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Name: Date: Period:

Cellular Transport Lab This lab MUST be completed in its entirety for credit. All pre-lab, in-lab, post-lab questions must be

answered thoughtfully. I’m asking you these questions to guide you through your lab report…your

answers should indicate whether you know what you’re doing or not.

The life of a cell is dependent on efficiently moving material into and out of the cell across the cell

membrane. All cells need sugars and oxygen to make energy to fuel daily life. Cells also need raw

materials to be able to repair themselves and to build new cells. And of course cells always need water

to remain healthy. All these materials have to move into a cell to feed it. On the other hand, cells

produce waste products during their daily activities. Cells make the waste product, carbon dioxide, when

they make energy. They also make the waste product ammonia when they digest proteins. Both of these

waste products have to be removed or the cell will be poisoned and die.

Most of these materials move passively—costing the cell no energy—through the process of diffusion.

Diffusion is the movement of molecules from an area of higher concentration of those molecules to an

area of lower concentration. Another way to phrase this is that molecules move down the concentration

gradient—a metaphorical “downhill” from high concentration to low concentration. A good metaphor

for this movement of molecules is what happens if you were to open a bottle of perfume in one corner

of a room. It would not be long before someone in the opposite corner of the room would smell the

perfume. The molecules moved from an area of higher concentration of perfume where the open bottle

was to an area of lower concentration of perfume like the opposite corner of the room. Eventually a

balance, or dynamic equilibrium, is reached. In other words, the concentration of perfume will be

approximately equal throughout the room and no net movement of perfume will occur from one area to

the other.

However, diffusion does not entirely explain the movement of ions and molecules into and out of the

cell. Sometimes a cell needs to move material against the concentration gradient. They need to move

materials from areas of low concentration to areas of higher concentration. This would be the case for

materials that are very valuable to the cell, like sugars, that the cell would use to make energy. That

would be like swimming upstream against the current, so it requires energy. The only way for cells to do

this is to use energy to pump the material “upstream” across the cell membrane. We call this process,

active transport, because it actively uses energy to move molecules either into or out of the cell. The

energy that the cell uses is in the form of ATP.

In this experiment you will measure the diffusion of small molecules through dialysis tubing, an example

of a selectively permeable membrane. Small dissolved molecules (solutes) and water molecules can

move freely through a selectively permeable membrane, but larger molecules will pass through more

slowly, or perhaps not at all. The size of the minute pores in the dialysis tubing determines which

substances can pass through the membrane.

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Pre-Lab Questions: Will require some research (keep track of your sources)

1. Describe why the cell membrane acts as a good barrier (structure/function of phospholipid bilayer,

protein channels, glycoproteins and glycolipids, etc).

2. What is dialysis tubing? How does it represent a cell membrane in this lab activity?

3. Why is it important that cells have the ability to exchange materials into and out of a cell? Give some

examples of materials that must move in or out. Materials that move across easily vs. materials thatdo

not.

4. How do molecules that cannot pass easily get across the membrane? List and discuss the different types

of active transport.

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5. Define diffusion and give examples of diffusion working in the human body.

6. Define osmosis and give examples of osmosis working in the human body. Discuss water potential here.

7. Discuss tonicity, or osmotic states. What are the different types, what happens to plant and animal cells in

hyper and hypotonic environments, which type of solution/environment do plant and animal cells prefer

and why?

8. Discuss cellular respiration in cells. Considering the equation, what do cells need to transport across the

membrane to support this process? Specifically, how are these materials exchanged?

Again…. In this experiment you will measure the diffusion of small molecules through dialysis tubing, an

example of a selectively permeable membrane. Small dissolved molecules (solutes) and water molecules

can move freely through a selectively permeable membrane, but larger molecules will pass through

more slowly, or perhaps not at all. The size of the minute pores in the dialysis tubing determines which

substances can pass through the membrane.

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Day 1- Diffusion

Test Procedure

Starch 1. 4 drops of Lugol’s Iodine (IKI) 2. Solution immediately turns from amber to blue-black

Glucose 1. 4 drops of Benedict’s solution 2. Solution turns from blue to bright orange when heated

1. Cut a 30cm piece of 2.5cm dialysis tubing and soak it in water until it is soft enough to work with. Tie off one end of the tubing (like a balloon) to form a bag. This will be our model “cell.” To open the other end, rub the end between your fingers until the edges separate. Why are we using dialysis tubing to represent a cell? 2. Pour 15mL of the 15% glucose/1% starch solution in the cell using a funnel. Tie off the other end of the tubing, leaving sufficient space for expansion of the contents in the cell. In case any solution spilled on the outside, rinse off the cell under running water and set aside in a beaker for now. Record the initial color of the solution in the cell in Section 1 of Table 1 (Experimental Observations). Distinguish between the sizes of glucose and starch molecules? Which would pass through a cell membrane easiest? 3. Now we need to perform tests on this solution we just used. Using a pipette, place a 2mL sample of the 15% glucose/1% starch solution into a clean test tube. Test the solution for the presence of glucose. Record the results in Section 2 of Table 1. How will you test for glucose? Why are you testing this solution to make sure that there’s glucose? 4. Using a pipette, place another 2mL sample of the 15% glucose/1% starch solution into a clean test tube. Test the solution for the presence of starch. Record the results in Section 3 of Table 1. How will you test for starch? Why are you testing this solution to make sure there’s starch?

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5. Place 200mL of water in a 250mL beaker. Now we need to perform the same tests on this fluid. Place a 2mL sample of the water into a clean test tube and test for the presence of glucose. Record the results in Section 2 of Table 1. 6. Place a second 2mL sample of the water into a clean test tube and test for the presence of starch. Record the results in Section 3 of Table 1. Why are you testing water for glucose and starch? 7. Now add Lugol’s iodine to the water in the beaker. Add only enough iodine to turn the water a medium amber color. Record this initial color of the solution in Section 1 of Table 1. 8. Now immerse the dialysis bag in the beaker. Cover the beaker and allow the experiment to stand undisturbed overnight. Why are you adding Lugol’s iodine to the beaker that you are putting your cell into? 9. Table 2 is to be used to make predictions of what you expect to occur overnight in the beaker. Fill in the Day 1 Initial Observations columns (Column A) from your observations today. Then complete your predictions for each section in Column B.

10. Complete the “Day 1 Initial State” diagram in Figure 1. You can represent movement with arrows

and use color pencils to indicate any color changes that may occur. You should also label the cell as

hypertonic or hypotonic. Please label the liquid in the beaker hypertonic or hyptotonic.

Experimental Hypothesis:

If glucose and starch are added to a model cell, then the water outside the cell will test ______ for

glucose and _____ for starch because glucose molecules can diffuse through the selectively permeable

membrane, while starch is too large to cross.

Null Hypothesis: you write this one out….

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Day 1-Osmosis Since all life takes place in water—either external waters or internal waters—we must also address the special case of the movement of water across cell membranes in our study of diffusion. The diffusion of water through a selectively permeable membrane is referred to as osmosis. As with the diffusion of solutes, water moves from a region of higher concentration of water to a region of lower concentration of water. This is often also stated as movement from a region of higher water potential to a region of lower water potential. Distilled water (pure water) has the highest concentration of water or the highest water potential. The concentration of water decreases as solutes—like sugars and salts— are dissolved in the water. Using the principles you learned in the first exercise on diffusion, we will now investigate the movement of water in and out of a model cell using sucrose as our solute. 1. Cut a 30cm piece of 2.5cm dialysis tubing and soak it in water until it is soft enough to work with. Tie off one end of the tubing (like a balloon) to form a bag. This will be our model “cell.” To open the other end, rub the end between your fingers until the edges separate. Why are we using dialysis tubing to represent a cell? 2. Measure out 15mL of concentrated (1.0 molar) sucrose solution and pour it into the dialysis bag using a funnel. Tie off the other end of the bag, leaving space for expansion of the contents in the bag. What is sucrose? Is it large or small? Should it be able to cross over a cell membrane easily? 3. In case any solution spilled on the outside, rinse off the model “cell” you just made by holding it under running water. 4. Carefully blot the outside of the “cell” with a paper towel. Mass the sucrose solution “cell” (in grams) on a scale and record the Day 1 Initial Mass in Table 1 (Osmosis Individual Data). Why are you massing this cell on day 1? What might you be looking for day 2? 5. Place the “cell” in an empty 250mL beaker. Now fill the beaker with distilled water so that the sucrose “cell” is submerged. Label the beaker with tape (“sucrose solution cell”). What does the water in the beaker represent? Is your cell hypo or hypertonic to its environment? 6. Cut a second 30cm piece of 2.5cm dialysis tubing and soak it in water until it is soft enough to work with. Tie off this tubing to make another “cell”. However, this time fill the bag with 15mL of distilled water.

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7. Carefully blot the outside of the bag with a paper towel. Mass the water “cell” (in grams) on a scale and record the Day 1 Initial Mass in Table 1. 8. Place the “cell” in an empty 250mL beaker. Now fill the beaker with sucrose solution so that the “water cell” is submerged. Label the beaker with tape (contents of beaker and contents of cell). Is this second cell hypo or hypertonic to its environment? 9. Cover the beakers and allow the experiment to stand undisturbed overnight. 10. Complete the Prediction column in Table 1. Experimental Hypothesis: If a sucrose solution is added to a model cell and placed in distilled water, then there will be a ____ change in mass to the model cell because water moves to where there is ________ solute during osmosis. Null Hypothesis: You write this one out… _____________________________________________________________________________________

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Day 2-Diffusion

1. It is now the second day. Record the final color of the solution in the cell and the final color of the solution in the beaker in Section 1 of Table 1. 2. Observe the colors of the solution in the cell and in the beaker as a test for starch and record the results for starch in Section 3 of Table 1. 3. Take a sample of the liquid in the beaker and test for the presence of glucose. Record the results in Section 2 of Table 1. 4. Take a sample of the liquid in the cell and test for the presence of glucose. Record the results in Section 2 of Table 1. What happened to the glucose that was in the cell? What happened to the starch that was in the cell? 5. Compare your predictions to your actual data. Any surprises? 6. Complete the “Day 2 Final State” diagram in Figure 1. Show final movement of molecules using arrows, label whether the cell is hypertonic or hypotonic to its environment, etc.

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Day 2-Osmosis 1. Retrieve your Osmosis beakers with the “sucrose solution cell” and “water cell”. 2. Carefully remove each cell from its beaker. Gently blot the outside of the “cell” with a paper towel. Mass each “cell” (in grams) on a scale and record the Day 2 Final Mass in Table 1. 3. Calculate the Change in Mass for each “cell”. Record the change in Table 1.

Change in Mass (ΔM) = Final Mass (MF) – Initial Mass (MI)

What does it mean if the Change in Mass is a positive number?

What does it mean if the Change in Mass is a negative number?

4. Obtain data from the other lab groups in your class to complete Table 2 (Osmosis Class Data). Calculate the class average. 5. Complete the diagrams in Figure 1. Be sure to indicate the movement of water with an arrow in each diagram, label the cell hyper or hypotonic. Label the environments hyper or hyptonic.

6. Complete the Summary Questions after you have completed Day 1 & 2 Results sections.

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Diffusion Results Diffusion Table 1: Experimental Observations

Initial Contents

1 Color of Solutions

2 Presence of Glucose

3 Presence of Starch

A Day 1

(Initial)

B Day 2 (Final)

A Day 1

(Initial)

B Day 2 (Final)

A Day 1

(Initial)

B Day 2 (Final)

Cell 15%

glucose 1% starch

Beaker H2O & iodine

Diffusion Table 2: Predictions

Initial Contents

4 Color of Solutions

5 Presence of Glucose

6 Presence of Starch

A Day 1

(Initial) From Table 1

B Day 2 (Final)

A Day 1

(Initial) From Table 1

B Day 2 (Final)

A Day 1

(Initial) From Table 1

B Day 2 (Final)

Cell 15%

glucose 1% starch

Beaker H2O & iodine

Diffusion Figure 1: Movement of a Solute Across a Membrane Label the diagrams below to identify the contents of the bag and the beaker in the Day 1 Initial State and in the Day 2 Final State of the experiment.

Diffusion Day 1: Initial State Diffusion Day 2: Final State

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Osmosis Results Osmosis Table 1: Individual Data

Set Up

Mass of Cell

Day 1 Initial Mass

Day 2 Final Mass

Change in Mass

Predicted Change in

Mass ( + or -)

A Sucrose solution in cell; Water in beaker

B Water in cell; Sucrose solution in beaker

Osmosis Table 2: Class Data

Set Up

Change in Mass of Model Cells

Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Total Class

Average

Sucrose solution in cell; Water in beaker

Water in cell; Sucrose solution in beaker

Osmosis Figure 1: Movement of Water Across a Membrane Label the diagrams below to identify the contents of the “cell” and the beaker. Clearly draw an arrow in each diagram to indicate the movement of water during the experiment.

Osmosis: Sucrose Solution in Cell - Osmosis: Water in Cell – Water in Beaker Sucrose Solution in Beaker

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Diffusion Questions: 1. Which substance(s) are entering the dialysis bag and which are leaving the bag? What experimental

evidence supports your answer?

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2. Explain the results you obtained by discussing concentration differences and membrane pore size.

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3. Although we didn’t measure it, what other molecule can we assume also moved across the

membrane? _________________________________

4. In assessing the movement of glucose, starch and iodine across the membrane in this experiment, you

generated qualitative data. Quantitative data use numbers to measure observed changes. How could

you redesign this experiment to be modified so that quantitative data could be collected to show that

water diffused into the dialysis bag.

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5. Based on your observations, compare the size of each of the following molecules (glucose molecules,

water molecules, iodine molecules, and starch molecules) to the size of the pores in the dialysis

membrane (use the options “greater than” or “less than”):

The size of glucose molecules are _________________________ the membrane pore size.

The size of water molecules are ____________________________ the membrane pore size.

The size of iodine molecules are _____________________________ the membrane pore size.

The size of starch molecules are ___________________________ the membrane pore size.

6. What results would you expect if the experiment was set up incorrectly: the water and iodine solution

was placed inside the dialysis bag and the starch and glucose solution was placed in the beaker?

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7. In many animals, glucose, rather than starch, is transported by the blood through the body to all cells.

In the digestive system, starches are digested by amylase to yield glucose. Based on the findings of this

lab, explain why the digestion of starch to glucose is necessary.

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8. Summarize the process of diffusion.

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Osmosis Questions:

1. Describe what happened to the water cell in the 1.0 Molar sucrose solution.

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2. Explain why this result occurred.

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3. Describe what happened to the sucrose cell in the distilled water.

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4. Explain why this result occurred.

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5. Summarize the process of osmosis.

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