Passive vs. Active Transport: Videos & Practice Problems

Transport across biological membranes occurs via passive and active mechanisms. Passive transport moves molecules from high to low concentration without energy, while active transport requires energy (ATP) to move molecules against their concentration gradient. Transport proteins are classified into three types: uniporters (transport one molecule in one direction), symporters (co-transport at least two molecules in the same direction), and antiporters (transport two molecules in opposite directions). Understanding these processes is crucial for grasping cellular function and homeostasis.

Passive vs. Active Transport

In this video, we're going to distinguish between passive and active transport. There are 2 general types of molecular transport or transport of very small molecules across biological membranes. These 2 general types of molecular transport are passive transport and active transport. Passive transport requires absolutely no energy whatsoever, and that's because passive transport transports molecules passively from an area of high concentration down to an area of low concentration. Active transport, on the other hand, does require energy, unlike passive transport, which does not require energy, and that's because active transport will transport molecules actively from an area of low concentration to an area of high concentration. Let's take a look at our example below to further distinguish between passive and active membrane transport.

Notice that we're showing you a little snippet of the map of the lesson from our previous lesson video, focusing on molecular transport of very small molecules. These can be transported across the membrane using one of these two types, either passive transport, which requires absolutely no energy whatsoever, or active transport, where energy is required. In these images, notice that number 1 corresponds with passive transport. Here we're showing you the biological membrane and, notice that these molecules are in high concentration on this side of the membrane, so we can label it as high concentration here. On this side of the membrane, notice there's quite a low concentration, and so with passive transport, molecules are going to be transported from an area of high concentration to an area of low concentration. The high concentration is here, low concentration is there, so it will be transported in this direction, the direction of the arrow that you see here. Passive is going to represent a process where absolutely no energy is required.

On the other hand, over here on the right-hand side, we're showing you active transport. Notice that with active transport, it's going to be transporting molecules from an area of low concentration towards an area of high concentration. Here we're focusing on these purplish molecules and notice up above here we have an area of high concentration of the purple molecules and down below we have an area of low concentration of the purple molecule. We can label this as low concentration. Notice that the direction of movement is going towards the area of higher concentration, from low concentration towards high concentration, and that is what makes this active transport. Active transport is going to require energy in the form of ATP, and recall ATP is this high-energy molecule that cells utilize for energy. You can think the 'a' in active transport is for the 'a' in ATP, which means that energy is required. So active means energy. This concludes our introduction to the difference between passive and active transport. Moving forward, we'll be able to talk more and more about the differences between the two and also different types of passive transport and different types of active transport. I'll see you guys in our next video.

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.

Answer: (C)

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

• A. Both active and passive transport move substances down their concentration gradients.
• B. Active transport is ATP dependent. Passive transport does not require energy.
• C. Active transport requires cell to cell communication. Passive transport does not require cell communication.
• D. Active transport can be performed without transport proteins while passive transport cannot.

Answer: (B)

Classes of Membrane Transport Proteins

In this video, we're going to introduce the classes of membrane transport proteins. Now, really there are 3 types of transport proteins that are classified according to how they operate or how they work. And so the very first type of transport protein that you all should know are the uniporters. Uni is a prefix that means 1 or singular, and so uniporters are going to transport just one molecule at a time in just one direction across the membrane. If we take a look at the image down below at the uniporter, notice that it's going to transport, this protein that's in the membrane right here is the uniporter, and uniporter proteins are going to transport just one molecule across the membrane in one direction. We have one molecule here in one direction across the membrane. This protein would be a uniporter.

Now, the second type of transport protein that you all should know are the symporters. The symporters are going to co-transport at least 2 molecules, greater than or equal to 2 molecules, at a time in the same direction across the membrane. You can think of the 's' in symporters for the 's' in same direction across the membrane. When we take a look at the image down below at the symporter here, which would be this protein here, notice that the symporter is going to transport at least 2 molecules across the membrane, and so notice that we have this red molecule right here, and we have the green molecule right here, and notice that both the red and the green molecule are being transported in the same direction across the membrane. And really, that is what makes this a symporter because they're being transported in the same direction across the membrane.

Now last but not least, the third type of transport protein you all should know are the antiporters. Anti is a prefix that basically means the opposite. And so antiporters are going to be transporting at least 2 molecules at a time, just like the symporters do, but instead of transporting them in the same direction across the membrane, antiporters are going to be transporting the 2 molecules in opposite directions across the membrane. Let's take a look over here at the image on the far right-hand side at the antiporter, which would be this membrane protein right here. Notice it's also transporting 2 molecules. It's transporting the red molecule in this direction and the green molecule in this direction. And because the 2 molecules are being transported in opposite directions, that's what makes this an antiporter. We can write opposite directions right here.

This here concludes the lesson on the different classes of membrane transport proteins, and we'll be able to see examples of all of these types as we move forward throughout our course. This here concludes our lesson, and I'll see you all 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

Answer: (D)

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.

Answer: (E)

Here’s what students ask on this topic:

What is the difference between passive and active transport?

Passive transport and active transport are two mechanisms for moving molecules across biological membranes. Passive transport does not require energy and moves molecules from an area of high concentration to an area of low concentration, following the concentration gradient. Examples include diffusion and osmosis. Active transport, on the other hand, requires energy in the form of ATP to move molecules against their concentration gradient, from an area of low concentration to an area of high concentration. This process is essential for maintaining cellular homeostasis and includes mechanisms like the sodium-potassium pump.

How do uniporters, symporters, and antiporters differ in their function?

Uniporters, symporters, and antiporters are types of transport proteins that facilitate the movement of molecules across cell membranes. Uniporters transport a single type of molecule in one direction. Symporters co-transport two or more molecules in the same direction across the membrane. Antiporters also co-transport two or more molecules, but in opposite directions. These proteins are crucial for various cellular processes, including nutrient uptake and waste removal.

Why does active transport require energy?

Active transport requires energy because it moves molecules against their concentration gradient, from an area of low concentration to an area of high concentration. This process is energetically unfavorable and cannot occur spontaneously. The energy required for active transport is typically provided by ATP (adenosine triphosphate), which is hydrolyzed to release energy. This energy is used to change the conformation of transport proteins, allowing them to move molecules across the membrane.

What are some examples of passive transport?

Examples of passive transport include simple diffusion, facilitated diffusion, and osmosis. Simple diffusion involves the movement of small, nonpolar molecules like oxygen and carbon dioxide directly through the lipid bilayer. Facilitated diffusion requires transport proteins, such as channel proteins or carrier proteins, to help move larger or polar molecules like glucose and ions across the membrane. Osmosis is the diffusion of water molecules through a selectively permeable membrane from an area of high water concentration to an area of low water concentration.

What role do transport proteins play in active and passive transport?

Transport proteins are essential for both active and passive transport. In passive transport, channel proteins and carrier proteins facilitate the movement of molecules down their concentration gradient without using energy. In active transport, transport proteins like pumps use energy from ATP to move molecules against their concentration gradient. These proteins ensure that essential molecules like ions, nutrients, and waste products are efficiently transported across the cell membrane, maintaining cellular function and homeostasis.