Cell Transport Mechanisms
1. To define the following terms:
differential permeability, passive
diffusion (simple diffusion, facilitated dif-
osmosis), solute pump, pinocytosis,
2. To describe the processes that account for the movement of sub- stances across the plasma membrane, and to indicate the driving force for each.
3. To determine which way substances will move passively through a dif- ferentially permeable membrane (given the appropriate information on concentration differences).
01_001_016_PhyEx8_AP_Ch01 1/10/08 5:27 PM Page 1
The diffusion of solute particles dissolved in water through a differentially permeable membrane is called
The diffusion of water through a differentially perme-
able membrane is called
Both simple diffusion and
osmosis involve movement of a substance from an area of its
higher concentration to one of its lower concentration, that is, down its concentration gradient.
Solute Transport Through
This computerized simulation provides information on the
passage of water and solutes through semipermeable mem-
branes, which may be applied to the study of transport mech- anisms in living membrane-bounded cells.
Simulating Dialysis (Simple Diffusion)
: Cell Transport Mechanisms and Per-
from the drop-down menu and click
video to see an actual dialysis experiment
performed. Then click
The opening screen
will appear in a few seconds (Figure 1.1). The primary fea-
tures on the screen when the program starts are a pair of glass beakers perched atop a solutions dispenser, a dialysis mem-
branes cabinet at the right side of the screen, and a data col- lection unit at the bottom of the display.
The beakers are joined by a membrane holder, which can
be equipped with any of the dialysis membranes from the
cabinet. Each membrane is represented by a thin colored line suspended in a gray supporting frame. The solute concentra-
tion of dispensed solutions is displayed at the side of each beaker. As you work through the experiments, keep in mind
that membranes are three-dimensional; thus what appears as
a slender line is actually the edge of a membrane sheet.
The solutions you can dispense are listed beneath each
beaker. You can choose more than one solution, and the
amount to be dispensed is controlled by clicking (
) to in-
crease concentration or (
) to decrease concentration. The
chosen solutions are then delivered to their beaker by click- ing the
button on the same side. Clicking the
button opens the membrane holder and begins the experi-
button will become a
button after it is
clicked once. To clean the beakers and prepare them for the
next run, click
a run stops the experiment and prepares the beakers for an-
other run. You can adjust the timer for any interval between 5 and 300 minutes; the elapsed time is shown in the small win- dow to the right of the timer.
To move dialysis membranes from the cabinet to the
membrane holder, click and hold the mouse on the selected
membrane, drag it into position between the beakers, and
then release the mouse button to drop it into place. Each
membrane possesses a different molecular weight cutoff
(MWCO), indicated by the number below it. You can think of
MWCO in terms of pore size; the larger the MWCO number,
the larger the pores in the membrane.
window in the data collection unit at
the bottom of the screen displays each experimental trial
(run). When you click the
button, your data is
recorded in the computer’s memory and is displayed in the
data grid at the bottom of the screen. Data displayed in the data grid include the...
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