Can I get someone to do this lab for me?
Name: Jade Beisner Period: 4 AP DIFFUSION OSMOSIS.LAB AP BIOLOGY LAB: DIFFUSION AND OSMOSIS PRE-LAB QUESTIONS *** Since we are doing this lab virtually this year you can ignore the class data tables. We will not be doing the inquiry section at the end. INTRODUCTION: Dialysis tubing allows molecules to diffuse through microscopic pores in the tubing. Molecules smaller than the pores can diffuse through the dialysis membrane along their concentration gradients. Molecules larger than the pore size are prevented from crossing the dialysis membrane. Part 1A: Diffusion Demonstration 1) Predict whether or not each of these is expected to pass through the dialysis membrane. Water yes Glucose Iodine Solution Starch 2) How will you know whether the iodine solution has crossed the dialysis membrane? Part 1B: In the following situations, assume the sucrose cannot diffuse through the dialysis membrane. 3) If a dialysis bag that 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. 4) 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 the equation and your work. Units are important. Calculate to the nearest tenth. Final Mass - Initial Mass (grams) x 100= 14.8% Initial Mass 1 Lab One: Diffusion and Osmosis Overview: In this lab you will: 1. Investigate the process of diffusion and osmosis in a model with membrane system. 2. Investigate the effect of solute concentration on water potential as it relates to living plant tissues. Objectives: Before doing this lab you should understand; ● The mechanisms of diffusion and osmosis and their importance to cells ● The effects of solute size and concentration gradients on diffusion across selectively permeable membranes ● The effects of a selectively permeable membrane on diffusion and osmosis between two solutions separated by the membrane ● The relationship between solute concentration and pressure potential and the water potential of a solution ● The concept of molarity and its relationship to osmotic concentration After doing this lab you should be able to: ● Understand the concept of water potential ● Measure the water potential of a solution in a controlled experiment ● Determine the osmotic concentration of living tissue or an unknown solution from experimental data ● Describe the effects of water gain or loss in animal and plant cells ● Relate osmotic potential to solute concentration and water potential INTRODUCTION: Many aspects of the life of a cell depend on the fact that atoms and molecules have kinetic energy and are constantly in motion. This kinetic energy causes molecules to bump into each other and move in new directions. One result of this molecular motion is the process of diffusion. Diffusion is the random movement of molecules from an area of higher concentration of those molecules to an area of lower concentration. For example, if one were to open a bottle of hydrogen sulfide (H2S has the odor of rotten eggs) in one corner of the room, it would not be long before someone in the opposite corner would perceive the smell of rotten eggs. The bottle contains a higher concentration of H2S molecules than the room does and therefore the H2S gas diffuses from the area of higher concentration to the area of lower concentration. Eventually, a dynamic equilibrium will be reached; the concentration of H2S will approximately equal throughout the room and not net movement of H2S will occur from one area to the other. Osmosis is a special case of diffusion. Osmosis is the diffusion of water through a selectively permeable membrane (a membrane that allows for diffusion of certain solutes and water) from a region of higher water potential to a region of lower water potential. Water potential is the measure of free energy of water in a solution. Diffusion and osmosis do not entirely explain the movement of ions or molecules into and out of cells. One property of a living system is active transport. This process uses energy from ATP to move substances through the cell membrane. Active transport usually moves substances against a concentration gradient, from regions of low concentration of that substance into regions of higher concentration. Exercise 1A: Diffusion (this will be done as a demonstration) In this experiment you will measure diffusion of small molecules through dialysis tubing, an example of a selectively permeable membrane. Small solute molecules and water molecules can move freely through a selectively permeable membrane, but larger molecules will pass through more slowly, or perhaps not at all. The movement of a solute 2 through a selectively permeable membrane is called dialysis. The size of the minute pores in the dialysis tubing determines which substances can pass through the membrane. A solution of glucose and starch will be placed inside a bag of dialysis tubing. Distilled water will be placed in a beaker, outside the dialysis bag. After 30 minutes have passed, the solution inside the dialysis tubing and the solution in the beaker will be tested for glucose and starch. The presence of glucose will be tested with Benedict’s solution, Testape, or Clinistix. The presence of starch will be tested with Lugol’s solution (Iodine Potassium-Iodide, or IKI). Procedure: 1. Obtain a 15-cm piece of 2.5-cm dialysis tubing that has been soaking in water. Tie off one end of the tubing to form a bag. To open the other end of the bag, rub the end between your fingers until the edges separate. 2. Test the 15% glucose/1% starch solution for the presence of glucose. Your teacher may have you do a Benedict’s test or use Testape of Clinistix. Record the result in Table 1.1. 3. Place 15 mL of the 15% glucose/1% starch solution in the bag. Tie off the other end of the bag, leaving sufficient space for the expansion of the contents in the bag. Record the color of the solution in Table 1.1. 4. Fill a beaker or cup two-thirds full with distilled water. Add approximately 4 mL of Lugol’s solution to the distilled water and record the color of the solution in table 1.1. Test this solution for glucose and record the results in Table 1.1. 5. Immerse the bag in the beaker solution. 6. Allow your setup to stand for approximately 30 minutes or until you see a distinct color change in the bag or in the beaker. Record the final color of the solution in the bag, and of the solution in the beaker, in Table 1.1. 7. Test the liquid in the beaker and in the bag for the presence of glucose. Record the results in Table 1.1. Table 1.1 Initial Contents Solution Color Solution Color Presence of Glucose Presence Of Glucose Initial Final Initial Final Bag 15% Glucose & 1% Starch creamy or white purple yes yes Beaker H2O & IKI brownish light brown no yes Analysis of Results 1. Which substance(s) are entering the bag and which are leaving the bag? What experimental evidence supports your answer? 2. Explain the results you obtained. Include the concentration of differences and membrane pore size in your discussion. 3 3. Quantitative data uses numbers to measure observed changes. How could this experiment be modified so that quantitative data could be collected to show that water diffused into the dialysis bag? You could weigh the bag before and after. 4. Based on your observations, rank the following by relative size, beginning with the smallest: glucose molecules, water molecules, IKI molecules, membrane pores, starch molecules. Water>iodine>glucose>membrane pores>starch 5. What results would you expect if the experiment started with a glucose solution and IKI solution inside the bag and only starch and water outside? Why? IKI would change purple in the container. Glucose would move from the inside to the outside. Water will move freely across the membrane. EXERCISE 1B: Osmosis In this experiment you will; use dialysis tubing to investigate the relationship between solute concentration and the movement of water through a selectively permeable membrane by the process of osmosis. When the two solutions have the same concentration of solutes, they are said to be isotonic to each other (iso- means same, -ton means condition, -ic