Pre Lab #6
Diffusion, Osmosis, and Tonicity
Group Members: Laghu Shakya, Alex Maican, Kelvin Chen, Ziye Lin
In this lab we will be gaining an understanding of how transport in membranes work. This is important because in our semi permeable cell membrane the mode of movement relies on transport. Some methods of transportation for molecules are simple diffusion, facilitated diffusion, active transport, exocytosis and osmosis. The reason molecules tend to move around when dissolved in a solution is because all molecules display random thermal motion and have kinetic energy. Kinetic energy is what allows the molecules to ...view middle of the document...
This is what we will use to understand how osmosis works in our cell membranes. Osmosis is the diffusion of water across a permeable membrane. There are three types of solutions in this case, hypotonic solution is a solution with a lower concentration of solutes and the cell expands as water moves in to the cell from the solution until equilibrium is reached. Hypertonic solution has a higher concentration of solutes and the cell in this case shrinks as no water leaves from the cell to the solution until equilibrium is reached. Isotonic solution is a solution where the concentration is similar inside and out and so there’s no change.
For our lab’s first procedure we will be observing the movement as we look at carmine red through a microscope and find its specific detailed focus and increase the heat and observe its motion. For the second procedure we will understand osmosis and how it works as we use dialysis tubing to figure out what happens as we place tubes with different concentrations of sucrose solution into specific sucrose solutions and we calculate the difference in weight every 15 minutes for an hour to figure out which solutions are hypertonic, hypotonic and isotonic. The third experiment consists solely of creating a graph that compares Total Weight (g) vs. Time (min).
1 Sample size of Carmine Red Suspension
1 Compound Light Microscope
1 Microscope slide
1 Cover slip
8 pieces of string
4 pieces of water soaked dialysis tubing (15 cm long)
1 sample size of 1% sucrose solution
1 sample size of 10% sucrose solution
1 sample size of 25% sucrose solution
4 small pieces of paper
3 individual beakers or 1 Large bowl
1 250-mL beaker
1 balance scale
1 graph paper
1 data sheet
Vodopich D.S Introduction to Cellular and Molecular Biology Lab. New York: McGraw-Hill, 2007, p64 – p69
1. Using a pipet, place a small drop of carmine red suspension on a microscope slide. Cover the slide with a cover slip using the proper technique and coming down on the specimen at a 45-degree angle.
2. First, focus on the specimen at the lowest magnification. Then rotate to the highest power. Be careful not to get any dye in the objective lens.
3. Work on fine focusing the image. Initially, the image will appear reddish grey, but with sharp focus you will see the thousands of molecules that are vibrating.
4. Check with your instructor to see if your microscope has had oil immersion magnification and if it is needed to easily view these particles.
5. Leave the microscope on and observe any changes with the moving particles as the heat changes.
1. Obtain eight pieces of string and four pieces of water-soaked dialysis tubing that are 15 cm long. Seal one of each tube by folding it into a basic knot and tying it tightly. Make sure not to tear the bag by being too aggressive.
2. Open the opposite end of the...