Exercise 1

Certain substances are able to diffuse across plasma membranes under the right conditions through selective permeability. The selection of these certain substances allows for cells to maintain homeostasis, as these substances move from higher concentration to lower concentration. The purpose of this experiment is to see whether or not Lugol’s will be able to diffuse across dialysis tubing, which acts as a membrane. Lugol’s turns black when it interacts with starch, which will make the diffusion easy to see. This is all based off of a caterpillar eating a plant. The starch present in the leaves causes the caterpillar to produce amylase, which breaks down starch. In one experiment, the tubing will contain starch and amylase, while the other tubing

3. Does the rate of diffusion change over time? How might this affect your calculated diffusion

Cells and molecules in the environment are constantly moving and changing, for cells to function properly there is a need for equilibrium to be met. The size of the cell and the solution outside of the cell affects the rate of diffusion and osmosis in the cell. Cells are constantly trying to reach an equilibrium with the molecules and substances around it, which is why there are such terms as: hypertonic, hypotonic and isotonic. The procedures allowed testing of whether or not surface area or volume increased diffusion and how different substance control diffusion. Cells are constantly moving to reach equilibrium through diffusion and osmosis.

2. Explain your observations in detail in terms of concentration gradient, diffusion, osmosis, osmotic pressure, passive transport, and active transport.

Watch the solute concentration windows at the side of each beaker for any changes in Na+ and K- concentrations. The Na+ transport rate stops before transport has completed. Why do you think that this happens?

3. Why do you think the urea was not able to diffuse through 20 MWCO? How well did the results compare with your predictions?

What two parameters are responsible for creating the movement (filtration and reabsorption) of fluid across the capillary wall?

When glucose carriers in the membrane were set to 500, the glucose transport rate for 2.00 mM of glucose was .0008 mM/min. Equilibrium was reached at 43 minutes. At 700 glucose carriers the rate was .0010 mM , and equilibrium was reached at 33 minutes. When the glucose carriers was set at 900 the rate was .012 mM/min, and equilibrium was reached at 27 minutes. After changing the glucose concentration to 8.0 mM, the glucose transport rate with 500 carrier proteins was .0023 mM/min, and equilibrium was reached at 58 minutes. With the simulation set at 700 carrier proteins the rate was .0031mM/min, and equilibrium was reached at 43 minutes. When the simulation was done with 900 carrier proteins the glucose transport rate was .0038, and equilibrium was reached at 35 minutes.

Two variables that affect the rate of diffusion are the MWCO membrane and the solute concentration. Increasing the membrane size and solute concentration will also increase the average diffusion rate. Decreasing the membrane size and solute concentration will reduce diffusion rates and can even prevent all diffusion.

7. Explain how incubation plant tissues in a series of dilutions of sucrose can give an

13. Understand the transportation of potassium and sodium across plasma membranes. (p. 10 bottom right, p. 20 bottom right, p. 21 diagram)

In this experiment, we will investigate the effect of solute concentration on osmosis. A semi‐permeable membrane (dialysis tubing) and sucrose will create an osmotic environment similar to that of a cell. Using different concentrations of sucrose (which is unable to cross the membrane) will allow us to examine the net movement of water across the membrane.

The difference is that along with large molecules, living cells prevent molecules with positive charges and solubility. This is not representing in dialysis tubing, and is only found in living cells because the tubing is only based on molecular size (98). When referring the rate of diffusion, the concentration gradient influences the diffusion rate, based on the factors of temperature. The ability for molecules diffuse from high to low concentrations primarily depends on the concentration gradient between the two areas.(96-99). My hypothesis for the study is that in the hypotonic, hypertonic, and isotonic solutions, the direction and rate of osmosis will determine based on the concentration inside the dialysis tubing. My prediction is that if the solution is hypotonic the results will decrease, if the solution is hypertonic the results will increase and if the solution is isotonic the solution will vary and or remain constant.

Review Sheet Results 1. Explain the effect that increasing the Na+ Cl- concentration had on osmotic pressure and why it has this effect. How well did the results compare with your prediction? Your answer: The increase of the Na+Cl- concentration increased osmotic pressure the Na+ Cl- molecules diffused through the 50 mwco membranes and didn't go through the 20 mwco membranes. the more Na+Cl- we added to the 20 mwco membrane, the more the osmotic pressure went up. When I looked at my results I noticed when Na+Cl- was added to the 50 mwco membrane, there was no increase in osmotic pressure. This is becasue the Sodium chloride couldn't diffuse through the 50 mwco membranes. The higher concentration of molecues on one side of the mwco membrane forces the water movement to move to the side of greater solute concentration. 2. Describe one way in which osmosis is similar to simple diffusion and one way in which it is different. Your answer: Osmosis is similar to simple diffusion because both of these precesses have the passive transport characteristic. This is where particles in a solution move from an area of high solute concentration to an are of low solute concentration. Also neither of these processes need energy from an outside source to function. Osmosis is different than simple diffusion because in osmosis, if we have a selectively permeable membrane, this membrane is

The next experiment was to test diffusion in agar solution. A petri dish with a layer of solidified agar had four holes punched in it using a No. 5 cork borer. Three holes were punched in a triangle shape with the fourth hole directly in the middle. There should be 15 mm between each outside hole and the middle hole. The three outside holes were filled with one drop each of potassium bromide, potassium Terri cyanide, and sodium chloride. The middle hole was filled with a drop of silver nitrate. It is very important to make sure that none of the holes overflow. After each has been filled allow to sit for an hour and observe the results.