Cells have the amazing ability to transport certain molecules in or out of their membrane. Some require no energy to do so (passive transport) while others require energy to be processed through (active transport). There is also the transportation of water across a membrane, which has its own term of osmosis. Too much of something can be taken in, or too little enters. This especially happens to plants, who require water (and sun) to live. Not enough water, as herbalists or any plant lover will know, will cause the plant to wilt. However, why consider cell membrane transportation?
Because it happens daily, whether it is a plant or our own bodies, this transfer of materials happens without us even knowing and learning about this may keep our bodies in better check. To test membrane transportation will require multiple steps. First, if a sucrose solution is added to potato strips, then they will all swell. Next, if three different temperatures of water are added to potassium permanganate, then the coldest of the temperatures will dissolve the potassium permanganate the slowest. The last test requires two different parts.
First, if a starch solution is added to a dialysis tubing and placed in an IKI solution, then the starch solution will go out and darken the IKI solution. Next, if the contents of the dialysis tubing, IKI solution, and distilled water are placed in Benedict’s Reagent, then only the contents of the dialysis tubing will test positive for sugars. In order to perform the experiment of testing the potato strips in sucrose solution, the subsequent steps should be followed. First, label 6 test tubes a-f. Next, place the 100 ml beaker on the digital scale and zero the scale.
Measure 17. 1 g of table sugar by putting it in the beaker. Then measure a total of 50 mL of distilled water by using a 25-mL graduated cylinder. Using the stirring rod, slowly add the 50 mL and stir until the sugar is completely dissolved. This is now a 1. 0 M (molarity) solution. Label a short stem pipet “DW” (distilled water), which will be used throughout the experiments. Use the 25 ml graduated cylinder to measure 5 mL of distilled water and add that to test tube “a”. Dry the graduated cylinder and wash with distilled water after each step after this.
Use the graduated cylinder to measure 1 mL of the 1. 0 M sucrose solution and use the “DW” pipet to add 4 mL of distilled water to test tube “b”, which is now a . 2 M solution. Then use the graduated cylinder to measure 2 mL of 1. 0 M sucrose solution and add 3 mL of distilled water to test tube “c”, which this creates a . 4 M solution. Measure 3 mL of 1. 0 M sucrose and 2 mL of distilled water to test tube “d”, which then creates the . 6 M solution. Measure 4 mL of the 1. 0 M sucrose solution and 1 mL of distilled water to test tube “e”, which creates the . 8 M solution.
Finally, measure 5 mL of the 1. 0 M sucrose solution and add to test tube “f”, creating the 1. 0 M solution. For this next part, use a cutting board, a sharp knife, a ruler, a potato, and a small piece of plastic wrap. Slice 12 pieces of potato into 5 x 5 x 20 mm and ensure the strips do not have any skin on them. Next, cover the digital scale with another piece of plastic wrap and zero the scale. Place 2 potato strips on the scale; record the mass in grams. Repeat these steps, ensuring not mix up the strips. Place the 2 weighed potato strips into test tube “a” and repeat for test tubes b-f.
Cover the test tubes with a piece of plastic wrap to prevent evaporation of the solutions, as they will now have to incubate for 24 hours. After 24 hours, record the masses of the strips using similar steps as before. When taking strips out, use tweezers to get out and set the strips on a paper towel for approximately 10 seconds to allow excess liquid to come off strips. Calculate and record mass differences along with percentage change. These next steps are to test for temperature variances in diffusion and how it affects diffusion.
First, use 3 perfectly dry test tubes and mark 7 cm from the base of each test tube. Place the test tubes in an empty cup. Use the tweezers to transfer 5 crystals to each of the test tubes, then label the 3 short, clear plastic cups “cold,” “ambient,” and “warm”. After labeling the cups, add 2-3 ice cubes to the “cold” cup, then fill with water until the cup is 34 full. Let that set for 5 minutes. Use the thermometer to measure the cold-water temperature and record data (The cold-water temperature should be close to 5°C). Fill the “ambient” cup 3/4 full with about 25°C water, though record exact temperature.
After that, fill the “warm” cup 34 full of water that is about 40°C, though again, record exact temperature of water. Use a short stem pipet to slowly add water from the cold cup to the first test tube and fill to the line. Record the initial observation of the solution in the test tube. Carefully place the test tube into the cold cup. Repeat the steps above for the “ambient” and “warm” cups. Observe each initial observation, then record observations after 5 and 10 minutes. For the testing of diffusion across a membrane, follow these steps. First, label 2 of the short plastic cups “1” and “2”.
The, use the graduated cylinder to add exactly 150 mL of distilled water to cup 1. While preparing for the next step, place the dialysis tubing in cup 1 and let it soak for about 5 minutes. Use the “DW” pipet to add 4 mL of distilled water to the graduated cylinder. Add 2 mL of starch solution and 2 mL of 20% glucose solution to cup 2 and mix thoroughly with the glass rod. Next, cut 2 rubber bands in one place and set aside. By this time, the dialysis tubing should be ready to be removed from cup 1. Set cup 1 aside for future use. “Fold the dialysis tubing about 1 72 cm from the end.
Tie the snipped rubber band around the folded end of the tubing, creating a seal. Test the seal with a small amount of distilled water. Use the following procedures as a guide: To open the unsealed end of the dialysis tubing, carefully rub the tubing between your fingers until the middle of the tubing opens… Use the pipet labeled ‘DW’ to add a small amount of distilled water to the dialysis tubing. If the tube leaks, tighten the knot in the rubber band and repeat the test. Discard the distilled water used to test the dialysis tubing” (Taft 2015).
Use a funnel on the open end of the dialysis tubing and slowly pour the glucose/ starch solution from cup 2. Press air from the dialysis tubing and fold the end of the tubing tying the end closed with the other rubber band. Ensure that there are no leaks from the tubing. Rinse outside of tubing with distilled water in case any solution was spilled. Set the dialysis tube aside on a paper towel and allow to dry. Observe solution in the tubing and record observations. Use the graduated pipet to slowly add 20 drops of IKI solution to the distilled water in cup 1 and mix thoroughly.
Record color of solution in cup 1, and then place the tubing in cup 1. Let tubing sit in the cup for 1 hour, then record the color of the solution in the cup and the color of the solution in the tubing. Open contents of tubing into cup 2. For the next phase, label 3 test tubes “1”, “2”, and “3”. Then with a ruler, place a dash 2 cm and 3 cm from the bottom of each test tube. With a short stem pipet, transfer 2 cm worth of solution from cup 1 to test tube one. With a different pipet, transfer 2 cm worth of solution from cup 2 to test tube 2. Last, fill test tube 3 up to the 2 cm mark with distilled water.
To all 3 test tubes, fill them up to the 3 cm mark with Benedict’s Reagent. Record observations of each test tube color. Then, to activate Benedict’s Reagent, get a beaker 12 full of boiling water and add the test tubes, allowing them to incubate for 10 minutes. Record observation of each test tube color. The first hypothesis mentioned, if a sucrose solution is added to potato strips, then they will all swell, was rejected due to all did not swell. In fact, only one did swell; the majority shrunk in mass, though there was the . 2 M sucrose solution that was out of pattern.
The next hypothesis, if three different temperatures of water are added to potassium permanganate, then the coldest of the temperatures will dissolve the potassium permanganate the slowest, held true. Looking at Data Table 2 and using color as an indicator, it was indeed a valid hypothesis. The third hypothesis tested, if a starch solution is added to a dialysis tubing and placed in an Ikl solution, then the starch solution will go out and darken the IKI solution, was incorrect. In fact, it was quite the opposite; the IKI solution went into the tubing.
The last hypothesis tested, if the contents of the dialysis tubing, IKI solution, and distilled water are placed in Benedict’s Reagent, then only the contents of the dialysis tubing will test positive for sugars, was true. In Data Table 4, it shows that the contents inside the tubing showed orange, which is a positive test for sugars. One item learned from these experiments is that a plastic tubing is able to absorb contents from outside of it. Though the dialysis tubing was thin, bottles of water or soda are about as thin. This was astonishing to me, as I believed plastic to be decently impenetrable.
