Module 3 Laboratory: The Cell and Diffusion and Osmosis
PART A—The Cell
1. What is a cell? (2 Points)
2. Cyanobacteria is a large prokaryote, typically referred to as blue-green algae. Cyanobacteria contains chlorophyll in thylakoids, instead of chloroplasts, and they are surrounded by a mucilaginous sheath. You have been asked to view cyanobacteria with a light microscope at 400x magnification and you observe the image below. Do you see nuclei? Why or why not? (4 Points)
3. You have been asked to observe and both Lactobacillus and Oscillatoria under the microscope using 400x magnification. The images you observe are below. How does the size of Lactobacillus cells compare with the size of the Oscillatoria cells? (2 Points)
4. You observed onion cells stained with iodine under the microscope, as seen in the image below, and you were able to see nuclei of onion cells. How would you explain the differences in the apparent shapes and positions of the nuclei of different cells? (4 Points)
5. Would you expect onion cells to have chloroplasts? Why or why not? (2 Points)
6. For a particular experiment, you prepare cells by mixing Janus Green B stain with sucrose and then mounting the cells in that solution. This makes observation of mitochondria possible, but the color fades after a short period of time. Why do you think sucrose is added to the stain in this procedure and why do you think mitochondria do not remain stained? (4 Points)
7. You viewed prepared slides of Amoeba and Paramecium and observe the images below. From what you have observed and learned about these organisms, would you expect either of these to have a cell wall? Why or why not? (4 Points)
PART B—Diffusion and Osmosis
The following procedure was performed to assess diffusion and osmosis. The data from the experiment is available, below.
1
Obtain eight pieces of string and four pieces of water-soaked dialysis tubing, each 15cm long. Seal one end of each tube by folding and typing it tightly.
2
Open the other end of the tube by rolling it between your thumb and finger.
3
Label and fill each of the bags as follows:
BAG A: 10mL 1% sucrose solution
BAG B: 10mL 1 % sucrose solution
BAG C: 10mL 10% sucrose solution
BAG D: 10mL 20% sucrose solution
4
For each bag, loosely fold the open end and press on the sides to push the fluid up slightly and remove most of the air bubbles. Tie the folded ends securely and check for leaks.
5
Gently blot excess water from the outside of the bags and weight each bag to the nearest 0.1g. Record the initial weights in the data table.
6
Place bags B, C, and D in a large beaker filled with 1% sucrose solution. Record the time the bags are placed into the beaker.
7
Place bag A in a 250mL beaker and fill the beaker with 150mL of 10% sucrose solution. Record the time the bag is placed in the beaker.
8
Remove each of the bags from the beaker in 15-minute intervals for 1 hour total. After removal, gently blot each bag dry and weight them to the nearest 0.1g. Record weights into the data table. Handle the bags gently to avoid leaks and quickly return the bags to their appropriate beaker.
Data Table:
0 mins
15 mins
30 mins
45 mins
60 mins
Initial weight (g)
Total weight (g)
Change in weight (g)
Total weight (g)
Change in weight (g)
Total weight (g)
Change in weight (g)
Total weight (g)
Change in weight (g)
Bag A
10.1
8.6
7.2
6.1
5.1
Bag B
9.9
9.8
9.7
9.6
9.5
Bag C
11.3
12.1
12.6
12.7
12.7
Bag D
11.3
12.7
12.9
12.8
12.6
8. Calculate the change in weight for each bag at each time point. (4 points)
9. In which bags did osmosis occur? Explain your answer. (4 Points)
10. Graph the data above using Excel with Time (in minutes) plotted on the x-axis and Total Weight (in grams) plotted on the Y axis. Be sure to include a graph title and axis labels. Include the data for all four bags as four separate curves on the same graph. Multiple online Excel tutorials are available to assist you in creating this graph. (6 Points)
11. Based on this data, what is the relationship between the gradient and the rate of diffusion? Explain. (2 Points)
12. Based on your understanding of osmosis, would you expect a piece of celery to wilt in salt solution? Explain. (2 Points)
13. What would you expect to happen to a red blood cell in salt solution? Explain. (2 Points)
14. Which molecule would you predict would diffuse faster, a substance of higher molecular weight or a substance of lower molecular weight? Why? (2 Points)
15. You performed a diffusion experiment and observed the following on your petri dish after 45 minutes. Which substance appeared to diffuse the fastest? Does this agree with your prediction from above? Why or why not? (4 Points)
16. Do molecules stop moving when diffusion stops? Explain your answer. (2 Points)
BIO 101
Chapters 4 and 5 Homework
1. What is one advantage and one disadvantage of the light microscope? What is one advantage and one disadvantage of the electron microscope? (2 Points)
2. List the three statements that make up the cell theory. (1 Point)
3. List and describe the function of the four basic cell structural similarities. (2 Points)
4. You are using a computer program to design a new single-celled organism. Discuss why a flat, plate-like cell will be more efficient in transporting materials than a spherical cell of the same volume. (1 Point)
5. Describe the function of each of the following cellular components: (2 Points)
a. Nuclear envelope
b. Smooth endoplasmic reticulum
c. Lysosomes
d. Ribosomes
6. Describe two characteristics of mitochondria and chloroplasts that have led scientists to believe they originated from a single-celled organism. (1 Point)
7. How does the structure of a plasmodesma differ from that of a gap junction? (1 Point)
8. The fluid mosaic model described the plasma membrane as a mosaic of components. Why is it advantageous for the plasma membrane to be fluid in nature? (1 Point)
9. Describe how a cell membrane changes with the following: (2 Points)
a. Saturated fatty acids
b. Unsaturated fatty acids
c. Cold temperatures
d. Cholesterol
10. Discuss why the following affect the rate of diffusion: (2 Points)
a. Molecular size
b. Molecular polarity
c. Solution density
d. Distance to be traveled
11. What will happen to an animal cell in a hypotonic solution? What will happen to a plant cell? (1 Point)
12. What is passive diffusion? Facilitated diffusion? Osmosis? Active transport? (2 Points)
13. What is endocytosis? What is exocytosis? How do these processes occur, in relation to the cell membrane? (2 Points)
PART A—The Cell
1. What is a cell? (2 Points)
2. Cyanobacteria is a large prokaryote, typically referred to as blue-green algae. Cyanobacteria contains chlorophyll in thylakoids, instead of chloroplasts, and they are surrounded by a mucilaginous sheath. You have been asked to view cyanobacteria with a light microscope at 400x magnification and you observe the image below. Do you see nuclei? Why or why not? (4 Points)
3. You have been asked to observe and both Lactobacillus and Oscillatoria under the microscope using 400x magnification. The images you observe are below. How does the size of Lactobacillus cells compare with the size of the Oscillatoria cells? (2 Points)
4. You observed onion cells stained with iodine under the microscope, as seen in the image below, and you were able to see nuclei of onion cells. How would you explain the differences in the apparent shapes and positions of the nuclei of different cells? (4 Points)
5. Would you expect onion cells to have chloroplasts? Why or why not? (2 Points)
6. For a particular experiment, you prepare cells by mixing Janus Green B stain with sucrose and then mounting the cells in that solution. This makes observation of mitochondria possible, but the color fades after a short period of time. Why do you think sucrose is added to the stain in this procedure and why do you think mitochondria do not remain stained? (4 Points)
7. You viewed prepared slides of Amoeba and Paramecium and observe the images below. From what you have observed and learned about these organisms, would you expect either of these to have a cell wall? Why or why not? (4 Points)
PART B—Diffusion and Osmosis
The following procedure was performed to assess diffusion and osmosis. The data from the experiment is available, below.
1
Obtain eight pieces of string and four pieces of water-soaked dialysis tubing, each 15cm long. Seal one end of each tube by folding and typing it tightly.
2
Open the other end of the tube by rolling it between your thumb and finger.
3
Label and fill each of the bags as follows:
BAG A: 10mL 1% sucrose solution
BAG B: 10mL 1 % sucrose solution
BAG C: 10mL 10% sucrose solution
BAG D: 10mL 20% sucrose solution
4
For each bag, loosely fold the open end and press on the sides to push the fluid up slightly and remove most of the air bubbles. Tie the folded ends securely and check for leaks.
5
Gently blot excess water from the outside of the bags and weight each bag to the nearest 0.1g. Record the initial weights in the data table.
6
Place bags B, C, and D in a large beaker filled with 1% sucrose solution. Record the time the bags are placed into the beaker.
7
Place bag A in a 250mL beaker and fill the beaker with 150mL of 10% sucrose solution. Record the time the bag is placed in the beaker.
8
Remove each of the bags from the beaker in 15-minute intervals for 1 hour total. After removal, gently blot each bag dry and weight them to the nearest 0.1g. Record weights into the data table. Handle the bags gently to avoid leaks and quickly return the bags to their appropriate beaker.
Data Table:
0 mins
15 mins
30 mins
45 mins
60 mins
Initial weight (g)
Total weight (g)
Change in weight (g)
Total weight (g)
Change in weight (g)
Total weight (g)
Change in weight (g)
Total weight (g)
Change in weight (g)
Bag A
10.1
8.6
7.2
6.1
5.1
Bag B
9.9
9.8
9.7
9.6
9.5
Bag C
11.3
12.1
12.6
12.7
12.7
Bag D
11.3
12.7
12.9
12.8
12.6
8. Calculate the change in weight for each bag at each time point. (4 points)
9. In which bags did osmosis occur? Explain your answer. (4 Points)
10. Graph the data above using Excel with Time (in minutes) plotted on the x-axis and Total Weight (in grams) plotted on the Y axis. Be sure to include a graph title and axis labels. Include the data for all four bags as four separate curves on the same graph. Multiple online Excel tutorials are available to assist you in creating this graph. (6 Points)
11. Based on this data, what is the relationship between the gradient and the rate of diffusion? Explain. (2 Points)
12. Based on your understanding of osmosis, would you expect a piece of celery to wilt in salt solution? Explain. (2 Points)
13. What would you expect to happen to a red blood cell in salt solution? Explain. (2 Points)
14. Which molecule would you predict would diffuse faster, a substance of higher molecular weight or a substance of lower molecular weight? Why? (2 Points)
15. You performed a diffusion experiment and observed the following on your petri dish after 45 minutes. Which substance appeared to diffuse the fastest? Does this agree with your prediction from above? Why or why not? (4 Points)
16. Do molecules stop moving when diffusion stops? Explain your answer. (2 Points)
BIO 101
Chapters 4 and 5 Homework
1. What is one advantage and one disadvantage of the light microscope? What is one advantage and one disadvantage of the electron microscope? (2 Points)
2. List the three statements that make up the cell theory. (1 Point)
3. List and describe the function of the four basic cell structural similarities. (2 Points)
4. You are using a computer program to design a new single-celled organism. Discuss why a flat, plate-like cell will be more efficient in transporting materials than a spherical cell of the same volume. (1 Point)
5. Describe the function of each of the following cellular components: (2 Points)
a. Nuclear envelope
b. Smooth endoplasmic reticulum
c. Lysosomes
d. Ribosomes
6. Describe two characteristics of mitochondria and chloroplasts that have led scientists to believe they originated from a single-celled organism. (1 Point)
7. How does the structure of a plasmodesma differ from that of a gap junction? (1 Point)
8. The fluid mosaic model described the plasma membrane as a mosaic of components. Why is it advantageous for the plasma membrane to be fluid in nature? (1 Point)
9. Describe how a cell membrane changes with the following: (2 Points)
a. Saturated fatty acids
b. Unsaturated fatty acids
c. Cold temperatures
d. Cholesterol
10. Discuss why the following affect the rate of diffusion: (2 Points)
a. Molecular size
b. Molecular polarity
c. Solution density
d. Distance to be traveled
11. What will happen to an animal cell in a hypotonic solution? What will happen to a plant cell? (1 Point)
12. What is passive diffusion? Facilitated diffusion? Osmosis? Active transport? (2 Points)
13. What is endocytosis? What is exocytosis? How do these processes occur, in relation to the cell membrane? (2 Points)
