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UMUC Biology 102/103
Lab3:Cell Structure and Function
INSTRUCTIONS:
·
On your own and without assistance, complete thisLab3AnswerSheet electronically
and submit it via theAssignments Folder by the date
listedintheCourse Schedule (underSyllabus).
·
To conduct your laboratory exercises, use the
Laboratory Manuallocated under Course Content. Read the
introduction and the directions for each exercise/experiment carefully before
completing the exercises/experiments and answering the questions.
·
Save your Lab3AnswerSheet in the following format: LastName_Lab3 (e.g.,
Smith_Lab3).
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You should
submit your documentas a Word
(.doc or .docx) or Rich Text Format (.rtf) file for best compatibility.
Pre-Lab
Questions
Identify
three major similarities and differences between prokaryotic and
eukaryotic cells.
Where
is the DNA housed in a prokaryotic cell? Where is it housed in a
eukaryotic cell?
Identify three structures which provide
support and protection in a eukaryotic cell.
Experiment
1: Cell Structure and Function
The structure of
a cell dictates the majority of its function. You will view a selection of
slides that exhibit unique structures that contribute to tissues function.
Materials:
Onion (allium) Root Digital Slide Images
Procedure
Examine the onion root tip digital
slide images on the following pages. Then, respond to the Post-Lab
Questions.
Onion Root Tip: 100X
Onion Root Tip: 1000X
Onion Root Tip: 1000X
Onion Root Tip: 100X. Each dark circle indicates a different nucleus.
Onion Root Tip: 1000X
Post-Lab Questions
1. Label each of
the arrows in the following slide image: A=Chromosomes,
B=Nucleus, C=Cytoplasm, D=Cell Wall
2.
What
is the difference between the rough and smooth endoplasmic reticulum?
3.
Would
an animal cell be able to survive without a mitochondria? Why or why not?
4.
What
could you determine about a specimen if you observed a slide image showing the
specimen with a cell wall, but no nucleus or mitochondria?
5.
Hypothesize
why parts of a plant, such as the leaves, are green, but other parts, such as
the roots, are not. Use scientific reasoning to support your hypothesis.
Experiment
2: Osmosis – Direction and Concentration Gradients
In this
experiment, we will investigate the effect of solute concentration on osmosis.
A semi-permeable membrane (dialysis tubing) and sucrose will create an osmotic
environment similar to that of a cell. This selective permeability allows us to
examine the net movement of water across the membrane. You will begin the
experiment with a 30% sucrose solution, and perform a set of serial dilutions
to create lower concentration solutions. Some of the sucrose concentrations
will be membrane permeable; while others will not be permeable (can you determine
why this is?).
Materials
(3) 250 mL
Beakers
(1) 10 mL Graduated Cylinder
(1) 100 mL Graduated Cylinder
Permanent Marker
*8 Rubber Bands (2 blue, 2 green, 2 red,
and 2 yellow)
60 g Sucrose (Sugar) Powder, C12H22O11
4 Waste Beakers (any volume)
*Paper Towels
*Scissors
*Stopwatch
*Water
*(4) 15 cm. Pieces of Dialysis Tubing
*Contains latex. Please handle wearing safety
gloves if you have a latex allergy.
*You Must Provide
*Be sure to measure and cut only the length
you need for this experiment. Reserve the remainder for later experiments.
Procedure
Use the permanent marker to label the
three 250 mL beakers as 1, 2, and 3.
Cut four strips of dialysis tubing,
each 15.0 cm long. Fill Beaker 3 with 100 mL of water and submerge the
four pieces of dialysis tubing in the water for at least 10 minutes.
After 10 minutes, remove one piece of
tubing from the beaker. Use your thumb and pointer finger to rub the
tubing between your fingers; this will open the tubing. Close one end of
the tubing by folding over 3.0 cm of one end (this will become the
bottom). Fold it again and secure with a yellow rubber band (use
Tie a knot in the remaining dialysis
tubing just above or just below the rubber band. This will create a seal
and ensures that solution will not leak out of the tube later in the
experiment.
To test that no solution can leak out,
add a few drops of water to the tubing and look for water leakage. If any
water leaks, tighten the rubber band and/or the knot in the tubing. Make
sure you pour the water out of the tubing before continuing to the next
step.
Repeat Steps 4 – 5 with the three
remaining dialysis tubes, using each of the three remaining rubber band
colors.
Reconstitute the sucrose powder
according to the instructions provided on the bottle’s label (your kit
contains 60 g of sucrose in a chemical bottle) . This will create 200 mL
of a 30% stock sucrose solution.
Use Table 2 to create additional
sucrose solutions that are 30%, 15% and 3% concentrated, respectively. Use
the graduated cylinder and waste beakers to create these solutions. Set
these solutions aside.
Table 2: Serial Dilution Instructions
Sucrose Solution
mL of Stock Sucrose Solution
Needed
mL of Water Needed
30%
10
0
15%
5
5
3%
1
9
3%
1
9
Pour 150 mL of the remaining stock
sucrose solution into Beaker 1.
Use some of the remaining stock
sucrose solution to create an additional 200 mL of a 3% sucrose solution
into Beaker 2.
Hint: Use your
knowledge of serial dilutions to create this final, 3% sucrose solution.
Measure and pour 10 mL of the
remaining 30% sucrose solution into the dialysis bag with the yellow
rubber band. Seal the top of this tubing with the remaining yellow rubber
band.
Measure and pour 10 mL of the 15%
sucrose solution in the bag with the red rubber band, and seal the top of
the dialysis tubing with the remaining red rubber band. 10 mL of the 3%
sucrose solution in the bag with the blue rubber band, and seal the
dialysis tubing with the remaining blue rubber band. The final 10 mL of 3%
sucrose solution in the bag with the green rubber band. Seal the dialysis
tubing with the remaining green rubber band.
Verify and record the initial volume
of solution from each bag in Table 3.
Figure 8: The dialysis bags
are filled with varying concentrations of sucrose solution and placed in one
of two beakers.
Place the yellow, red, and blue banded
tubing in Beaker 2. Place the green banded tubing in Beaker 1 (Figure 8).
Hypothesize whether water will flow in
or out of each dialysis bag. Include your hypotheses, along with
supporting scientific reasoning in the Hypotheses section at the end of
this procedure.
Allow the bags to sit for one hour.
While waiting, pour out the water in the 250 mL beaker that was used to
soak the dialysis tubing in Step 1. You will use the beaker in Step 19.
After allowing the tubing to sit for
one hour, remove them from the beakers.
Carefully open the tubing. The top of
the tubing may need to be cut off/removed as they tend to dry out over the
course of an hour. Measure the solution volumes of each dialysis bag using
the 100 mL graduated cylinder. Make sure to empty and dry the cylinder
completely between each sample.
Record your data in Table 3.
Table 3: Sucrose Concentration vs. Tubing Permeability
Band Color
Sucrose %
Initial Volume (mL)
Final Volume (mL)
Net Displacement (mL)
Yellow
Red
Blue
Green
Hypothesis:
Post-Lab Questions
1. For each of the tubing pieces, identify whether the
solution inside was hypotonic, hypertonic, or isotonic in comparison to the
beaker solution in which it was placed.
2. Which tubing increased the most in volume? Explain
why this happened.
3. What do the results of this experiment this tell
you about the relative tonicity between the contents of the tubing and the solution
in the beaker?
4. What would happen if the tubing with the yellow
band was placed in a beaker of distilled water?
5. How are excess salts that accumulate in cells
transferred to the blood stream so they can be removed from the body? Be sure
to explain how this process works in terms of tonicity.
6. If you wanted water to flow out of a tubing piece
filled with a 50% solution, what would the minimum concentration of the beaker
solution need to be? Explain your answer using scientific evidence.
7. How is this experiment similar to the way a cell
membrane works in the body? How is it different? Be specific with your
response.
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