1. Diffusion And Osmosis Lab

Diffusion Lab. Shannan Muskopf September 16, 2009. Most chapters follow the cell structure topic with one on the cell membrane and diffusion and osmosis. The result is: Osmosis: The diffusion of water through a differentially permeable membrane. Observe the demonstration and answer Q14 on the answer sheet. Diffusion and Osmosis Modified 2003 from AP Bio Lab Manual Introduction: In this exercise you will measure diffusion of small molecules through dialysis tubing, an example of a semi.

The cell membrane plays the dual roles of protecting the living cell by acting as a barrier to the outside world, yet at the same time it must allow the passage of food and waste products into and out of the cell for metabolism to proceed. How does the cell carry out these seemingly paradoxical roles? To understand this process you need to understand the makeup of the cell membrane and an important phenomenon known as diffusion.

Diffusion is the movement of a substance from an area of high concentration to an area of low concentration due to random molecular motion. All atoms and molecules possess kinetic energy, which is the energy of movement. It is this kinetic energy that makes each atom or molecule vibrate and move around.

(In fact, you can quantify the kinetic energy of the atoms/molecules in a substance by measuring its temperature.) The moving atoms bounce off each other, like bumper cars in a carnival ride. The movement of particles due to this energy is called Brownian motion. As these atoms/molecules bounce off each other, the result is the movement of these particles from an area of high concentration to an area of low concentration. This is diffusion. The rate of diffusion is influenced by both temperature (how fast the particles move) and size (how big they are). Part 1: Brownian Motion In this part of the lab, you will use a microscope to observe Brownian motion in carmine red powder, which is a dye obtained from the pulverized guts of female cochineal beetles. Materials.

Glass slide. Toothpick. Carmine red powder. Coverslip. Tap water Procedure. Obtain a microscope slide and place a drop of tap water on it. Using a toothpick, carefully add a very minuscule quantity of carmine red powder to the drop of water and add a coverslip.

Observe under scanning, low, and then high power. Lab Questions. Describe the activity of the carmine red particles in water. If the slide were warmed up, would the rate of motion of the molecules speed up, slow down, or remain the same? Part 2: Diffusion across a Semipermeable Membrane Because of its structure, the cell membrane is a semipermeable membrane. This means that SOME substances can easily diffuse through it, like oxygen, or carbon dioxide. Other substances, like glucose or sodium ions, are unable to pass through the cell membrane unless they are specifically transported via proteins embedded in the membrane itself.

Whether or not a substance is able to diffuse through a cell membrane depends on the characteristics of the substance and characteristics of the membrane. In this lab, we will make dialysis tubing “cells” and explore the effect of size on a molecule’s ability to diffuse through a “cell membrane.”. Materials. 2 pieces of dialysis tubing.

Thread. Phenolphthalein. Iodine. Wax pencil. 2 beakers. NaOH. Starch solution.

Pipettor. Pipette Procedure. Using a wax pencil, label one beaker #1. Label the other beaker #2. Fill beaker #1 with 300 ml of tap water, then add 10 drops of 1 M NaOH. Do not spill the NaOH—it is very caustic!. Fill beaker #2 with 300 ml of tap water, then add iodine drops drop by drop until the solution is bright yellow.

Now prepare your 2 dialysis tubing “bags.” Seal one end of each dialysis tube by carefully folding the end “hotdog style” 2 times, then “hamburger style” 1 time. Tie the folded portion of the tube securely with string.

It is critical that your tubing is tightly sealed, to prevent leaks. Add 10 ml of water and three drops of phenolphthalein to one of your dialysis tube bags. Seal the other end of the bag by carefully folding and tying as before.

Thoroughly rinse the bag containing phenolphthalein, then place it in into the beaker containing the NaOH. Add 10 ml of starch solution to the other dialysis tube. Again seal the bag tightly and rinse as above. Place this bag containing the starch solution into beaker #2. Let diffusion occur between the bags and the solutions in the beakers. After 10 minutes, observe the color changes in the two bags and the external solutions.

Draw a picture of each system below. Data Record the colors (below) and label contents inside and outside the bags (above): Beaker 1 Beaker 2 Initial Final Initial Final Color inside bag Color outside bag (in beaker) Lab Questions. Which substance diffused across the membrane in beaker #1? How do you know?. Which substance diffused across the membrane in beaker #2? How do you know?.

Why might some ions and molecules pass through the dialysis bag while others might not? Part 3: Osmosis and the Cell Membrane Osmosis is the movement of water across a semipermeable membrane (such as the cell membrane).

The tonicity of a solution involves comparing the concentration of a cell’s cytoplasm to the concentration of its environment. Ultimately, the tonicity of a solution can be determined by examining the effect a solution has on a cell within the solution. By definition, a hypertonic solution is one that causes a cell to shrink. Though it certainly is more complex than this, for our purposes in this class, we can assume that a hypertonic solution is more concentrated with solutes than the cytoplasm.

This will cause water from the cytoplasm to leave the cell, causing the cell to shrink. If a cell shrinks when placed in a solution, then the solution is hypertonic to the cell.

If a solution is hypotonic to a cell, then the cell will swell when placed in the hypotonic solution. In this case, you can imagine that the solution is less concentrated than the cell’s cytoplasm, causing water from the solution to flow into the cell. The cell swells!

Finally, an isotonic solution is one that causes no change in the cell. You can imagine that the solution and the cell have equal concentrations, so there is no net movement of water molecules into or out of the cell. In this exercise, you will observe osmosis by exposing a plant cell to salt water. Prediction What do you think will happen to the cell in this environment? Draw a picture of your hypothesis. Materials.

Elodea leaf. Microscope slide. Coverslip. 5% NaCl solution Procedure. Remove a leaf from an Elodea plant using the forceps. Make a wet mount of the leaf.

Use the pond water to make your wet mount. Observe the Elodea cells under the compound microscope at high power (400 X) and draw a typical cell below. Next, add several drops of 5% salt solution to the edge of the coverslip to allow the salt to diffuse under the coverslip.

Observe what happens to the cells (this may require you to search around along the edges of the leaf). Look for cells that have been visibly altered. Results Draw a typical cell in both pond and salt water and label the cell membrane and the cell wall. Lab Questions. What do you see occurring to the cell membrane when the cell was exposed to salt water?

Why does this happen?. Describe the terms hypertonic, hypotonic and isotonic. How would your observations change if NaCl could easily pass through the cell membrane and into the cell? Part 4: Experimental Design You and your group will design an experiment to determine the relative molecular weights of methylene blue and potassium permanganate. You may use a petri dish of agar, which is a jello-like medium made from a polysaccharide found in the cell walls of red algae. You will also have access to a cork borer and a small plastic ruler. Materials.

1 petri dish of agar. Methlylene blue. Potassium permanganate. Other? Design Your experiment design should include all of the following portions:. Hypothesis.

Experimental design. Data. Conclusions. Further questions/other comments.

Laboratory 1, AP Biology 2011 Spurthi Tarugu, Kavinmozhi Caldwell, Chelsea Mbakwe, Radha Dave, Navya Kondeti Abstract: The basic principles of Osmosis and Diffusion were tested and examined in this lab. We examined the percent increase of mass and molarity of different concentrations of sucrose in the dialysis bag emerged in distilled water and the potato cores emerged in concentrations of sucrose. The data reinforces the principles of Osmosis and Diffusion, and in a biological context, we can simulate how water and particles move in and out of our own cells. Introduction: Molecules are in constant motion; they tend to move from areas of high concentration, to areas of low concentration. This broad principle is divided into two categories: diffusion and osmosis. Diffusion is the random movement of molecules from an area of higher concentration to an area of lower concentration. This is considered a passive form of transportation because it does not require any additional energy to transport the molecules.

In the body, carbon dioxide and oxygen can diffuse across cell membranes. Osmosis is a special type of diffusion where water moves through a selectively permeable membrane from a region of higher water potential to a region of lower water potential. In our body, water diffuses across cell membranes through osmosis.

Water potential is the measure of free energy of water in a solution and is shown with the use of the symbol Ψ. Water potential is affected by two factors: osmotic potential (Ψπ) and pressure potential (Ψp). Osmotic potential is dependent on the solute concentration, and pressure potential which is the energy that forms from exertion of pressure either positive or negative on a solution. The equation to find the sum of water potential is: Water Potential = Pressure Potential + Osmotic Potential Ψw = Ψp + Ψπ The purpose of this lab is to observe the physical effects of osmosis and diffusion and determine if it actually takes place. We hypothesize that, because molecules diffuse down a concentration gradient, the mass of the dialysis tubes will increase, and we believe that as the molarity increases, the percent of change in mass will also increase. Methods: Part 1: First, soak 6 dialysis tubing in distilled water until you can open one end.

One you get the top of the tube, tie a knot at the opposite end to prevent any liquid from leaking out. Next, fill each tube about half way with a different solution (0.0M sucrose-distilled water, 0.2M sucrose, 0.4M sucrose, 0.6M sucrose, 0.8M sucrose, and 1.00M sucrose). Once you have all 6 tubes filled with the solutions, remove excess air, and tie the tops with strings. Mark the tubes or string with markings so that you can distinguish between the varying concentrations of sucrose. The marking won’t appear on the tube so it is best to color the strings a certain way and write down what color represents what solution on a separate piece of paper. Weigh each bag separately using an electronic balance and record the initial mass on a table (Table 1.1).

Next, get a 250 mL beaker and fill it to 200 mL with distilled water (or tap water). Then place all 6 tubes in the beaker,and let them sit there for 20 minutes. After 20 minutes, remove the bags from the beaker, and carefully blot each one to remove excess water. Weigh each one again on an electronic balance and record the masses on a table ( Table 1.1).

Calculate percent change and record on table ( Table 1.1). On a separate table, collect all class data and find the average of all percent changes for all of the different solutions. Look at the Results Section to see what the table layout should look like. Part 2: First pour 100 mL of each of the solutions (0.0M sucrose-distilled water, 0.2M sucrose, 0.4M sucrose, 0.6M sucrose, 0.8M sucrose, and 1.00M sucrose) into a 250 mL beaker; you will have 6 beakers in total.

Make sure you label each beaker with the solution and a group member’s name. Obtain a potato and a cork borer (5 mm in inner diameter). Use the cork borer to cut out 24 potato cylinders. Each cylinder must be 3 cm in length.

Remove any potato skin that you may find on the cylinders. Group the 24 potatoes in groups of 4. You should have 6 groups of potato cylinders. Now, measure the mass of each group. Record the initial masses of all the groups in the table ( Table 2.1).

Once you have done that you will place each group of potatoes into a different beaker. Cover each beaker with plastic wrap. Let them sit overnight. The next day, record the temperatures of the sucrose solutions in each beaker.

Diffusion And Osmosis Lab

Record the temperature in the table ( Table 2.1). Remove one group of potato cylinders, blot with a paper towel to remove excess water, and measure the group’s mass. Record in the table ( Table 2.1). Do this for the other 5 groups. Calculate the percent change in mass. Record data of percent change in mass onto the table ( Table 2.1). Collect the classes data, and determine class average.

Copy this data onto a table (Table 2.2). Look at the Results Section to see what the table layout should look like. Take note that each group in our class was assigned one solution and told to have only one group of potato cylinders due to limited supplies, hence Table 2.1 has data for only one solution. Results Table 1.1 — Dialysis Bag — Individual Group Data. 1.Describe the relationship between the increase of mass and the molarity of sucrose within the dialysis bags.

As the percent change in mass increased, the molarity increased and decreased due to flawed measurements. Because our data isn’t accurate a clear relationship cannot be determined. However, as the molarity of the sucrose within the dialysis bags increases, more water should’ve been diffused into the bag by osmosis causing an increase in mass.

This would’ve performed a direct relationship between the mass and molarity of the sucrose within the dialysis bags if the measurements were accurate. Predict what would happen in an experiment if all the dialysis bags were placed in a 0.6M sucrose solution instead of distilled water.

Draw your predicted line on your graph for Table 1.2 and label it “0.6M prediction.” Our data, as well as the class data, for the dialysis tubing section of the lab showed that, because solutions move from areas of high concentration to low concentration, water moved into the tubing, increasing the overall mass. We believe that sucrose is too big of a molecule to pass through the semi-permeable membrane, so if the water to sucrose ration both within the tubing and outside of the tubing is the same, there should be no increase in mass.

If a potato is allowed to dehydrate by sitting in the open air, would the water potential of potato cells increase of decrease? Explain by using the water potential formula from the introduction. Water moves from a high concentration to a low concentration. Because the potato is dehydrating, it has a low concentration of water inside, so water would move into the potato, which means it will have a decrease in water potential.

If a plant cell has lower water potential than its surrounding environment and if pressure equals 0, is the cell hypertonic or hypotonic to its environment? What would have to happen for the contents of the cell to be isotonic to its environment? The plant cell has a higher solute potential/concentration than its surrounding which means that the surrounding environment has a higher water potential. As a result water from the surrounding will move into the cell by the process of osmosis. Because of the cells lower water potential, compared to its environment, we say this cell is hypotonic which means that the cell has lower osmotic pressure than its surrounding. In order for the contents of the cell become isotonic there would be have to be an equal amount of osmotic pressure between cell and its environment. How could this lab technique be applied in finding out which apples, Macintosh or Delicious are sweeter? Sweetness in apples is determined by how much sucrose or other sugars it contains. In our dialysis tubing section of the lab, we saw that an increase in sucrose molarity resulted in a greater percent increase in mass.

Using this same pattern, if we cut slices of both types of apples, immersed them in distilled water, and record the percent of change in mass, than we can compare the results and see which of the two apples has the higher percent of change in mass. That apple would be the sweeter one. Conclusion The purpose of this lab was to describe the physical mechanism of osmosis and diffusion and describe how molar concentration affects diffusion. We have now observed how solutions diffuse in different situations, always from a high concentration to a low concentration, and how molar concentration affect diffusion, as the molarity goes up, more solution is diffused. We hypothesized that because molecules diffuse down a concentration gradient, the mass of the dialysis tubes will increase, and also that as the molarity increases, the percent of change in mass will also increase. Our data unfortunately did not support our conclusion due to errors.

Some of the dialysis tubes decreased in mass. One explanation is that we might not have tied the strings at the top of the tubing tight enough, resulting in solution leaking out. The overall class data for the dialysis tubing, however, does support our hypothesis and we realize our errors. Literature Cited “PHSchool – The Biology Place.” Prentice Hall Bridge Page. Pearson Education, June 2007.

Moulton, Glen E. “Cell Theory, Form, and Function: Fluid Mosaic Model of Membrane Structure and Function — Infoplease.com.” Infoplease: Encyclopedia, Almanac, Atlas, Biographies, Dictionary, Thesaurus.

Free Online Reference, Research & Homework Help. — Infoplease.com.