Download Passive Transport

Across the Membrane
Movement of cellular materials
in and out of the cell.
Cell membranes help organisms
maintain homeostasis by controlling
what substances may enter or leave
cells.
Passive vs. Active Transport:
• Movement of substances without energy input
by the cell is a passive transport process
.
• Movement of substances with energy input by
the cell (ATPs) is an active transport process.
Diffusion
Diffusion – (simplest type of passive transport)
The random movement of molecules from an area of
higher concentration to an area of lower
concentration.
It is driven by the kinetic energy of the molecules.
• Diffusion movement occurs with, (or down)
the concentration gradient.
• A concentration gradient is a difference
in concentration of molecules across a
space.
• Diffusion will eventually cause the concentration
of molecules to be the same throughout the
space.
• When the concentration of molecules are the
same throughout the space, equilibrium is
reached and the concentration gradient
disappears.
• When equilibrium is reached, there is no net
movement of molecules
Diffusion & the cell membrane
The ability of substances to diffuse across a cell
membrane depends upon the size and type of
the molecules, as well as the chemical nature of
the cell membrane.
Cell membranes are selectively-permeable in
that they allow only certain substances to pass.
Molecules that dissolve in lipids (such as
CO2 O2), diffuse through the cell membrane.
Small molecules that aren’t soluble, move
through membrane pores (such as H2O).
Osmosis
The process by which a solvent (such as
water) diffuses across a selectivelypermeable membrane (such as a cell
membrane) is called osmosis.
Osmosis always occurs with the
concentration gradient, since it is a form of
diffusion.
THREE DIFFERENT SOLUTIONS:
Isotonic, Hypotonic, & Hypertonic
Norway’s Osmosis Energy Power Plant
– Time (Dec. 13, 2010)
Norway’s Statkraft state-owned power company has
opened a prototype power plant that uses the principle of
osmosis to develop water pressure to move an electricity
generating turbine.
The plant opened in November of 2009 in Tofte, Norway,
along the Oslo Fjord. Water from the Tofte River falls into
a vessel separated from salty fjord water by a thin,
selectively-permeable membrane. The membrane lets
freshwater force its way through to the enclosed
saltwater side, where pressure builds, pushing water
through a pipe to drive a turbine.
The plant generates less that a watt of energy per
square mile (5 watts per square mile make it
cost effective). A new membrane will be tested
soon to increase efficiency. Stein Erik
Skillhagen, (head of the program) foresees 30
osmotic powerplants by 2030.
Facilitated Diffusion
It is a type of passive transport in which
molecules that cannot diffuse rapidly
into the cell, pass through pores in the
cell membrane.
Carrier proteins help move molecules
across the membrane. They bind to the
molecule they carry. The carrier molecule
changes shape to shield the molecule from
the interior of the cell membrane.
DIFFUSION THROUGH ION
CHANNELS:
Ion channels provide small passageways across the
membrane for the purpose of ion diffusion.
Ions such as Na+ & Cl- , that are not soluble in lipids,
can move through specific ion channels (Na+ moves
through Na+ channels)
Gated Ion Channels
• Some ion channels are always open, while
others are called gated channels and may
open or close in response to stimuli such
as:
• stretching of the cell membrane
• chemicals in the cell cytoplasm
• chemicals in the cell’s external
environment
• electrical signals