Overton's Plasmolysis

Question 1

what was the purpose of the Overton’s plasmolytic experiment?

Answer 1

to determine the osmotic pressure of plant cells in different extracellular solutions varying in sucrose concentration

Question 2

What is osmotic pressure called in plant cells?

Answer 2

turgor pressure

Question 3

How is rigidity of plant tissues established?

Answer 3

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

Question 4

what plants were used in lab?

Answer 4

Elodea leaf cells

Question 5

What does hypertonic solution mean? what does this make water do?

Answer 5

the solution has more solutes than the inside of the cell

water moves out of the cell

Question 6

What does hypotonic solution mean? What does this make water do?

Answer 6

the solution has less solutes than the inside of the cell

water moves into the cell

Question 7

What does isotonic mean?

Answer 7

the inside of the cell and the extracellular solution have an equal amount of solutes

Question 8

what concentrations (M) of sucrose were the Elodea cells exposed to?

Answer 8

0.2, 0.3, 0.4, 0.5, 0.6 M

Question 9

Which sucrose concentration resulted in the lowest % of elodea cells plasmolyzed?

Answer 9

0.2 M

Question 10

Which sucrose concentration resulted in the highest % of elodea cells plasmolyzed?

Answer 10

0.6M

Question 11

Describe the trend of % plasmolysis when the Elodea cells were exposed to increasing concentrations of sucrose

Answer 11

linear

the higher concentration of sucrose, the more cells plasmolyzed

Question 12

Describe the Overton Plasmolytic Method

Answer 12

a change in cell volume occurs if a cell is put into a solution which contains molecules to which the cell membrane is impermeable

Question 13

What did CE Overton discover?

Answer 13

when plant cells were exposed to a medium containing concentrated sucrose, rapid plamolysis occurs

Question 14

What did Overton conclude about permeability and ethanol vs. sucrose? Why could he conclude this?

Answer 14

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

Question 15

If a solute is impermeable to the plasma membrane, what will happen to the cell? why?

Answer 15

the cell will plasmolyze because the solution will be hypertonic and water will osmose out of the cell

Question 16

If a solute is permeable to the plasma membrane, what will happen to the cell?

Answer 16

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

Question 17

What is the rate of penetration of non-electrolytes determined by?

Answer 17

permeant: lipid solubility

molecular structure

molecular size

Question 18

How do non-electrolytes penetrate the cell membrane?

Answer 18

passing transport = diffusion along a concentration gradient

Question 19

Describe how permeant solubility in lipids effects the diffusion of non-electrolytes across the cell membrane (aka the rate of penetration)

Answer 19

rate of penetration increases with increasing lipid solubility of the permeant

Question 20

How is the solubility of a compound in lipids classified?

Answer 20

by the ratio of its solubility in an organic solvent vs in water (ex. ether: water partition coefficient)

Question 21

What is the ether: water partition coefficient?

Answer 21

the ratio of a compound’s solubility in diethyl ether (organic solvent) vs. water (inorganic solvent)

Question 22

Describe how molecular structure effects the rate of penetration of a non-electrolyte?

Answer 22

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

Question 23

Describe how molecular size affects the penetration rate?

Answer 23

the larger a molecule is, the more difficult it will be for it to pass through the membrane

Question 24

Which 4 molecules were used in this experiment?

Answer 24

methanol

ethylene glycol

propylene glycol

glycerol

Question 25

Which of the 4 molecules used had the most rapid penetration? explain

Answer 25

methanol

has the largest partition coefficient (most soluble), smallest molecule, and has the least OH groups

Question 26

Which of the 4 molecules used had the lowest penetration rate? explain

Answer 26

glycerol

largest molecule, most OH groups (most polar), smallest partition coefficient