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Lab 3: Cell Structure and Function
1. Identify three major similarities and differences between prokaryotic and eukaryotic cells.
2. Where is the DNA housed in a prokaryotic cell? Where is it housed in a eukaryotic cell?
3. 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.
Onion (allium) Root Digital Slide Images
1. 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|
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?).
(3) 250 mL Beakers
*You Must Provide
*Be sure to measure and cut only the length you need for this experiment. Reserve the remainder for later experiments.
1. Use the permanent marker to label the three 250 mL beakers as 1, 2, and 3.
2. 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.
3. 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
4. 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.
5. 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.
6. Repeat Steps 4 – 5 with the three remaining dialysis tubes, using each of the three remaining rubber band colors.
7. 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.
8. 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|
9. Pour 150 mL of the remaining stock sucrose solution into Beaker 1.
10. 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.
11. 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.
12. 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.
13. 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.|
14. Place the yellow, red, and blue banded tubing in Beaker 2. Place the green banded tubing in Beaker 1 (Figure 8).
15. 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.
16. 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.
17. After allowing the tubing to sit for one hour, remove them from the beakers.
18. 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.
19. 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)|
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.