Concentration Gradients and Diffusion - Online Tutor, Practice Problems & Exam Prep

A concentration gradient is the difference in the concentration of a substance between two areas. Molecules move down their concentration gradient from high to low concentration without energy, while moving against it requires energy. Diffusion is the net movement of substances from high to low concentration until equilibrium is reached. For example, when dye is added to water, it diffuses until evenly distributed. Understanding these concepts is crucial for grasping processes like cellular respiration and homeostasis.

Concentration Gradients and Diffusion

In this video, we're going to begin our lesson on concentration gradients and diffusion. A concentration gradient is defined as a difference in the concentration of a substance between two different areas. If we're comparing two areas and one area has a higher or lower concentration than another area, then a concentration gradient exists because there's a difference in the concentration between those two areas. However, if we're comparing the concentration of two areas and there's no difference in the concentration, then no concentration gradient exists. That's why a concentration gradient is really just a difference in the concentration of a substance between two areas.

Now a molecule will be moving with or down its concentration gradient when that molecule is going from an area of high concentration down to an area of low concentration. Conversely, a molecule will be moving against or up its concentration gradient when that molecule is going from an area of low concentration to an area of high concentration. Let's take a look at this image down below to clear up that idea. Notice that this image is all about concentration gradients, and it's broken up into two halves. On the left-hand side, we have a high concentration of these pink molecules, whereas on the right-hand side, we have quite a low concentration.

If one of these pink molecules moves from an area of high concentration towards an area of low concentration, the molecule movement is represented by the biker here, then this means that the molecule will be moving down or with its concentration gradient, moving from the area of high concentration down to the area of low concentration. Just like it doesn't really take a lot of energy for a biker to cruise down a hill, it also does not take any energy for a molecule to move down or with its concentration gradient from areas of high concentration towards areas of low concentration. Here we can indicate that absolutely no energy is required.

Now over here on the right-hand side, notice that we have an image that has an area of low concentration of pink molecules on the left-hand side, and an area of much higher concentration of the pink molecule on the right-hand side. If a molecule is trying to move from an area of low concentration towards an area of high concentration and the movement of the molecules is represented by this biker going uphill, this means that the molecule would be moving up or against its concentration gradient. Just like it would take a lot of energy for a biker to bike up a hill, it takes energy for a molecule to move up or against its concentration gradient from an area of low concentration to an area of high concentration. Here we're saying that energy is required.

This concludes our introduction to the concentration gradient and also molecules moving with or down the concentration gradient and against or up the concentration gradient. We'll be able to get some practice applying these concepts as we move forward in our course. In our next lesson video, we'll talk more about diffusion. I'll see you guys in our next video.

Diffusion

In this video, we're going to talk about diffusion. Diffusion is the net movement of a substance from an area of high concentration down to an area of low concentration, and molecules have a natural tendency to diffuse with or down their concentration gradients from an area of high concentration to an area of low concentration. Let's take a look at this example image down below at the diffusion of dye and water. Notice that in this image, the blue circles represent water molecules, whereas the red circles represent dye molecules. Over here on the far far left, notice that this person is adding a drop of dye to this beaker of water.

Initially, when the person first adds the drop of dye, there's quite a high dye concentration in this one initial area, but in other areas of the beaker like here and over here and right here, you can see that there's quite a low dye concentration. There's really no dye at all. What starts to happen is diffusion is going to start to occur and the dye is going to start to diffuse to areas of low concentration, as we see here, from an area of high concentration down to an area of low concentration. That's what's starting to happen over here in this beaker. It's starting to diffuse and it's going to continue to diffuse from areas of high to areas of low concentration until equilibrium has been reached.

Equilibrium is just when the entire beaker has equal concentrations of the dye and the dye is evenly distributed throughout the beaker. This is the idea of diffusion. This concludes our introduction to diffusion 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.

Which of the following statements about diffusion is true?

• A. It's a process where water moves across a semi-permeable membrane to a region of high solute concentration.
• B. It requires an expenditure of energy by the cell.
• C. It's a process where molecules move from a region of lower concentration to a region of higher concentration.
• D. It's a process where molecules move from a region of higher concentration to a region of lower concentration.

Here’s what students ask on this topic:

What is a concentration gradient and how does it affect molecular movement?

A concentration gradient is the difference in the concentration of a substance between two areas. It affects molecular movement by dictating the direction in which molecules will naturally move. Molecules tend to move from an area of high concentration to an area of low concentration, a process known as moving down or with the concentration gradient. This movement does not require energy. Conversely, moving molecules from an area of low concentration to an area of high concentration, known as moving up or against the concentration gradient, requires energy. Understanding concentration gradients is crucial for grasping processes like cellular respiration and homeostasis.

What is diffusion and how does it relate to concentration gradients?

Diffusion is the net movement of a substance from an area of high concentration to an area of low concentration. It is directly related to concentration gradients because it occurs down the concentration gradient. For example, when dye is added to water, the dye molecules will move from the area of high concentration (where the dye was added) to areas of low concentration until equilibrium is reached. At equilibrium, the dye is evenly distributed throughout the water. Diffusion is a passive process, meaning it does not require energy, and it is essential for many biological processes, including nutrient absorption and gas exchange.

Why does moving molecules against a concentration gradient require energy?

Moving molecules against a concentration gradient requires energy because it involves transporting molecules from an area of low concentration to an area of high concentration. This process is akin to pushing a boulder uphill; it goes against the natural tendency of molecules to move from high to low concentration. Energy is needed to overcome this natural tendency and is usually provided by ATP (adenosine triphosphate) in biological systems. This type of transport is known as active transport and is crucial for maintaining cellular functions, such as ion balance and nutrient uptake.

How does equilibrium relate to diffusion?

Equilibrium in the context of diffusion refers to the point at which the concentration of a substance is equal throughout a given space. During diffusion, molecules move from areas of high concentration to areas of low concentration. This movement continues until the concentration of the molecules is uniform across the space, achieving equilibrium. At equilibrium, there is no net movement of molecules in any particular direction, although individual molecules may still move randomly. Understanding equilibrium is important for comprehending how substances like gases and nutrients are distributed in biological systems.

What are some real-life examples of diffusion?

Real-life examples of diffusion include the following: 1) Perfume spreading in a room: When perfume is sprayed, the molecules move from an area of high concentration (near the spray) to areas of low concentration, eventually filling the room. 2) Oxygen and carbon dioxide exchange in the lungs: Oxygen diffuses from the alveoli (high concentration) into the blood (low concentration), while carbon dioxide diffuses from the blood (high concentration) into the alveoli (low concentration) to be exhaled. 3) Sugar dissolving in water: When sugar is added to water, the sugar molecules diffuse from the area of high concentration (where the sugar was added) to areas of low concentration until evenly distributed.