QUIZ:
Which organelle:
1.Makes proteins
2.Packages and ships proteins
3.Makes ATP from carbohydrates
4.Define amphipathic.
5.Labels:
A
B C
A.
B.
C.
D.
E.
D
E
Membrane Transport
 Passive: osmosis, diffusion
Active: endocytosis, exocytosis
Molecules move randomly and continuously.
Impacts change their direction.
High
Low
Concentration gradient drives the NET
movement of molecules
Permeability
Osmosis
Movement of
water across
a membrane
from high
concentration
to low
concentration
Another rule of thumb:
Cell A
Cell B
Concentration of solutes
The greater (steeper) the concentration
gradient, the faster the rate of diffusion.
Cell A will diffuse faster
Inside
Cell
Outside
Cell
Effect of temperature
on diffusion
Cell A
Cell B
Temperature °C
Cell B will diffuse faster
38°
22°
Cell A
Cell B
Active Transport
© Brooks/Cole - Thomson Learning
Sodium-potassium Pump
© Brooks/Cole - Thomson Learning
3 factors that affect movement of
molecules across membranes
• Effect of Concentration: the greater the concentration
difference across the membrane, the faster the rate of
diffusion (agar blocks)
• Effect of Temperature: the higher the temperature, the
faster the rate of diffusion due to increased energy of
solute molecules (agar blocks)
• Effect of Pore Size: only solutes small enough to pass
through the pores of a membrane are able to diffuse
(dialysis: iodine moved in, glucose moved out, starch
remained in)
Objective 3: Recognize the role of water
potential in regulating the movement of water
across membranes and note factors that affect
water potential.
Objective 4: Describe the tonicity of biological
solutions
Water potential: the potential energy of
a volume of water; expressed as a
pressure
Definitions
Osmosis - the diffusion of water
across membranes
Which way will the water go?
Quick Time™a nd a TIFF ( Uncomp res sed) deco mpre ssor are n eede d to s ee this picture .
Definitions
QuickTi me™ and a TIFF (U ncompressed) decompressor are needed to see this picture.
• Solute - the substance dissolved in a
liquid (e.g., sugar, salt)
• Solvent - the liquid in which the solute is
dissolved (e.g., water)
“Free” water molecules can
pass through membrane.
These solute molecules are too
big to pass through membrane.
Higher water potential
Lower water potential
Obj. 4: Tonicity of solutions
• Hypotonic - solution that contains FEWER
solute particles than another solution
• Hypertonic - solution that contains MORE solute
particles than another solution
QuickTime™ and a TIFF (Uncompress ed) decompress or are needed to s ee this picture.
Rule of Thumb
• The net movement of WATER is from hypotonic
conditions to hypertonic conditions.
• If two systems are equal in the number of
dissolved particles, they are said to be isotonic
and no net change in volumes will occur.
Hypotonic
Hypertonic
Notes on Diffusion and Osmosis
• Both solutes and solvents (water) can diffuse across a
membrane and the concentration difference will eventually
equalize
• We are interested in the period of time before the system
equalizes (becomes isotonic), to observe which direction
diffusion is occurring
• Always pay attention to both solutes and solvents in
a question - both may be important!
Objective 5: Recognize the role of the cell
wall and of the vacuole in producing
turgor pressure to maintain the shape of
the plant cell.
QuickTi me™ and a T IFF (Uncom pressed) decom pressor are needed to see t his pict ure.
Distilled water
Salt water
Plant cells ONLY
Cell and cell wall do not change size.
Vacuole swells and shrinks.
The pressure that develops between the cell
wall and vacuole is called TURGOR
pressure.
Egg in
Distilled water
Egg in
Sugar water
H2O
H2O
Water moves from hypotonic conditions to
hypertonic conditions.
Water is hypOtonic
Egg is hypERtonic
Water is hypERtonic
Egg is hypOtonic
Distilled water
Sugar water
H2O
H2O
Discussion questions
Many hospital patients receive intravenous liquids to
replace body fluids. These liquids are generally complex
solutions of salts and sugars. If all the patient needs is
fluid, why doesn’t the physician simply inject pure
water?
Why can’t we drink salt water?
Dialysis tubing is a model for a cell membrane.
Starch & glucose
Iodine solution
Dialysis tubing is a model for a cell membrane.
Iodine + starch=blue
Cells have a selectively permeable membrane
Starch & glucose
Glucose
Iodine
Iodine solution
Predict the effects of temperature and
concentration gradients on diffusion rates
Concentration gradients
Sodium hydroxide solution
5%
0.5%
Agar Blocks
Started with 0%, diffused 5%
5-0=5
Started with 0%, diffused 0.5%
0.5 - 0 = 0.5
Much greater concentration gradient