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Diffusion

Diffusion

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This lesson will explain how substances move across a cell membrane through the process of diffusion as well as discuss why this process is important in our bodies.

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Tutorial
Welcome to today’s lesson on diffusion. In this lesson today, you are going to learn about the process of diffusion. Specifically, you will learn about the:
  1. Process of Diffusion
  2. Purpose of Diffusion


1. PROCESS OF DIFFUSION

Simply put, diffusion is the movement of molecules down a concentration gradient.

Diffusion
Movement of molecules from an area of high concentration to an area of low concentration.
Concentration Gradient
The difference in concentration of a substance between two areas.
A concentration gradient is the difference in the number of molecules of a substance across a space. When a substance is diffusing, it's moving from an area of high concentration to an area of low concentration. Diffusion is the movement of molecules from an area of high concentration to an area of low concentration without using any of the cell's energy. Diffusion is a type of passive transport, meaning that it doesn't require any energy from the cell in order for this to happen.

Passive Transport
The movement of molecules across a membrane without the use of energy.

2. PURPOSE OF DIFFUSION

The purpose of diffusion basically is just to even out the concentration of molecules across the space.

IN CONTEXT

Take a look at the image below as an example of diffusion using food coloring. Here you have a fishbowl and imagine that you drop some green food coloring into it.

When you first drop the food coloring into the fishbowl, it'll all be clumped up in that space right where you dropped it; but slowly, those molecules are going to start to spread out. They're going to move to an area of high concentration, right where they were dropped into an area of low concentration.

The rest of this for this fishbowl doesn't have any green food coloring molecules so those molecules are going to spread out from that area of high concentration to that area of low concentration.

When diffusion is done, those molecules will be equally spread or equally distributed throughout the water in that fishbowl. So you would notice, when you first dropped the food coloring in, you would see just this area of green, but after diffusion occurs, all of the water would then be green, and you would know that those molecules had spread out evenly, or diffused evenly, from an area of high to low concentration.

Below is another image example in a cell. Outside of the cell, you might have a certain solute that you have in high concentration. You have a lot of it outside of the cell, but you don't have very much of it inside of the cell.

Naturally, those molecules are going to diffuse from an area, again, of high concentration to low concentration. You're going to see these molecules outside of the cell diffuse across the plasma membrane into the cell.

Again, when diffusion has happened, you would have an equal number of molecules outside as you would inside. These will continue to diffuse into the cell until it's equal on either side of the cell.

This lesson has been a brief overview on the process and purpose of diffusion and how molecules will move from an area of high concentration to an area of low concentration naturally, without the use of cell energy.


Keep up the learning and have a great day!

Source: this work is adapted from sophia author Amanda Soderlind.

TERMS TO KNOW
  • Diffusion

    Movement of molecules from an area of high concentration to an area of low concentration

  • Concentration Gradient

    The difference in concentration of a substance between two areas

  • Passive Transport

    The movement of molecules across a membrane without the use of energy