Chemiosmosis | Gradient, Diagram, Process & Steps

Rana Ahmed, Amanda Robb
  • Author
    Rana Ahmed

    I received the bachelor’s degree of Science from Microbiology Department, Faculty of Sciences, Suez Canal University, Egypt. I carried out my Pre-Masters in Applied and Medical Microbiology at the Suez Canal University. In addition, I finished Post-Graduate studies regarding a Diploma in Physiology and Biochemistry, and a Diploma in Bioinformatics. During the past three years, I gained a strong background in creating and reviewing outstanding learning scientific resources. Moreover, I look over recently published papers to create high-quality scientific contents for global education.

  • Instructor
    Amanda Robb

    Amanda has taught high school science for over 10 years. She has a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. She is also certified in secondary special education, biology, and physics in Massachusetts.

Discover chemiosmosis. Find the chemiosmosis definition, chemiosmosis steps, and chemiosmosis diagram. Learn about the role of chemiosmosis in the body. Updated: 02/15/2022

What is Chemiosmosis?

Chemiosmosis is the movement of ions from high concentration to low concentration through a selectively permeable membrane. Chemiosmosis depends on the diffusion principle. Diffusion is the movement of particles from high concentration to low concentration, in other words, the movement of particles down their concentration gradient . A gradient means that the concentration of particles is greater on one side than on the other.

There are numerous examples of diffusion in the real world such as the following:

  • A drop of ink submerged in a cup of water will diffuse and affect the color of the water.
  • Sugar dissolves and sweetens the water without the need for stirring.
  • The detecting of an odor of perfume sprayed into the air.


The diffusion of ink in a cup of water

diffusion of ink in a cup of water


There are also many diffusion processes that occur in living organisms:

  • Toxic and waste substances are eliminated from the human body through diffusion.
  • The exchange of gases within the two lungs.
  • In the kidneys, the diffusion of waste materials, salt, and water.
  • The transportation of molecules within plant and animal cells requires diffusion.

There are three types of transport:

  • Simple diffusion: The movement of particles from high concentration gradient to the low concentration gradient
  • Osmosis: The process in which solvent molecules move across a semipermeable barrier from a less concentrated solution to a more concentrated one.
  • Facilitated diffusion: The movement of particles from higher concentration gradient to lower concentration gradient with the help of transport proteins.

These three types are passive which means they don't require energy as substances move down their concentration gradient, unlike active transport which is the movement of substances from lower concentration to higher concentration, that is, movement of substances against their concentration gradient. Active transport requires energy to allow substances to move against a concentration gradient.


The movement of ions from high concentration to low concentration through semi-permeable membrane by transport protein

movement of ions from high concentration to low concentration through semi-permeable membrane by transport protein



The process of osmosis

process of osmosis



The difference between passive transport and active transport which requires energy

active vs passive transport


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.

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  • 1:52 How Does Chemiosmosis Work?
  • 2:43 Chemiosmosis in the Body
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Chemiosmosis Model

The chemiosmosis is a coupling model in the mitochondria and its process is discussed below in detail.

Chemiosmosis Process

Chemiosmosis is the movement of ions according to the electrochemical gradient over a semipermeable membrane structure. Chemiosmosis substance moving from high to low concentration, and also moving from high charge to low charge. A gradient of electrochemical potential, generally for an ion that may travel across a membrane, is referred to as an electrochemical gradient. The chemiosmosis process is directly related to the synthesis of ATP (which stands for adenosine triphosphate) during cellular respiration by the movement of hydrogen ions across a membrane. Hydrogen ions (protons) will diffuse from a high proton concentration area to a low proton concentration area, that is to say, hydrogen ions will move down their proton gradient.

The generation of ATP takes place in the energy factory of the cell which is the mitochondria; the mitochondria consists of various structures including the inner membrane, outer membrane, and matrix which is a space within the inner membrane.


The structure of mitochondria

structure of mitochondria.


Cellular respiration takes place in subsequent three stages: glycolysis, Krebs cycle (citric acid cycle), and electron transport chain. Glycolysis takes place in the cytoplasm while the citric acid cycle takes place in the matrix and the electron transport chain happens at the inner mitochondrial membranes. The citric acid cycle requires pyruvate, which is delivered into the mitochondrial matrix during glycolysis. The citric acid cycle is a sequence of chemical events that remove high-energy electrons and utilize them in the electron transport chain to make ATP. The electron transport chain is a collection of proteins and chemical compounds. Electrons are transferred from one member of the transport chain to another by redox reactions. A redox reaction is the collection of oxidation and reduction reaction that involves the losing and gaining of elections, respectively.

Both the intermembranous space and the inner mitochondrial membrane are involved in the electron transport chain. The electrons move through a sequence of redox reactions to release energy. The majority of this energy is either wasted as heat or used to pump hydrogen ions (H+) from the mitochondrial matrix to the intermembranous space, resulting in a proton gradient, which is utilized in chemiosmosis by the protein ATP-synthase to produce a huge amount of ATP. The generation of ATP by the chemiosmosis process in mitochondrial membranes is called oxidative phosphorylation. The driving factor for ATP synthesis is a larger concentration of protons outside the inner membrane of the mitochondria than within the matrix. Substrate-level phosphorylation is a metabolic process that produces ATP by directly transferring a phosphate group from a substrate to ADP.

Chemiosmosis Diagram

The provided diagram shows the process of chemiosmosis and its components.


The chemiosmosis process

chemiosmosis diagram


Chemiosmosis Steps

Chemiosmosis is the process through which cells produce ATP for energy in the cellular respiration process. It generates energy in the same way as a water wheel generates power. ATP synthase functions similarly to a water wheel in the inner membrane of mitochondria, producing ATP by driving ADP and phosphate together.

  • Electron carriers such as NADH and FADH provide electrons to the electron transport chain during chemiosmosis.
  • The electrons create changes in the structures of the proteins, allowing H+ to pass through a selectively permeable cell membrane.
  • Because of the positive charge of the hydrogen ions and their aggregation on one side of the membrane, the unequal distribution of hydrogen ions gradient across the membrane creates an electrochemical gradient
  • After the gradient is generated, protons diffuse down the gradient via ATP synthase, a transport protein. Chemiosmosis refers to the movement of hydrogen ions across the membrane via ATP synthase.
  • The flow of hydrogens catalyzes the pairing of phosphate with ADP, resulting in the formation of ATP.

So the role of chemiosmosis in the body is to generate about 90% of the ATP during cellular respiration. ATP is the energy currency of cells that has the main role in storing and transferring energy in the cells.


ATP synthase

ATP synthase



The structure of ATP

ATP structure


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.

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Video Transcript

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.

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Frequently Asked Questions

What is the role of chemiosmosis in photosynthesis?

The chemiosmosis reaction takes place in the matrix of the chloroplast known as the stroma which has a high amount of protons (hydrogen ions). Chemiosmosis is important in photosynthesis as proton gradient develops across the semipermeable cell membrane of the chloroplast, which is coupled with the creation of ATP molecules.

How does chemiosmosis produce ATP?

Chemiosmosis refers to the movement of hydrogen ions across the membrane via ATP synthase. When protons diffuse down the gradient via ATP synthase, the flow of hydrogen catalyzes the pairing of phosphate with ADP, resulting in the formation of ATP.

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