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Diffusion & Osmosis Lab
biology (169)
Coastal Carolina Community College
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PRE-LAB QUESTIONS
1. Compare and contrast diffusion and osmosis. – Diffusion and osmosis both typically
refer to the movement of molecules from high to low concentration areas, so they have that in common. However, osmosis refers to the movement of water molecules, where diffusion refers to any molecule.
Draw a picture of a cell in isotonic, hypotonic, and hypertonic states.
Why don’t red blood cells swell or shrink in blood? – Red blood cells do not swell or shrink in blood because blood is an isotonic solution.
How do osmotic power plants work? – Osmotic power plants work by utilizing osmosis as the method of generating electricity.
Research the structures that protect plant and animal cells from damage resulting from osmotic pressure. Write a few paragraphs explaining what they are, how they work, and where they are located. – There are different structures within cells that protect plant and animal cells from damage resulting from osmotic pressure. One structure found specifically in plant cells outside the plasma membrane that protects and supports the cell is the cell wall. In animal cells, one structure providing protection against damage resulting from osmotic pressure could be the cell membrane. In addition to this, the vesicles in animal cells help as well. When water enters a vesicle, the vesicle contracts, forcing the water to be squeezed back outside the cell.
EXPERIMENT 1: DIFFUSION THROUGH A LIQUID
Data Tables
Table 1: Rate of Diffusion in Corn Syrup
Time (sec) Blue Dye Red Dye 10 0=7mm 1=14mm 20 1cm=10mm 1=15mm 30 1=11mm 1=17mm 40 1=12mm 1=18mm 50 1=12mm 2=20mm 60 1=13mm 2=21mm 70 1=15mm 2=23mm 80 1=16mm 2=25mm 90 1=16mm 2=25mm 100 1=16mm 2=26mm 110 1=17mm 2=26mm 120 1=17mm 2=26mm
Does the rate of diffusion change over time? Why or why not? – The rate of diffusion slowly began to decrease. This is because one equilibrium is reached, the diffusion rates slow down.
Do you think your results would change if the corn syrup was replaced with water? Why or why not? – I think the results would change drastically because the substances differ from each other quite a bit.
EXPERIMENT 2: DIFFUSION – CONCENTRATION GRADIENTS
AND MEMBRANE PERMEABILITY
Data Tables
Table 3: Indicator Reagent Data
Indicator Starch PositiveControl (Color) Starch NegativeControl (Color) Glucose PositiveControl (Color)
Glucose Negative Control (Color) Glucose Test Strip n/a n/a Green Yellow IKI Dark blue Light brown n/a n/a
Table 4: Diffusion of Starch and Glucose Over Time
Indicator Dialysis Bag After 1 Hour Beaker Water After 1 Hour Glucose Test Strip Yellow Green
IKI No color changed to darkblue Light/pale yellow
Post-Lab Questions
- Why is it necessary to have positive and negative controls in this experiment? – Positive and negative controls are essential in this experiment. The purpose of these controls is to ensure there is no glucose that could influence color changes in the strips when the actual experiment is conducted.
EXPERIMENT 3: OSMOSIS – DIRECTION AND
CONCENTRATION GRADIENTS
Hypothesis: If the solutions are hypertonic then the net displacement will be greater.
Scientific Reasoning: A hypertonic solution would cause water to flow outside the cell.
Data Tables
Table 6: Sucrose Concentration vs. Tubing Permeability
Band Color Sucrose %
Initial Volume (mL)
Final Volume (mL)
Net Displacement (mL) Yellow 30 10 13 3 Red 15 10 11 1. Blue 3 10 10 0 Green 3 10 6 4
Post-Lab Questions
For each dialysis bag, identify whether the solution inside was hypotonic, hypertonic, or isotonic in comparison to the beaker it was placed in. – The first two dialysis bags contained hypertonic solutions inside, the third one contained a hypotonic solution, and the last one contained an isotonic solution.
Which dialysis bag increased the most in volume? Why? – The first (yellow) dialysis bag increased the most in volume due to the water diffusing into the solution, increasing the volume.
What does this tell you about the relative tonicity between the contents of the tubing and the solution in the beaker? – The solution from the first bag contained a hypotonic solution when compared to the second bag meaning water from the solution outside the bag moved inside the bag.
What would happen if the tubing with the yellow rubber band was placed in a beaker of distilled water? – The volume would increase even more because the solution would be hypotonic compared to the distilled water.
Suppose you had a 90% sucrose solution in one of the beakers instead of a 3% sucrose solution. How might this change your results? – This might change the results by changing the direction of the water’s movement.
Describe the similarities and differences between the dialysis bag and a cell membrane. Be specific. – The dialysis bag and a cell membrane because they both contain a semi- permeable membrane. However, there are still a few differences. For instance, facilitated diffusion is not an option in a dialysis bag, whereas in a cell membrane, it can occur.
If you want water to flow out of a dialysis bag filled with a 50% sucrose solution, what would the minimum concentration of the beaker solution need to be? – The minimum concentration of the beaker solution would have to be 51% so that the solution must be hypertonic. This would cause the water to flow out of the bag and into the beaker.
concentrations may have influenced the water potential of the potato cells because sugar can decrease the overall mass of the potato. Sugar has a low water potential, which means water would move outside of the cell, which is why the mass of the potato would decrease.
Based on the data from this experiment, hypothesize which potato has the highest natural sugar concentration. Explain your reasoning. – The sweet potato has the highest natural sugar concentration due to the value of the net displacement.
Did water flow in or out of the plant (potato) cells? How do you know this? – In certain potatoes water flowed in and in others, water flowed out. I know this due to the results in the net displacement category on the data table. If the net displacement is positive, this means that water has flowed outside the plant cell. Only one russet potato had a negative result meaning water only flowed into one plant cell.
Would this experiment work with other plant cells? What about animal cells? Why or why not? – This experiment can be replicated with other plant cells due to the cell wall providing protection against osmotic pressure and preventing the cell to burst in a hypotonic solution. However, it cannot be replicated in an animal cell because animal cells lack a cell wall, meaning it would inevitably burst.
From what you know of tonicity, what can you say about the plant cells and the solutions in the test tubes – I can say that water will continue to move from the side of higher concentration to the lower side until both solutions are isotonic.
What do your results indicate about the concentration of the cytoplasm in the potato cells at the start of the experiment? – The results indicate that cytoplasm in the potato cells is lighter than water.
If the potato is allowed to dehydrate by sitting in open air, would the cells absorb more or less water? Explain. – The cells would be able to absorb more water because of an increase in the solute concentration present in the cells because of osmosis.
Diffusion & Osmosis Lab
Course: biology (169)
University: Coastal Carolina Community College
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