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Lab Report #1

Introduction

A cell’s plasma membrane is known to be selectively permeable. This implies that the membrane is selective on what substances can pass in and out of the cell. There are two methods of transport that occur through the plasma membrane. One method of transport is called active process which uses ATP energy to transport substances through the membrane. The other method is called passive process which does not require the use of ATP energy. During passive processes, molecules are transported through the membrane by differences in concentration or pressure between the inside and outside of the cell. Two important types of passive process are diffusion and filtration. Every cell in the human body uses diffusion as an important transport process through its selectively permeable membrane. During diffusion, molecules that are small enough to pass through a membrane’s pores or molecules that can dissolve in the lipid section of a membrane move from an area of higher concentration to an area of lower concentration. The kinetic energy that all molecules possess is the motivating force in diffusion. Facilitated diffusion occurs when molecules are too large to pass through a membrane or are lipid insoluble. In this process, carrier protein molecules located in the membrane combine with solutes and transport them down the concentration gradient. Filtration is another type of passive process and, unlike diffusion; this is not a selective process. The pressure gradient on each side of the membrane as well as the membrane pore size depends on the amount of solutes and fluids in the filtrate. During filtration, water and solute molecules pass through a membrane from an area of higher hydrostatic pressure to an area of lower hydrostatic pressure. This means that water and solutes would pass through a selectively permeable membrane along the pressure gradient. To gain a better understanding of a cell’s selectively permeable membrane and the passive processes of simple diffusion, facilitated diffusion, and filtration, three experiments were conducted. Materials and Methods

Activity 1: Simulating Dialysis (Simple Diffusion)
Materials:
▪ two glass beakers
▪ four dialysis membranes: 20 (MWCO), 50 (MWCO), 100 (MWCO), and 200 (MWCO) ▪ membrane holder
▪ membrane barrier
▪ four solutes: NaCl, Urea, Albumin, and Glucose
▪ solution dispenser
▪ deionized water
▪ timer
▪ beaker flush

This experiment was conducted first by placing the 20 (MWCO) dialysis membrane into the membrane holder. The membrane holder joined the two glass beakers; one on the left side and one on the right side. Then, 9.00 mM of NaCl concentration was dispensed into the left beaker. Deionized water was dispensed in the right beaker. When the timer was started, the barrier that surrounded the membrane holder was lowered to allow the contents of each beaker to come in contact with the membrane. After the 60 minutes of compressed time elapsed, results were read and recorded. Finally, each beaker was then flushed for preparation of the next experiment run. These exact steps were followed using each dialysis membrane size (20, 50, 100, and 200) as well as with each solute (NaCl, Urea, Albumin, and Glucose). There were a total of sixteen runs in this experiment. Activity 2: Simulating Facilitated Diffusion

Materials:
▪ two glass beakers
▪ membrane builder
▪ membrane holder
▪ glucose concentration
▪ solution dispenser
▪ deionized water
▪ timer
▪ beaker flush

In this experiment, the first step was to adjust the glucose carrier to 500 in order to correctly build the membrane. Next, a membrane was built in the membrane builder by inserting 500 glucose carrier proteins into it. Then, the newly built membrane was placed into the membrane holder that joined the two glass beakers. The two glass beakers were joined on the left and right sides of the...
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