Now, when it comes to membrane transport, we're going to say that to perform its functions, a cell continuously needs to exchange substances with the extracellular fluid, so basically outside of itself. We're going to say, membrane transport allows cells to take in essential substances and expel waste products. Now here when it comes to membrane transport mechanisms, they can be broadly categorized into 2 types. We have our passive transport and we have our active transport. We're going to say here with passive transport, this does not require energy and substances move down the concentration gradient. But with active transport, we're going to say it requires energy and substances move against the concentration gradient. So here we have our membrane transport which is broken down into passive transport and active transport. Active requires energy. And with passive transport, it can be further broken down into simple diffusion and facilitated diffusion where we need some assistance for it to occur. Now, here remember a concentration gradient, this is the difference in concentration of a substance over a distance. And we'll see how to distinguish between active and passive transport.
Membrane Transport - Online Tutor, Practice Problems & Exam Prep
Membrane Transport Concept 1
Video transcript
Membrane Transport Example 1
Video transcript
Here it says, in the electron transport chain or ETC, complexes 1, 3 and 4 pump H+ ions from the mitochondrial matrix which has a low hydrogen ion concentration to the intermembrane space where we have a high H+ ion concentration. What type of membrane transport is this? Alright. So, what's happening here? Well, we're taking H+ from an area where the concentration of H+ is low, and we're pumping it to where it is high. This is the opposite of what we should expect because typically, we would have the movement of ions from an area of high concentration to an area of low concentration. This is what passive transport would be. Here we're doing the exact opposite. We're taking where H+ ions are low and pumping them somewhere where it's already high. There's gonna be a resistance there, which means we're gonna have to supply energy in order to do this. Because of that, this represents active transport. We're working against the concentration gradient. Again, normally we want to go from high concentration to low concentration, but here the opposite is occurring, which means energy will be needed. So again, option A, active transport, would be the best answer.
During respiration, oxygen gas diffuses into cells spontaneously. Which type of transport is this?
Active transport
Passive transport
Both
None of the above
Membrane Transport Concept 2
Video transcript
In this video, we'll take a look at different types of membrane transport mechanisms. Now, here we're going to discuss how non-polar molecules, polar molecules, and ions move across the cell membranes differently. Because of this, we'll need different types of mechanisms.
The first one is simple diffusion. Here, this is the movement driven by concentration gradients. We're going to say that small, non-polar molecules and water are involved. Examples would be oxygen, CO2, or steroids. If we take a look here, we're going to say this is the outside of the cell and this is the inside of the cell, we can see that these particles are just kind of going through the lipid bilayer, going from the outside, through the bilayer, and winding up on the inside of the cell. This represents simple diffusion.
Next, we have facilitated diffusion. This is gradient-driven and it's through a protein channel. Now, here we're going to discuss dealing with polar molecules and ions. Examples would be glucose, water, chloride ions, and bicarbonate. If we take a look here, we have our integral protein, which, remember, goes through the entire thickness of our lipid bilayer. We're going to say that these particles are going through the protein channel, which goes on both sides of the lipid bilayer. So they go through here, which is on the outside, and exit out here onto the inside. This would be facilitated diffusion, where we are using the protein channel to help move the particles from the outside to the inside of the cell.
Then finally, we have active transport. In this, we're going to say protein channels or pumps use energy to move substances against a concentration gradient. We're going to say this is highly selective and regulated, with different pumps for different substances. Some examples are our Sodium Potassium Pumps, which move sodium out and then potassium inside the cell. So, if we take a look here, energy is involved, and that's what makes this active transport. It's not just simply having an integral protein; we also have the inclusion of energy in order for our particles to go in and out of the cell.
Alright. Just remember, we have different types of membrane transport mechanisms, and they deal with the transporting of materials inside and out of the cell. This involves non-polar molecules, polar molecules, ions, and when it comes to active transport, the inclusion of energy.
Membrane Transport Example 2
Video transcript
This example question asks, "How would a molecule of stearic acid cross the cell membrane?" Remember, stearic acid represents a saturated fatty acid. It has the shorthand notation of 18:0, meaning it has 18 carbons and 0 pi bonds. Due to this large number of carbons, it is considered a nonpolar molecule. Remember, fatty acids tend to be nonpolar overall because of their long hydrocarbon tail. Since it is a nonpolar molecule, it is most likely going to cross the cell membrane by simple diffusion. Remember, simple diffusion is the transport mechanism of choice when it comes to small nonpolar molecules, as well as water. Therefore, the answer here would be option a.
How would you expect an H+ ion to move out of the cell if [H+] inside the cell is lower than extracellular fluid?
Simple diffusion
Facilitated diffusion
Active transport
None of these
In oxidative phosphorylation, H+ ions from the intermembrane space of mitochondria to the mitochondrial matrix, which type of membrane transport is this?
Simple diffusion
Facilitated diffusion
Active transport
None of these