For diffusion to occur, there must be:
a. A selectively...

Question

For diffusion to occur, there must be:

a. A selectively permeable membrane

b. Equal amounts of solute

c. A concentration difference

d. Some sort of carrier system

e. All of the above

Accepted Answer

Welcome back, everyone select all of the following choices which need transport proteins to diffuse across the plasma membrane. We've got a which is ethanol B ions, C oxygen or choice d both ions and oxygen or choice E both ethanol and ions. We're going to refer to the following sketch of a plasma membrane. So just showing this sketch, we can observe that we've got these black circles which are representative of polar heads making up the plasma membrane which then are connected to nonpolar tails making up the internal portion of the plasma membrane. And then we have an example of two types of proteins represented by the purple figures in this illustration. So let's start again by labeling the polar heads and the nonpolar tails of the plasma membrane. And looking at the first type of protein, we're going to recognize this as a channel protein. So recall that a channel protein is useful for polar substances such as the water molecule where we have two hydrogens bonded to an oxygen atom. This water molecule being polar is not going to be able to cross the barrier of the plasma membrane which has an internal nonpolar layer. Due to its polarity. And so the channel protein is useful for molecules such as water to be able to cross through its channel as a way of facilitated diffusion through the plasma membrane. But it is again, only able to do so with the help of this channel protein. And then we have the second protein which does not have a full channel that I've depicted in this illustration. Due to the fact that this is a carrier protein and recall that carrier proteins will undergo confirmational changes or will bind to specific sites of certain molecules. Which are we can think of an example such as glucose, another polar molecule which is much larger than water or we can think of ions like the calcium two plus ion, which is because it's charged will not be able to by itself pass through the uncharged nonpolar internal phospho lipid bilayer. So these carrier proteins will undergo confirmational changes and bind to specific sites on either glucose or the ions to allow them to be able to pass through the phospho lipid bilayer of the plasma membrane. Now, with regard to molecules that are nonpolar such as carbon dioxide and oxygen because they are nonpolar molecules, they can undergo simple passage through the fossil lipid bilayer and they would do so via simple diffusion. So with all of this understood, let's consider our answer choices. We have choice. A ethanol recall that ethanol is also considered a polar molecule. If we recall its structure in a simple bond line diagram. We would recognize that there is a net dipole moment which is in an upward direction since there are partially positive charged or electro positives hydrogen and carbon atoms where the oxygen atom and ethanol specifically in the hydroxyl group portion, the oh group here has that partially electron negative charge being more electron negative than carbon and hydrogen within the structure. So it has a net dipole moment going up, which is also attributed by the lone pairs present on oxygen, which contributes to asymmetry in the structure and therefore ethanol is polar. So being polar, then ethanol should be able to cross the phospho lipid bilayer only with the help of either a channel protein or a carrier protein. So we'll place a check mark for choice. A since transport proteins would be needed for ethanol to diffuse. Since it is polar, then we have choice B ions as we stated, ions are charged. And because the nonpolar tails of the fossil lipid bilayer are uncharged, then ions would also therefore need transport proteins in order to diffuse across the plasma membrane. So we'll place a checkmark by choice B and then we have choice C oxygen. As we stated, oxygen is a nonpolar structure or molecule, it is recalled diatomic and just consists of two oxygen atoms which are double bonded with two lon pairs on itself. It is a symmetrical molecule and all the dipoles that would be present are canceled. And so this is nonpolar and will not need the assistance of transport protein. So we can rule out choice C as well as choice D since it includes choice C oxygen. So this means that we can then confirm that choice. E both ethanol and ions would need the assistance of transport proteins in order to diffuse across the fossil lipid bilayer of the plasma membrane. This is our final answer. I hope that this made sense and let us know if you have any questions.

For diffusion to occur, there must be:
a. A selectively permeable membrane
b. Equal amounts of solute
c. A concentration difference
d. Some sort of carrier system
e. All of the above

Key Concepts

Diffusion

Selectively Permeable Membrane

Concentration Gradient

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