Diffusion And Osmosis Lab 733e3z

Kevin Huang Period 1 11/02/12 Diffusion and Osmosis Lab Write-Up Procedure 2: Modeling Diffusion and Osmosis a. Prelab Questions  Why is it important for an IV solution to have salts in it? An IV solution must be isotonic to blood.  What would happen if you were given pure water in an IV? Since the IV solution would be hypotonic to your blood, the cells in your body would absorb too much water and burst. You would probably die.  How would you determine the best concentration of solutes to give a patient in need of fluids before you introduced the fluids into the patient’s body? You could do bloodwork to find the patient’s current fluid and electrolyte levels.  How can you use weights of the filled cell models to determine the rate/direction of diffusion? What would be an appropriate control for the procedure you just described? If a cell loses weight, the direction of diffusion will be out of the cell, and vice versa. The rate of diffusion can be calculated from the change in mass divided by time. An appropriate control would have water both inside/outside the cell.  Suppose you could test other things besides weights of the dialysis tubes. How could you determine the rates/directions of diffusion of water, sucrose, NaCl, glucose, and ovalbumin? You could use a U-tube and put different solutions on different sides of the U-tube.  Will protein diffuse? Will it affect the rate of diffusion of other molecules? Protein will not diffuse because it is too large, but it will affect the rate of diffusion of other molecules by altering osmolarity. b. Data Table Solution in Cell Water 1M NaCl 5% Ovalbumin

Solution Outside Cell Water 5% Ovalbumin 1M NaCl

Initial Mass of Cell 18.07 g 14.38 g 14.43 g

Final Mass of Cell 15.42 g 13.67 g 13.98 g

% Change in Mass -14.67% -4.94% -3.12%

c. Analysis/Discussion All of the pairs we tested had a change in weight, probably due to leakage from the dialysis tubing. However, the control (water and water) should not have had a change in weight, because the water inside the tubing is isotonic to the water outside the tubing. A 1 M NaCl solution was hypotonic to a 1 M sucrose solution, because a dialysis tube with sucrose inside and NaCl outside gained weight, while a dialysis tube with NaCl inside and sucrose outside lost weight. By the same reasoning, the glucose was hypotonic to the sucrose, while the NaCl was hypotonic to the glucose. In order of increasing tonicity, NaCl would be least, glucose would be moderately, and sucrose would be most hypertonic. The protein solution has a low molarity, because it was hypotonic to almost every solution except water. Diffusion of glucose can be tested with living cells, which need glucose to carry out cellular respiration. Solute concentration inside a living cell can be determined by immersing the cell in a variety of osmotic environments. The environment which causes no net uptake of water is isotonic to the cell, and thus the tonicity of that environment is equal to the tonicity of the solutes in the cell.

Kevin Huang Period 1 11/02/12 Procedure 3: Observing Osmosis in Living Cells a. Prelab Questions  What would happen if you applied saltwater to the roots of a plant? Why? The roots would not absorb the saltwater, because the roots already have a very low (negative) water potential.  What are two different ways a plant could control turgor pressure? Plants can control turgor pressure through release/uptake of water from vacuoles or through plasmolyzing/becoming turgid.  Will water move into/out of a plant cell if the cell has a higher water potential than its surrounding environment? It will move out of a plant cell. b. Data Table Solution Clear Red Yellow Green Blue

% Change in Mass 13.85% -28.20% 1.54% -16.50% -25.30%

c. Analysis/Discussion Most cells are small in order to preserve a high surface-to-volume ratio. A high surfaceto-volume ratio allows for adequate uptake of nutrients by the cell; a low ratio would result in cell death from a lack of nutrients. Most cells have cell membranes with many convolutions to further increase this surface-to-volume ratio. Organelles like mitochondria, ER, and Golgi Body have membranes with many convolutions to increase surface-to-volume ratio, and thus, the amount of product produced. For example, the many folds in the inner membrane of the mitochondria (cristae) increase the surface area available for efficient ATP production. Osmosis occurs even when a cell is in an isotonic solution; water is still being exchanged between the cell and the solution, but there is no net uptake of water.