Osmosis and Diffusion Lab

Osmosis and Diffusions Lab Report

Mod. 19, AP Biology

Abstract. In this lab our group’s goals were to conduct multiple experiments in hopes to find a difference in our data. We used different amounts of sucrose in each beaker that contained the same concentrate of potato to see if we could reach a better understanding of diffusion and osmosis by recording the weights of the contents in each beaker. This lab experiment we conducted helped us understand the fundamentals and schematics of how diffusion and osmosis occurs.

Introduction

In this lab, we experimented with the process of osmosis and diffusion using potatoes, sucrose, and water. Foraging refers to the mammalian behavior associated with searching for food. The optimal foraging theory assumes that animals feed in a way that maximizes their net rate of energy intake per unit time (Pyke et al. 1977). An animal may either maximize its daily energy intake (energy maximizer) or minimize the time spent feeding (time minimizer) in order to meet minimum requirements. Herbivores commonly behave as energy maximizers (Belovsky 1986) and accomplish this maximizing behavior by choosing food that is of high quality and has low-search and low-handling time (Pyke et al. 1977).

       The central place theory is used to describe animals that collect food and store it in a fixed location in their home range, the central place (Jenkins 1980). The factors associated with the optimal foraging theory also apply to the central place theory. The central place theory predicts that retrieval costs increase linearly with distance of the resource from the central place (Rockwood and Hubbell 1987). Central place feeders are very selective when choosing food that is far from the central place since they have to spend time and energy hauling it back to the storage site (Schoener 1979).

       The main objective of this lab was to observe osmosis take place within potatoes and dialysis tubes. Osmosis occurs within and outside of cells. By examining the potatoes’ and the tubes’ mass, we hope to see the mass change. The purpose of this lab was to learn about the osmosis. We wanted to know potatoes and dialysis tube can show signs of a process similar to osmosis in the right environment.

      

Methods

Procedure: (PART I - work in groups of 4)

        **PRE-LAB: Students will make the various sucrose solutions beforehand.**

1.     Obtain six, ~20c cm strips of pre-soaked dialysis tubing.

2.     Tie off one end of each piece with `twisty ties’ to form 6 bags.

3.     Pour 25 mL of each of the following sucrose solutions into separate bags:

a.     0.0M sucrose—distilled water

b.     0.2 M sucrose

c.      0.4M sucrose

d.     0.6M sucrose

e.     0.8M sucrose

f.      1.0M sucrose

4.     Remove excess air from each bag and tie off with `twisty ties’.

5.     Rinse each bag under tap water to remove sucrose from the string and outside surfaces

6.     Carefully blot the outside of each bag and record the initial mass of each bag in Table 1.1.

7.     Place each bag in one of three 250 mL beakers (or cup if that is the only option) and fill with distilled (or tap if that is the only option) water to the 200 mL mark. Label beaker with appropriate information.

8.     Let stand for 20 minutes

9.     At the end of 20 minutes, remove the bags and carefully blot each.

10. Determine the mass and record in Table 1.1 for the solutions you were assigned.

11. Record data of percent change in mass in Table 1.2 (both in your tables and also on the class computer).

Procedure: (PART II – work in groups of 4)

**PRE-LAB: Students will make the various sucrose solutions and potato cores beforehand.**

1.     Obtain 100 mL of each of the sucrose solutions and pour each solution into a separate, labeled 250 mL beaker (or cup if that is the option).

2.     Use a cork borer (approximately 5mm in inner diameter) to cut 24 potato cylinders. Cut each cylinder to segments 3 cm in length. Remove any skin found on the cylinders.

3.     Determine the mass of 4 of the cylinders together, and record in Table 2.1. Put these 4 cylinders into one of your sucrose solutions.

4.     Do the same for 4 other cylinders and place in your second sucrose solution.

5.     Do the same for the remaining cylinders (in groups of 4) and place n the remaining sucrose solutions.

6.     Cover the beakers with plastic wrap.

7.     Let stand overnight.

8.     The next day, record the temperature of the sucrose solutions in Table 2.1.

9.     Remove the cores from one of the beakers, blot them gently on paper towel and determine their combined mass. Do the same for your two other beakers.

10. Record the final masses and calculate percent change in Table 2.1.

11. Record data of percent change in mass in Table 2.2 (both in your tables and also on the class computer).

Results

Part I - Membrane Demonstration

Contents of Beaker	Initial Mass	Final Mass	Mass Difference	% Change in Mass
0.0M sucrose	3.82 g	3.89	.07	1.80%
0.2M sucrose	5.25 g	6.09	.84	16.0%
0.4M sucrose	3.14 g	3.2g	.06 g	1.88%
0.6M sucrose	4.58 g	5.03 g	.45 g	8.95%
0.8M sucrose	1.98 g	1.70 g	-.28 g	14.14% decrease
1.0M sucrose	4.46 g	4.15 g	-.31 g	6.95% decrease

Part II - Potato Demonstration

Contents of Beaker	Initial Potato Mass	Temperature	Final Potato Mass	Mass difference	% Mass Change
0.0M sucrose	7.17 g	76F	7.14 g	-.03 g	.41% decrease
0.2M sucrose	10g	76F	5.96 g	-4.04 g	40.4% decrease
0.4M sucrose	11g	76F	11.89 g	.89 g	7.49%
0.6M sucrose	10.5g	76F	5.5 g	-5.0 g	47.62% decrease
0.8 M sucrose	15.00 g	76F	10.35 g	-4.65	31% decrease
1.0 M sucrose	10.20 g	76F	7.45 g	-2.75	26.96% decrease

Discussion

The result of the lab after

The lack of any observed difference in mean circumference between chewed and not chewed trees does not agree with our hypothesis that beavers will prefer smaller trees to larger ones. Our hypothesis was based on the idea that branches from smaller trees will require less energy to cut and haul than those from larger trees. Our finding is in accordance with other studies (Schoener 1979), which have suggested that the value of all trees should decrease with distance from the water but that beavers would benefit from choosing large branches from large trees at all distances. This would explain why there was no significant difference in circumference between chewed and not-chewed trees.

This lab gave us the opportunity to observe how a specific mammal selects foods that maximize energy gains in accordance with the optimal foraging theory. Although beavers adhere to the optimal foraging theory, without additional information on relative nutritional value of tree species and the time and energy costs of cutting certain tree species, no optimal diet predictions may be made. Other information is also needed about predatory risk and its role in food selection. Also, due to the large number of students taking samples in the field, there may have been errors which may have affected the accuracy and precision of our measurements. In order to corroborate our findings, we suggest that this study be repeated by others.

Conclusion

The purpose of this lab was to learn about diffusion and osmosis within potatoes and dialysis tubes. We were able to see that the potato cells diffused the water through osmosis from within, and the water outside of the tube diffused water, and entered the tube through osmosis. We also learned that the results aren’t always going to match the original theory. For instance, one of our tubes lost mass in the second trial, which could have been a result of a leaking tube, or incorrect initial measurements. For the most part, what was expected occured.

Nishiura, P. J. (n.d.). Lecture Outline Biology 4 Section FV. Retrieved 10 8, 2013, from Brooklyn College City University of New York: http://academic.brooklyn.cuny.edu/biology/bio4fv/page/semes.htm