Testing Diffusion Of Molecules Across The Cell Membrane Essay

The same type of experimental process was used in the other experiments of temperature, and enzyme, substrate, and ionic concentration. For example, for temperature, they replaced the distilled water in the cuvettes with water of different temperatures of 3, 15, 25,37,and 100 degrees Celsius. Then, after the colorimeter was calibrated, the absorbance and transmittance of the data was collected for 2 minutes in increments of 20

After the solution had reached the desired temperature of 80°C, a stir bar was placed inside the flask and the titration using the KMnO4 solution began. The titration process was considered completed when the solution had changed color from clear to a light pink. Once the color change was apparent, the final volume of the KMnO4 solution used was recorded. The process was then completed once more to ensure accurate results.

In a cell, diffusion occurs across a selective permeable membrane of the cell that allows the cell to regulate and control the passage of substances. As well as controlling what passes through the membrane, the selective permeability also controls how quickly those allowed substances are able to pass through the cell membrane. When a cell is placed in a hypotonic solution, the substance wants to quickly diffuse through the cellular membrane in attempt to balance the concentration. Due to this, too much of the substance enters the cell causing the cell to swell and rupture, otherwise known as hemolysis. The purpose of this lab is to test if and how the factor of polarity of a molecule affects the diffusion rate of those molecules through a permeable red blood cell membrane in a sample of ovine blood. Testing this factor and its effect on diffusion rate is important in the biological world as it helps understand how our body regulates our own substances and molecules within us, but also how our body will react and respond to other substances such as medicines. It is hypothesized that this factor of polarity will determine how quickly or slowly molecules will diffuse across the cell membrane. Smaller molecules that have relatively low polarity will be able to cross the membrane more easily and at a faster rate than those molecules that

Diffusion is the transfer of molecules from an area that has a higher concentration to an area that has a lower concentration. Osmosis is the diffusion of water. The purpose of this experiment was to study the process of osmosis. In order to test osmosis, eggs that had been soaking in vinegar were taken and placed in four beakers of solution with different levels of glucose. Using this experiment we were able to determine the rate of osmosis of different solutions, with various amounts of glucose, through eggs. In the results of this lab it was found that the eggs were either hypertonic or hypotonic and that the

10 microliters of the sample is then added and the assay absorption is measured at 340nm. If absorbance was above 1.5, samples were diluted.

After weighing dialysis tubing of starch/sodium sulfate and adding the solution to two test tubes, the tubing was placed in a beaker containing a solution of albumin and glucose. Next, 1.0 mL of albumin and glucose were then placed in two test tubes labeled solution start. The tubing in the albumin/glucose solution was kept inside the solution for 75 minutes. Every 15 minutes the solution and tube was mixed (Keith et al., 2010).

The purpose of these experiments is to examine the driving force behind the movement of substances across a selective or semiperpeable plasma membrane. Experiment simulations examine substances that move passively through a semipermeable membrane, and those that require active transport. Those that move passively through the membrane will do so in these simulations by facilitated diffusion and filtration. The plasma membrane’s structure is composed in such a way that it can discriminate as to which substances can pass into the cell. This enables nutrients to enter the cell, while keeping unwanted substances out. Active

All cells contain membranes that are selectively permeable, allowing certain things to pass into and leave out of the cell. The process in which molecules of a substance move from an area of high concentration to areas of low concentration is called Diffusion. Whereas Osmosis is the process in which water crosses membranes from regions of high water concentration to areas with low water concentration. While molecules in diffusion move down a concentration gradient, molecules during osmosis both move down a concentration gradient as well as across it. Both diffusion, and osmosis are types of passive transport, which do not require help.

There were several steps completed to prepare for the experiment. Three dialysis tubes were filled with approximately the same volume of distilled water and then were tied shut. The initial mass (in grams) of the tubes was taken using a triple beam scale. I then filled three 500 mL beakers with 400 mL of water each and dissolved different masses of solute (table sugar) in each beaker in order to make 5%, 10%, and 20% solutions. The beakers were labeled accordingly, and then 20 g, 40 g, and 80 g (respectively) of table sugar was weighed out using a digital scale and placed into the corresponding beakers. The sugar was stirred in using a stirring rod until all of the solute was completely dissolved.

To study the effects of hypotonic, hypertonic and isotonic solutions on plant and animal cells.

In this experiment, I wanted to find out if vinegar, water, dyed water, and/or salt water can go through the membrane of a chicken egg. Before starting my experiment, I read that the cell membrane controls what goes in and out of the cell and found I also learned that small enough molecules can go in and out of the cell through the process of diffusion. In addition I learned that the two different types of diffusion, passive and active transport, determine whether the process of diffusion is going to use energy or not.

How does changing a solution’s concentration of solutes affect the movement of molecules across a cell membrane?

The difference is that along with large molecules, living cells prevent molecules with positive charges and solubility. This is not representing in dialysis tubing, and is only found in living cells because the tubing is only based on molecular size (98). When referring the rate of diffusion, the concentration gradient influences the diffusion rate, based on the factors of temperature. The ability for molecules diffuse from high to low concentrations primarily depends on the concentration gradient between the two areas.(96-99). My hypothesis for the study is that in the hypotonic, hypertonic, and isotonic solutions, the direction and rate of osmosis will determine based on the concentration inside the dialysis tubing. My prediction is that if the solution is hypotonic the results will decrease, if the solution is hypertonic the results will increase and if the solution is isotonic the solution will vary and or remain constant.

The Transport of Substances Across the Plasma Membrane The plasma membrane or, the cell surface membrane, is made almost entirely of protein and lipid. The plasma membrane controls the movement of substances into and out of a cell. It is partially permeable so some substances cross more easily than others.

Why is diffusion and osmosis important and what were the reasons of the experiments performed? Osmosis helps keep the water levels in cells at homeostasis and diffusion tries to reach equilibrium by moving to an area of lower concentration. The two experiments were designed and performed to test the rate of diffusion by measuring the size of the phenolphthalein agar block and the weight of the dialysis tubes. To begin with, the experiments, The Rate of Diffusion and Cell Size, was to test whether the rate of diffusion was affected by the volume and surface area. It was hypothesized that the volume and surface area of the phenolphthalein agar block and the dialysis tubing will have affect on the rate of diffusion.