What is Chemiosmosis? - Definition & Process

What Is Diffusion?

Chemiosmosis is the process of a molecule moving from high to low concentration, based on its charge and concentration inside a cell. This sounds pretty complicated. So, before talking about chemiosmosis, it will be important to understand a basic rule of the world: diffusion.

Diffusion is when anything moves from high concentration to low concentration. Think about food coloring in a jar of water. When the food coloring is first added to the water, it is concentrated in the center, but because there is less food coloring in other parts of the water, over time the food coloring spreads out or diffuses.

There are many more examples, such as delicious smells wafting from the kitchen during a holiday meal or warm air moving outwards from the house during the winter. The examples are so ubiquitous because diffusion is everywhere! Everything always moves from where there is more to where there is less. Check out the pictures of food coloring diffusing through a beaker of water.

How Does Diffusion Happen in Cells?

There are some special examples of diffusion that occur inside cells. Cells have a plasma membrane, or outer barrier, that only lets certain things in or out. This allows substances to build up on one side of the membrane if there isn't a door to let them through. This creates what we call a gradient. A gradient is a situation in which there is more of a substance on one side than another. Energy can be stored in a gradient over the plasma membrane. If one substance is concentrated on one side of the membrane, it will want to diffuse until the concentrations are even.

Because this process occurs naturally, when it finally does happen, energy is released. The cell can harness this energy to do amazing things. Channel proteins allow substances to diffuse through the plasma membrane. Notice there are more of the blue circles outside the cell, so by diffusion they move into the cell.

How Does Chemiosmosis Work?

Chemiosmosis is a special type of diffusion that happens over the plasma membrane. Chemiosmosis not only takes concentration into consideration, but also electrical charge. Thus, chemiosmosis exclusively has to do with the movement of ions (charged atoms) across the plasma membrane.

Diffusion not only works to equalize concentration on both sides of the membrane, but also to equalize charge. If there are more positive ions outside compared to inside the cell, positive ions will want to move down their electrical gradient into the cell. However, chemiosmosis also takes into consideration the concentration gradient. The molecule flows based on where there is more of its charge to where there is less and from a higher to lower concentration. The ion is flowing down its electrochemical gradient.

Chemiosmosis in the Body

All cells need energy, called ATP. Think of ATP as money. Each cell needs so much money to pay the bills every month, so just like people, they need to make money. The way the cell does this is through a process called cellular respiration, which starts with ingesting food and ends with making ATP.