are two different types of transport  Active (Requires energy) -Moves substances against the concentration gradient (like climbing back up a slide)

Facilitated Diffusion  Passive transport - Requires no energy.  Proteins embedded in the plasma membrane help particles pass from a high concentration to a low concentration.

Diffusion  Particles move from an area of high concentration to an area of low concentration  Moves “down” or “with” the concentration gradient  Does not require energy

Osmosis  Movement of WATER across a cell membrane  Cell has no control  continues to move until [inside] = [outside] called dynamic equilibrium  [ ]- means “the concentration of”

Types of Solutions  Isotonic – [water inside] = [water outside]  Cell stays the same  Hypotonic – [water inside] < [water outside]  solutes are higher inside the cell  water flows in, cell swells  cell could burst if continues  Hypertonic – [water inside] > [water outside]  solutes are higher outside the cell  water leaves cell, cell shrinks

Types of Solutions Isotonic Hypotonic Hypertonic Water particle Solute particle

Types of Solutions Effects on Animal Cells The pictures below are red blood cells in different concentrations of salt solution. Identify which pictures are hypotonic, isotonic, and hypertonic solutions. Isotonic Hypertonic Hypotonic

Types of Solutions Effects on Plant Cells Which of these cells are in a hypotonic solution? Hypertonic solution? How can you tell? Hypotonic Hypertonic

Active Transport  Requires energy  moves from an area of low concentration to an area of high concentration  moves “up” or “against” the concentration gradient  glucose moved from blood stream into liver for storage

Active Transport

Moving large particles across the cell membrane  Endocytosis – movement of large particles into the cell  Exocytosis – movement of large particles out of the cell Endocytosis Exocytosis

3 kinds of endocytosis that take materials into the cell:  Phagocytosis “Cell Eating” – solids  Pinocytosis “Cell Drinking” – liquids with small solutes

Exocytosis