Cell Size: Diffusion in simulated agar cells
Name:
Purpose: To study the effects of Cell Size (Surface Area and Volume) on Diffusion
Materials:
Pink Phenolphthalein agar block; razor blade / scalpel; safety goggles; O.lM HCl; ruler; 2 plastic cups; paper towel; centimeter
ruler
Procedure Part 1:
1. Use your razor blade and ruler to create 3 agar blocks from your chunk of agar. You will require a 1 cm cube, a 2 cm cube, and a 3
cm cube. The cubes will be used to represent cell of different sizes.
2. Place the three agar blocks into a plastic cup. Ensure that the blocks are not touching one another.
3. Completely cover the blocks with O.lM HCl. The HCl represents the necessary cellular materials that must reach the inside of the
cells.
4. Observe carefully. When you observe that the HCl has reached the center of one of the blocks, remove all the cubes from the base
and place them on a piece of paper towel. Cut the blocks in half using your razor blade. Observe carefully and complete the
observations below.
Procedure Part 2:
1. Create two more 1 cm cube cells from your remaining agar. Use your razor blade to make nicks in the surface of one of the cells.
Cut carefully, you do not want to "lose" any of the agar.
2. Place the two cubes (one solid and one with a nicked surface) into a beaker. Ensure that the blocks are not touching one another.
3. Completely cover the blocks with O.lM HCl. Observe carefully. When you observe that the HCl has reached the center of one of
the blocks, remove both the cubes from the base and place them on a piece of paper towel. Cut the blocks in half using your razor
blade. Observe carefully and complete the observations below.
4. When you have finished both part one and part 2, rinse the HCl down the sink with plenty of water and place the agar cubes into
the garbage. Wash and return your glassware. Clean your work area. Wash your hands thoroughly with soap and water.
5. After reading the procedure, create a hypothesis to explain what you think is going to occur. In your hypothesis, you must use the
words cell size and rate of diffusion. (Remember: If …then )
Hypothesis:
Part 1-
Part 2-
Observations:
Part 1. Neatly draw and color a cross section diagram of each "cell" cut in half. Label your diagrams to illustrate what has occurred.
1 cm cube
2 cm cube
3 cm cube
Part 2. Neatly draw and color a cross section diagram of each "cell" cut in half. Label your diagram to illustrate what has occurred.
1 cm cube ( no nicks in surface)
1 cm cube ( nicked surface)
Questions Part 1:
1.
Complete the following chart. Be sure to include correct units:
Cell size
Surface area
Volume
Surface area to
volume ratio
(S.A. : volume)
% of cube HCl did
not reach
(vol. of pink left/total
volume of cube)
3 cm cube
2 cm cube
1 cm cube
(Remember:
Lx W x H
=
Volume of a Cube; Number of sides x L x W
=
Surface area of a Cube)
___________________2. Anything that the cell takes in, like oxygen and food, or let's out, such as carbon dioxide, must go through
the cell membrane. Which column in the chart represents the amount of membrane around the cell?
___________________3. The cell contents, nucleus and cytoplasm, use the oxygen and food while producing waste. Which column
in the chart represents the contents of the cell?
___________________4. As the cell grows larger, does the Surface Area to Volume ratio become larger, smaller or stay the same?
___________________ 5. Which cell has the greatest total surface area to volume ratio?
___________________6. Which cell has the greatest chance of survival?
Questions Part 2
___________________7. Analyze your results in part two. What is the experimental variable being tested?
___________________8. What are the experimental controls?
___________________9. What feature do the "nicks” represent in real cells?
___________________10. a) Which cell, Cell A or Cell B would be found lining the walls of the small intestine?
b) Identify the visible feature that allowed you to correctly identify the intestinal cell and explain how this
feature aids the cell in carrying out its specific function.
11. How do single cell animals maintain efficient gas diffusion?
12. Why can't certain unicellular organisms like bacteria grow to become the size of a small fish?
Conclusion: Summarize your experimental findings; how does the surface area to volume ratio effect how fast diffusion can take
place? Use the words: surface area / volume ratio, cell size, and rate of diffusion to explain WHY you are made up of
100,000,000,000,000 cells rather than just one giant cell. In your answer explain why the "cell's requirements” reached the center of
the smallest cell first. Be detailed and factual.