Passive vs. Active Transport - Online Tutor, Practice Problems & Exam Prep

Transport across biological membranes occurs via two main processes: passive transport and active transport. Passive transport requires no energy, allowing molecules to move from areas of high concentration to low concentration, often through facilitated diffusion. In contrast, active transport necessitates energy, typically from ATP, to move molecules against their concentration gradient. Membrane proteins facilitate these processes, categorized as uniporters (transporting one molecule), symporters (co-transporting two molecules in the same direction), and antiporters (transporting two molecules in opposite directions).

Passive vs. Active Transport

Alright. In this video, we're going to distinguish between passive and active transport, which is something that you guys have done before in your previous biology courses. So again, nothing really new here and this should be a piece of cake for you guys. We're also going to start to explore our membrane transport map. So we know that we're going to explore this map by exploring the leftmost branches first. We're going to start with molecular transport of very small molecules, and you can see in this map here that molecular transport of small molecules can be categorized into 2 different groups. The passive transport group and the active transport group. And again that's the main focus of this video that there are 2 general types of processes that transport molecules across biological membranes: the passive transport and the active transport.

Now, over here on the left-hand side, what we're showing you is passive transport, which again you might recall from your previous biology courses just means that there's going to be absolutely no energy input. And so, moving forward in our lesson, the word "passive" is going to mean that there is no energy input, and that's exactly what happens in passive transport. If there's no energy input, what this means is that molecules are going to be diffusing across the membrane from areas of high concentration down to areas of low concentration, just like what you see over here in this image.

Now over here on the right-hand image, what you'll notice is we've got active transport, and with active transport, you can see that "active" is going to represent that there is a need for energy. So moving forward in our lesson, "active" is going to be symbolic of the requirement of energy. In this process, what you'll see is that usually, ATP is the molecule that provides the energy for active transport, and in active transport, instead of molecules diffusing from high to low concentration, they actually diffuse from low to high concentration, and that's exactly what we see here with these purple molecules. They're diffusing from low concentration towards the higher concentration, which is against their natural tendency, and that's why it requires energy.

Now here in our center table, notice we have a table with all of these different columns here and rows I should say, and we've got these two columns, this one and this one, and again, the blue is going to represent passive transport and the yellow is going to represent active transport. In terms of an energy input, of course, as we've already mentioned with passive transport, there's absolutely no energy input, simple as that. And with active transport, of course, there is going to be an energy input, so we can put "yes", and usually that energy is coming from ATP, as you'll see when we move forward and discuss active transport in more detail.

Now in terms of the movement of the molecules relative to their gradient, in passive transport, as we already discussed, molecules are traveling down or with their concentration gradients, from areas of high concentration down to areas of low concentration. Whereas with active transport over here, of course, they're going to be traveling up their gradient or against their gradient from areas of low concentration to areas of high concentration, again as we already indicated.

Now, in terms of being thermodynamically favorable, because passive transport requires no energy, that means that it is indeed thermodynamically favorable. And, of course, if it's thermodynamically favorable, in terms of being spontaneous, it means that it will be spontaneous, and it will be an exergonic process. An exergonic process, as we know, has a negative ΔG or a negative change in Gibbs free energy, and this will be relevant later in our course when we're talking about how to calculate the thermodynamic favorability of membrane transport later in our course. But in terms of active transport, on the other hand, thermodynamically favorable, we can say that it is not thermodynamically favorable. So, no, it is not thermodynamically favorable. And that means, of course, that it will not be spontaneous, and instead of being exergonic, it will actually be endergonic, meaning that it will have a positive ΔG or a positive change in Gibbs Free Energy.

Now in terms of protein facilitation, whether or not a protein is required for passive transport, the answer to that is sometimes. Sometimes a protein is required for passive transport to occur, and other times a protein is not required for passive transport. Whereas with active transport on the other hand, protein facilitation is always required. And so you'll be able to see over here that there is a protein here embedded in the membrane that allows for active transport to occur. And so really what you can think of these 2 different groups of transport, passive versus active, is that passive transport over here does not require energy. So it's almost like downhill movement traveling from areas of high concentration down to areas of low concentration. Because no energy is required notice that this guy is just watching passively as the ball travels down the hill. Whereas with active transport over here notice that the transport is going to be from low concentration to high concentrations, and that is going to require energy. So you can see the guy here has to push the molecule into the area of high concentration, and that requires energy usually in the form of ATP.

As we move forward in our course, we're going to break down passive transport even more, and later we'll break down active transport even more. So hang on tight. Let's practice the concepts that we've learned here in our next video. So I'll see you guys there.

Passive membrane transport processes include___________.

• A. Consumption of ATP for energy.
• B. The use of transport proteins to move a substance from low to high concentration.
• C. Movement of a substance down its concentration gradient.
• D. Movement of a substance up its concentration gradient.

What is the difference between active and passive transport across a plasma membrane?

• A. Active transport is used to move substances down their concentration gradient, where passive transport is used to move substances against their concentration gradient.
• B. Active transport is ATP dependent, whereas passive transport does not require energy for movement across the plasma membrane.
• C. Active transport implies that the cell is working with other cells, whereas passive transport implies that the cell does not cooperate with other cells.
• D. Active transport means that the cell is aggressively going after substances that it wants to bring into the cell, whereas passive transport means that the cell just waits for the substance to cross the membrane.

Passive vs. Active Transport

In this video, we're going to introduce the classes of passive and active membrane proteins. There are three types of passive and active membrane proteins that are classified according to how they operate. The very first type here is going to be the uniporter, and "uni" is a prefix that means one. These membrane transport proteins will only transport just one molecule at a time, as its name indicates, and it will transport one molecule at a time in just one direction. So, pretty simple. If you take a look down below at the image, what you'll see is that number one is our uniporter, and as you can see, it will transport just one molecule at a time in one specific direction.

Now, the second type of membrane protein that we have here is going to be the symporter, and symporters are going to co-transport at least two molecules, more than one molecule, at a time in the same exact direction. You could think that the "s" in symport is for the "s" in the same direction. When you take a look down below at our image of the symporter here, what you'll notice is it is indeed taking two molecules, either two of the same molecules or two different molecules, doesn't matter. Here we're showing two different molecules, and it's taking these two molecules and transporting them in the same exact direction, in this direction here.

In our last type of transporter, number three here, what we have is the antiporter, and as its name implies, it's going to co-transport at least two molecules just like the symporter, but this time it's not transporting them in the same direction. This time it's transporting them in opposite directions. If we take a look down below at our image here of the antiporter, notice that it is indeed transporting two molecules, the red one here and the green one down here. But again, notice this time they're not being transported in the same direction, they're actually being transported in opposite directions. This concludes our introduction to the classes of passive and active membrane transport proteins, and I'll see you guys in our next video.

A transport protein that simultaneously transports two different molecules in different directions is called:

• A. A uniporter.
• B. A symporter.
• C. An equilibrium protein.
• D. An antiporter.
• E. A simple diffuser.

Which option below best describes a transporter that requires ATP to move molecules A and B out of the cell?

• A. An active antiporter.
• B. A passive antiporter.
• C. A passive symporter.
• D. An active uniporter.
• E. An active symporter.

Here’s what students ask on this topic:

What is the main difference between passive and active transport?

The main difference between passive and active transport lies in energy usage and direction of molecule movement. Passive transport does not require energy and moves molecules from areas of high concentration to low concentration, following the concentration gradient. Examples include simple diffusion and facilitated diffusion. In contrast, active transport requires energy, usually from ATP, to move molecules against their concentration gradient, from low concentration to high concentration. This process is essential for maintaining cellular functions and homeostasis.

How do uniporters, symporters, and antiporters differ in their transport mechanisms?

Uniporters, symporters, and antiporters are types of membrane transport proteins that differ in their transport mechanisms. Uniporters transport a single type of molecule in one direction. Symporters co-transport two or more molecules in the same direction, often coupling the movement of one molecule with another. Antiporters also co-transport two or more molecules, but in opposite directions. These proteins play crucial roles in both passive and active transport processes, facilitating the movement of molecules across the cell membrane.

Why is ATP required for active transport?

ATP is required for active transport because it provides the necessary energy to move molecules against their concentration gradient, from areas of low concentration to high concentration. This process is thermodynamically unfavorable and non-spontaneous, meaning it requires an input of energy to occur. ATP, or adenosine triphosphate, supplies this energy by undergoing hydrolysis, which releases energy that is then used by transport proteins to move molecules across the cell membrane.

What are some examples of passive transport processes?

Examples of passive transport processes include simple diffusion, facilitated diffusion, and osmosis. Simple diffusion involves the movement of small, nonpolar molecules directly through the lipid bilayer from high to low concentration. Facilitated diffusion requires the assistance of membrane proteins, such as channels or carriers, to transport larger or polar molecules across the membrane. Osmosis is the diffusion of water molecules through a selectively permeable membrane from an area of low solute concentration to high solute concentration.

How does facilitated diffusion differ from simple diffusion?

Facilitated diffusion differs from simple diffusion in that it requires the assistance of membrane proteins to transport molecules across the cell membrane. Simple diffusion involves the direct movement of small, nonpolar molecules through the lipid bilayer from high to low concentration. In contrast, facilitated diffusion is necessary for larger or polar molecules that cannot easily pass through the lipid bilayer. These molecules are transported via specific carrier proteins or channel proteins, which provide a pathway for their movement down the concentration gradient.