Overton's Plasmolysis Flashcards
what was the purpose of the Overton’s plasmolytic experiment?
to determine the osmotic pressure of plant cells in different extracellular solutions varying in sucrose concentration
What is osmotic pressure called in plant cells?
turgor pressure
How is rigidity of plant tissues established?
by having turgor pressure/osmotic pressure
when the intracellular content is hypertonic to the extracellular fluid (has more solutes), the osmotic pressure pushes on the cell wall and when multiple plant cells are pushing on each other, the plant tissues become rigid
what plants were used in lab?
Elodea leaf cells
What does hypertonic solution mean? what does this make water do?
the solution has more solutes than the inside of the cell
water moves out of the cell
What does hypotonic solution mean? What does this make water do?
the solution has less solutes than the inside of the cell
water moves into the cell
What does isotonic mean?
the inside of the cell and the extracellular solution have an equal amount of solutes
what concentrations (M) of sucrose were the Elodea cells exposed to?
0.2, 0.3, 0.4, 0.5, 0.6 M
Which sucrose concentration resulted in the lowest % of elodea cells plasmolyzed?
0.2 M
Which sucrose concentration resulted in the highest % of elodea cells plasmolyzed?
0.6M
Describe the trend of % plasmolysis when the Elodea cells were exposed to increasing concentrations of sucrose
linear
the higher concentration of sucrose, the more cells plasmolyzed
Describe the Overton Plasmolytic Method
a change in cell volume occurs if a cell is put into a solution which contains molecules to which the cell membrane is impermeable
What did CE Overton discover?
when plant cells were exposed to a medium containing concentrated sucrose, rapid plamolysis occurs
What did Overton conclude about permeability and ethanol vs. sucrose? Why could he conclude this?
that ethanol must be capable of diffusing through a cell membrane
concluded this because when plant cells were exposed to ethanol, the intracellular and extracellular concentration of ethanol quickly equalized and there was no clear plamolysis or there was also deplasmolysis
If a solute is impermeable to the plasma membrane, what will happen to the cell? why?
the cell will plasmolyze because the solution will be hypertonic and water will osmose out of the cell
If a solute is permeable to the plasma membrane, what will happen to the cell?
the intracellular and extracellular concentrations of the solute will equalize and there will be no net flow of water so the cell will either quickly plasmolyze and deplasmolyze or the cell will not plasmolyze
What is the rate of penetration of non-electrolytes determined by?
permeant: lipid solubility
molecular structure
molecular size
How do non-electrolytes penetrate the cell membrane?
passing transport = diffusion along a concentration gradient
Describe how permeant solubility in lipids effects the diffusion of non-electrolytes across the cell membrane (aka the rate of penetration)
rate of penetration increases with increasing lipid solubility of the permeant
How is the solubility of a compound in lipids classified?
by the ratio of its solubility in an organic solvent vs in water (ex. ether: water partition coefficient)
What is the ether: water partition coefficient?
the ratio of a compound’s solubility in diethyl ether (organic solvent) vs. water (inorganic solvent)
Describe how molecular structure effects the rate of penetration of a non-electrolyte?
the more polar a molecule is, the more difficult it will be for the molecule to pass through the hydrophobic/nonpolar cell membrane
aka the more hydroxyl groups present
also consider the symmetry - if there’s a nonpolar and polar side, the nonpolar side will make it easier for it to pass
Describe how molecular size affects the penetration rate?
the larger a molecule is, the more difficult it will be for it to pass through the membrane
Which 4 molecules were used in this experiment?
methanol
ethylene glycol
propylene glycol
glycerol
Which of the 4 molecules used had the most rapid penetration? explain
methanol
has the largest partition coefficient (most soluble), smallest molecule, and has the least OH groups
Which of the 4 molecules used had the lowest penetration rate? explain
glycerol
largest molecule, most OH groups (most polar), smallest partition coefficient
