Question Description
Question 3. Describe the Brownian motion in your own words:
Question 4. Describe, in your own words, how this observation indicates that all visible and invisible molecules are in motion?
After approximately one hour, measure the diameter (in millimeters) of the circle the solutions diffused.
Potassium permanganate: Methylene blue:
Examine your Petri dish. Shade the agar in the diagram to demonstrate the movement of the solutions in the diagram below. Shade to show where the concentration of the potassium permanganate is higher and where it is lower.
Top view of Petri dish: Side view of Petri dish:
Question 5. Your Petri dish illustrates the most basic characteristic of diffusion. Complete the following to understand this basic principle:
The net diffusion of potassium permanganate appears to be from the area of its ___concentration to the area of its concentration.
(“lower to higher” – or – “higher to lower”?)
Question 6. In addition to concentration, molecular weight of a diffusing molecule is also an important factor that can determine the rate (speed) of diffusion. We happen to know that potassium permanganate’s molecular weight is 150, while that of methylene blue molecule is 374.
Use your own observations (above) to explain how molecular weight appears to affect the rate of diffusion here:
Question 7. Based on the results, what is the relationship between molecular weight and diffusion rate?
Circle one: Inverse Direct
State the basis of your conclusion:
Question 8. How would you expect the dyes to be distributed in the agar gel after several days? Would you expect to still see evidence of a concentration gradient?
Question 9. Calculate the molecular weights for the following molecules so you can predict which will diffuse more rapidly.
Note: Molecular weights are calculated by adding up the atomic weights (masses) for all the atoms that make up a given molecule.) Look at the Periodic Table on the wall in the laboratory. It will give you the atomic weights of all the atoms in the two molecules below.
Calculate the weight of these two molecules. Show your work here:
Water: H2O Sucrose: C12H22O11
Question 10. Which substance, water or sucrose, is more likely to be able to diffuse through a semipermeable membrane, and on what basis did you make your decision?
Question 11. Phospholipids are each made of the phosphate-containing “head” which is hydrophilic (easily combine with water), and two long fatty acid chains which are hydrophobic (do not combine with water, fatty acids are oils). Color the circular phosphate heads blue; color the fatty acid chains of the phospholipids red. Then label them hydrophobic and hydrophilic based on your reading above.
Figure 1. Selectively Permeable Cell Membrane
Question 12. Observe Figure 1. What kinds of molecules are able to pass through the phospholipid bilayer membrane easily? What kinds of molecules are not able to pass through easily? What are the characteristics of each (charge, polar vs. nonpolar), and size?
Move easily
Do not move easily
Because water is a small and flat molecule (despite it being polar), it can either pass through the phospholipid bilayer membrane. It can more quickly pass into and out of cells through tunnel-like proteins called aquaporins that traverse the cell membrane.
Question 13. Label the aquaporin protein in Figure 1. What does the aquaporin allow to pass through the membrane?
Question 14. Define the terms Solvent and Solute:
Question 15. Below is a diagram of three model cells filled with three different solutions. Make a prediction. Review Figure 2 and complete the Table 1 to its right. For column 4, predict whether the “model cell” will increase or decrease in weight after one hour. (Hint: Will the net diffusion of water be into the “model cell” or into the beaker?)
Table 1: Prediction for Model Cells
Cell Letter
% solutes in cell
% water in cell
Increase or decrease after 1 hour?
A
B
C
Figure 2. Diagram showing the experimental set up for the 3 model cells
Ace my homework – Write down the colors of the solutions here:
1% 25% 50%
At 15-minute intervals, for 1 hour, record the “total weight” of each cell in Table 2
Calculate the net mass change for each model cell in the last row of Table 2.
Net mass change = Final mass (at time 60) – initial mass (at time 0)
Table 2. Change in Mass of Three Model Cells by Osmosis over Time
Mass (g)
Time (minutes)
Cell A
Cell B
Cell C
0
15
30
45
60
Net mass change
Question 16. How do your results compare with your prediction in Table 1? Graph the Osmosis data
Get custom essay samples and course-specific study resources via course hero homework for you service – Include the data for the three model cells as 3 separate curves (lines) using three different colors on the same graph. Create a key for identifying the colored line according to its corresponding Cell letter and % Solutes.
Ace my homework – Write the title “Change in Mass of Three Model Cells with Varying Concentration of Solutes via Osmosis over Time” at the top of the graph.
Question 17. Do the words hypertonic, hypotonic, and isotonic refer to the solute or solvent concentration?
Question 18. Which solution has the highest concentration of water (the “solvent”): a 1% Sucrose solution or a 50% Sucrose solution?
Question 19. Look at your osmosis data in Table 1:
Did the water move into or out of all three model cells? If not, is this what you expected?
Would you describe the environment outside the three model cells as hypertonic or hypotonic?
Question 20. A concentration gradient for water must exist between the inside and the outside of a cell’s membrane for osmosis to occur. Observe the graph. Which of the three model cells represents the one with the steepest concentration gradient of water?
Question 21. The steepest concentration gradient of water should result in the highest rate of diffusion (osmosis). Examine your Table 3 osmosis data for the 15 to 30-minute interval. Did the greatest changes in weight occur in the model cells with the greatest concentration gradients of water?
Question 22: A cell can be placed in various solutions. Based on the information in the above reading and the concentration gradient, fill in the following table:
In the second and third columns, write “more,” “less,” and “the same amount of.”
In first blank of the fourth column, write in or outside.
In the second blank of the fourth column, write in, outside of, inside of, into, or equally in and out of.
A cell placed in a hypertonic solution has …
__________ solutes than the surrounding environment
__________ water than the surrounding environment.
The water __________ the cell will move __________ the cell.
A cell placed in a hypotonic solution has …
__________ solutes than the surrounding environment
__________ water than the surrounding environment.
The water __________ the cell will move __________ the cell.
A cell placed in an isotonic solution has …
__________ solutes than the surrounding environment
__________ water than the surrounding environment.
The water __________ the cell will move __________ the cell.
Draw a picture of each cell in its solution to the left of the description help you clarify this.
Question 23. Draw a sketch of several red blood cells observed in each of the three environments. Label their plasma membranes. In the last row write whether water moved into or out of the cells, or whether there was no change.
Hypertonic
Isotonic:
Hypotonic
Drawing:
Description of relative size and shape of cells
Water movement?
Important: The red blood cells in the isotonic solution are in a “normal” osmotic condition, the same as when they were in the living animal. If we assume that the cell membrane is semipermeable, do you think water is moving in and out of the cell membrane in an isotonic environment? Describe the equilibrium.
Question 24. Notice these plant cells are shaped different than the animal cells (human cheek cells). What give these plant cells the brick-like shape?
Question 25. Note the green, jelly-bean shaped chloroplasts. Where are they located within the cell? In the center or around the edge near the cell membrane and cell wall?
Question 26. Sketch several Elodea (plant) cells in the space below to the left titled “Cells in tap water.” Label with a word(s) and an arrow pointing to their cell walls, central vacuoles, and chloroplasts.
Tap water
Hypertonic
Drawing:
Description of relative size and shape of cells
Water movement?
Question 27. Where are the chloroplasts now in relation to the center or the cell wall?
Question 28. What had to have happened to the water in the central vacuole for the chloroplasts to be located where they are now after placing hypertonic solution on the slide?
Question 29. Observe the large plastic model of a plant cell. Notice that the central vacuole occupies most of the plant cell’s mass. The fluid concentration within this vacuole, called cell sap, contains a high concentration of salt, sugar and protein molecules. How does this help explain the large size of the central vacuole in the Elodea cells when placed in fresh tap water? (Hint: osmosis plays a part here.)
Question 30. The plant phenomenon observed above is called plasmolysis. In one word, what has happened to the Elodea cell?
Question 31. Notice that a plant cell, unlike an animal cell, has not only a plasma (cell) membrane, but also has a cell wall encasing it. Did the cell wall appear to swell, shrink or remain the same during your observations?
Question 32. Placing the wilted elodea cells (or wilted lettuce leaves that you might put into a salad) into tap water causes the plant cells to become turgid once again. Explain, in terms of osmosis, why the elodea leaf (or lettuce leaf) becomes “crisper” after placing it in tap water:
Question 33. Explain why the Elodea (plant) cells did not lyse when placed in tapwater as did the animal cells (red blood cells). In other words, what is the reason that there is a difference between animal and cell’s response to being placed in these various solutions?
REVIEW
Question 34. Compare animal and plant cells in varying solutions:
An animal cell placed in a(n)
Will
· lose water
· gain water
· maintain same water
Causing the cell to
· be unaffected
· shrink (crinkle)
· or swell (explode)
Hypertonic solution
Isotonic solution
Hypotonic solution
A plant cell placed in a(n)
Will
· lose water
· gain water
· maintain same water
Causing the cell to
· swell (be unaffected, normal, turgid)
· become flaccid (drooping plant)
· or plasmolyzed (wilting plant)
Hypertonic solution
Isotonic solution
(see your textbook)
Hypotonic (tap water) solution
