Osmosis
The movement of water molecules across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration. is the The movement of molecules from an area of higher concentration to an area of lower concentration. of water A collection of two or more atoms held together by chemical bonds., from a region where they are in higher The concentration of a solution tells us how much of a substance is dissolved in water. The higher the concentration, the more particles of the substance are present., to a region where they are in lower concentration, through a Also called semi-permeable. A partially permeable membrane allows water and other small molecules to pass through, but not larger molecules such as starch. membrane.
A dilute Mixture formed by a solute and a solvent. contains a high concentration of water molecules, while a concentrated solution contains a low concentration of water molecules.
The slideshow shows an example of osmosis showing the direction of movement of water between two different concentrations of sugar solutions:
Image caption, Water molecules move from solution 1 to solution 2 by osmosis
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When the concentration of water is the same on both sides of the membrane, the movement of water molecules will be the same in both directions. There will be no The overall effect of something when all additions and deductions are calculated. movement of water molecules.
Similar observations will be made with solutions containing different The dissolved substance in a solution., for instance, salt instead of sugar.
Osmosis across living cells
Cells contain dilute solutions of Electrically charged particle, formed when an atom or molecule gains or loses electrons., sugars and The building blocks that make up a protein molecule.. The cell membrane is partially permeable. Water will move into and out of cells by osmosis.
Plant cells
Isolated plant cells placed in a dilute solution or water will take in water by The movement of water molecules across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration.. If the soil is wet or moist then A specialised cell that increases the surface area of the root epidermis to improve the uptake of water and minerals. will also take up water by osmosis. Leaf cells of land plants, unless it is raining or the The amount of water vapour in the atmosphere measured as a percentage. is high, will have a tendency to lose water.
Plant cells have a strong A carbohydrate. It forms the cell wall in plant cells. Outer structure which provides support and prevents the cell from bursting from the uptake of water by osmosis. Plant, fungal and bacterial cell walls have different structures and chemical compositions. outside the A selectively permeable membrane surrounding the cell and controlling the entry and exit of materials.. The cell wall is fully permeable to all molecules. It supports the cell and stops it bursting when it gains water by osmosis.
Under normal circumstances, the cells in all organisms live in a safe equilibrium. They have enough water to live but not too much. They also have the correct amount of salts and sugars. If individual cells are placed in different solutions, we can see how important it is that equilibrium is maintained in living organisms.
Pure water
In pure water, the cell contents push against the Outer structure which provides support and prevents the cell from bursting from the uptake of water by osmosis. Plant, fungal and bacterial cell walls have different structures and chemical compositions. and the cell becomes Enlarged and swollen with water. Having turgor. Description of a plant cell in which the vacuole has swollen due to water gain by osmosis.. Fully turgid cells support the stems of non-woody plants.
Concentrated solution
In a more concentrated solution, the cell contents lose water by osmosis and the cells shrink. The cell membrance starts to pull away from the cell wall. The cell becomes Soft and floppy..
Highly concentrated solution
In a very concentrated solution, the cell membrane pulls away from the cell wall completely; this is plasmolysis.
Animal cells
Animal cells also take in and lose water by osmosis. They do not have a cell wall, so will change size and shape when put into solutions that are at a different concentration to the cell contents.
For example, red blood cells:
In animals, the concentration of body fluids, The liquid part of the blood containing useful things like glucose, amino acids, minerals, vitamins (nutrients) and hormones, as well as waste materials such as urea. and Fluid which is derived from blood plasma that passes through the walls of capillaries. must be kept within strict limits. If cells lose or gain too much water by osmosis, they do not function efficiently.