# bigg bio lab 2

Diffusion/Osmosis Pre-Lab

Introduction: Dialysis tubing allows molecules to diffuse through microscopic pores in the tubing. Molecules that are smaller than the pores can diffuse through the dialysis membrane along the concentration gradients. Molecules that are larger than the pore size are prevented from crossing the dialysis membrane. Answer questions in complete sentences. For problems, show equations and work with units and appropriate significant figures. Part IA:

In the following situations, assume the sucrose cannot diffuse through the dialysis membrane. If a dialysis bag contains a 0.2 M solution of sucrose is placed in a beaker of distilled water, will the dialysis bag gain or lose mass? Explain why. Hypothesis: It will lose mass

Explanation: The solution will move out in order to be balanced with the environment surrounding it A dialysis bag has an initial mass of 26.3 g and a final mass of 30.2 g. Find the percent change in mass. Show your work! Work: (mass initial – mass final)/(mass initial) x 100%= 14.83% Part IB:

With the data below, calculate the percent change in mass, graph the data, determine where the percent change in mass crosses the X axis, determine the solute potential of the potato if the room temperature is 24oC, and finally determine the water potential of the potato. Contents in Dialysis Tubing

Initial Mass in grams

Final Mass in grams

Percent Change in Mass

0.0 M

22.0

27.0

22.73%

0.2 M

24.6

26.4

7.32%

0.4 M

23.5

23.2

-1.28%

0.6 M

23.7

20.4

-13.93%

0.8 M

19.9

15.6

-21.61%

1.0 M

21.3

16.2

-23.93%

Where the line crosses the X axis0.3M

Solute potential of the potato: 14.81 bars

Water potential of the potato: 14.81 bars

Work:

Solute potential: (ψS) = – iCRT = (-2)(.3)( 0.0831)(297)=14.81 bars Water potential: ψ = ψP + ψS = = water potential= 0 + 14.81= 14.81 LAB PART 2

Part 1: What factors limit cell size?

1. What is surface area? Area of given surface

2. What is volume? Area inside a shape

3. What cellular function is negatively impacted by an increase in cell size? The division of multicellular embryos

4. What happens if a cell gets too large? They divide

5. Name two ways in which a large cell can minimize the negative effects of its size. They divide or become long and skinny

Part 2: Surface Area and Volume

In this section, you will compare the surface areas and volumes of three different cubes. Each cube represents a different cell. 6. Use the sliders to change the cell dimensions to those listed in Table 1. Complete Table 1 by recording the following data for each cell:

Indicate the area of one surface (Column 2).

Record the surface area and volume (Columns 3 & 4).

Calculate and record the ratio of surface area to volume (Column 5). Determine and record the distance from the center of the cell to the closest face (Column 6).

7. As cells get larger, does the surface area-to-volume (SA/V) ratio get larger, smaller, or remain the same? It varies. Initially, it declined but then it became larger. 8. How does the change in the SA/V ratio compare with the change in distance from the center of the cell to the nearest face? The distance from the center is always increasing, where the SA/V ratio is not.

Part 3: How can a cell change its SA/V ratio without changing its overall volume?

Refer to Table 2. Imagine that Row 1 contains data for a large cell, Row 2 contains data for that same cell, after dividing, and Row 3 contains data for that same cell, after it changes shape. These changes are pictured below:

Return to Site 3 and use the sliders to change the cell dimensions to those listed in Table 2. 9. Complete Table 2, just as you did Table 1.

10. Would the total volume occupied by the cell(s) change when the first cell divides (several times) to form eight cells? Explain. No, the total volume of all 8 would still equal the volume of the initial cell 11. Did the surface area...

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