Lab 4 Diffusion and Osmosis PDF

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Lab 4 Diffusion and Osmosis

BIO201L

Student Name: Robert Prieskorn Access Code (located on the lid of your lab kit): AC-QHNVPF8

Pre-Lab Questions: ”1. Compare and contrast diffusion and osmosis.” Compare: Diffusion and osmosis are both passive transporters. Diffusion and Osmosis both flow from a higher to lower concentration gradient. Contrast: Osmosis requires a semi-permeable membrane. Diffusion does not requires a semi-permeable membrane. Diffusion allows movement of any particle. Osmosis only permits movement of solvent. ”2. What is the water potential of an open beaker containing pure water? ” There is no water potential. ”3. Why don’t red blood cells swell or shrink in blood? ” RBCs are isotonic in the blood.

Experiment 1: Diffusion through a Liquid Table 1: Rate of Diffusion in Corn Syrup Time (sec)

Blue Dye

Red Dye

10

0.2cm

0.5cm

20

0.6cm

1.2cm

30

0.8cm

1.4cm

40

1.0cm

1.5cm

50

1.2cm

1.7cm

60

1.2cm

2.1cm

70

1.3cm

2.1cm

80

1.5cm

2.1cm

90

1.5cm

2.2cm

Lab 4 Diffusion and Osmosis

BIO201L

Time (sec)

Blue Dye

Red Dye

100

1.5cm

2.4cm

110

1.6cm

2.5cm

120

1.8cm

2.7cm

Table 2: Speed of Diffusion of Different Molecular Weight Dyes

Structure

Molecular Weight

Total Distance Traveled (mm)

Speed of Diffusion (mm/hr)*

Blue Dye

793g/mol

18mm

540mm/hr

Red Dye

496g/mol

27mm

810mm/hr

*To get the hourly diffusion rate, multiply the total distance diffused by 30.

Post-Lab Questions ” 1. Examine the plot below. How well does it match the data you took in Table 1? ”

Lab 4 Diffusion and Osmosis

BIO201L

The illustrated graph closely represents my results as far as which dye diffuses quicker. My time to diffusion is skewed from the graphs illustration for reasons unknown. ”2. Which dye diffused the fastest? ” The red dye diffused the quickest. ”3. How does the rate of diffusion correspond with the molecular weight of the dye? ” The molecular weight of the red dye is less so it diffused quicker. ”4. Does the rate of diffusion change over time? Why or why not? ” Yes. Factors like particle mass and temperature are factors that can control the rate of diffusion.

Experiment 2: Diffusion - Concentration Gradients and Membrane Permeability Table 3: Indicator Reagent Data

Indicator

Starch Positive Control (Color)

Starch Negative Control (Color)

Glucose Positive Control (Color)

Glucose Negative Control (Color)

Glucose Test Strip

n/a

n/a

Brown

Blue

IKI

Green

Yellow

n/a

n/a

Lab 4 Diffusion and Osmosis

BIO201L

Table 4: Diffusion of Starch and Glucose Over Time Indicator

Dialysis Bag After 1 Hour

Beaker Water After 1 Hour

Glucose Test Strip

Light Brown

Brown

IKI

Dark Blue

Yellow

Post-Lab Questions ”1. Why is it necessary to have positive and negative controls in this experiment? ” To ensure the results are accurate because of the independent variable. ”2. Which substance(s) crossed the dialysis membrane? Support your response with data-based evidence. ” The iodine and glucose crossed the dialysis membrane. The dialysis bag remained a red color indicating that the starch was left. The glucose and iodine diffused because they are smaller molecules. ”3. Which molecules remained inside of the dialysis bag? ” Starch is what stayed in the dialysis bag. ”4. Did all of the molecules diffuse out of the bag into the beaker? Why or why not? ” No. The only molecules that diffused were iodine and glucose. The color changes identified did not indicate that the starch diffused. The starch molecules were not able to diffuse because they were too big.

Experiment 3: Osmosis - Direction and Concentration Gradients ”Hypothesis: ” The greater the percentage of sucrose the more net displacement is yielded. Table 6: Sucrose Concentration vs. Tubing Permeability Band Color

Sucrose %

Initial Volume (mL)

Final Volume (mL)

Net Displacement (mL)

Yellow

30%

10mL

12mL

2mL

Red

15%

10mL

11mL

1mL

Blue

3%

10mL

9mL

-1mL

Lab 4 Diffusion and Osmosis

BIO201L

Band Color

Sucrose %

Initial Volume (mL)

Final Volume (mL)

Net Displacement (mL)

Green

3%

10mL

7.5mL

-2.5mL

Post-Lab Questions ”1. For each of the tubing pieces, identify whether the solution inside was hypotonic, hypertonic, or isotonic in comparison to the beaker solution it was placed in. ” Yellow= Hypertonic dialysis bag, Hypotonic beaker solution Red-Hypertonic dialysis bag, Hypotonic beaker solution Blue=Hypotonic dialysis bag, Hypotonic beaker solution Green=Hypotonic dialysis bag, Hypertonic beaker solution ”2. Which tubing increased the most in volume? Why? ” The yellow dialysis bag. The yellow dialysis bag contained the most hypertonic solution allowing the molecules in the bag to move until equilibrium was met. ”3. What does this tell you about the relative tonicity between the contents of the tubing and the solution in the beaker? ” That the tubing solution is hypertonic and the solution in the beaker is hypotonic. ”4. What would happen if the tubing with the yellow band was placed in a beaker of distilled water? ” The yellow dialysis bag solution would decrease due to diffusion. The higher concentration would try to equalize the external solution (distilled water). ”5. Osmosis is how excess salts that accumulate in cells are transferred to the blood stream so they can be removed from the body. Explain how this process works in terms of tonicity. ” As salt accumulates it will shift the water potential difference between the cell and the blood. To correct this the body will let the salt pass through a semi-permeable membrane from the higher concentration, the cell, to the lower concentration, the blood, where it will be voided. ”6. How is this experiment similar to the way a cell membrane works in the body? How is it different? Be specific with your response. ” This experiment is nearly identical in how osmosis works in the body. The differences I was not able to identify. The permeation worked with its intended mode of transport and illustrated exactly how osmosis works. ”7. If you wanted water to flow out of a tubing piece filled with a 50% solution, what would the minimum concentration of the beaker solution need to be? Explain your answer using scientific evidence. ” Osmosis works from a higher concentration gradient to a lower concentration gradient, so the beaker solution would need to be 51% or greater concentration..

Experiment 4: Osmosis - Tonicity and the Plant Cell Table 7: Water Displacement per Potato Sample

Lab 4 Diffusion and Osmosis

BIO201L

Initial Final Net Displacement Displacement Displacement (mL) (mL) (mL)

Potato

Potato Type and Observations

Sample

1

Sweet Potato: Skin has a red/ orange hue to it. Potato is quite firm.

1A

7mL

10mL

3.0mL

1

Sweet Potato: Skin has a red/ orange hue to it. Potato is quite firm.

1B

6mL

7mL

1.0mL

2

Russet Potato: Skin is “gritty” feeling. Skin is brown. Potato is “softer” than the sweet potato.

2A

6mL

8mL

2.0mL

2

Russet Potato: Skin is “gritty” feeling. Skin is brown. Potato is “softer” than the sweet potato.

2B

5mL

6mL

1.0mL

Post-Lab Questions ”1. How did the physical characteristics of the potato vary before and after the experiment? Did it vary by potato type? ” The physical color of the potatoes did not change. At the beginning of the experiment the sweet potato was very firm and the russet not as firm, at the end of the experiment the potatoes that were exposed to the NaCl solution were more flimsy. ”2. What does the net change in the potato sample indicate? ” The change in the potato samples indicate the amount of solute that has either entered or exited the potato. ”3. Different types of potatoes have varying natural sugar concentrations. Explain how this may influence the water potential of each type of potato. ” If the sugar content is high more water will be enter into the potato to maintain equilibrium. ”4. Based on the data from this experiment, hypothesize which potato has the highest natural sugar concentration. Explain your reasoning. ” The sweet potato has a higher sugar concentration which will yield a greater water displacement. I believe water will enter the potato with the greatest sugar content to

Lab 4 Diffusion and Osmosis

BIO201L

try and equalize it. This water will be kept inside creating a greater water displacement. ”5. Did water flow in or out of the plant cells (potato cells) in each of the samples examined? How do you know this? ” Water flowed both in and out the potato cells. This is supported by the final displacement results. ”6. Would this experiment work with other plant cells? What about with animal cells? Why or why not? ” This experiment would work with other plant cells but not with animal cells. Plant cells have a cell wall to allow for reduction and expansion, animals don’t have this and would cause the cell to pop. ”7. From what you know of tonicity, what can you say about the plant cells and the solutions in the test tubes? ” I can interpret that the beakers containing NaCl solution were hypertonic and the beakers containing water were hypotonic. This was deduced by how much water the potatoes gained. ”8. What do your results show about the concentration of the cytoplasm in the potato cells at the start of the experiment? ” My results reflect that the concentration of the cytoplasm of potatoes were at a lower concentration resulting in water movement from the cytoplasm. ”9. If the potato is allowed to dehydrate by sitting in open air, would the potato cells be more likely to absorb more or less water? Explain. I hypothesize that the potato cell would be more likely to absorb more water through osmosis after being dehydrated....