Osmosis facts for kids
Osmosis (/ɒzˈmoʊ.sɪs/) is the movement of solvent (liquid) molecules through a membrane, from one solution to another, which happens without an outside force.
Solvent will move to the side that has a higher concentration of solutes, or dissolved particles — and thus a lower concentration of solvent. This happens because the membrane is selectively permeable: the solvent can pass through, but the solute cannot. Solvent molecules move randomly, and so the concentrations on both sides become more equal.
Osmosis is important in biological (living) systems, as biological membranes are semipermeable. In general, these membranes are impermeable to large molecules such as ions, proteins, and polysaccharides. They are permeable to non-polar or hydrophobic molecules like lipids and small molecules like oxygen, carbon dioxide, nitrogen, and nitric oxide. Permeability depends on solubility, charge, or chemistry, as well as solute size. Water molecules travel through the plasma membrane, vacuole or protoplast by diffusing across the phospholipid bilayer.
Osmosis provides the main way water is gets in and out of cells. The turgor pressure of a cell is largely maintained by osmosis across the cell membrane between the cell interior and its environment.
Cell membranes
The plasma membrane of a cell is semi-permeable, which means it allowed the entry of certain molecules in or out, it lets small molecules pass through, but blocks larger molecules,. The membrane also has ports or gateways which get certain macromolecules through. This is active transport, which uses energy and is selective. It is outermost covering of the animal cell. It is made up of proteins and lipids.
Description
Osmosis is the movement of a solvent across a semipermeable membrane toward a higher concentration of solute. In biological systems, the solvent is typically water, but osmosis can occur in other liquids and even gases.
When a cell is submerged in water, the water molecules pass through the cell membrane from an area of low solute concentration to high solute concentration. For example, if the cell is submerged in saltwater, water molecules move out of the cell. If a cell is submerged in freshwater, water molecules move into the cell.
When the membrane has a volume of pure water on both sides, water molecules pass in and out in each direction at exactly the same rate. There is no net flow of water through the membrane.
Osmosis can be demonstrated when potato slices are added to a high salt solution. The water from inside the potato moves out to the solution, causing the potato to shrink and to lose its 'turgor pressure'. The more concentrated the salt solution, the bigger the loss in size and weight of the potato slice.
Chemical gardens demonstrate the effect of osmosis in inorganic chemistry.
Role in living things
Osmotic pressure is the main agent of support in many plants. The osmotic entry of water raises the turgor pressure exerted against the cell wall, until it equals the osmotic pressure, creating a steady state.
When a plant cell is placed in a solution that is hypertonic relative to the cytoplasm, water moves out of the cell and the cell shrinks. In doing so, the cell becomes flaccid. In extreme cases, the cell becomes plasmolyzed – the cell membrane disengages with the cell wall due to lack of water pressure on it.
When a plant cell is placed in a solution that is hypotonic relative to the cytoplasm, water moves into the cell and the cell swells to become turgid.
Osmosis is responsible for the ability of plant roots to draw water from the soil. Plants concentrate solutes in their root cells by active transport, and water enters the roots by osmosis. Osmosis is also responsible for controlling the movement of guard cells.
Osmosis also plays a vital role in human cells by facilitating the movement of water across cell membranes. This process is crucial for maintaining proper cell hydration, as cells can be sensitive to dehydration or overhydration. In human cells, osmosis is essential for maintaining the balance of water and solutes, ensuring optimal cellular function. Imbalances in osmotic pressure can lead to cellular dysfunction, highlighting the importance of osmosis in sustaining the health and integrity of human cells.
In unusual environments, osmosis can be very harmful to organisms. For example, freshwater and saltwater aquarium fish placed in water of a different salinity than that to which they are adapted to will die quickly, and in the case of saltwater fish, dramatically.
Related pages
Images for kids
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The "endosmometer" invented by Dutrochet
See also
In Spanish: Ósmosis para niños
