osmosis LAb(2)

Name AP Lab 4: Diffusion, Osmosis, and Water Potential Before you begin this lab, review the relevant information in the content and in your textbook. Also prepare by reading over this lab in the AP Biology Investigative Lab Manual on pages S51-S54. Prelab (IMPORTANT): Watch the following video throughout these labs https://www.youtube.com/watch?v=LeS2-6zHn6M Diffusion demo: (min 2:42 of video). Watch the above video carefully, record data below, and answer the analysis questions. In this ac±vity, we will witness the diffusion of different par±cles across a selec±vely permeable membrane. We use the term “selec±vely permeable” to discuss how a membrane lets some par±cles go in or out, but not all par±cles. This membrane is an ar±ficial plas±c tube, not a real cell membrane. It selects par±cles based on their size – if a par±cle is small enough to go through the small holes of the tubing, then it can cross. If a par±cle is too large, then it does not cross. We will have several par±cles inside or outside the cell in this experiment, and we will be able to see what they do over the course of 20-30 minutes. Particles: IKI – has a orange-brown color unless it is in the presence of starch – then it turns blue-black starch glucose – we will use test strips that turn different colors if glucose is present Data: Put “Xs” in the table below if the par±cle is present in that loca±on Start of the experiment Particle Is it outside the cell? Is it inside the cell? IKI starch glucose End of the experiment Particle Is it outside the cell? Is it inside the cell? IKI \ glucose Conclusion: 1. Which par±cles were able to cross the cell membrane? Which par±cles were NOT able to cross the cell membrane? How do you know (cite evidence from our observa±ons)? This study source was downloaded by 100000852590013 from CourseHero.com on 10-13-2023 22:50:22 GMT -05:00

https://www.coursehero.com/file/212378090/osmosis-lab-final-1docx/ 2. How do par±cles naturally move? You cannot say that par±cles always move from outside to inside or inside to outside – what is the rule demonstrated here? 3. For the par±cles that moved, did they ALL move to the other side? What is the rule here? Lab 1: Effects of Osmotic Potential Differences Across a Membrane Materials:  6 ~ 20 cm strips of dialysis tubing  0.0 M sucrose solution – distilled water  0.2 M sucrose solution  0.4 M sucrose solution  0.6 M sucrose solution  0.8 M sucrose solution  1.0 M sucrose solution  Distilled water  Timer  Digital scale  6 clear plastic cups To make sucrose solutions: Add the number of grams of sucrose according to the table below and fill to the 100mL line with distilled water. You may need to heat the water to get the higher concentrations of sucrose to dissolve. You’ll use this for BOTH labs. Molarity Grams sucrose per 100 mL solution 0.2 6.8 0.4 13.7 0.6 20.5 0.8 27.4 1 34.2 Lab 1 Hypothesis : Think about what your variables are and construct a hypothesis predicting the relationship between them. ________________________________________________________________________________________ ________________________________________________________________________________________ Procedure: You will conduct the experiment using the virtual lab here (don’t worry about recording this data, you’ll be provided data): https://video.esc4.net/video/assets/Science/Biology/Gateway%20Resources/cell%20homeostasi s %20virtual%20lab%20-%20activity/index.html Answer the questions after the virtual lab here. 1. Which dialysis tubes had li²le or no change in mass a³er a 24-hour period? 2. Why was pure water used as a control group? This study source was downloaded by 100000852590013 from CourseHero.com on 10-13-2023 22:50:22 GMT -05:00

mass by 20 minutes to calculate a rate of osmosis. As the concentra±on gradient increases between outside and inside, what happens to the rate of osmosis? Lab 2: Determining the Water Potential of Potato Cells In animal cells, the movement of water into and out of the cell is influenced by the relative concentration of solute on either side of the cell membrane. If water moves out of the cell, the cell will shrink. If water moves into the cell, the cell may swell or even burst. In plant cells, the presence of a cell wall prevents the cells from bursting, but pressure does eventually build up inside the cell and affects the process of osmosis. When the pressure inside the cell becomes large enough, no additional water will accumulate in the cell even the though cell still has a higher solute concentration than does pure water. The movement of water through the plant tissue cannot be predicted simply through knowing the relative solute concentrations on either side of the plant cell wall. Instead, the concept of water potential is used to predict the direction in which water will diffuse through living plant tissues. In a general sense, water potential is the tendency of water to diffuse from one area to another under a given set of parameters . Water potential is expression in bars, a metric unit of pressure equal to about 1 atmosphere and measured with a barometer. Water potential is abbreviated by the Greek letter psi (Ψ ) and has two major components: Materials:  0.0 M sucrose solution – distilled water  0.2 M sucrose solution  0.4 M sucrose solution  0.6 M sucrose solution  0.8 M sucrose solution  1.0 M sucrose solution  Distilled water Procedure: Watch the video starting at 5:35  Timer  Digital scale (food scale works great) or triple-beam balance  Potato  Potato peeler  6 clear plastic cups  Plastic wrap Hypothesis: __________________________________________________________ Data Concentration of sucrose solution outside the potatoes (inside unknown solute concentration) 0.0 M (water) 0.2 M 0.4 M 0.6 M 0.8 M 1.0 M

This study source was downloaded by 100000852590013 from CourseHero.com on 10-13-2023 22:50:22 GMT -05:00 https://www.coursehero.com/file/212378090/osmosis-lab-final-1docx/ Class mean 21.88% 7.25% -7.91% -11.82% -25.88% -30.95% Class standard deviation 15.6% 25.4% 8.8% 21.8% 19.5% 6.5% Class sample size (n) 15 13 13 14 9 10 Analysis: Prepare a corresponding graph of your findings. Be sure your graph indicates positive and negative changes in mass as indicated above and below the x axis. Remember to follow good graphing procedures by labeling each axis including units and giving the graph a title. Use a best fit line to determine where the line crosses the X axis. The black lines represent the x and y axes. This point of intersection represents the point at which the potato cells do not change in mass, meaning that the solute concentration of the potato cells is isotonic to the external solution.

 i = Ionization constant (for sucrose this is 1.0 because sucrose does not ionize in water)  C = Molar concentration (determined above)  R = Pressure constant (R = 0.0831 liters bars/mole K)  T = Temperature K (273 + o C of solution) Please take a moment to review help information on page 52-53 of your student lab manual as well as the recorded synchronous session on water potential to help you make the following calculations. First calculate the solute potential (Ψ S ) of the sucrose solution. Show answers and work here. Knowing the solute potential (Ψ S ) of the sucrose solution and that the pressure potential of the solution is zero (Ψ P = 0) allows you to calculate the water potential of the solution. The water potential will be equal to the solute potential of the solution. Ψ = 0 + Ψ S or Ψ = Ψ S The water potential of the solution at equilibrium will be equal to the water potential of the potato cells. What is water potential of the potato cells? Ψ potato cells = ___________ bars Reasoning paragraph – Please construct a reasoning paragraph explaining the following: 1. Identify your independent and dependent variables 2. What is the relationship between variables (discuss the trend you see) 3. Why does this trend occur? 4. Discuss the concept of water potential and the two physical factors that affect it. This study source was downloaded by 100000852590013 from CourseHero.com on 10-13-2023 22:50:22 GMT -05:00 https://www.coursehero.com/file/212378090/osmosis-lab-final-1docx/ Powered by TCPDF (www.tcpdf.org)