Active Transport - Online Tutor, Practice Problems & Exam Prep

Active transport is essential for moving molecules against their concentration gradients, requiring energy. There are two types: Primary Active Transport, which directly uses ATP hydrolysis, and Secondary Active Transport, which relies on the concentration gradient of another molecule. A classic example of primary active transport is the sodium-potassium pump, which exports 3 sodium ions and imports 2 potassium ions, maintaining vital concentration gradients. Secondary active transport, exemplified by the sodium-glucose transporter, utilizes the sodium gradient to drive glucose uptake against its concentration gradient, highlighting the interconnectedness of these transport mechanisms.

Active Transport

In this video, we're going to begin our lesson on active transport. There are just two main types of active transport that you all should know, both requiring energy to transport molecules. This is because the molecules are going to be transported against their concentration gradients from areas of low concentration to areas of high concentration, and that's why it requires energy. Now, the first type of active transport you all should know is Primary Active Transport. Primary Active Transport is going to be directly driven by an energy source such as ATP hydrolysis, for instance. Primary Active Transport is directly linked to ATP. The second type of active transport that you all should know is Secondary Active Transport. Unlike Primary Active Transport, Secondary Active Transport is not driven directly by ATP hydrolysis; instead, it is driven by another molecule's concentration gradient. As we move forward in our course, we'll be able to talk more about both Primary Active Transport and Secondary Active Transport.

But let's take a look at our image down below, which shows a snippet of the map of the lesson on membrane transport. Here we're showing you Active Transport, which requires energy, so energy is required. Once again, there are two main types of active transport. The first is Primary Active Transport, which is driven directly by ATP. The second type of Active Transport is Secondary Active Transport, which is not driven directly by ATP; instead, Secondary Active Transport is driven by another molecule's concentration gradient. Here we're showing an image of one molecule powering the transport of another molecule against its concentration gradient.

Talk more details about Primary Active Transport and Secondary Active Transport. I'll see you guys in our next videos.

Primary Active Transport

So now that we know from our last lesson video that there are 2 types of active transport, primary active transport, and secondary active transport. In this video, we're going to focus on Primary Active Transport. And so Primary Active Transport is an ATP-driven process that transports molecules against their concentration gradients, from areas of low concentration to areas of high concentration, and that is why it requires energy in the form of ATP. Now once again, primary active transport is going to be driven directly by energy derived from ATP hydrolysis. And really this is the biggest difference between primary and secondary active transport. Primary active transport is directly linked to ATP hydrolysis, but secondary active transport is not, as we'll learn moving forward talking about secondary active transport in another video.

Now, primary active transport can be used to generate and maintain very very important concentration gradients for survival. And so we'll be able to talk about a very very important primary active transport example in our next lesson video. But for now, let's take a look at the image that we have down below which is showing us primary active transport. And so notice here we have a membrane, here in the middle, and notice that primary active transport is going to require the use of a membrane protein, and that membrane protein is going to use ATP directly, as we indicated up above, in order to transport molecules against their concentration gradient from an area of low concentration over here on this side of the membrane because there are only 3 molecules, and it's still pumping them towards an area of higher concentration, and so you can see there is a much higher concentration over here.

And so because this purple molecule is being pumped against its concentration gradient, it requires active transport. And because ATP is used directly, it is a form of primary active transport. And so ATP here is really providing the energy that is required to pump the molecule across the membrane. And so this here concludes our introduction to primary active transport, and we'll be able to see a very specific example of primary active transport in our next lesson video when we talk about the sodium-potassium pump. So I'll see you guys in that video.

Active Transport Example 1

Alright. So here we have an example problem that's asking what is the main difference between active transport and facilitated diffusion? And we've got these 4 potential answer options down below. And so what we need to recall is that facilitated diffusion is not a type of active transport. Facilitated diffusion is a type of passive transport which means that absolutely no energy is required for facilitated diffusion and this is because molecules will be transported down their concentration gradients from an area of high concentration to an area of low concentration. And so when we take a look at option a here, notice it says facilitated diffusion uses proteins but active transport does not. And this is actually a false option, so we can cross it off our list. Now this is because both facilitated diffusion and active transport use proteins. And so, the facilitated diffusion require is, recall, is facilitated by a protein. And active transport also requires a protein as well. So both facilitated and active transport require proteins and that is not the main difference between them. Now skipping over option B really quick, going to option C, notice it says active transport occurs across the plasma membrane but facilitated diffusion does not, and once again this is not going to be true. Of course, active transport and facilitated diffusion are both going to allow for molecules to be transported across a plasma membrane and so they both allow for that. So that is not the main difference between the two. And then taking a look at option D here, it says active transport and facilitated diffusion both use proteins to move substances against their concentration gradients. Now we already indicated that active transport and facilitated diffusion both use proteins. That part is true. But they don't both move substances against their concentration gradients. Only active transport moves substances against their concentration gradients from areas of low concentration to areas of high concentration. But facilitated diffusion, which again is a type of passive transport, it does not pump molecules against their concentration gradients, it pumps molecules down their concentration gradients. So that means that option D here is also not going to be true. And this only leaves option B here as the correct answer, which says active transport uses ATP to power transport, but facilitated diffusion does not. And so we know from our last lesson video that more specifically, it's primary active transport that uses ATP directly to power transport. And facilitated diffusion, which is once again a type of passive transport, does not require any energy. So it certainly does not use ATP to power transport. And so option B here is going to be the correct answer for this example problem, and that concludes this example, so I'll see you all in our next video.

The force driving simple diffusion is ________, while the energy source for active transport is ________.

• A. a concentration gradient; ADP
• B. a concentration gradient; ATP hydrolysis
• C. transmembrane pumps; an electrochemical gradient
• D. phosphorylated carrier proteins; ATP

Primary Active Transport: Na+/K+ Pump

In this video, we're going to talk about a classic example of primary active transport in the sodium-potassium pump. And so once again, the sodium-potassium pump is a classic example of primary active transport. And as its name implies, the sodium-potassium pump is going to pump or move sodium and potassium ions across the plasma membrane. But more specifically, the sodium-potassium pump is going to move the sodium and potassium ions in opposite directions across the plasma membrane, which means that the sodium-potassium pump is an antiporter, which recall from our previous lesson videos just means that some molecules will be pumped across the membrane towards the outside of the cell whereas other molecules are going to be pumped across the membrane to the inside of the cell in opposite directions, and so that is what makes this an antiporter. Now it turns out that three sodium ions are going to be exported towards the outside of the cell, whereas two potassium ions are going to be imported towards the inside of the cell. And so what can help you remember that it's three sodium ions that are being exported is that the sodium here has three characters to it. It has the n, it has the a, and it has the plus. And so this, because it has three characters, can remind you that it's actually three sodium ions that are going to be exported towards the outside of the cell. And the potassium symbol here has only two characters. So it has the k and it has the plus. And so that can help remind you that it's two potassium ions that are going to be imported towards the inside of the cell. Now what can also help you remember that, potassium is going to be imported towards the inside of the cell.

Let's take a look at our image down below to clear up some of this, and notice that right here in the middle embedded in this plasma membrane that we see right here is the sodium-potassium pump. And notice that the sodium-potassium pump is going to take three sodium ions and those three sodium ions are going to be exported towards the outside of the cell. So notice the outside of the cell is up above on this side of the membrane, whereas the inside of the cell is down below. So three sodium ions are going to be pumped or exported towards the outside of the cell. And if that continuously happens over and over again, then there's going to be a low concentration of sodium on the inside of the cell. So, remember the brackets here represent the concentration of sodium ions on the inside of the cell. It's going to be really low if it keeps pumping them towards the outside. And of course, that means that on the outside, over time, there's going to be quite a high concentration of sodium ions on the outside of the cell. And as the sodium ions get pumped, of course, we know that potassium ions are also going to be pumped, but it's actually just two potassium ions that are going to be imported. And so the two potassium ions get imported towards the inside of the cell. And that means that on the outside of the cell, if the potassium ions keep getting pumped in, there's going to be a low concentration of potassium ions on the outside of the cell. And on the inside of the cell over time, it's going to build up and there's going to be quite a high concentration of potassium ions on the inside of the cell. And notice that with each pump here, three sodiums out and two potassiums in, that ATP hydrolysis is required. And the ATP here is really what's providing the energy to pump these molecules against their concentration gradients from areas of low concentration towards areas of high concentration in both scenarios. So from areas of low concentration towards areas of high concentration.

This requires energy and this is primary active transport because ATP is directly linked. Now over here on this right side of the image, we just have another way to help you remember that, hey, the sodium ions get pumped to the outside of the cell and the potassium ions get pumped to the inside of the cell. And so you can think that the cell here is like a club. It's club intracellular, and so you can see that the nucleus here is like the disco DJ of the club. And you could even think that these strobe lights here are kind of like the cytoskeleton of the cell. And so notice that the sodium-potassium pump is really going to act like these bouncers to the club. And so you can see that the sodium ions, when they try to enter the cell, they say, brah, can we enter into the club and the sodium-potassium pump because they're sodium and they're Na?. The sodium-potassium pump says, nah. You can't enter. You cannot enter. And so that can help you remember that, hey, the sodium is not going to enter the cell. They're going to get pumped towards the outside of the cell. However, when the potassium try to get into the club, they say, well, hey, we're back. Let us in. And the sodium-potassium pump, because potassium is made up with a k, they just say, k, come on in. And so potassium is able to get into the club real easy, and so that can help remind you that, hey, potassium is going to be able to get into the cell because the sodium-potassium pump says, k, come on in. And the sodium over here will not be able to get into the cell because when they try to enter, the sodium-potassium pump says, nah. And so, this here concludes our introduction to the sodium-potassium pump and how it is a classic example of primary active transport. And we'll be able to get some practice applying these concepts as we move forward throughout our course. So I'll see you all in our next video.

A sodium-potassium pump ________.

• A. Transports 3 potassium ions out of a cell and 2 sodium ions into a cell and produces a molecule of ATP.
• B. Transports 3 sodium ions out of a cell and 2 potassium ions into a cell using energy from ATP hydrolysis.
• C. Transports 3 potassium ions out of a cell and 2 sodium ions into a cell using energy from ATP hydrolysis.
• D. Transports 3 sodium ions out of a cell and 2 potassium ions into a cell and generates an ATP in each cycle.

Which of the following defines the type of transport by the sodium-potassium pump?

• A. Active transport through a symporter.
• B. Passive transport through a symporter.
• C. Active transport through an antiporter.
• D. Passive transport through an antiporter.

Secondary Active Transport

So now that we've covered primary active transport, in this video, we're going to focus on secondary active transport. Recall from our previous lesson videos that secondary active transport is not directly driven by ATP hydrolysis—that is primary active transport. Instead, secondary active transport is directly driven by another molecule's concentration gradient, and it's powered by this gradient instead of being powered by ATP hydrolysis like primary active transport. However, that being said, secondary active transport, although it may not be directly driven by ATP hydrolysis, is indirectly driven by primary active transport and ATP hydrolysis. The concentration gradient that directly drives secondary active transport is actually built using primary active transport or PAT, which we've abbreviated here for our lesson.

In order to better understand secondary active transport, we're going to take a look at a classic example: the sodium-glucose secondary active transporter. Below we have an image of this sodium-glucose transporter, and notice that the image has these numbers 1, 2, 3, and 4. The numbers that you see in the image correspond with the ones we've mentioned above in the text. This shows the four steps of sodium-glucose secondary active transport. In the very first step, you'll notice that sodium ions can be transported against their concentration gradient using primary active transport. Notice that the sodium ion, shown in step number 1, is being pumped across the membrane towards the area of higher sodium concentration, while there's a lower sodium concentration inside the cell. Since sodium is being pumped from low to high concentration, it requires energy. ATP is directly linked to this process of pumping sodium across the membrane; thus, it is a form of primary active transport.

In step number 2, this generates a higher concentration of sodium ions on the outside of the cell. You can see there are way more sodium ions outside, indicating a higher concentration than inside the cell. This concentration gradient of sodium is generated by primary active transport. Step number 3 involves another molecule—glucose, shown in green. Notice the glucose molecules have a higher concentration inside the cell, which is opposite to that of the sodium. Here, secondary active transport comes into play because sodium is going to be transported down its concentration gradient from an area of high concentration to an area of low concentration without requiring energy. In fact, it releases energy, which can power the transportation of glucose against its concentration gradient from an area of low concentration of glucose to an area of high concentration of glucose inside the cell.

To better understand this, let's review the example. Sodium is transported down its concentration gradient, which does not require energy for molecules to move down their gradients. Instead, it releases energy, and that released energy is used to power the movement of glucose against its concentration gradient. This is a type of active transport since the molecule is being transported against its concentration. Although it's not driven directly by ATP, it's driven by the concentration gradient of sodium being transported down. This makes it a classic example of secondary active transport. Secondary active transport is driven by the concentration gradient of another molecule instead of ATP hydrolysis. Notice that there's no ATP in this vicinity, just the concentration gradient of sodium that powers the secondary active transport of glucose being transported against its concentration gradient.

This concludes our introduction to secondary active transport, and we'll be able to get some practice applying these concepts as we move forward in our course. I'll see you all in our next video.

How are primary and secondary active transport related?

• A. They both use ATP to move molecules
• B. Primary active transport establishes a concentration gradient, but secondary active transport doesn't
• C. Secondary active transport uses the concentration gradient established by primary active transport
• D. Primary active transport moves one molecule, but secondary active transport moves two
• E. None of the above

Here’s what students ask on this topic:

What is the difference between primary and secondary active transport?

Primary active transport directly uses energy from ATP hydrolysis to move molecules against their concentration gradients. A classic example is the sodium-potassium pump, which moves 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell. Secondary active transport, on the other hand, does not directly use ATP. Instead, it relies on the concentration gradient of another molecule, often established by primary active transport. For instance, the sodium-glucose transporter uses the sodium gradient created by the sodium-potassium pump to move glucose against its concentration gradient.

How does the sodium-potassium pump work in primary active transport?

The sodium-potassium pump is a membrane protein that uses ATP to transport 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell. This process is essential for maintaining the cell's electrochemical gradient. ATP hydrolysis provides the energy needed to change the pump's conformation, allowing it to bind and release Na⁺ and K⁺ ions in opposite directions. This active transport mechanism is crucial for various cellular functions, including nerve impulse transmission and muscle contraction.

What is an example of secondary active transport?

A classic example of secondary active transport is the sodium-glucose transporter. This transporter uses the energy from the sodium gradient, established by the sodium-potassium pump, to move glucose into the cell against its concentration gradient. Sodium ions move down their concentration gradient, releasing energy that is then used to transport glucose from an area of low concentration outside the cell to an area of high concentration inside the cell. This process is vital for glucose absorption in the intestines and kidneys.

Why is ATP necessary for primary active transport?

ATP is necessary for primary active transport because it provides the energy required to move molecules against their concentration gradients. In primary active transport, ATP hydrolysis releases energy, which is used to change the conformation of transport proteins, allowing them to bind and move molecules from areas of low concentration to areas of high concentration. This process is essential for maintaining cellular homeostasis and functions such as nutrient uptake, waste removal, and ion balance.

How does the sodium-glucose transporter function in secondary active transport?

The sodium-glucose transporter functions by using the energy from the sodium gradient, created by the sodium-potassium pump, to move glucose into the cell against its concentration gradient. Sodium ions move down their concentration gradient, releasing energy that powers the transport of glucose from an area of low concentration outside the cell to an area of high concentration inside the cell. This mechanism is crucial for glucose absorption in the intestines and kidneys, ensuring that cells receive the necessary glucose for energy production.