Diffusion Through Membrane

INTRODUCTION: Cell membranes are selectively permeable and regulate which substances can pass and how much of each substance can enter and exit at a given time interval[1]. Selective permeability is essential for the ability of cells to absorb nutrients, remove waste, and maintain a stable internal environment different from the surrounding (maintain homeostasis)[1]. Substances such as water, ions and molecules required for cellular processes can enter and exit the cells through a passive process such as diffusion[2]. Diffusion is the process by which a substance moves from an area of ​​high concentration to an area of ​​lower concentration[3]. Therefore, over time, the net motion of the molecules continues until the concentrations are equal[3]. In a cell, there may be different diffusion rates and directions for different molecules[1]. Simple passive diffusion occurs when small molecules pass through the lipid bilayer of a cell membrane[4]. Facilitated diffusion uses carrier proteins in the membrane to allow certain substances that cannot pass through the cell membrane[4].
MATERIALS: Dialysis tubing or plastic bags, string or unwaxed dental floss, Glucose Indicator Solution, test tube rack, concentrated glucose solution, funnel, tap water, 7 test tubes, starch solution, paper towels, droppers of pipettes, safety goggles, Starch Indicator Solution, 250 mL beaker, hot water bath, test tube holder
METHOD: First, make a cell with a dialysis tube. Take a 20 cm long dialysis tube. The dialysis tubing is provided in your lab bridge solutions box. The tubing is clear nearly invisible and packaged within a sealable plastic bag. Take care when opening the sealable plastic bag so as not to damage the dialysis tubing. İt will act as a membrane in this experiment. Soak it in warm tap water for a few minutes. You should then be able to pull the ends apart gently, forming it into a tube. Rubbing the ends of the tubing between your fingers under water is sometimes helpful when attempting to open the tube. Close one end of the tube by folding the end and closing it with a piece of string, rubber, or floss. The goal is to seal this tip completely. Pour glucose solution into the tube until it is about 1/4 full. Next, add enough starch solution to fill the tube about halfway. You can use a funnel to make this easier. Tie the top of the tube in the same way you tied the bottom. The tube should not leak from either end. Gently mix the contents of the tube by turning it upside down and back again. Check for leaks. Rinse the "cell" you made by holding it under running water. Place the cell in a beaker and add water until it is covered. Add Starch Indicator Solution (containing iodine) to the water in the beaker. Add enough to make the water an amber color. Wait an hour and observe. Then write down your observation result.

RESULT:

DISCUSSION: A concentration gradient exists when a membrane separates two different concentrations of molecules. Heavier molecules move slower in diffusion. Within a system, different substances in the environment each diffuse at different rates according to their own gradients. Channel proteins can assist in the facilitated diffusion of polar and charged substances through the plasma membrane by forming a hydrophilic tunnel. Take care when opening the sealable plastic bag so as not to damage the dialysis tubing. Keep the tip of the dropper bottle clear of the rim of the graduated cylinder to avoid contamination. Starch must be digested because it’s molecules are too large to diffuse across the cell’s membranes. Facilitated diffusion can increase the diffusion rate of certain molecules at low concentrations.
REFERENCES:
1.     https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/facilitated-diffusion/a/diffusion-and-passive-transport
2.     http://www.tiem.utk.edu/~gross/bioed/webmodules/diffusion.htm
3.     https://courses.lumenlearning.com/bio2labs/chapter/sample-lab-report/
4.     https://courses.lumenlearning.com/boundless-ap/chapter/transport-across-membranes/#:~:text=Materials%20move%20within%20the%20cell,the%20plasma%20membrane%20by%20diffusion.&text=Diffusion%3A%20Diffusion%20through%20a%20permeable,gradient%20(into%20the%20cytoplasm).