Diffusion and Osmosis Lab Report

Topics: Diffusion, Semipermeable membrane, Osmosis Pages: 8 (2788 words) Published: February 13, 2011
Hands On Approach to Diffusion and Osmosis

A. Plant and Animal Cell Diffusion and Osmosis
In this experiment we observed carmine powder to better understand the concept of Brownian motion and the role of molecular movement in diffusion. The particles continuously moved in a completely random fashion, and the smaller particles moved with more speed than the larger particles. B. Potato Core Experiment

In this experiment we estimated the osmolarity of potato tuber tissue by submersing different potato cores into sucrose solutions of 0.0-0.6M, and weighing the potato. We concluded that the osmolarity of the potato was about 0.4M since the weight of the potato did not change after it was incubated in the solution with 0.4M. We also found that the potato was hypertonic to sucrose solutions of 0.0-0.3M and hypotonic to 0.5-0.6M.

C. Dialysis Tubing Experiment
We tested the permeability of the dialysis tubing to glucose, starch, and iodine. Initially, glucose and starch were placed into the bag, and iodine outside of the bag in the beaker. We used the iodine test for the presence of starch which proved positive inside of the bag, and Benedict’s reagent for glucose which was positive outside of the bag. We therefore concluded that only small molecules like glucose and iodine can permeate through the bag, starch is too large. Introduction

This lab has several key objectives. First, to learn about diffusion and osmosis, and the different factors that affect the rate at which these processes take place. In order for cells to maintain a stable state, they must be able to regulate the particles that move through the cytoplasm, and across its membranes. Diffusion and osmosis are the two physical processes that insure these things take place for the cells to operate smoothly. Second, to gain a better understanding of the role of selectively permeable membranes in osmosis, and to learn about the significance of hypotonic, isotonic, or hypertonic solutions in relation. It is even possible to reversing osmosis! This process is used as method of water purification because it enables salt and wastes to be permeated out of the fresh water (Eisenberg, Middlebrooks, 1986). Most importantly, the purpose of this lab was to learn to apply these concepts to the cellular and environmental levels that we encounter in everyday life. Here are the specific points to each experiment.

A. Plant and Animal Cell Diffusion and Osmosis
The purpose of this experiment was to observe the carmine particles in motion in order to gain a better understanding of the Brownian movement and the role of kinetic energy in diffusion. Brownian motion and diffusion can play a major role in the transportation of different particles in many different cellular processes. One example is that diffusion carries actin monomers to the site where they polymerize into F-actin- the framework for the cytoskeleton in plants and animals! (Akkas 1989).

B. Potato Core experiment
The purpose of this experiment was to try to estimate the osmolarity of the potato tuber tissue after submersing it in a series of sucrose solutions with different molarities. The solution in which the incubated potato has the smallest change in weight will be approximately equal to the osmolarity of the potato. We hypothesized that the osmolarity of the potato would be 0.3M. Based on this hypothesis, we predicted that if the osmolarity of the potato were 0.3, then the percent weight change would be (almost) zero. Cells are primarily composed of water, and are termed selectively permeable since they allow water to move freely through the cytoplasm, but block the flow of macromolecules (Morgan, Carter 2005). Osmosis is the diffusion of water through a selectively permeable membrane from an area of low solute/high water concentration (hypotonic) to an area of high solute/low water concentration (hypertonic). Osmotic pressure is the force that can be applied...
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