Diffusion, Osmosis, and Water Potential Lab

Lab Activity C: Imagine that you are an agri-science consultant to a large corporate farm that raises 7,000 acres of wheat on desert land adjoining the Mediteranean Sea. Just before the water matures, all the wells used for irrigation water run dry. The farm manager wants to irrigate the fields with water drawn from the Mediterranean. From previous test, you know that the average solute potential of root tissue taken from the wheat fields is -11.13 bars. You test the seawater and determine its solute potential to be -24.26 bars. What will you advice the farm manager and why?

I would tell the farm manager not to use seawater. Because the sea has a lower water potential than the root of the wheat, the Mediterranean sea would dehydrate the roots. The water will move out of the roots and into its surroundings, making it harder for the plants to grow due to dehydration.

Lab Activity B: Write a hypothesis that this experiment is designed to test.

If there is a higher sucrose concentration, the dialysis bag will experience a higher percent change in mass than with a lower sucrose concentration

Lab Activity B: What does the change in mass indicate?

The change in mass of the dialysis bag indicates that there is more water moving into the bag than out of it.

osmosis

The diffusion of water molecules across a semipermeable membrane

Diffusion

The movement of molecules from areas of higher concentration to areas of lower concentration

Lab Activity A: Does this activity account for the diffusion of all the molecules you listed on Figure 2 and in your predictions? If not, what data could have been collected to show the net directions of diffusion of this molecule or molecules?

This activity does account for all of the molecules listed in figure 2, but not all the molecules in my predictions. The activity doesn't include how the water moves during this process. To do the water, we would have to follow the steps in activity b, which would measure the change of the mass before and after diffusion.

water potential

concept used to combine the differences in solute concentration and pressure to predict the direction in which water will diffuse through living plant tissues.

What is IKI

reacts with starch to five a dark blue, almost black color. When IKI reacts with starch, it becomes part of the starch molecule and is removed from the solution.

Hypertonic solutions

solutions that cause cells to shrink or shrivel due to loss of water. too much solute

What are we investigating?

the passage of materials through a semipermeable membrane by passive transport

Hypotonic solutions

those with lower solute concentrations and higher water concentrations; cells placed in these solutions gain water; and if they lack a cell wall, may burst

How to determine solute potential

ψs = -iCRT Where i = ionization constant (for sucrose, this value is 1) C = molar concentration of sucrose per liter at equilibrium (must be determined experimentally, and can easily be read of the graph of the data) R = pressure constant (0.0831 liter bar/mole K) T - temperature of solution in Kelvins (K - celsius + 273)

Lab Activity B: Calculate the percent change in mass. Use the following formula. Record the results in Table 2 for all the concentration tested in class.

% change in mass = Change in mass/initial mass x 100%

Semipermeable membrane

A membrane that allows some molecules to pass through but does not allow other molecules to pass through.

What does osmosis depend on and why is it still efficient?

A process that depends upon random motion might seem inefficient, but so many water molecules are involved and they move so fast, that it is estimated that a red blood cell floating in blood plasma gains an amount of water equal to 125 times its own volume every second. It also loses the same amount of water each second, all by osmosis. This occurs because the concentration of solutes in the blood plasma is the same as the concentration of solutes in red blood cells.

Isotonic solutions

Solutions that have the same solute concentrations

Lab Activity B: List at least three variables that could influence the outcome of this experiment? Briefly describe the method of control used for each of these variables.

Three variables that could influence the outcome of this experiment are the amount of water, the amount of solution with sucrose, and the amount of time it is left for. The amount of water was decided to stay at 160-170 mL for each while the amount of sucrose was decided to be 25mL. Thirty minutes was how long the dialysis bag was left in the sucrose and water solution.

What is the unit for water potential?

bars

What is the membrane in this lab

dialysis tubing, is semi permeable because it has submicroscopic holes through it.

Ways molecules pass through the membrane

expend energy (active transport), or through processes driven by the kinetic (thermal) energy of molecules (passive transport)

Lab Activity C: How to find C value?

find the point where the line of your data crossed the 0 lind (x-axis) of the grid. This is the equilibrium point; at this point there is no net gain or loss of water from the potato cells. Read the corresponding value of sucrose molarity for this point. This is the molar concentration of sucrose that produces equilibrium. Below, record this concentration of sucrose as your experimentally determined value for C.

Lab Activity A purpose

I will fill a beaker with about 170ml distilled water. I will add about 4 ml of IKI solution to the beaker. You need to record the initial solution color in Table 1. I will dip a glucose test strip into the solution and you will record the initial glucose test results in Table 1. Use the + symbol to indicate a positive test result for the glucose and the - symbol to indicate a negative result. I will use a glucose test strip to test the glucose/starch solution. You need to record these results in Table 1. I will demonstrate how to fill a dialysis tubing with glucose/starch solution. Pay attention so you know how to do this since you will be doing this in Part B of this lab. The dialysis tubing will be immersed in the beaker for 30 minutes.

cytolyze

the bursting of a cell

Lab Activity B: When you drink a glass of water, most of it is absorbed by osmosis through the cells linking your small intestine. Drinking seawater can actually dehydrate the body. How?

The seawater has more solute (salt) than the regular water. Through osmosis, the cells attempt to balance the amount of salt on both sides of the cell membrane, which has salt enter the cell and water to exit the cell, causing dehydration.

crenate

when a cell shrinks due to water loss

Water potential equation

Ψ = Ψs + Ψp Water potential = solute potential + pressure potential

Lab Activity C: Procedure

In this activity you will investigate water potential by immersing potato cores in a sucrose solution and determining the change in mass, if any, of the cores. You will graph the data and use the graph to determine a value for C. Using the experimentally determined value for C, you will then calculate a value for ψs. Procedure The cup given to you has a label on it that will tell you which sucrose solution you are assigned to use. Use a cork borer to cut four cylinders of potato tissue from the potato. Do not stab your hand with the cork borer. Trim both ends of each cylinder to remove the skin. Cut each cylinder tinto actions that are approximately 3 cm in length. Use cause when slicking the cylinders so you do not injure yourself or others. Use a balance to determine the total mass of all the potato sections. Record this as the initial mass on Table 3. Place all of the potato sections into your labeled cup. Pour 100 ml of the assigned sucrose solution into the cup. Cover the cup with plastic wrap. (Why do you think this step is necessary?) Let potato cores sit overnight. Remove the potato sections from the sucrose solution. Blot them on paper towels to remove excess solution. Use a balance to determine the final mass. Record this in Table 3. Use a thermometer to take the temperature of the solution before you dump it down the drain and rinse the cup.

Molecular movement description

Molecules are in constant random motion. By chance, a molecule's motion may move it toward the membrane (Figure1). If it collides with the membrane wall, it rebounds. If its motion takes it toward a pore, it may either pass through the pore, or it may rebound, depending upon the size of the molecules relative to the diameter of the pore. Molecules that are small enough to pass through the posters can pass through in either direction. Notice that on one side of the membrane solute molecules have displaced some of the water molecules. Thus, there is higher concentration of water molecules on the opposite side of the membrane. More water molecules are available to collide with the membrane on the side having the higher concentration of water. Thus, although water molecules will move in both directions across the membrane, more will move front he side having the higher concentration to the side having the lower concentration.

Lab Activity A: Compare your results with your predictions. Do you find any conflicts that would cause you to revise your predictions? If so, explain.

My results did not all match my predictions. I believed that the IKI would move into the bag and that the glucose would move into the cup, which were both correct. I also thought that the starch would move into the IKI solution in the cup. I later found that to be incorrect because the starch molecules are too big to pass through the semi permeable membrane, in this case, the dialysis tubing.

Lab Activity C: A 1cm diameter, 6 cm long core is removed from a carrot (see figure3). The resulting hole is filled with corn syrup (highly concentrated sugar), and a glass tube is inserted into the hole to make a watertight seal. The carrot is suspended in a cup of pure water. Beginning with the carrot cells adjoining the hole, and going out to the carrot epidermal cells exposed to the water, describe what will happen to the carrot cells. Also, what will happen to the level of liquid in the glass tube and why?

Syrup Level in the tube would rise. higher potential in the carrot than the tube, water would move into the tube. Thus lowering the water in the carrot so the water in the cup would go into the carrot. You also needed to address the cells layers of the carrot from the inside to the outside. The carrot cells will expand, since the water potential is higher outside of the carrot cells. The outer layer of the carrot would expand more than inner layers tho.

Lab Activity A: What does your data tell you about the sizes of the molecules relative to the pore size of the dialysis tubing?

The data tells me that a polysaccharide like starch is too big to pass through the dialysis tubing. The pore size is too small while the polysaccharide is too large.

Lab Activity B: What is the Dependent Variable?

The dependent variable is the percent change in mass of the dialysis bag.

Lab Activity A: Where does each solution move?

The dialysis bag at this point is now a purple color while the cup liquid is still yellow. The starch did not move outside of the bag because the molecules were too large, but the glucose moved into the cup. The IKI moved into the dialysis bag as well.

Lab Activity B: In which, if any, of the experimental setups were the solutions in the bag and outside of the bag isotonic to each other?

The experimental setup with 0.0M of solute was isotonic. While there was a percent change, the change was so small that it isn't impactful on the relationship inside and outside of the setup.

Lab Activity B: On the basis of this graph, write a statement that expresses the relationship of solute concentration and direction of net movement of water molecules in osmosis.

The higher sucrose molarity there is, the more water moves into the dialysis bag. This is shown by the increasing percent change between the final and initial dialysis bag mass as the solute concentration increases.

Lab Activity B: What is the Independent Variable?

The independent variable is the sucrose molarity.

Lab Activity B: What variable is being tested in this experiment?

The variable being tested in this experiment is the movement of water.

Lab Activity C: A chef chops vegetables into a bowl of water. Would you expect the vegetable slices to gain or lose water? Explain your answer in terms of water potential

The vegetable slices would gain water because while the interior does have some water, the bowl would have more. In terms of water potential, the vegetable slices have a lower water potential than the surrounding water, and would therefore gain water.

Lab Activity B: Procedure

You will investigate the influence (if any) of solute concentration on the net movement of water molecules through a semipermeable membrane. The solute you will use is sucrose in the following molar concentrations. 0.0M (distilled water) 0.2M 0.4M 0.6M 0.8M 1.0M Procedure: Pour 160 - 170 ml of distilled water into a beaker. Obtain a piece of dialysis tubing that has been soaked in water. The tubing should be soft and pliable. Roll the tubing between your thumb and index finger to open it. Tie a strong knot in the other end. This will form a bag. Using a small funnel, pour 25 ml of the solution you were assigned into the dialysis bag. Smooth out the top of the bag, running it between your thumb and and index finger to expel the air. Tie off the open end of the bag. Leave enough room in the bag to allow for expansion. Dry the bag on a paper towel and then determine its mass. Record this as the initial mass on the class data sheet. If more than one person does this solution average together all the masses that get listed there and when the lab is complete only one mass should be input into Table 2, the averaged mass. Immerse the dialysis bag in the water in the cup. Make sure that the portion of the bag that contains the sucrose solution is completely covered by the water in the cup at all times. Wait 30 minutes before continuing to the next step. After 30 minutes, remove the bag from the cup and dry it on paper towels. Mass the bag and record the final mass on the class data sheet. Again only the final averaged mass will be input into your data table below.