Diffusion and Osmosis assignment

Before getting started please read through the entire lab and answer the pre-lab questions on page 45. Re-read the Brownian Motion section in your lab manual and then watch the following video to see a demonstration. Next watch the video below looking at a suspension of carmine dye in water and answer the questions for Exercise I. in your Potato Cell Osmolarity Scientific Report. This week we will be using dialysis tubing to demonstrate selective permeability. Please re-read the background materials and procedure for Exercise II. and fill out the question hypothesis and prediction sections in your lab report. Next watch the video below to see how we would fill a dialysis bag with a glucose and starch solution (simulating the glucose and starch found in the cytoplasm of a cell). Now that the dialysis tubing has been filled and rinsed we take the initial weight seen below. Now it is time to place the filled dialysis tubing into a beaker with iodine. Remember from our biomolecules section when iodine reacts with starch we will see a dark blue/black color form. We will repeat the dialysis tubing set up and place the filled tubing in a second beaker without iodine so that we can perform a Benedicts test to look for the movement of glucose after the incubation period. You will see these two set ups below and we will follow them over the course of 60 minutes. At 0 minutes: After 15 Minutes: After 60 Minutes: Completed Experiment: After the 60 minute incubation time we re-weight our dialysis tubing as seen below. Using the images above fill out Tables 1 and 2 in your lab report. The final test that we will need to conduct is a Benedicts test to look for the movement of glucose. Please see the results of the Benedicts test below and fill out Table 3. in you lab report. Finish this section with a strong conclusion statement. Benedicts Test Post-Incubation: In this weeks lecture we learned about tonicity the ability of a solution to cause a cell to gain or lose water. Please re-read the background information on Osmosis (under Part II.) and the osmotic behavior of plant cells (Exercise I). Remember that when we are talking about tonicity we are comparing two adjacent solutions. Lets imagine that we are comparing the solution inside a cell with a solution outside the cell. If the solution outside the cell was isotonic the solute concentration is the same as that inside the cell and we would see no net water movement across the plasma membrane. Now lets imagine that the solution outside the cells was hypertonic. In this case the solute concentration is greater than that inside the cell so water would move out of the cell. Lastly if the solution outside the cell was hypotonic the solute concentration is less than that inside the cell and so water would move into the cell. In Exercise I. we use the light microscope to examine Elodea an aquarium plant immersed in either an isotonic hypertonic or hypotonic solution. Using the descriptions of tonicity above think about what would happen to the Elodea as it is placed in each of the three different solutions. Would the Elodea cells gain or lose water or would there be no net movement of water? Imagine what this is doing to the central vacuole of the Elodea and how the chloroplasts within the cytoplasm would look as a result. Observe the three images of Elodea below after being placed in solutions labeled A B and C. Record your observations in Table 4. of your lab report and determine the tonicity of solutions A B and C. Solution A Solution B Solution C In our last experiment this week we will be determining the osmolarity the number of solute particles per 1 L of solvent of potato cells. We will do so by immersing potato samples into sucrose solutions with varying molarity and determining the percent change in weight of each potato sample. Please read the background materials and procedure for Exercise II. and watch the video below. For our experiment we cut out 7 potato cylinders and take their initial weight. We then place each potato cylinder into one of the following sucrose solutions: 0M 0.1M 0.2M 0.3M 0.4M 0.5M or 0.6M. We wait for 2 hours and then we re-weigh each potato cylinder to look at whether the potato gained or lost water. Remember that if a potato cell is placed in a hypertonic solution it will lose water and if it is placed in a hypotonic solution it will gain water. The water loss or gain affects the weight of the potato cylinder. If we are looking for the osmolarity of potato cells we are looking for the sucrose solution where there is no net movement of water and thus no weight gain or loss. Using the values listed in the table below determine the percent change in weight for the potato cylinders placed in each sucrose molarity (Hint: the equation for percent change in weight is in your lab manual). Please record these values in Table 5. of your lab manual. Notice that some of your percent change in weight values are positive (meaning that the potato cylinder gained weight) and some of you values are negative (meaning that the potato cylinder lost weight). When you graph these values in your scientific report this week your data should span over two quadrants. The osmolarity of potato cells is where the linear trendline crosses the x-axis as described in the video. This is the experiment that we will be writing about in your formal scientific report this week. Please fill out the Potato Cell Osmolarity Scientific Report. The directions on this document are slightly different from what you have in your lab manual so please read it carefully. Requirements: docs ‘