Cell Membrane Transport


Cell Membrane Transport

Cell Membrane

l  Also called the plasma membrane

l  Is a semi-permeable lipid bilayer

l  Semi—only some

l  Permeable—passes through

l  Lipid—made of fats

l  Bi—two

l  Layer—flat sheets

Structure of Cell/Plasma Membrane

l  Composed of two phospholipid layers (bilayer)

l  There are other molecules embedded in the membrane (proteins, carbohydrates)

l  The fluid mosaic model describes the membrane

Function: Plasma/Cell Membrane

l  Forms a boundary between inside and outside of the cell

l  Controls passage of materials include:

l  Water

l  Glucose

l  Nutrients

l  Protects and supports the cell

l  Transmits chemical signals across cell Chemical signals are transmitted across the cell membrane

l  Receptors bind with ligands and change shape

Characteristics of Cell/Plasma Membrane

l  The cell membrane is selectively permeable

l  Some molecules can cross the membrane while others cannot                  

l  The cell membrane is a double layer of membranes of fat that only let certain things get in and out of a cell.

l  Also called the “gatekeeper” of the cell because it does in essence choose what enters or does not

l  There are two types of receptors

l  Intracellular receptor

l  Membrane receptor

Cell Transport Osmosis and Diffusion

l  Materials move across membranes because of concentration differences/gradient.

l  Substances move from high to low concentration.

Passive transport does not require energy input from cell.

l  Molecules can move across cell membrane through passive transport.

l  There are two types of passive transport:

l  Diffusion

l  Osmosis

Diffusion and osmosis are types of passive transport.

l  Molecules diffuse down a concentration gradient.

l  From High to Low


l  Movement of molecules, other than water, from an area of HIGH concentration to an area of LOW concentration

l  No ATP energy is used.

l  Example:

l  Spraying air freshener in a room and eventually smelling it across the other side

l  Some molecules cannot easily diffuse across the cell membrane

l  Substances that are not soluble in lipids, like glucose and amino acids, must have help getting across the membrane.

l  Facilitated diffusion is diffusion through transport proteins

l  Does not require energy

Factor Affect Diffusion

l  Size of the molecules

l  Large molecules do not pass through easily

l  Temperature

l  The warmer the water or atmosphere the faster the reaction of diffusion

l  Size of concentration gradient

l  The greater the concentration difference the faster the reaction

Does diffusion ever stop?

l  NO… because particles are in constant motion

l  When the # of particles is equal on both sides of the membrane then equilibrium is reached

l  When particles reach equilibrium the rate of diffusion is equal across the membrane


l  There are three types of solutions:

l  Isotonic

l  Hypertonic

l  Hypotonic           

l  Osmosis is the diffusion of water molecules across a semipermeable membrane.

l  Water molecules move from high to low concentration.

l  Example:

l  Water moving from your small intestine to the bloodstream

Active Transport, Endocytosis, and Exocytosis

l  Cells also use energy to transport materials that cannot diffuse across a membrane

l  Active Transport requires energy input from a cell and enables a cell to move a substance against its concentration gradient.

l  Active transport is powered by chemical energy (ATP)

l  Remember:

l  Passive transport requires no energy from the cell

l  Active transport occurs through transport protein pumps.

l  Cells use active transport to maintain homeostasis.

l  Two types of Active Transport:

l  Endocytosis

l  Exocytosis

l  A cell can import and export large materials or large amounts of materials in vesicles during the processes of Endocytosis and Exocytosis.


l  Process of taking material into the cell

l  Phagocytosis is a type of Endocytosis.

l  Cells require energy to transport material in endocytosis.


l  Process of expelling materials from the cell

l  Cell requires energy to transport materials in endocytosis.

     Cell Membrane Transport PPT

Cell Membrane Transport PDF

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