Exercise 4: Membranes
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OBJECTIVES:
Investigate the nature of the cell membrane
Explore how compounds or molecules pass through differentially permeable membranes
Investigate Osmoregulation
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CELL MEMBRANES
Read: pp. 28-34
1. What determines the flow of water through the membrane?
Concentration
Hypotonic
Task
Solute
inside
1LowGRADIENTS
OSMOSIS AND CONCENTRATION
Solute outside
High
Bag
A
Table 1. Osmosis
B
Isotonic
Hypertonic
Same
High
Same
Explanation
Low
C
D
Initial
Wt.
0 min
Total
Wt.
15min
Wt.
Total
Change Wt.
Bag A
Bag B
Bag C
Bag D
Team
1
30min
Wt.
Change
Total
Wt.
45min
Wt.
Change
60min
Total
Wt.
Wt.
Change
Explanation
2
Tube #
Contents
1
5mL 10% NaCl
Readable Print
(yes/no)
Explanation
Figure 1.
Osmosis
Perform
Procedure 3.7
on pp.30
Use Table 3
to record the
experimental
data. Note:
Table 2- Wt.
Change refers
to the weight
change of the
dialysis bad
(“the cell”) as
compared to
the initial
weight.
MAKE PREDICTIONS:
Bag A
Bag B
Bag C
Bag D
Figure 2: Using the figure 2a-d above, draw in the movement of water according to your predictions. Use the
table below to explain the reasoning for your predictions.
Concentration
Hypotonic
Isotonic
Hypertonic
Low
Same
High
High
Same
Explanation
Low
Solute inside
Table
Solute outside
2.
Bag
A
B
Osmosis Experiment Predictions
C
Based on what you know about osmosis, formulate hypotheses (Ho and Ha) for what you expect to occur (in
relationDto bag weight) in each of the bags over time. Write both hypotheses in the space provided and explain
your reasoning for each.
0 min
15min
30min
45min
60min
Initial
Total
Wt.
Total
Wt.
Total
Wt.
Total
Wt.
Wt.
Wt.
Change Wt.
Change Wt.
Change Wt.
Change
Bag A
Bag B
Bag C
Bag D
Team
Explanation
1
Ho:
3.
Descri
be any
proble
ms
Ha:
Concentration
Hypotonic
Isotonic
Hypertonic
Low
Same
High
High
Same
Explanation
Low
Solute inside
Solute outside
Bag
A
B
C
Table 2: Observed Results
D
you
may
have
encou
0 min
15min
ntered
Initial
Total
Wt.
Total
during
Wt.
Wt.
Change Wt.
your
Bag AExcel, construct a
Using
experi
Bagthat
B depicts the
graph
ment.
Bag
C
changes noted in each bag
Did
Bag
D Make sure to
over
time.
this
Team
label
the axes correctly and
affect
plot1each bag as a separate
your
curve.
results
2
? If so,
explai
Tube #
Contents
n how.
Questions:
30min
Wt.
Change
Total
Wt.
45min
Wt.
Change
60min
Total
Wt.
Wt.
Change
Explanation
Readable Print
(yes/no)
Explanation
1
5mL 10% NaCl
2. Describe
any changes
observed or measured
during your experiment. Did
2 support your
5mL 0.9% NaCl
these
predictions? Explain.
Bag3A:
5mL distilled water
Tube #
Bag B:
Contents
1
Bag C:
5mL 10% NaCl
2
Bag D:
5mL 0.9% NaCl
3
Readable Print
(yes/no)
Explanation
5mL distilled water
Extracellular Environment
4. (a) Is your null hypothesis
or alternative hypothesis
supported by your data?
Explain. (b) Do you reject or
fail to reject your null
hypothesis?
highes
t rate
of
osmos
is?
How
can
you
tell?
Why?
Task
2:
Brow
nian
Move
ment
5. Which bag had the
Perform Procedure 3.4 on pp. 29
Questions:
6. What factors control the Brownian Motion?
7. What direction are the particles moving?
8. How does Brownian motion affect the rate of diffusion?
______________________________________________________________________________
Task 3 - DIFFUSION
AND
DIFFERENTIALLY
PERMEABLE MEMBRANES
Perform Procedure 3.5 on pp. 30. Make your predictions below.
MAKE PREDICTIONS:
Team 1
Team 2
Figure 3. Diffusion Experiment Predictions
Concentration
Hypotonic
Isotonic
Hypertonic
Low
Same
High
Solute inside
Table
Solute outside
3.
High
Same
Low
Bag
Explanation
Diffusion
Experiment Prediction Explanation
A
Based on what you know about diffusion, formulate hypotheses (Ho and Ha) for what you expect to occur in each
B over time. Write both hypotheses in the space provided and explain your reasoning for each.
of the bags
Ho:
C
D
0 min
15min
30min
45min
60min
Initial
Total
Wt.
Total
Wt.
Total
Wt.
Total
Wt.
Wt.
Wt.
Change Wt.
Change Wt.
Change Wt.
Change
Bag
A
Observe each beaker for no more than 30 minutes. Note any color changes in the two bags’ contents and the
Bag B solutions in the space provided.
surrounding
Bag C
Bag D
Team
Explanation
1
Ha:
2
Tube #
Contents
1
5mL 10% NaCl
2
5mL 0.9% NaCl
3
5mL distilled water
Tube #
Contents
Readable Print
(yes/no)
Readable Print
Explanation
Explanation
Questions:
9. What is the best explanation for the color change that occurred?
10. Based on your results, which molecules (phenopthalien, iodine, starch, sodium hydroxide) passed through
the membrane? Explain.
Team 1:
Team 2:
11. Based on your results, which molecules (phenopthalien, iodine, starch, sodium hydroxide) did not pass
through the membrane? Explain.
Team 1:
Team 2:
12. Describe any problems you may have encountered during your experiment. Did this affect your results? If so,
explain how.
13. (a) Is your null hypothesis or alternative hypothesis supported by your data? Explain. (b) Do you reject or
fail to reject your null hypothesis?
14. What reasons can you provide for the movement of these molecules across the membrane and not others?
Task 4 - DIFFUSION OF GASES
Perform Procedure 3.6 on pp.30
Formulate null and alternative hypotheses describing which gas should move faster and why? State Ho and Ha in
the space provided below.
Ho:
Ha:
NOTE: This procedure will be demonstrated by your TA.
CAUTION:
HCl is a concentrated acid and can harm you and your clothes.
NH4OH is very irritating to the eyes and nose.
Using a ruler, measure the distance (cm) that each gas traveled in the tube. Record these distances in the space
provided below.
NH4 OH: ________________
HCl: _____________________
Questions:
15. What is the ratio of HCl: NH4OH distances?
16. What is the ratio of the molecular weights?
17. Is diffusion rate directly or inversely proportional to molecular weight?
18. Do you reject or fail to reject your null hypothesis? Explain.
19. How would an increase in temperature affect the rate of gas diffusion?
Task 5 - HEMOLYSIS OF BLOOD CELLS
Perform Procedure 3.8 on pp. 33
Formulate hypotheses (Ho and Ha) regarding your expectations for the outcome to the blood cells in each tube.
State your hypotheses in the space provided. Make sure to include your reasoning.
Ho:
Ha:
Concentration
Hypotonic
Isotonic
Hypertonic
Low
Same
High
High
Same
Explanation
Low
Solute inside
Solute outside
Bag
A
B
C
D
MAKE PREDICTIONS in Table 4:
0 min
15min
30min
45min
60min
Initial
Total
Wt.
Total
Wt.
Total
Wt.
Total
Wt.
Wt.
Wt.
Change Wt.
Change Wt.
Change Wt.
Change
Bag4.ARBC Predictions Table
Table
Bag B
BagHold
C each tube in front of a printed page to determine whether or not you can read the print through the
Note:
Bag D Record your results in Table 5.
solution.
Team
Explanation
1 5:
Table
2
Tube #
Contents
1
5mL 10% NaCl
2
5mL 0.9% NaCl
3
5mL distilled water
Tube #
Contents
Readable Print
(yes/no)
Readable Print
(yes/no)
Explanation
Explanation
Concentration
Solute inside
Hypotonic
Isotonic
Hypertonic
Low
Same
High
High
Same
Explanation
Low
Solute outside
Bag
A
B
C
D
Bag A
Bag B
Bag C
0 min
Initial
Total
Wt.
Wt.
15min
Wt.
Total
Change Wt.
30min
Wt.
Change
45min
Total
Wt.
Wt.
Change
60min
Total
Wt.
Wt.
Change
Questions:
20. Did the results correspond to your predictions?
21. Describe any problems you may have encountered during your experiment. Did this affect your results? If so,
explain how.
22. (a)Is your null hypothesis or alternative hypothesis supported by your data? Explain. (b) Do you reject or fail
to reject your null hypothesis?
23. If person’s blood volume drops due to injury or sever dehydration, why do doctors administer isotonic
saline intravenously instead of pure water?
24. What osmotic regulatory challenges would a fish living in freshwater have versus a fish living in salt water?
Task 6: Osmoregulation
Osmosis is the transport of water through a semi-permeable membrane down its concentration gradient.
Osmosis is responsible for the fluid transport out of the kidney tubules and gastrointestinal tract, into
capillaries, and across cell membranes. Tonicity classifications are relative terms describing the concentration of
one environment to another. Hypertonic solutions contain a higher solute concentration than a compared
solution. When concentrations are the same between both solutions, they are isotonic. Hypotonic refers to a
solution that has a lower solute concentration than the solution on the opposing side of the membrane.
Organisms maintain homeostasis through osmoregulation, the active regulation of the osmotic pressure of
their fluids. Osmotic pressure comes from the ability of a solvent and the inability of a solute to pass through a
semi permeable membrane. When cells are placed in extreme environments, drastic effects on the cells can be
observed. Sheep’s red blood cells lyse when placed in a hypotonic solution, a process called hemolysis. When
plant cells are placed in hypertonic solutions plasmolysis occurs. This process involves the loss of water
through osmosis, which
causes the plant’s plasma membrane to pull away from the cell wall. Today you will subject living cells to
environments with different concentrations of a solute and observe their responses.
Directions: In the table below, predict the reaction of the following cell types in the different
environments.
Table 6.
Concentration
Hypotonic
Isotonic
Hypertonic
Low
Same
High
High
Same
Explanation
Low
Solute inside
Solute outside
Bag
A
B
C
D
Initial
Wt.
0 min
Total
Wt.
15min
Wt.
Total
Change Wt.
Bag A
Bag B
Bag C
Bag D
Team
1
30min
Wt.
Change
Total
Wt.
45min
Wt.
Change
60min
Total
Wt.
Wt.
Change
Explanation
2
Tube #
Predictions
1
Contents
Readable Print
(yes/no)
Explanation
5mL 10% NaCl
2
5mL 0.9% NaCl
I. Sheep’s Blood- Red Blood Cells
1. Place a drop of the blood from tube 1 (from Task 5) onto a clean slide and then add a cover slip. Repeat the
3 procedure for tubes 2 5mL
distilled
water
same
and 3.
Mark the
slides with the appropriate tube number so that you can be certain
which slide contains blood from which tube.
Readable Print
Tube #
Contents
Explanation
(yes/no)
2. Examine each slide under the microscope. Determine if the cells are crenate (shriveled), have burst (so only
1
5mL
10%
NaCl healthy and round. Record the results in Table 7.
fragments
remain) or whether
they
appear
2
5mL 0.9% NaCl
II. Cheek
Cells
1. Using a toothpick, gently scrape the inside of your cheek. Add one drop of the isotonic NaCl solution to a clean
slide. Stir the scrapping from the toothpick into the drop of water and then add a drop of methylene blue
3
5mL distilled water
Extracellular Environment
followed by a coverslip. Repeat this procedure for the hypertonic and hypotonic solutions.
2. Examine each slide under the microscope. Determine if the cells are crenate, lysed, or appear healthy and
round. Record your results in Table 7.
III. Elodea Cells
1. Collect one leaf from a spring of Elodea. Add a drop of isotonic solution to a clean slide. Place the leaf, with the
top surface facing up, in the drop of isotonic solution on the slide. Add a coverslip.
2. Examine each slide under the microscope. Record your results in Table 7.
Concentration
Hypotonic
Isotonic
Hypertonic
Low
Same
High
High
Same
Explanation
Low
Solute inside
Solute outside
Bag
A
B
C
D
Initial
Wt.
0 min
Total
Wt.
15min
Wt.
Total
Change Wt.
Bag A
Bag B
Bag C
Bag D
Team
1
30min
Wt.
Change
Total
Wt.
45min
Wt.
Change
60min
Total
Wt.
Wt.
Change
Explanation
2
Tube #
1
Observed
Results
Contents
Readable Print
(yes/no)
Explanation
5mL 10% NaCl
2
5mL 0.9% NaCl
3
5mL distilled water
Tube #
Contents
1
5mL 10% NaCl
2
5mL 0.9% NaCl
Readable Print
(yes/no)
Explanation
Table 7.
Figure 4. Response of plant cells to a.
extracellular environments
hypotonic and b. hypertonic
Questions:
25. Compare and contrast the reaction
hypotonic solution compared to the
the animal cell had to the
plant cell.
26. Compare and contrast the reaction the animal cell had to the hypertonic solution compared to the plant cell.
27. What factors might affect the speed of water movement in or out of a cell?
28. Did the results correspond to your predictions?
29. Describe any problems you may have encountered during your experiment. Did this affect your results? If so,
explain how.
30. (a)Is your null hypothesis or alternative hypothesis supported by your data? Explain. (b) Do you reject or fail
to reject your null hypothesis?
______________________________________________________________________________
Response of Single Celled Organisms to Environmental Stimuli
Living organisms respond to outside stimuli. Their ability to sense and respond to the local environment
increases their survival rate. In this exercise, you will design an experiment to examine the response of an
Amoeba to a particular environmental stimulus.
1. Choose the stimulus that you would like to test (e.g. temperature, light, salinity, acidity) and record it below.
2. Formulate hypotheses (Ho and Ha) about your predictions on how you expect the Amoeba to react in response
to the stimulus. Write your hypotheses in the space provided.
3. Decide how to test your hypotheses. Describe your experimental design in the space below: