Diffusion Lab 4.1 experiment B p. 87 (in the lab manual) 4.2 experiment B p. 93 (in the lab manual) 4.3 experiment A p. 96 (in the lab manual)
<-- these are the actual labs
we need all of the usual parts - 3 sep abstract things, 3 separate intros, 3 separate procedures, 3 separate datas( 3 drawings) and charts and whatever), whatever), 3 separate conclusions, a lab bench and quiz, and one current event David: I¶ll do the conclusion questions and data for 4.1 and 4.2 Luke: you are going to do the conclusion questions and data for 4.3 Is there anything else you guys need me to do? I feel like I don¶t have as much work as everyone else Nadia; I¶ll do the lab bench, current event, and lab quiz! and im going to do the procedures for all three Kristen:you are going to do the introductions for all three and the abstract
Kristen¶s parts: In this lab, we determined how ho w different molarities of sucrose changed the overall mass of a potato piece. In this lab, we determined the effects of osmosis through a semi permeable membrane, a dialysis bag imitating a cell¶s membrane, using h ypertonic and hypotonic solutions. In this lab, we examined tugor pressure and plasmolysis using the diffusion of hypertonic and hypotonic solutions through an onion¶s cell wall. POTATO INTRO: For plants, the amount of water in their cel ls is extremely crucial for the ongoing functions and daily activities that keep th e cells alive. The amount of water relative to the osmotically active substances in a plant cell is ver y important for a cell¶s survival, and it must be maintained. The molarities, or the solute concentrations, affect the cell¶s weight and the cell¶s volume. If the plant cell is immersed in a hypotonic solution, then the weight and volume will increase at intervals at which the cell takes in the water. If a plant ce ll is submerged in a hypertonic h ypertonic solution, then the weight and volume will decrease as water exits the cell. ONION INTRO: The presence of a cell wall in a plant organism is vital for its survival, but without a large central vacuole v acuole that can maintain its water intake and output, the plant will cease to live. These central vacuoles react rea ct to the stimuli of a plant¶s environment, environ ment, by responding to the different molarities of solutions. If a plant cell is surrounded by a hypertonic solution, then the vacuole will regulate water out of the cell, as the inter ior of the cell, the protoplast, shrinks and pulls away from the cell wall. This response is known as plasmolysis. When Wh en a plant cell is immersed in a hypotonic solution, the vacuole will accept more water than it outputs, and therefore the protoplast will expand in response to more water being added to the cell. However, unlike animal cells, a plant cell can never lyse because of too much water pressure. Its cell wall restricts too much expansion o f the
protoplast, and when a cell reaches the maximum of water its cell wall will allo w, a high turgor pressure will result, which will stop further water from entering the cell. Turgor pressure is the pressure that the protoplast puts on the cell wall as a result of the water intake or output. If the turgor pressure becomes too high, it will force water through the membrane and push it out of the cell.The ideal state for a plant cell is to be completely turgid, which allows stability for the plant.
DIALYSIS INTRO: Dialysis bags are extremely important in the medical fields and are used throughout hospitals nation wide. Dialysis tubing is a flat tube that is made of reg enerated cellulose fibers. These fibers create a selectively permeable membrane, which only allows some substances to pass through and not others, just like a cell membrane. Depending on the molecular weight of the substance, it will either pass through the pore with ease or not pass through the tubing at all. This membrane is an example of diffusion, which is commonly seen in animal and plant cells. Unlike dialysis tubing, a membrane of a cell consists of a phospholipid bilayer with proteins embedded to allow the passage of substances that can not passively diffuse through.
Nadia µs Parts: Lab Bench Design the Experiment: Diffusion & Osmosis
Exercise
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1:
Diffusion
In this activity, you fill a dialysis bag with a suga r/starch solution and immerse the bag in a dilute iodine solution. W ater, sugar, starch, and iodine molecules will all be in motion, and each molecule will move to a region of its lower concentration, unless the molecule is too large to pass through the membrane. Your task is to determine relative size of the various molecules and gather evidence of molecular movement. Hint: One piece of information that will help you is to recall that when iodine comes in contact with starch, it chan ges from an
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orange-brown color to blue-black. For more information, review the section on Concentration Gradient. Return to Design of the Experiments. Analysis of Results. Diffusion
& Osmosis Exercise
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3: Water Potential of Potato Cores
This activity is very similar to Exercise 2, except that you use cores from potatoes instead of dialysis bags. You submerge the cores in solutions of varying sucrose concentrations. When you calculate the percent change in mass, some of the cores will have gained weight while others will have lost weight, depending on the movement of water. You then graph this data and determine which concentration of the sucrose solution is in equilibrium with the cores. Since you know that the pressure potential of the surrounding solution in an open beaker is zero, you can now calculate the water potential.
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Lab Quiz
1. Which beaker(s) contain(s) a solution that is hypertonic to the bag? a. Beaker 3 b. Beakers 2 and 4 c.
Beakers 1, 2, and 5
d. Beaker 4
e. Beakers 3 and 4
ANSWER: c. Beakers 1, 2, and 5
2. Which bag would you predict to show the least change in mass at the end of the experiment? a. The bag in Beaker 1 b. The bag in Beaker 2 c.
The bag in Beaker 3
d. The bag in Beaker 4 e. The bag in Beaker 5
ANSWER: c. The bag in Beaker 3
3. Arrange the beakers in order of the mass of the bags inside them after the experiment has run for 30 minutes. List the bag that loses the most mass first. a. 1, 2, 3, 4, 5 b. 1, 5, 2, 3, 4 c.
4, 3, 2, 5, 1
d. 3, 2, 1, 4, 5
e. 2, 1, 5, 3, 4
ANSWER: e. 2, 1, 5, 3, 4
4. In beaker B, what is the water potential of the distilled water in the beaker, and of the beet core? a. Water potential in the beaker = 0, water potential in the beet core = 0 b. Water potential in the beaker = 0, water potential in the beet core = -0.2 c.
Water potential in the beaker = 0, water potential in the beet core = 0.2
d. Water potential in the beaker cannot be calculated, water potential in the beet core = 0.2 e. Water potential in the beaker cannot be calculated, water potential in the beet core = 0.2
ANSWER: b. Water potential in the beaker = 0, water potential in the beet core = -0.2
5. Which of the following statements is true for the diagrams?
a. The beet core in beaker A is at equilibrium with the surround ing water. b. The beet core in beaker B will lose water to the surrounding environment. c.
The beet core in beaker B would be more turgid than the beet core in beaker A.
d. The beet core in beaker A is likely to gain so much water that its cells will rupture. e. The cells in beet core B are likely to undergo plasmolysis.
ANSWER: a. The beet core in beaker A is at equilibrium with the surround ing water.
SCORE : 4/ 5 Current Event - These current events have to do with how diffusion can contribute to causing certain diseases. http://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/pulmonary/interstit ial-lung-disease/ http://www.ehow.com/how-does_5019245_lungs-together-control-blood-pressure.html
Procedures for all 3 experiments: 4.1
experiment B p. 87 (in the lab manual) 1. Place a drop of water on a slide 2. Touch the edge of the dissecting needle to the drop of water, and next into the dry carmine. 3.Mix the carmine on the needle with the drop of water on the slide and cover with a coverslip and observe. 4. Look at it with the microscope focused on one particle of carmine on low power, then on high power. 5. Record the results. experiment B p. 93 (in the lab manual) 1. Observe and record observations of the two demonstration microscopes with Elodea in solutions A and B. 4.2
4.3
experiment A p. 96 (in the lab manual) 1. Get 100 mL of DI water and 100 mL of each sucrose solutions and put them in seperate labeled 250 mL beakers/paper cups. 2. Using a sharp cork borer, cut seven cylinders of potato. Push the border through the potato, twisting it. Once filled, take the potato o ut, repeat this until you have seven cylinders of potato that tare 5 cm long.
3. Put all the samples in a petri dish and keep covered to prevent them from drying out. 4.Place one cylinder between the folds of a paper towel to blot it. 5. Weigh it to the nearest 0.01 g on the aluminum sheet on balance. Cut the cylinder lengthwise, making two long halv es put them into a water beaker, record the time that this happens.6. 6. Repeat steps four and five with each cylinder, placing potato pieces in the appropriate incubation solution from 0.1 to 0.6 M. Incubate for 1.5-2 hours. 7. Swirl each beaker every 10-15 minutes as the potato cylinders incubate. 8. Record the time the pieces are remove calculate the incubation time and record. 9. Record the final weight after weighing the potato pieces. 10. repeat this procedure for all samples and record you data.
David¶s parts: Solution
Original Contents
Original Color
Final Color
Color After Benedict¶s Test
Bag
Sucrose and Starch
Clear
Purple
Green
Beaker
H2O and I2KI
Amber Yellow
Amber Yellow
Green
Control
Water
Clear
Clear
Blue
Source
Experiment 4.1
B Data Table:
4.1 Experiment
B Conclusion Questions: 1. What is the significance of the final colors and the colors after the Benedict¶s tests? Did the results support your hypothesis? Explain, giving evidence from the results of your tests. Yes,
the results supported our hypothesis. The final color of the bag was purple, indicating that the I2KI from the beaker solution entered the bag. The final color of the beaker was amber yellow, indicating that the starch from the bag did not enter the beaker . The final color of the control remained clear because nothing was done to it at this point. The final color of the bag after the Benedict¶s test was green, indicating that there was sugar in the bag. The final color of the beaker after the Benedict¶s test was green, indicating that the sugar from the bag solution entered the beaker . The final color of the control was blue after the Benedict¶s test, indicating that there was no presence of sugar in the control solution. 2. How can you explain your results? The dialysis tubing is permeable to the I2KI and not permeable to the starch because the final color of the bag turned purple while the final color of the beaker remained amber yellow, meaning the I2KI moved across the dialysis bag from the beaker into the bag while the starch was unable to move from the bag to the beaker . The dialysis tubing is also permeable to the sugar because the final color of the beaker after the Benedict¶s test turned green, meaning the sugar moved across the dialysis bag from the bag into the beaker . The final color of the control after the Benedict¶s test turned blue, meaning that no presence of sugar would yield a color different than green. 3.
From your results, predict the size of I2KI molecules relative to glucose and starch.
The size of I2KI molecules are approximately the same size or smaller than glucose molecules and definitely smaller than starc h molecules. Glucose molecules are also definitely smaller than starch molecules. This conclusion can be drawn because the starch molecules weren¶t able to pass through the dialysis tubing, while the glucose and I2KI molecules could. 4. What colors would you expect if the experiment started with glucose and I2KI inside the bag and starch in the beaker? Explain. The final color of the beaker would be purple, while the final color of the bag would be amber yellow . With starch unable to pass through the dialysis tubing and I2KI able to pass through the dialysis tubing, I 2KI would enter the beaker and turn the beaker solution purple. The final color of the bag and beaker after the Benedict¶s test w ould be green because regardless of where sugar, I2KI, or starch is, sugar is able to pass through the dialysis tubing. Thus, sugar would reach equilibrium and be present in both solutions, so both solutions would turn gree n. 4.2 Experiment
1.
B Conclusion Questions: Based on your predictions and observations, which solution is hypertonic? Hypotonic?
Solution
A is hypertonic because it has a high concentration of salt, and the solution
has a higher concentration of solute than the cell. Solution B is hypotonic because it contains no solute, and thus the solution has a lower concentration of solute than the cell. 2.
Which solution has the greatest osmolarity?
Solution
A has the greatest osmolarity.
3. Would you expect pond water to be isotonic, hypertonic, or hypotonic to Elodea cells? Explain. Pond water would be e xpected to be hypotonic because pond water is the natural home for Elodea. In its natural environment, the net flow of water is from the surrounding medium into the Elodea. If the net flow of water is into the cells, then pond water must be hypotonic. 4.
Verify your conclusions with your laboratory instructor.
Completed.
Experiment 4.2
B Data Table:
Solution
Appearance/Condition of Cells
A
The protoplast of the Elodea cell shrank away from the cell wall. There is a large distance between the cell wall and protoplast. The Elodea cell is plasmolyzed.
B
The protoplast of the Elodea cell moved closer to the cell wall. There is hardly a distance between the cell wall and protoplast. The Elodea cell is turgid.
Luke¶s
parts:
Experiment 4.3
A Data Table
Contents In Beaker
Initial Mass
Final Mass
Mass Difference
Percent Change in Mass
Distilled Water
1.70
2.02
.32
+ 18.82%
0.2 M Sucrose
1.73
1.76
.03
+ 1.73%
0.4 M Sucrose
1.73
1.47
.26
- 15.03%
0.6 M Sucrose
1.73
1.25
.48
- 27.75%
0.8 M Sucrose
1.72
1.11
.61
- 35.46%
1.0 M Sucrose
1.78
1.22
.56
- 31.46%
Figure 4.6
Conclusion Questions 1. At a little over 0.2 M Sucrose, the curve crosses the zero change line on the graph. This signifies that at this point, the addition of more sucrose will continue to pro duce a negative value for the % change in weight. 2. This information can help us determine the osmolarity of the potato tuber tissue because the graph gives us the amount of sucrose in the potato tuber tissue by default, and how much the weight of the tissue will change as we increase the concentration of sucrose in the solution that the potato tuber tissue is contained in. 3. In more dilute concentrations of sucrose, the weight of potato pieces increases after incubation. Other factors that influence the about of water taken up by the potato pieces includes temperature, particle size, and time given.
