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An isotonic solution refers to two solutions having the same osmotic pressure across a semipermeable membrane. This state allows for the free movement of water across the membrane without changing the concentration of solutes on either side.



having a higher osmotic pressure than a particular fluid, typically a body fluid or intracellular fluid.



Diffusion is the net passive movement of particles (atoms, ions or molecules) from a region in which they are in higher concentration to regions of lower concentration. It continues until the concentration of substances is uniform throughout.


Partially permeable membrane

partially permeable membrane A membrane that is permeable to the small molecules of water and certain solutes but does not allow the passage of large solute molecules. This term is preferred to semipermeable membrane when describing membranes in living organisms.



Osmosis is the movement of water molecules through a selectively permeable membrane from higher water concentration to a lower water concentration - or - down a concentration gradient.



having a lower osmotic pressure than a particular fluid, typically a body fluid or intracellular fluid.


Gas exchange

The primary function of the lungs involving the transfer of oxygen from inhaled air into the blood and the transfer of carbon dioxide from the blood into the exhaled air.


Active transport

the movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy.



Simple organisms, such as the amoeba and earthworm, have a moist, permeable external surface. Oxygen can pass into them through this surface by diffusion. A large surface area is needed for effective gas exchange - so larger, more complex, organisms have special organs such as gills and lungs.



Exchanges in the roots. The role of the roots is to absorb water from the soil by osmosis and dissolve mineral ions from the soil by active transport. ... Root hair cells have several adaptations: the tube-like protrusion provides a greater surface area across which water and mineral ions can be exchanged.

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