Cell Membrane Structure
Hydrophilic
Hydrophobic
Hydrophilic
Structure of Cell Membrane
Protein
________
____
Protein
Protein
Cytoskeleton
_______
• Energy is not needed for
movement of materials
across membrane
• The process by which
molecules of a substance
move from areas of higher
concentration to areas of
lower concentration
–Ex. Air freshener, perfume
• Equilibrium
occurs when the concentrations of the
substances on both sides of the
membrane are the same
• Permeability
the ability of a substance to diffuse
across a membrane
• Selective Permeability
only allowing certain substances to
pass through the membrane
• Diffusion of water molecules
through a selectively permeable
membrane
• Water tends to move across a
membrane from a dilute solution
(more water) into a concentrated
solution (less water)
http://www.stolaf.edu/people/giannini/flashanimat/transport/osmosis.swf
• Isotonic solution
concentration of water is the same inside
and outside of the cell, so equal movement
of water occurs
http://www.stephsnature.com/lifescience/osmosisanimations.htm
• Hypertonic solution
concentration of water is higher inside the
cell, so water moves out of the cell and the
cell shrinks
http://www.stephsnature.com/lifescience/osmosisanimations.htm
Hypotonic solutionconcentration of water is lower inside the
cell, so water moves into the cell and
plant cells swell, but animal cells will
burst
Example:
http://www.stephsnature.com/lifescience/osmosisanimations.htm
• Molecules are carried across a
membrane in the direction of
lowest concentration by a
carrier protein (still passive
transport – no energy needed)
• http://www.d.umn.edu/~sdowning/Membranes/diffusionani
mation.html
• An energy-requiring process
that enables material to move
across a cell membrane against
a concentration difference (from
low to high)
http://glencoe.mcgrawhill.com/sites/9834092339/student_view0/chapte
r5/primary_active_transport.html
(once on website – press loop to run it in a loop)
• Process of taking materials into the cell
by infolding the cell membrane (forming a
pocket)
1. Phagocytosis - when large particles
are taken into the cell
ex. Amoebas eating
http://www.stolaf.edu/people/giannini/flashanimat/cel
lstructures/phagocitosis.swf
2. Pinocytosis - when liquid is taken
into the cell
• When large molecules are
expelled (removed) from
the cell; usually wastes
http://www.stanford.edu/group/Urchin/GIFS/exocyt.gif
Diffusion & Osmosis Activity
1)
In figure 1, where is the area of high concentration of
ink?
•
in the middle/bottom of the beaker
2. In figure 2, draw what happens after you add ink to
water.
3. What process have you shown on your model?
•
Diffusion
4. One side of the beaker in Figure 3 contains a dissolved substance, and
the other side does not. Which side of the beaker has the highest
concentration of water?
• Right side
5. In Figure 3, draw an arrow across the membrane showing the direction
that water will tend to move.
6. What process is shown in this model?
• Osmosis
7. If the membrane in the beaker were impermeable, would the
concentration of salt parts on either side of the membrane change?
• No because impermeable means nothing can move
8. Suppose you did the experiment in Figure 3 with sugar instead of salt.
Would the results be similar? Explain.
• Yes because sugar and salt are similar
molecules
2% salt
0% salt
10% salt
2% salt
9. Is the concentration of water higher in Beaker B or in the cellophane bag?
•In the bag
10. What would happen if you put the bag in Beaker B? Would the concentration
of salt in the bag stay the same? Why or why not?
•Water would move out of the bag
•No, the concentration of salt would actually increase in the bag
11. If you put the bag in Beaker A, in which direction would the water move?
•Into the bag
12. If you put the bag in Beaker C, would the concentration of salt in the bag
change? Explain.
•No, because they are the same (already at equilibrium)
13. In the space below, draw diagrams showing the
cellophane bag inside each of the three beakers. Draw
arrows to show the direction of water into or out of the
bag.
0% salt
2% salt
Hypotonic
10% salt
2% salt
Hypertonic
2% salt
2% salt
Isotonic