This virtual lab has four sections:
Sections 1 and 2 discuss the principles of diffusion. First, you will be using a simulation that discusses some principles of diffusion. Next, you will watch a demonstration of a diffusion lab using starch and iodine that tests these principles.
Sections 3 and 4 discuss the principles of osmosis. Like the first two sections, you will first use a simulation that discusses osmosis followed by a demonstration of an osmosis lab that tests these principles.
During each simulation, you will have to read very short pieces of text as well as observe short simulations in order to answer sets of questions.
For the lab demonstrations, all questions are answered from the observations and data of each demonstration, based on what you should learn about the principles of diffusion and osmosis.
Diffusion is the process by which molecules spread from an area of higher concentration to an area of lower concentration. This process occurs due to the movement of particles and continues until there is an equal distribution of molecules throughout the space, reaching a state of equilibrium (although, the particles continue moving, but they do so in such as way that equilibrium is generally maintained).
Key Characteristics of Diffusion:
Concentration Gradient: Diffusion occurs along a concentration gradient, meaning it moves from areas of higher concentration to areas of lower concentration.
Passive Process: It does not require energy (ATP) because it relies on the kinetic energy of particles.
Factors Affecting Diffusion:
Temperature: Higher temperatures increase kinetic energy, accelerating diffusion.
Molecule Size: Smaller molecules diffuse more quickly than larger ones.
Medium: Diffusion occurs faster in gases than in liquids or solids due to the greater spacing of molecules.
Examples:
Perfume spreading in a room.
Oxygen and carbon dioxide exchange in the lungs.
Nutrient absorption in cells.
Follow along with the simulation projected on BB and use it along with the reading above to help answer 1-6.
Diffusion is the movement of particles from areas of
The type of energy that diffusion uses to move particles is
At the very beginning of the simulation (projected on Blackboard), which side had the greatest concentration of blue particles?
Eventually side A and side B will come to equilibrium, which is when the concentration is
When the temperature is higher, the movement of the molecules is
There are two containers used in this lab - a dialysis tube and a beaker.
When this lab is set-up:
in which container is the concentration of iodine the highest?
in which container is the concentration of starch the highest?
What color indicates when starch interacts with iodine?
At the conclusion of the diffusion lab (in the video, above):
Was the color of the fluid in the beaker changed:
Was the color of the fluid in the dialysis tube changed:
Where did you see evidence that starch and iodine interacted (in the dialysis tube or in the beaker):
Which substance (starch or iodine) was able to cross through the the dialysis tube?
Why did this substance cross through the dialysis tube (think about the reading about diffusion)?
Which substance was not able to cross through the plastic of the dialysis tube?
Osmosis is the process by which water molecules move across a semipermeable membrane from an area of lower solute concentration (hypotonic solution) to an area of higher solute concentration (hypertonic solution). This movement continues until there is an equal concentration of solutes on both sides of the membrane, reaching equilibrium. Recall that a solution is made of two things - a solute (salt, sugar, proteins, etc.) and a solvent (usually water).
Semipermeable Membrane: Osmosis occurs through a semipermeable membrane that allows only certain molecules (like water) to pass while blocking others (like certain solutes).
Passive Process: It does not require energy (ATP) because it relies on the movement of water molecules using kinetic energy.
Concentration Gradient: Water moves from a hypotonic solution (low solute concentration) to a hypertonic solution (high solute concentration).
Factors Affecting Osmosis:
Temperature: Higher temperatures increase the kinetic energy of water molecules, speeding up the process.
Solute Concentration: As the difference in solute concentration on either side of the membrane increases, the rate of osmosis will also increase.
Solution Types (Highly Important):
1. Hypertonic solution - will have a higher solute concentration than the hypotonic solution.
- When cells are placed in a hypertonic solution, water leaves the cell causing it to shrink.
2. Hypotonic solution - will have a lower solute concentration than the hypertonic solution.
- When cells are place in a hypotonic solution, water floods the cell, and it may burst.
3. Isotonic solution - exist when both solutions have equal solute concentrations.
- When cells are in this solution, water will enter and leave the cell at the same rate, the cell will not change in size or volume.
Examples:
Absorption of water by plant roots.
Movement of water in and out of red blood cells.
Regulation of fluid balance in cells and tissues.
Key Concept - if possible, water will always move toward the hypertonic solution.
Follow along with the simulation projected on BB, along with the reading above, to help answer 9-15.
Osmosis is the movement of
What is almost always the solvent?
Would osmosis apply in a situation in which there are no particles dissolved in water?
In the simulation, to which side did the water move to?
Why is this so?
It is best for living cells to be in what type of solution?
Consider why this may be so - this type of solution helps the cell to maintain their
Living cells that are placed in hypertonic solutions will lose
This is because water will always osmose toward the
If a cell is placed in a hypotonic solution, it will
If this (the answer the the first blank) continues to happen, the cell will eventually
Question - what evidence would model the action of osmosis in a lab setting?
This demonstration tests the principles of osmosis by comparing different solutions:
distilled water (pure water that has nothing dissolved in it) versus the solution inside of a set of deco cubes (gelatinous cubes)
sucrose solution (sucrose + water) versus the solution inside of a set of deco cubes (gelatinous cubes)
Remember, osmosis is concerned with the movement of water across a semipermeable membrane. Also recall that in osmosis, water will tend to move toward the hypertonic solution.
In this demonstration, the presenter will place three deco cubes in a distilled water solution and three deco cubes in a sucrose solution. Both sets of deco cubes will be permitted to soak for the same length of time - 120 minutes. The mass of the deco cubes will be taken prior to soaking, after 20 minutes of soak time, after 40 minutes of soak time, and after 120 minutes of soak time.
Observe For This:
**Changes in mass (she improperly refers to this as "weight")**
If the deco cubes gained mass at the end of the demonstration, they likely gained water
If the deco cubes lost mass at the end of the demonstration, they likely lost water
If the mass of the deco cubes is unchanged, they neither gained nor lost water.
Question to consider when interpreting the data from this section:
What would a change or non-change of the mass for each set of deco cubes after the demonstration tell you about the types of solution in each set-up (think about where water tends to move)?
Three Basic Types of Solutions:
Hypertonic - solution with the highest solute concentration.
Hypotonic - solution with the lowest solute concentration.
Isotonic - when both solutions have equal solute concentrations.
I promise that I read the above section, titled, "Read this before you move forward."
During the set-up of the lab (use the above video):
Initial Mass of the deco cubes in the DI (distilled) water?
Initial Mass of the deco cubes in the sucrose solution?
After 20 minutes of "soak time" in each solution (use the above video):
Mass of the deco cubes in the DI (distilled) water?
Mass of the deco cubes in the sucrose solution?
After 40 minutes of "soak time" in each solution (use the above video):
Mass of the deco cubes in the DI (distilled) water?
Mass of the deco cubes in the sucrose solution?
After 120 minutes of "soak time" in each solution (use the above video):
Mass of the deco cubes in the DI (distilled) water?
Mass of the deco cubes in the sucrose solution?
What was the initial mass of (from #17):
Deco cubes in the DI (distilled) water?
Deco cubes in the sucrose solution?
What was the final mass (after 120 minutes) of (from #20):
Deco cubes in the DI (distilled) water?
Deco cubes in the sucrose solution?
What was the change of mass of (change of mass = final mass - initial mass):
(If it lost mass, record this as a negative number; example: -1.1)
Deco cubes in the DI (distilled) water?
Deco cubes in the sucrose solution?
In the trial in which the deco cubes were placed in the DI water (for the first two blanks, the answer is either - deco cubes or the DI water):
where was the hypertonic solution?
where was the hypotonic solution?
How do you know?
In the trial in which the deco cubes were placed in the sucrose solution (for the first two blanks, the answer is either - deco cubes or the sucrose solution):
where was the hypertonic solution?
where was the hypotonic solution?
How do you know?
In which solution did the deco cubes gain the most mass (DI water or sucrose solution)?
Which solution would have been the most like a hypotonic solution for each of these trials (DI water or sucrose solution)?
How do you know (be brief)?
Which solution was the most like a hypertonic for each of these trials (DI water or sucrose solution)?
How do you know (be brief)?
Consider that the concentration of salt in normal blood cells is 0.9%.
If you were sick and in the hospital, especially with something like the flu, you might become dehydrated and would need to receive an IV of saline solution to return your body's fluid levels to homeostasis (to maintain the size and volume of your cells).
What is the concentration of the IV saline (salt) solution given to you by the hospital?
Imagine someone who has become ship-wrecked on an island in the middle of the Pacific Ocean without immediate access to freshwater.
The island is surrounded by water that has a salt concentration of approximately 3.5%.
If the typical concentration of salt in human cells is approximately 0.9%, explain, from the concept of osmosis, why drinking seawater is a bad idea.
(I must regrade this.)