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Transport in and out of cells
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understand what is meant by passive transport (diffusion, facilitated diffusion), active transport (including the role of ATP as an immediate source of energy), endocytosis and exocytosis understand the involvement of carrier and channel proteins in membrane transport

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  • September 25, 2024
  • 2
  • 2024/2025
  • Class notes
  • Gu
  • All classes

Subjects

  • biology
  • transport
  • a level biology
  • cell transport

Written for

  • A/AS Level
  • PEARSON (PEARSON)
  • Biology
  • 9BN0 (9BN0)
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diffusion of water - osmosis
● water diffuses through the partially permeable membrane through tiny spaces in the
phospholipid bilayer and specialised channel proteins called porins


osmosis
● the movement of water molecules from a more dilute solution to a more concentrated
solution through a partially permeable membrane
○ osmosis will continue until the solutions either side of the membrane are
isotonic


water potential and osmotic pressure
● water potential is a measure of the tendency of water to pass from one place to
another
● water potential (Ψ) is measured in Pascals (Pa) or kilopascals (kPa)
● pure water has the highest water potential as the molecules have the greatest
freedom to move
○ pure water has a water potential of zero
● therefore more concentrated solutions (molecules have less freedom to move) have
more negative numbers




diffusion (passive)
● higher concentration to lower concentration
● small, non-polar particles can diffuse through the phospholipid diagram (e.g.,
oxygen)
● some polar molecules (like carbon dioxide) are able to pass through due to their
small size
○ typically polar molecules will not diffuse through the phospholipid bilayer


facilitated diffusion (still passive)
● larger, polar particles cannot pass through the phospholipids
● the hydrophobic tails of the bilayer provide a barrier to hydrophilic molecules
● therefore proteins are needed

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