Diffusion_and_Osmosis

downloaded from

Scholarfriends

https://scholarfriends.com Downloaded by: writerforacademic@gmail.com | https://scholarfriends.com/singlePaper/273800/lab-experiment-che-physical-pre-labquestions-diffusion-and-osmosis Distribution of this document is illegal.

Diffusion and Osmosis PRE-LAB QUESTIONS 1. A concentration gradient affects the direction that solutes diffusion. Describe how molecules move with respect to the concentration.

If a concentration gradient exists molecules will move from areas of high concentration to areas of low concentration until the concentration gradients have equalized.

2. How does size affect the rate of diffusion?

Size affects the rate of diffusion because of membrane permeability factors. If a molecule is too large, it may not be able to fit through the pore and the diffusion will become restricted.

3. Does polarity affect the rate of diffusion? Explain your answer.

Polarity affects the solubility of a molecule in a solution. Phospholipid bilayers include hydrophilic heads and hydrophobic tails. They chemically allow small, non-polar molecules to freely diffuse. This is passive transport. Although, hydrophilic molecules cannot pass through a phospholipid bilayer through passive transport because they will be repelled when they encounter the hydrophobic tails of the membrane.

4. If a piece of celery is placed in a glass of pure water, are the celery cells hypertonic, hypotonic or isotonic compared to the water? In which direction will water move?

The celery cells are hypertonic compared to the pure water. Water will flow into the cells.

5. What is the water potential of pure water?

0kPa 6. Why don’t red blood cells swell or shrink in blood plasma?

Red blood cells do not swell or shrink because they are isotonic (having the same osmotic pressure as other solutions).

©eScience Labs, LLC 2018

Diffusion and Osmosis 7. Research how osmotic power plants work. Summarize what you learned in 1-2 paragraphs. Include references to information sources used.

In osmotic power plants, we draw freshwater and seawater into separate chambers separated by a membrane. The salt in the sweater draws the freshwater through the membrane, causing the pressure on the seawater side to increase. The pressure corresponds to a water column of 120 m and can be utilized in a turbine to generate electricity.

How does Osmotic Power work? (n.d.). Retrieved from https://www.sciencefocus.com/science/how-does-osmotic-power-work/#targetText=How does Osmotic Power work?,of osmosis to generate electricity.&targetText=Osmosis is a common biological,membrane, to balance the concentrations.

(n.d.). Retrieved from http://large.stanford.edu/courses/2017/ph240/wulff2/.

©eScience Labs, LLC 2018

Diffusion and Osmosis EXPERIMENT 1: DIFFUSION THROUGH GELATIN Data Tables Purpose (What question is this experiment designed to answer?): How long will it take to diffuse based on the size of the molecules

Hypothesis (Based on what you’ve learned in the pre-lab materials, write and If/Then statement regarding the outcome of this experiment.): In this lab, if acetic acid, methylene blue, and a combination of both are used in gelatin to measure the rate of diffusion. Then only the test tube including the acetic will diffuse faster than the other two tubes because it is lighter.

Table 1: Diffusion Data

A

Distance After 4 Hours (mm) 5 mm

Distance After 24 Hours (mm) 10 mm

B

5 mm

15 mm

C

2.5 mm

10 mm

Test Tube

Claim (What are the results of your experiment?): The acetic acid diffused the fastest out of all 3 test tubes.

Evidence (What data did you collect that supports your claim? Explain the meaning behind the data and the calculations.): Per the results in table 1, test tube B (acetic acid) moved the furthest/fastest over a 24-hour period which supports the claim above. The data is important because it shows how the amounts moved by centimeters and then calculated to millimeters.

Post-Lab Questions 1. Create a graph of your results with time (seconds) on the x-axis and distance of diffusion (mm) on the y-axis. There should be one line for each solution on your graph.

©eScience Labs, LLC 2018

Diffusion and Osmosis Diffusion through Gelatin 16

Distance (millimeters)

14 12 10 8 6 4 2 0 Methylene (tube A)

Acetic Acid (tube B) 14400

Both (tube C)

86400 Seconds

2. Which solution diffused the fastest?

The acetic acid diffused the fastest.

3. Does the rate of diffusion correspond with the molecular weight of the solution? Explain your answer.

The rate of diffusion does correspond with the molecular weight because methylene blue has a weight of 319.9 g/mol and acetic acid has a molecular weight of 60.05 g/mol.

Acetic acid is lighter so it was easier for it to diffuse through the gelatin while methylene blue is heavier so it was much bigger to diffuse through the gelatin.

4. Why do you think there was or was not a correlation between molecular weight and rate of diffusion?

I think there was a correlation between molecular weight and rate of diffusion since acetic acid traveled the farthest because it was the lightest.

5. What does the rate of diffusion tell you about limitations of cell size?

©eScience Labs, LLC 2018

Diffusion and Osmosis Smaller, lighter noncomplex cells diffuse easier than larger, heavier complex cells.

Reflection (Discuss what you have learned by doing this experiment. How have your ideas changed? Do you have any new questions? What connections did you make between the lab and lecture?): The only new question I have is since methylene blue is 319.9g/mol, I figured gravity would play a role in helping the heavier molecule travel further through the gelatin. If that is not true, then it does make sense that acetic acid traveled further since it’s lighter, hence being easier to diffuse.

©eScience Labs, LLC 2018

Diffusion and Osmosis EXPERIMENT 2: DIFFUSION CONCENTRATION GRADIENTS AND MEMBRANE PERMEABILITY Data Tables Table 2: Indicator Reagent Data Indicator

Starch Positive

Starch Negative

Glucose Positive

Glucose Negative

Glucose Test Strip

n/a

n/a

Green

Yellow

IKI Solution

Dark purple

Amber

n/a

n/a

Table 3: Diffusion of Starch and Glucose Over Time Indicator Glucose Test Strip IKI

Dialysis Bag After 60 Minutes Green

Beaker Water After 60 Minutes Yellow

Dark purple

amber

Post-Lab Questions 1. State your hypothesis.

In this lab, I am analyzing the data regarding the movement of molecules related to selective permeable membranes. My hypothesis is that the glucose molecules will move through the selective permeable membrane because they are smaller in size and the starch molecules will not pass through due to their large size.

2. Why is it necessary to have positive and negative controls in this experiment?

Positive and negative controls are necessary because they help show a baseline to compare when obtaining reliable results. The positive control shows the results of an active reagent. Whereas the negative control exhibits the results of no active reagent.

3. Draw a diagram of the experimental set-up. Use arrows to depict the movement of each substance in the dialysis bag and the beaker.

©eScience Labs, LLC 2018

Diffusion and Osmosis

4. Which substance(s) crossed the dialysis membrane? Support your response with databased evidence.

No substances crossed the dialysis membrane. This is supported with the data in table 3, which shows negative results in the substrate for both glucose and starch. Meaning that the glucose test strip was yellow, which is indicative of no glucose, and the IKI was amber which is indicative of no starch per the negative controls in table 2.

5. Which molecules remained inside of the dialysis bag?

Starch and glucose remained inside the dialysis bag because the molecules were too large to pass through. When the dialysis bag was tested for both starch and glucose, the

©eScience Labs, LLC 2018

Diffusion and Osmosis glucose test strip was green which is indicative of glucose and the IKI was purple which is indicative of starch.

6.

Did all of the molecules diffuse out of the bag into the beaker? Why or why not?

None of the molecules diffused out of the bag into the beaker. The starch molecules did not pass through since they are too big. This is proven by the results mentioned in question 4, because the starch and glucose molecules are too big to pass through the selective permeable membrane.

Reflection (Discuss what you have learned by doing this experiment. How have your ideas changed? Do you have any new questions? What connections did you make between the lab and lecture?): This helped show that smaller molecules pass permeable membranes easier than large complex molecules such as starch. This lab also helped show why positive and negative controls are so important so that you have a visual to come back to, to make sure your experiment is going correctly.

©eScience Labs, LLC 2018

Diffusion and Osmosis EXPERIMENT 3: OSMOSIS TONICITY AND THE PLANT CELL Data Tables Purpose (What question is this experiment designed to answer?): How will salt effect the potato cells regarding osmosis tonicity?

Hypothesis (Based on what you’ve learned in the pre-lab materials, write and If/Then statement regarding the outcome of this experiment.): If the potatoes are soaked in a salt solution for an hour, then water will diffuse out of the potato plant cells.

Table 4: Water Displacement per Potato Sample Initial Final Net Displacement Displacement Displacement (mL) (mL) (mL)

Potato Type

Potato Observations

Sample

Yukon

Rough texture, tan color, medium size

A

6

8

2

Yukon

Rough texture, tan color, medium size

B

5

7

2

Red

Red color, lumpy, Rough texture, small size

A

15

14

-1

Red

Red color, lumpy, Rough texture, small size

B

10

8

-2

Claim (What are the results of your experiment?): When they Yukon potato was measured for displacement between samples A (water solution) and B (salt solution) the results were

©eScience Labs, LLC 2018

Diffusion and Osmosis inconclusion as the change is displacement was the same between the samples. However, regarding the red potato, sample B (salt solution) displaced less than sample A (water solution).

Evidence (What data did you collect that supports your claim? Explain the meaning behind the data and the calculations.): Per the data in table 4, the Yukon potato had a positive increase in water distribution for both samples A and B when compared to the original displacement test. The red potato had a negative water displacement.

Post-Lab Questions 1. How did the physical characteristics of the potato vary before and after the experiment?

Did it vary by potato type?

Both the Yukon and the Red potatoes were firm to the touch, even when cut open, prior to being placed in either the water or salt solutions. However, once the potatoes were placed in test tube B (salt solution) for one hour, the texture became looser and more flexible for the Red potato. Little to no change for the Yukon potato.

2. What does the net change in the potato sample indicate?

The Yukon A and B potato samples had positive changes in displacement, indicating that water was absorbed into the potatoes after they had been soaked in the water and salt solutions for one hour. The Red A and B potato samples had negative changes in displacement, indicating that water diffused out of the samples after they had been soaked in water and salt solutions for one hour.

3. Different types of potatoes have varying natural carbohydrate concentrations. Explain how this may influence the water potential of each type of potato.

Diffusion goes from higher to lower concentrations of a particular substance through permeable membrane. For example, if there is a lower concentration of water within a potato that is submerged in water due to more sugars being present inside the potato, then water will diffuse into the potato until there is an equilibrium in concentrations. As a result, potatoes with higher natural sugar concentration will generally have water diffuse into the potato as the water flows from solution with low solute to high solute

©eScience Labs, LLC 2018

Diffusion and Osmosis concentration until equilibrium. This then causes the potatoes to increase in weight because of water gain. In potatoes with lower natural sugar concentration, the water diffuses outside of the potato causing a decrease in weight due to water loss.

4. Based on the data from this experiment, hypothesize which potato has the highest natural carbohydrate concentration. Explain your reasoning.

The Yukon potato has the highest natural sugar concentration because the potato increased in displacement while the Red potato decreased in displacement.

5. Did water flow in or out of the potato cells in each of the samples examined? How do you know this?

Water diffused into the Yukon A and B potatoes because there was a positive change in water displacement after soaking the potatoes in both water and salt solutions. Water diffused out of the Red A and B potatoes because there was a negative change in water displacement after soaking the potatoes in both water and salt solutions.

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 because they are able to generate the osmotic pressure with the structural integrity of the wall which will allow them to refrain from bursting in hypotonic solutions. Animals cells would not work because they will rupture in pure water.

7. From what you know of tonicity, are the potato cells in hypertonic, hypotonic or isotonic compared to the solutions in the tubes?

Potatoes are both; hypotonic like the Yukon potato which swelled in size, and hypertonic like the red potato that shrunk in size.

8. What do your results show about the concentration of solutes in the cytoplasm in the potato cells at the start of the experiment?

©eScience Labs, LLC 2018

Diffusion and Osmosis Results show the concentration of the cytoplasm in the potatoes at the start of the experiment is lighter than water. This indicates that when osmosis occurs with the pure water, the cells will obtain the water and increase in weight.

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.

If the potato is allowed to dehydrate by sitting in open air, it would tend to lose water molecules and become hypertonic. The cells would have the ability to absorb more water at a faster rate.

10. Compare and contrast the appearance of the plant cells in Sample A vs. Sample B.

Red potato sample A plant cells were either unchanged or had little shrinkage compared to sample B plant cells that has shrunk in size.

11. What is the explanation for the differences you observed?

Red potato sample A plant cells were hypertonic and isotonic because there was little shrinkage or no growth in the cell walls versus the red potato sample B plant cells which were hypertonic. Yukon potato samples A and B were both hypotonic because there was growth in the cell walls.

Reflection (Discuss what you have learned by doing this experiment. How have your ideas changed? Do you have any new questions? What connections did you make between the lab and lecture?): The connections I made between lab and lecture are about hypertonic, hypotonic and isotonic solutions and how they react with different cells.

©eScience Labs, LLC 2018