What is osmosis? - Trends in science (2023)

Osmosis refers to the movement of molecules across a selectively permeable membrane. In osmosis, the molecules spread along the membrane gradient until the concentrations of molecules on both sides of the membrane are approximately equal. Osmosis is a crucial process in biological organisms that helps control levels of molecules such as lipids, nitrogen, carbon dioxide, water and oxygen. Osmosis is the primary method of transporting water in and out of cells and this function is essential in maintaining cell homeostasis.

This is the short answer to what osmosis is. However, let's take a closer look at how osmosis affects the movement of molecules across a membrane and affects cell function.

Definition of osmosis

The process is called osmosisDispersion of solvent moleculesThrough a semi-permeable membrane, they move from an area of ​​higher concentration of molecules to an area of ​​lower concentration, or in other words, molecules move from more concentrated solutions to more dilute solutions. The movement of molecules continues until the concentration gradient — the number of molecules distributed in a given area — is more or less evenly distributed. The solvent most commonly transferred by osmosis is water, although other solvents such as gases and other liquids can occasionally undergo osmosis.

The membranes through which solvent molecules move are semipermeable in the sense that only certain types of molecules pass through. Large, polar molecules such as polysaccharides, proteins, ions and similar molecules cannot move through the membrane. However, small non-polar molecules such as nitrogen, oxygen, etccarbon dioxidecan move across the membrane.

When there are solutions on both sides of a semi-permeable membrane, dissolved particles cannot pass through the membrane alone. Instead, solvent molecules move across the membrane. As the solvent molecules disperse, the system approaches equilibrium. The more evenly the particles are distributed, the more stable the system.

Examples of osmosis

Examples of osmosisinvolve the reaction of red blood cells when placed in a freshwater sample. Red blood cells in the body have a semi-permeable membrane that allows water to flow across the membrane. Since the concentrations of dissolved molecules such as ions in the red blood cells are higher than the concentrations outside the cell, water outside the cell moves through the membrane due to osmosis. This movement causes the red blood cells to swell because the concentration of molecules in the red blood cells cannot reach equilibrium. The cell membrane exerts pressure on the cell contents, thereby affecting how much water enters the cell. The cell often absorbs more water than it can hold, leading to cell rupture. Related to this phenomenon is the term 'osmotic pressure', which refers to the level of external pressure required to ensure that there is no net movement of molecules across a semipermeable membrane.

Another example of osmosis is the movement of minerals and salts in water. The water itself flows into the cells. The passage through the plasma membrane and the osmotic process help maintain the proper salt concentration.Glucose, IWaterThis is necessary to prevent cell damage. This process can be observed in action using marine fish. Marine fish have evolved to live in waters with high concentrations of salt. Due to the high salt concentration in the water, the fish cell must have a lower salt concentration. Therefore, the salt in the environment draws water out of the fish's body and the osmotic process is regulated in this way.

Freshwater fish, on the other hand, need to maintain homeostasis in a slightly different way. As you can imagine, the salt concentration in the cells of freshwater fish is higher than in the environment. Thanks to osmosis, these fish do not need to drink water because the salt contained in their cells absorbs water.

Osmosis is critical to the survival of human cells and the human body as a whole, with osmosis regulating the proper functioning of the kidneys. Kidney cells use osmosis to take up water from the waste products of other organ systems. In fact, kidney dialysis is an example of an osmotic process. People with kidney disease undergo kidney dialysis, which removes waste products from the blood by pulling particles through a dialysis membrane. The particles are then transferred to a tank filled with dialysis solution. Red blood cells remain in the blood itself because they are too large to cross the membrane, but waste products are removed.

It is also believed that the wrinkling of human skin after prolonged immersion in water is the result of osmosis, although recent research has challenged this assumption.

osmosis varieties

There are types of osmosis such as reverse osmosis and forward osmosis. Reverse osmosis is a process where pressure forces solvents to flow through membranes. In reverse osmosis, one side of the membrane retains the solute while pure solvent is pushed to the other side of the membrane. In reverse osmosis, the solvent is shifted from its standard location in an area of ​​high concentration to an area of ​​low solute concentration with excessive osmotic pressure.

Forward osmosis separates water from solutions containing other solutes. The higher osmotic pressure solution is used to force water through the semi-permeable membrane so that the "feed" solution (lower osmotic pressure solution) becomes more concentrated as the higher pressure solution is diluted. The newly diluted solution is then either sent to secondary processing or used directly. Forward osmosis is widely used for water treatment, desalination and water purification.

history of osmosis

The osmosis process was first documented around 1748 by Jean-Antoine Nollet. While Jean-Antoine Nollet was the first to describe the phenomenon, the correct term was coined by French physician René Joachim Henri Dutrochet. Dutrochet based the word osmosis on the words "exosomiasis" and "endosmosis". Moritz Traube developed more sophisticated techniques for measuring osmotic flow in 1867.

Diffusion

Diffusionis another method of mass transport in biology and chemistry, and while it also involves the movement of molecules, it differs from osmosis in important ways.

Diffusion occurswhen molecules, ions and water leave or enter cells. One speaks of cell diffusion when molecules move from an area of ​​higher concentration to an area of ​​lower concentration. This movement continues until both halves of the region have approximately the same number of molecules, until the distribution of molecules is approximately equal. Different cells can have different diffusion rates.

There are many types of diffusion in biology, with the two most common forms of diffusion being active transport and passive transport. The difference between these two different forms of fiction is that active transport uses energy to move molecules from an area of ​​lower concentration to an area of ​​higher concentration, while passive transport moves molecules naturally from an area of ​​higher concentration Concentration to be distributed in an area of ​​lower concentration.

Passive transport occurs naturally when substances move through a semipermeable membrane without expenditure of energy. The transport speed of the substance depends on the permeability of the membrane. The cell membrane controls what types of substances can pass through it, allowing some substances to pass through the cell membrane while blocking others. The permeability factor affects how easily substances can move through a membrane, an example of this is the cell wall. Plant cells have cell walls that surround the inner cell membrane. This structure has very low permeability and keeps most molecules trapped to the outside.

Facilitated Diffusioncan be considered a subspecies of passive transport. Due to the facilitated diffusion, special transport proteins enable molecules to move more easily through the cell membrane. These transport proteins allow larger molecules to cross the cell membrane while males were unable to. Molecules such as glucose are transported across the membrane and diffuse by facilitated diffusion. In facilitated diffusion, a carrier protein binds to a molecule and the molecule is pulled across the cell membrane by this protein.

Active transport is the conceptual opposite of passive transport, in which molecules are moved from an area of ​​lower concentration to an area of ​​higher concentration. Basic active transport uses metabolic energy to move molecules across the cell membrane. However, there is a type of active transport called secondary active transport. While cellular transport systems are used for the transport of molecules in this secondary form of transport, ATP is not used for this. Instead, entropy and ion pumps are used to transport molecules, resulting in a difference in chemical potential.