Cell Membrane Function (Diffusion Lab Follow-up Notes)

Analysis - Question 1 Define diffusion and use one of the experiments to explain how this was shown. Diffusion is due to the random movement of particles which results in the overall movement of particles from a region of high concentration to a region of low concentration.

Continued Question 1 This occurred when the KMnO4 and the green food colouring were added to water, as well as when the iodine was added to ethanol. All three substances spread out from the high concentrated area where they were added to each substance. This was noted by the colour spreading throughout the container to areas that did not have any colour or to low concentrated areas.

What is the result of this movement? Over time the particles become evenly distributed throughout the container. However, they remain in constant motion or Dynamic Equilibrium

Define Dynamic Equilibrium The point reached when the numbers of particles entering and leaving a region are equal. Movement is continuous, but produces no overall change.

Analysis - Question 2 Diffusion will sometimes not occur, even though there is a concentration imbalance. Why? Which part of the demonstration illustrated this? “Like Dissolves Like” (polar substances dissolve in polar substances and non-polar substances dissolve in non-polar substances) To diffuse, both particles involved must be charged/polar or both must be not charged. Since water has a slight charge (polar) and iodine has no charge (non-polar) iodine will not diffuse in water. Iodine will, however, diffuse in ethanol, since ethanol is like iodine and carries no charge (non-polar).

Diffusion Demonstration Review 3. State three factors that will affect the rate of diffusion. Indicate where possible when this was observed in the lab AND include how the rate was affected. Three factors that affect the rate of diffusion are temperature, state and polarity. When hot and cold water were used with solid KMnO4 diffusion occurred faster in hot water. When cold water was used with solid KMnO4 and liquid green food colouring diffusion occurred faster with the liquid green food colouring. ‘Like dissolve in like’ so iodine which is non-polar will not dissolve in water which is polar.

Other factors stirring/pressure applied will increase the rate of diffusion the more concentrated the substance the faster it will diffuse

Diffusion Across a Membrane Diffusion across a membrane is very similar to regular diffusion, only there is a barrier to cross. This barrier allows some things through, but other things cannot pass through called semi permeable or selectively permeable which is our cell membrane. So, diffusion still occurs for some molecules, but larger or ionic molecules need to find another way through the membrane. Click Here

Diffusion Across a Membrane What is Facilitated Diffusion? A form of diffusion where the molecules cannot pass through the lipid portion of the plasma membrane. The molecules, instead, diffuse through transport proteins. Why might some molecules not be able to pass through the cell membrane? Molecules which are too large, or molecules that carry a charge cannot pass through. The molecules that are too large can simply not fit between the phospholipids. The molecules which are charged cannot easily pass through the non-polar lipid tails.