The Balancing Act of Life  Homeostasis – process by which an organisms maintains a relatively stable internal environment  Examples: Thermoregulation – maintaining body temperature Water regulation – keeping enough water in your body Regulating oxygen, blood sugar, and blood pH

Various methods of thermoregulation

Plasma Membrane  Function: The plasma membrane encloses the cell and protects it.  Function: It lets certain particles into and out of the cell.  Surrounds all cells

MOVEMENT THROUGH THE PLASMA MEMBRANE  How do materials or substances enter or leave cells?

THE PLASMA MEMBRANE IS PICKY!  Selective Permeability - the membrane can pick and choose what particles can pass through it.

PLASMA MEMRANE  Plasma membranes are made of phospholipids, proteins, and sometimes cholesterol.

THE PHOSPHOLIPID A A phospholipid - made up of a glycerol attached to 2 fatty acids and a phosphate group.  The fatty acids are hydrophobic (hate water).  The phosphate group is hydrophilic (likes water).

Reference

THE BILAYER STRUCTURE  The plasma membrane is a bilayer of phospholipids.

DRAW THIS IN NOTES!

THE BILAYER STRUCTURE  The plasma membrane is a bilayer of phospholipids.  Reference Reference

OTHER STRUCTURES IN THE MEMBRANE...  Animal plasma membranes have cholesterol in between phospholipids to slow their movement.

MEMBRANE PROTEINS  Proteins are embedded in membranes.  Some are on the inner or outer surfaces, some go the entire way through the bilayer.

MEMBRANE PROTEINS’ JOBS  Regulate which particles can pass through membrane (transport)  Act as enzymes in chemical reactions  Act as markers on outside and inside of cell to identify self

Membrane Video 0:45 – 1:57

WAYS TO MOVE THROUGH THE MEMBRANE:  1. Active transport requires energy to move the molecules through the plasma membrane.  2. Passive transport does not require energy, and occurs spontaneously.

PASSIVE TRANSPORT  The principle means of passive transport is diffusion.  Diffusion is the movement of molecules from a HIGH concentration to a LOW concentration.

Reference

 Equilibrium occurs when two opposing actions occur at the same rate.  Diffusion occurs when a system is not at equilibrium.

FACTORS THAT AFFECT DIFFUSION:  Temperature - higher temperature means more energy and molecules will diffuse faster.  Size - Smaller molecules will move more rapidly than larger molecules

REAL-LIFE EXAMPLES  CO 2 and O 2 diffuse across plasma membranes.  Oxygen moves from an area of high concentration to an area of low concentration from your lungs to your blood to your cells.

 As chemical reactions in the cell use up oxygen they produce CO 2.  The concentration of CO 2 inside the cell increases so that more CO 2 is inside of the cell.  Therefore CO 2 diffuses into your blood and then into your lungs where it is exhaled.

OSMOSIS  The movement of water from a high concentration to a low concentration.  It is the diffusion of water.  This can cause cells to burst or shrink.

Osmoregulation  Saltwater organisms have to get rid of salt and conserve water.  Freshwater organisms have to get salt and get rid of excess water.

FACILITATED DIFFUSION Helping diffusion along  Proteins help certain chemicals pass through a plasma membrane  Requires no energy (still moves from high to low)  Usually needed for slightly larger molecules like glucose

High Concentration Low Concentration Cell Membrane Glucose molecules Protein channel

High Concentration Low Concentration Cell Membrane Glucose molecules Protein channel

ACTIVE TRANSPORT  When a cell needs energy to move from low to high concentration.  Proteins pump molecules through membrane  Molecules move against diffusion (from low to high concentration)  Works against diffusion

Reference

OTHER WAYS CELLS GET MATERIALS...  Vesicles – a membrane-bound sac that is used to transport materials inside of a cell  Endocytosis – the plasma membrane engulfs and takes materials into the cell in a vesicle  Exocytosis – vesicles with chemicals move to plasma membrane and fuse with membrane. The chemicals are then released out of the cell  Endo and Exo are both forms of ACTIVE TRANSPORT

Exocytosis Video