Simple Diffusion: Definition, Examples And Its Functional Importance.

Simple Diffusion Definition

Simple diffusion: the flow of solutes over a semipermeable protective layer or the movement of a particle across a solution’s concentration gradient is described as simple diffusion. The hydrogen bonds formed between water molecules and solutes enable simple diffusion. Hydrogen bonding is strengthened when solitary solute molecules are accompanied by water molecules. Hydrogen bonds, on the other hand, are very transitory.

As an outcome of this, the solution is continuously churned. This contributes to the solute’s homogenous spread throughout the solution. Simple diffusion might occur across cell membranes, between the single phospholipids that compose the membrane, when the molecules are tiny enough. Osmosis is a simple diffusion process in which water travels through a cell membrane along a concentration gradient.

Despite simple diffusion, cell membranes frequently contain specialised membrane proteins that facilitate the movement of molecules through the membrane. Facilitated diffusion is the term for this. Facilitated diffusion is a term that refers to both active and passive transport of solutes all over a membrane. Adenosine triphosphate (ATP) is utilised to provide energy to the proteins engaged in active transport.

Active transport systems, as opposed to simple diffusion, allow molecules to move in the opposite direction of their gradient. Diffusion is used in many biological processes, including the transportation of oxygen, water, and other tiny molecules to the body’s cells. While numerous solutes may diffuse over the membrane, protein channels are often included in cells to help in the process.

Examples of Simple Diffusion

Carbon Dioxide

Carbon dioxide is a very tiny molecule that readily dissolves in water. If you’ve ever experienced a bubbly soda, you’ll understand what I mean. You may be surprised to learn that the same method is used to transport carbon dioxide created by your cells into your circulation and out via your lungs.

Carbon dioxide is a gas that is tiny enough to permeate through your body’s tissues and out. If you retain your breath for an extended period of time, you will sense a burning “need to breathe.” Carbon dioxide accumulates in sensitive nerve tissues throughout your circulatory system, lungs, and brain, resulting in this. When you reintroduce breathing, the carbon dioxide in your system dissipates. Numerous gases in the atmosphere, like oxygen, nitrogen, and many more, may achieve this via your lungs.


Bacteria, being the basic creatures that they are, have no other means of obtaining nutrients except by diffusing them over the cell membrane. While most nutrients are transported by assisted diffusion, oxygen, water, and tiny nutrients are delivered to the cytoplasm via simple diffusion. Because bacteria lack specialised organelles to contain or move chemicals inside their cells, they depend on simple diffusion to ensure resources are available for the reactions that drive their biological processes.

Related Biology Terms

  • FacilitatedDiffusion  – The movement of a material over a cell membrane with the help of specific integrated transport proteins.
  • Proteins are used to help in the diffusion of a solute across a cell membrane gradient, this is known as passive transport.
  • Active Transfer is the employment of proteins and energy to transport substances across a membrane, even in opposition to their gradient.
  • Osmosis is the natural process by which water diffuses through a solution or a membrane along a gradient. 


  1. A cube of salt is dropped into a glass of water. After an hour, the cube had disappeared. Which of the following happened?
  2. Some organisms have proteins in their cell membranes called aquaporins, which provide a route for water to pass easily through the membrane. However, water will travel by osmosis through the membrane without these proteins. If the cell is exposed to a highly hypotonic environment, water rushes through both the aquaporins and the cell membrane into the cell. Which of the following is happening? 
  3. Oxygen used for respiration is a very small molecule. In some small organisms, no respiratory organs are needed because oxygen moves directly through the cell membrane and into each cell. Which process is responsible for this?


  1. This is a case of simple diffusion. Table salt is made of a matrix of two ions: sodium (Na+) and chloride (Cl–). The water in the glass immediately started working molecules off of the block as soon as it was dropped into the glass. The hydrogen bonds formed between water molecules and the salt ions pull the salt ions apart and distribute them evenly between the water molecules. As water works its way into the block, the salt molecules eventually become completely surrounded by water molecules. The hydrogen bonds continue to move the water molecules around and completely surround each salt ion until the salt is no longer visible in the solution.
  2. The simple diffusion of water is known as osmosis. It has a separate name to distinguish it from when water travels without its solutes, as in the case of water travelling through the cell membrane. The solutes originally distributed in the water are left behind as the water rushes to balance the concentration of solutes within the cell. Aquaporins are special membrane proteins that facilitate the diffusion of water into the cell.
  3. Oxygen travels throughout marine environments thanks to simple diffusion. Oxygen usually forms a bond with a second oxygen molecule and travels as O2. These small molecules can form hydrogen bonds and are also small enough to diffuse directly through cell membranes. Even in large organisms, no special proteins are needed to move oxygen into cells; it diffuses directly from the lungs into blood cells and throughout the body.
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