Passive Transport

The Cell Membrane Surrounds the cell and allows substances to pass in and out of the cell Made up of lipids called PHOSPHOLIPIDS, arranged in TWO layers. The structure is referred to as a PHOSPHOLIPID BILAYER. PHOSPHOLIPID

The phospholipids have a HYDROPHILIC HEAD and a HYDROPHOBIC TAIL.   HYDROPHILIC = “water loving” HYDROPHOBIC = “water fearing”

PROTEINS are interspersed among the lipids PROTEINS are interspersed among the lipids. These proteins act as channels to let things in and out of the cell.

The molecules in the cell membrane are able to move and mix – this is called the FLUID MOSAIC MODEL video

Passive Transport Molecules in our bodies such as water, oxygen, sugars and carbon dioxide must be able to move from place to place or cell to cell. Cell membranes are selectively permeable, meaning that only certain substances can pass through.

Three kinds of passive transport: SIMPLE DIFFUSION FACILITATED DIFFUSION OSMOSIS Do not require energy

Simple Diffusion Molecules move from an area of high concentration to an area of low concentration Called moving down the concentration gradient

Many small molecules are able to pass through the cell membrane by simple diffusion. Once there are an equal number of molecules on each side of the cell membrane, the cell has reached DYNAMIC EQUILIBRIUM. Diffusion Simulation

Small molecules can move straight through the phospholipid bilayer

Facilitated Diffusion Large ions and molecules (ex. sugar, sodium) cannot pass through the membrane easily Membranes have transmembrane proteins that act as channels to the cell to help the molecule pass through

Facilitated Diffusion Simple Diffusion Facilitated Diffusion - Ions/ molecules pass directly through the membrane’s phospholipid bilayer - Diffusing particles are assisted through the membrane by transmembrane carrier proteins Simple Diffusion Facilitated Diffusion - Ions/ molecules pass directly through the membrane’s phospholipid bilayer - Diffusing particles are assisted through the membrane by transmembrane carrier proteins