Diffusion Basics
What is the movement of molecules from an area of high concentration to low concentration called?
Diffusion
What is the diffusion of water across a selectively permeable membrane called?
Osmosis
In the dialysis bag experiment, what structure was the dialysis tubing modeling?
A selectively permeable cell membrane.
What type of transport moves molecules from high concentration to low concentration and does not require cellular energy?
Passive Transport
A plant cell is placed into a hypertonic solution. Will water move into or out of the cell?
Out of the cell
During diffusion, molecules move down their concentration _____.
Gradient
In which type of solution does a cell generally gain water?
Hypotonic
Why did we use iodine in the dialysis bag experiment?
To test for the presence of starch. Iodine turns dark blue/black when starch is present.
What type of passive transport uses a membrane protein to help molecules cross the membrane?
Facilitated Diffusion
What happens to a plant cell when it loses a significant amount of water in a hypertonic solution?
The cell membrane pulls away from the cell wall. This is called plasmolysis
Name two factors that can increase the rate of diffusion.
Higher temperature, steeper concentration gradient, smaller molecule size, or greater surface area.
In which type of solution does a cell generally lose water?
Hypertonic
Why did we use Benedict's solution?
To test for reducing sugars such as glucose.
What type of transportation requires energy from the cell?
Active Transport
What happens to an elodea plant cell when salt is added to the surrounding water?
The surrounding solution becomes hypertonic, causing water to leave the cells and plasmolysis to occur.
A drop of food coloring is placed into a beaker of water. Eventually, the color spreads throughout the water. What process is occurring?
Diffusion
What happens to a typical animal cell placed in a hypotonic solution?
Water enters the cell, causing it to swell and potentially burst.
Why was starch unable to diffuse through the dialysis tubing while glucose could?
Starch molecules were too large to pass through the pores of the dialysis tubing, while the smaller glucose molecules could pass through.
Oxygen is small and nonpolar. How can it cross the plasma membrane?
Simple diffusion directly through the phospholipid bilayer.
You observe that the chloroplasts in an Elodea cell appear to have moved toward the center of the cell and away from the cell wall. What process is this evidence of?
Plasmolysis caused by water leaving the cell through osmosis.
True or False: Molecules stop moving once equilibrium is reached.
False. Molecules continue moving randomly, but there is no net movement in one direction.
A cell is placed into a solution with a higher solute concentration outside the cell. Which direction will water move?
Water moves out of the cell toward the area with the higher solute concentration.
If the solution outside the dialysis bag turns blue/black after the experiment, what does that tell you?
Starch moved out of the dialysis bag, meaning the tubing was permeable to starch.
Glucose cannot easily pass through the hydrophobic interior of the phospholipid bilayer. How can glucose enter a cell?
Through facilitated diffusion using a membrane transport protein.
A student says, "The glucose moved because the solution was stirred." What evidence from the dialysis bag experiment would better demonstrate that glucose actually crossed the membrane?
A positive Benedict's test on the appropriate solution would provide evidence that glucose was present there after the experiment.