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Osmosis

Osmosis

  • Osmosis: The movement of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential.
  • Osmosis is a special type of diffusion as it only involves water particles.
  • In the context of a partially permeable membrane, water molecules move randomly in between the membrane. However, because there are more water molecules on one side than the other, there’s a steady net flow of water in the region with fewer water molecules.
  • The previously concentrated solution will become more dilute; it’s as if the water molecules are trying to even up on both sides.

Water transport

Root hair cells

  • Root hair cells are found on the surface of plant roots. They have millions of long thin extensions which reach into the surrounding soil to get all the mineral salts and water possible.
  • They take in water by osmosis. This gives the plant a big surface area for absorbing water from the soil.
  • However, they take in minerals by active transport, which is the movement of particles against the concentration gradient. They have to do this as the concentration of minerals in the soil is usually lower than the concentration in the plant.
  • Active transport requires energy from respiration.