Simple Diffusion: Definition & Examples

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  • 0:02 What Is Simple Diffusion?
  • 2:05 Simple Diffusion Process
  • 2:47 Example of Simple Diffusion
  • 3:43 Lesson Summary
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Lesson Transcript
Instructor: Nadine James

Nadine has taught nursing for 12 years and has a PhD in Nursing research

This lesson will provide you with a definition of simple diffusion. Also, an example and illustration will be provided to support your understanding of the process.

What Is Simple Diffusion?

In a solution or gas that has an area of high numbers of particles and an area of lower numbers of particles, the particles will diffuse, or move, from the area of higher to the area of lower concentration. This is known as simple diffusion, or passive diffusion.

Simple diffusion does not require energy. Instead, it happens by random motion. Random motion is defined as movement that occurs by chance because there is no order or regular system by which the movements of the particles shift in a solution or gas.

These areas of higher or lower numbers of particles in a solution or gas are separated by a membrane. A membrane is a thin substance that may allow substances to pass through it or not. Therefore, a membrane is classified as permeable (which means things can pass through it), impermeable (which means things can't pass through it), or semi permeable (which means things can pass through it by diffusion). In the case of simple diffusion, the membrane is semi permeable, which means the particles or solutes can pass through it by random motion.

To help you understand this process, think of a small brook with flowing water. Imagine that the brook has small leaves and other debris in the water. Then imagine there is a window screen in the brook. The screen represents the semi permeable membrane, and the leaves and other debris in the water represent particles. In this case, small leaves and debris can pass through the screen while larger leaves and debris cannot pass.

So, let's put it all together. Concentration gradient is the process by which particles, which are sometimes called solutes, move through a solution or gas from an area of higher number of particles to an area of lower number of particles. The actual movement is called diffusion. Solutes moving through a solution or a gas happen by random motion along the concentration gradient until there are equal numbers of particles in the two areas.

Simple Diffusion Process

There are actually three types of diffusion. We've been talking about simple diffusion (also known as passive diffusion), but there's also facilitative diffusion and active transport. We will only go into detail about the focus of this lesson: simple diffusion.

An easy way to see simple diffusion in action is to drop food coloring into a cup of water. If you have ever done this, you have likely noticed that the food coloring is concentrated when dropped into the cup of water. However, as a few seconds pass, the particles become lighter in color as they move to the lower concentration level. Again, this happens without energy, which is why it is known as passive diffusion.

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