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, exemplified by the sodium-potassium pump that moves 3 sodium ions out and 2 potassium ions in, and secondary active transport, which relies on the concentration gradient of another molecule, like sodium, to transport glucose against its gradient. Understanding these processes is crucial for grasping cellular function and homeostasis.

Active Transport

In this video, we're going to begin our lesson on active transport. And really, there are just 2 main types of active transport that you all should know which both require energy in order to transport molecules, and 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 that you all should know is Primary Active Transport. And so Primary Active Transport is going to be directly driven by an energy source such as ATP hydrolysis for instance. And so primary active transport is directly linked to ATP.

Now, the second type of active transport that you all should know is secondary active transport. And secondary active transport is not going to be directly driven by ATP hydrolysis like primary active transport. Instead, secondary active transport is going to be directly driven by another molecule's concentration gradient. And so as we move forward in our course, we'll be able to talk more details about both primary active transport and secondary active transport. But let's take a look at our image down below, which notice is showing us a little snippet of the map of the lesson on membrane transport. So here we're showing you active transport, and notice active transport is going to require energy, so energy is required.

And once again, there are 2 main types of active transport. The first is primary active transport, which is going to be driven directly by ATP, and then the second type of active transport is secondary active transport, which is not driven directly by ATP. Instead, secondary active transport is going to be driven by another molecule's concentration gradient. And so here what we're showing you is an image of 1 molecule powering the transport of another molecule against its concentration gradient. And so, this here concludes our introduction to active transport.

And once again, as we move forward in our course, we're going to talk more details about primary active transport and secondary active transport. So 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 important concentration gradients for survival. And so we'll be able to talk about a 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 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 toward 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 four 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 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 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. 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 3 sodium ions are going to be exported towards the outside of the cell, whereas 2 potassium ions are going to be imported towards the inside of the cell.

It has the n, it has the a, and it has the plus. And so this, because it has 3 characters can remind you that it's actually 3Na⁺ ions that are going to be exported towards the outside of the cell. And the Potassium symbol here has only 2 characters. So it has the k and it has the plus, and so that can help remind you that it's 2K⁺ ions that are being imported towards the inside of the cell. Now what can also help you remember that, Potassium are going to be imported towards the inside of the cell is to just think of a pumpkin.

Because if you think about a pumpkin, it'll tell you that the sodium-potassium pump is going to pump K⁺ into the cell. And so if you remember pump gen, you'll remember that, hey, potassium ions get pumped into the cell or imported into the cell. So 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 right here. And notice that the sodium-potassium pump is going to take 3Na⁺ ions and those 3Na⁺ ions are going to be exported toward 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 3Na⁺ 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 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 i

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 going to be directly driven by another molecule's concentration gradient. It's going to be powered by another molecule's concentration gradient instead of being powered by ATP hydrolysis like primary active transport is.

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 actually going to take a look at a classic example in 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 you see in the image correspond with the numbers that we have up above here in the text.

This is really showing you the 4 steps that there are for this sodium glucose secondary active transport example. In the very first step here, what you'll notice is that sodium ions can be transported against their concentration gradient using primary active transport. Notice that the sodium ion is being pumped across the membrane in this direction, towards the area of higher sodium concentration, whereas there's a lower sodium concentration inside the cell. Because sodium is being pumped against its concentration gradient from low to high concentration, it's going to require energy. Notice that ATP is directly linked to this process of pumping sodium across the membrane.

And because ATP is directly linked here, it is a form of primary active transport just like what we mentioned above, sodium being transported against its concentration gradient using primary active transport. But we've already covered primary active transport, so this is not anything new to us. In number 2, what this is going to generate is a higher concentration of sodium ions on the outside of the cell. There's a much higher concentration of sodium than inside the cell, where there's a lower sodium ion concentration.

This is because this primary active transport generates this concentration gradient of sodium. But then what we also need to realize is in this image in number 3, there's another molecule involved here, glucose, which we have in green. Notice down below we have glucose as well, in these green hexagons. The glucose molecules actually have a higher concentration on the inside of the cell, which is opposite to that of the sodium.

The sodium has a higher concentration on the outside of the cell. The glucose has a higher concentration on the inside of the cell. This is really where 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, and that does not require any energy. In fact, it can provide and release energy. As the sodium gets transported down its concentration gradient, it's actually going to provide the energy.

It's going to power the transportation of glucose against its concentration gradient from the area of low concentration of glucose towards the area of high concentration of glucose. Notice that no ATP is directly involved. There's no ATP in this vicinity at all. Because it's not driven directly by ATP, it's going to be driven by the concentration gradient of sodium being transported down its concentration gradient. This makes this a classic example of secondary active transport.

As we mentioned above with secondary active transport, it's going to be driven by the concentration gradient of another molecule instead of ATP hydrolysis. Here with secondary active transport, notice that there's no ATP at all in this vicinity. It's just this concentration gradient of sodium going down its concentration that powers the secondary active transport here of glucose being transported against its concentration gradient. This here 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, from areas of low concentration to high concentration. 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, to drive the movement of substances. For instance, the sodium-glucose transporter uses the sodium gradient created by the sodium-potassium pump to transport glucose against its concentration gradient.

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

The sodium-potassium pump is a classic example of primary active transport. It uses energy from ATP hydrolysis to move 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell, against their respective concentration gradients. This process involves the binding of Na⁺ ions to the pump, ATP hydrolysis, and the subsequent release of Na⁺ ions outside the cell. Then, K⁺ ions bind to the pump, which returns to its original conformation, releasing K⁺ ions inside the cell. This cycle helps maintain essential concentration gradients for cellular functions.

What is an example of secondary active transport?

A classic example of secondary active transport is the sodium-glucose transporter. This transporter uses the sodium gradient established by the sodium-potassium pump (a primary active transport mechanism) to move glucose into the cell against its concentration gradient. Sodium ions move down their concentration gradient, releasing energy that is used to transport glucose molecules from areas of low concentration to high concentration inside the cell. This process does not directly use ATP but relies on the energy stored in the sodium gradient.

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 then used to change the conformation of transport proteins, allowing them to move substances from areas of low concentration to high concentration. For example, in the sodium-potassium pump, ATP hydrolysis provides the energy to transport 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell, maintaining essential concentration gradients for cellular functions.

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

The sodium-glucose transporter functions in secondary active transport by using the sodium gradient established by the sodium-potassium pump. Sodium ions move down their concentration gradient into the cell, releasing energy. This energy is then used to transport glucose molecules against their concentration gradient, from areas of low glucose concentration outside the cell to high glucose concentration inside the cell. This process does not directly use ATP but relies on the energy stored in the sodium gradient created by primary active transport.