Diffusion
The movement of material from an area of higher concentration to an area of lower concentration.
Osmosis
The diffusion of water from an area of high concentration to an area of low concentration.
What was the purpose of this lab?
The purpose of this lab was to design a setup to test diffusion through a semipermeable membrane and to test osmosis in onion cells with salt solution and distilled water.
Selectively Permeable Membrane
It allows some molecules and other particles to enter and exit while blocking others.
Can the selective permeability of the membrane change?
In a cell it can change depending on changes in its internal and external environment of the cell.
Is there always flow throughout the cell and the solution?
Yes, there always is flow because the materials are always in movement so there will always be flow but both inside and outside of the cell will be equal in concentration. It's called dynamic equilibrium.
How do you know starch did not diffuse out of the cell?
If starch diffused out of the cell the iodine solution (the indicator) would become bluish black because when iodine and starch mix it changes color but the solution outside the cell stayed amber so starch did not diffuse out the cell.
How do you know glucose did diffuse out of the cell?
Glucose diffused out of the cell because the indicator strip for glucose changed color, indicating a positive result.
What is the indicator for starch?
Iodine
What is the indicator for glucose?
Glucose test strip and a change of color.
What color does starch and iodine turn when mixed?
Bluish-black
What color does glucose indicator strip turn when a positive test for glucose occurs?
Blue/green
Since glucose was able to diffuse through the membrane but starch was not what does that say?
It says that glucose is smaller than starch so its able to pass through the membrane but starch cannot. Starch is too big to diffuse.
Was starch able to pass through the membrane? What does that mean in scientific terms?
No, the membrane is not selectively permeable to starch because of the size of the starch.
Was glucose able to pass through the membrane? What does that mean in scientific terms?
Yes, the membrane is selectively permeable to glucose because of the small size of the glucose.
What happened when you added salt solution to the onion cell? What does that mean?
The cell wall stayed the same, but the cell membrane shrank, showing that the salt water is a hypertonic solution, so water from inside diffused outside the cell to maintain equilibruim. Hypertonic = shrink
What happened when you replaced the salt solution back with distilled water? What does that mean?
The cell membrane size increases showing that the distilled water is a hypotonic solution, so water outside the cell diffused into the cell. Hypotonic = swell
Did starch diffuse out of the dialysis tubing? Why or why not?
No starch did not, the starch is too big to fit through the pores.
Did glucose diffuse out of the dialysis tubing? Why or why not?
Yes it did, the glucose was small enough to fit through the pores.
What materials diffused through the membrane?
What materials did not diffuse through the membrane?
Iodine and glucose diffused through the membrane and starch did not diffuse.
Which is bigger starch or glucose?
Starch
Draw a picture or explain the initial state and final state of the dialysis tubing experiment?
In the final state glucose was outside the dialysis tubing and iodine was inside and outside the dialysis tubing.
Hypotonic
Greater amount of solute inside the cell than outside. The cell swells/gets bigger.
Isotonic
Same amount of solute inside and outside the cell. The cell remains the same size.
Hypertonic
Greater amount of solute outside the cell than inside the cell. The cell shrinks/gets smaller.