EXERCISE 9: diffusion and osmosis
In the Movement of Water across a Selectively Permeable Membrane Lab, which thistle had the most diluted corn syrup?
30% corn syrup b/c it caused the most water to move from the breaker into the thistle, making it the most diluted.
When testing osmosis by measuring thistle tube height, what is the first step in the procedure?
Apply membranes to the thistle tubes
When testing tonicity in Elodea cells, once Elodea cells were placed in distilled water, what did you observe?
Cell membranes pressed tightly against the cell walls and there where full central vacuoles
What is an example of osmosis?
Cells of our kidneys reabsorb water to prevent it from all leaving through our urine.
What is a major difference between red blood cells and Elodea cells?
Elodea cells have a cell wall, which protects them from bursting.
Hypotonic solution
Higher concentration inside the cell than outside (water goes in)
Hypertonic solution
Higher concentration outside the cell than inside (water goes out)
Where your results supported for the "Tonicity in Elodea Cells" lab hypothesis?
I observed that due to the hypertonic solution, water is leaving the cell, which supports the hypothesis.
What type of cells do a hypertonic solution show when looking under a microscope?
It showed crenated cells because the water was leaving the red blood cells
Selective Permeable membranes
Membranes are selective due to their structure (phospholipid bilayer)
What type of cells have cell walls that protect them from bursting and which do not?
Plant cells have cell walls, animal cells do not.
Isotonic
Same concentration of solute both inside and outside the cell. Net movement of water.
What was your hypothesis for the "Tonicity in Elodea Cells" lab?
The Elodea placed in a hypertonic solution will shrink because osmosis will draw water out of the cells, causing their volume to decrease.
What is tonicity?
The ability of a solution to change the volume of a cell through osmosis.
What happens to cells exposed to a hypertonic solution?
The cells will cause the plasma membrane to pull away from the cell wall as the vacuole inside the plant cell loses water.
What causes the increase in the level of the sugar solution in the diffusion over the membrane lab?
The diffusion of water into the thistle tube.
Why would a fresh water plant die if you placed it into a hypertonic salt-water march environment?
The hypertonic 10% NaCl solution produced the shrunken Elodea cells
What was your hypothesis in the "Movement of Water across a Selectively Permeable Membrane" lab?
The more water is drawn up into the thistle tube, the higher the concentrations of corn syrup.
What is osmosis?
The movement of water across a selectively permeable membrane from a hypotonic solution.
Do your results for the "Movement of Water across a Selectively Permeable Membrane" lab support your hypothesis?
Yes because 30% corn syrup, which was the highest concentration, had the highest amount of water with 12 mL.
Osmosis
diffusion of water across a differentially permeable membrane. The movement of water across a selectively permeable membrane from a hypotonic solution (low solute, high water) into a hypertonic solution (high solute, low water).
Lighter molecules diffuse ____ and heavier diffuse ____.
faster; slower
Where do you dispose items contaminated with blood?
in the biohazard container
You made a wet mount slide of each blood/solution mixture when testing for tonicity. What did you learn from this?
in the tube with the highest concentration of solutes, the cells had shriveled (crenated).
Phenolphthalein
is a pH indicator that turns red in basic solutions.
Iodine
is a starch indicator that changes color from yellow to dark blue in the presence of starch.
Hemolysis
is the destruction of red blood cells due to the influx of water
Diffusion
is the passive movement of particles. The direction depends on the concentration gradient, heat, and pressure (always high-->low).
Dialysis
is the separation of substances by means of their unequal diffusion through a deferentially permeable membrane.
Plasmolysis
is the shrinking of the cytoplasm in response to diffusion of the cell.
Dialysis tubing
is used to model a differentially permeable membrane. In differentiation to the cell membrane, it is only selective based only on molecular size.
What are the characteristics of a tonicity solution?
it is related to solute content, gives info about potential changes in cell volume when cells are placed in that solution, and is related to membrane permeability to solutes.
When the potato appears crisp what can you determine about the solution?
it was a hypertonic distilled water solution.
When the potato appears limp what can you determine about the solution?
it was a hypertonic solution
Rate of diffusion depends on _____
size, polarity, and solubility.
What prevents a plant cell from bursting in a hypotonic solution?
the cell wall
Brownian Movement
the erratic random movement of microscopic particles in a fluid, as a result of continuous bombardment from molecules of the surrounding medium.
Water potential
the potential energy of water per unit volume relative to pure water in reference conditions. It quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure and matrix effects such as capillary action.
Tonicity in cells refers to the concentration of solute in a solution outside of a cell, relative to
the solute concentration of the cytoplasm
What can you assume when testing the tonicity of red blood cells, if the solution became transparent after adding blood cells?
the solution was hypotonic and the cells had burst.
When testing tonicity of red blood cells, if the solution became transparent after adding blood cells, you could assume____.
the solution was hypotonic and the cells had burst.
Why does a hypotonic environment cause a cell to swell or burst?
the water in the solution moves into the plant cell, the solutes in the solution have a lower concentration than the solute concentration inside the plant cell, and the water is moving down its concentration gradient from high to low.
What does it mean when cells are crenated?
the water is leaving the cells.
What happens when you place celery into a hypotonic freshwater solution?
the water should enter the celery cells and cause the cells to swell.
When testing tonicity in potato strips, you soaked potato strips in different solutions. Based on what were you able to determine the tonicity of the solutions?
whether the potato was crisp or limp
