Cell Transport Mechanisms and Permeability

1. Record your hypothesis about what will happen when Biuret solution is mixed with the solutions from test tubes 1, 2, 3, and 4 here. Be sure to use scientific reasoning to support your hypothesis.

2. Explain your observations in detail in terms of concentration gradient, diffusion, osmosis, osmotic pressure, passive transport, and active transport.

What would happen if you increased the driving pressure? Use the simulation to arrive at an answer. The concentration remained the same but the filtrate rate increased.

Phospholipids make up most of the cell membrane, in a phospholipid bilayer. Phospholipid molecules form two layers, with the hydrophilic (water loving) head facing the extracellular fluid and the cytosol (intracellular) fluid, and the hydrophobic (not water loving) tails facing one another. The cell membrane is constructed in such a way that it is semipermeable, and allows oxygen, CO2 and lipid soluble molecules through easily, while other molecules like glucose, amino acids, water, and ions cannot pass through quite as easily. That is the meaning behind the chant “some things can pass, others cannot!”.

Explain the effect that increasing the Na+ Cl- concentration has on osmotic pressure and why it has this effect. How well did the results compare with your prediction?

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

Two variables that affect the rate of diffusion are the MWCO membrane and the solute concentration. Increasing the membrane size and solute concentration will also increase the average diffusion rate. Decreasing the membrane size and solute concentration will reduce diffusion rates and can even prevent all diffusion.

We hypothesize that as the solute concentration increases, more water will diffuse into the dialysis tubing (shown by a greater percent increase in mass).

Based on the results of your experiment, would you reject or accept the hypothesis that you produced in question 1? Explain how you determined this.

A major determinant of diffusion in a biological system is membrane permeability. Small, uncharged molecules pass through cellular membranes easily, while most and/or charged molecules cannot pass through the membrane. The movement of water across a selectively permeable membrane, like the plasma membrane

1. Why do you think it is important to have a membrane surrounding each of our trillions of cells? Expect varying answers, but the idea is have the students understand the plasma membrane separates the cells from their environment and each other while also regulating the material within each cell. 2. What are two distinctive physical features of phospholipids? Heads are polar (water soluble, hydrophilic) and tails are nonpolar (water hydrophobic).

The hypothesis states 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. In order to test the predictions of the hypotonic, hypertonic, and isotonic hypothesis for the solution  made during the study,  four samples of sucrose were taken and placed into two different beakers each containing a different concentration. Then dialysis tubing A was placed into beaker 1 with B, C, and D placed into beaker 2 for 45 minutes and weighted at 15 minute intervals. My finding in the study was that each of the four samples changed from their initial weight and for the most part accurately proved the hypothesis.

The density decreases. Density of the liquid sample is the mass divide by the volume. If the mass stays constant and the volume increases then the density of the liquid sample will decrease.

Exercise 1: Cell Transport Mechanisms and Permeability: Activity 3: Simulating Osmotic Pressure Lab Report Pre-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1. Which of the following is true of osmosis? You correctly answered: c. It is a type of diffusion. 2. Which of the following occurs when a hypertonic solution is added to cells? You correctly answered: d. The cells shrink. 3. The variable that affects osmotic pressure is You correctly answered: a. the concentration of nondiffusing solutes. 4. The net movement of water would be into the cell in a You correctly answered: b. hypotonic solution.

Cells are always in motion, energy of motion known as kinetic energy. This kinetic energy causes the membranes in motion to bump into each other, causing the membranes to move in another direction – a direction from a higher concentration of the solution to a lower one. Membranes moving around leads to diffusion and osmosis. Diffusion is the random movement of molecules from an area of higher concentration to an area of lower concentration, until they are equally distributed (Mader & Windelspecht, 2012, p. 50). Cells have a plasma membrane that separates the internal cell from the exterior environment. The plasma membrane is selectively permeable which allows certain solvents to pass through