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

Passive transport involves the movement of molecules across biological membranes without energy input, occurring from areas of high to low concentration. In contrast, active transport requires energy, typically from ATP, to move molecules against their concentration gradient. Membrane transport proteins are classified into three types: uniporters (transporting one molecule), symporters (transporting two molecules in the same direction), and antiporters (transporting 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 briefly distinguish between passive transport and active transport. There are 2 general types of molecular transport of small molecules across biological membranes: passive transport and active transport. Notice that passive transport is numbered with number 1 and active transport with number 2. The number 1 in our image corresponds with passive transport, and the number 2 corresponds with active transport. It's important to keep this in mind.

Passive transport, as its name implies, requires absolutely no energy because it is passive. Passive transport does not require energy because molecules are transported down or with their concentration gradients from an area of high concentration to an area of low concentration, which is how molecules naturally diffuse. This is why it requires no energy.

On the other hand, active transport, as its name implies, requires an energy input because it is an active process. Active transport needs energy because molecules are transported against or up their concentration gradients from an area of low concentration to an area of high concentration, which is not the natural tendency for molecules to diffuse. Therefore, it requires an energy input to actively transport these molecules.

As we move forward in our course, we will mostly discuss passive transport but will discuss more about active transport later. Let's take a look at our image below to better understand the difference between passive and active membrane transport.

Notice on the left-hand side of the image, we are showing an example of passive transport. You will see our biological membrane in the middle with a relatively high concentration of molecules on one side of the membrane, labeled as high concentration. On the other side of the membrane, there's a relatively low concentration of those same molecules. These molecules are being transported across the membrane from the area of high concentration to the area of low concentration, characterizing passive transport which requires no energy.

On the right-hand side, we're showing active transport. Here, the biological membrane utilizes a membrane protein, indicated by the green structure. On one side of the membrane, there's a high concentration of purple molecules, while on the other side, the concentration is low. These molecules are being transported against or up their concentration gradient, in the direction from low to high concentration. This is active transport, and it often requires energy, typically in the form of ATP. Active transport means that an energy input is necessary.

Later in our course, we will be able to distinguish between primary active transport and secondary active transport. But we'll discuss more on active transport after covering the different types of passive transport. This concludes our brief lesson on passive versus active transport, and we'll be able to learn much more and apply these concepts as we move forward. So, I'll see you all 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.

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.

Classes of Membrane Transport Proteins

In this video, we're going to briefly discuss the classes of membrane transport proteins. There are three types of membrane transport proteins that can be used for either passive transport or active transport, and these three types of transport proteins are classified according to how they operate. Notice that we have the three types of membrane transport proteins numbered down below, and those numbers correspond to the image down below as well.

The first type of membrane transport protein that you should be aware of are the uniporters. The root 'uni' means one or singular, and so uniporters are membrane transport proteins that transport just one molecule at a time in just one direction across the membrane. If we take a look at our image down below on the left-hand side, notice we're showing you our uniporter, which is the membrane transport protein embedded in the membrane here. It's transporting just one molecule across the membrane at a time in just one direction. You can think of Uniporter as just one molecule being transported.

The second type of membrane transport protein is going to be the symporters. The symporters transport ≥2 molecules at a time, so multiple molecules at a time, but these molecules that are being transported at the same time are going to be transported across the membrane in the same direction. If we take a look at our image down below in the middle, notice we're showing you our symporter which is the membrane transport protein embedded in the membrane here. It is transporting two molecules, the red molecule and the green molecule, across the membrane in the same direction. You can think that the 's' in symporter is for the 's' in same direction.

The third and final type of membrane transport protein that we're going to discuss is the antiporter. The root 'anti' implies opposite, and antiporters co-transport ≥2 molecules at the same time. However, these two molecules are going to be transported in opposite directions across the membrane. That is what distinguishes the antiporter from the symporter. If we take a look at our image down below on the right-hand side, we're showing you our antiporter, and it's transporting two molecules, the red molecule and the green molecule, across the membrane. However, notice that the red molecule is being transported in the opposite direction as the green molecule. Because these two molecules are being transported in opposite directions, that is what makes this an antiporter.

This here concludes our brief lesson on these three classes of membrane transport proteins, and we'll be able to apply these concepts as we move forward in our course. 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

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 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 down their concentration gradient from an area of high concentration to an area of low concentration. Examples include diffusion and facilitated diffusion. Active transport, on the other hand, requires energy, usually 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 often involves membrane proteins such as pumps. Understanding these differences is crucial for comprehending how cells maintain homeostasis and regulate their internal environments.

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

Uniporters, symporters, and antiporters are types of membrane transport proteins that facilitate the movement of molecules across cell membranes. Uniporters transport a single type of molecule in one direction. Symporters move two or more molecules in the same direction across the membrane. Antiporters transport two or more molecules in opposite directions. These proteins play essential roles in both passive and active transport, helping cells to efficiently manage the intake and expulsion of various substances necessary for cellular function.

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 not naturally favorable and thus requires an input of energy to proceed. The energy is typically provided by ATP (adenosine triphosphate). The energy from ATP is used to change the conformation of transport proteins, allowing them to move molecules across the membrane. This mechanism is crucial for maintaining cellular functions such as nutrient uptake, waste removal, and ion balance.

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

Membrane transport proteins are essential for both passive and active transport. In passive transport, proteins like channels and carriers facilitate the movement of molecules down their concentration gradient without using energy. In active transport, proteins such as pumps use energy, often from ATP, to move molecules against their concentration gradient. These proteins ensure that essential molecules like ions, nutrients, and waste products are efficiently transported in and out of cells, maintaining cellular homeostasis and function.

Can you explain the concept of concentration gradient in the context of passive and active transport?

A concentration gradient refers to the difference in the concentration of a substance between two regions. In passive transport, molecules move down their concentration gradient, from an area of high concentration to an area of low concentration, without requiring energy. This natural diffusion process helps in the equal distribution of molecules. In active transport, molecules move against their concentration gradient, from an area of low concentration to an area of high concentration, which requires energy input. Understanding concentration gradients is fundamental to grasping how substances are transported across cell membranes.