Types of Transport


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•  Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport

Cellular membranes possess two key qualities:

  • They are semi-permeable (only certain materials may freely cross – large and charged substances are typically blocked)
  • They are selective (membrane proteins may regulate the passage of material that cannot freely cross)

Movement of materials across a biological membrane may occur either actively or passively

Passive Transport

Passive transport involves the movement of material along a concentration gradient (high concentration  low concentration)

Because materials are moving down a concentration gradient, it does not require the expenditure of energy (ATP hydrolysis)

There are three main types of passive transport:

  • Simple diffusion – movement of small or lipophilic molecules (e.g. O2, CO2, etc.)
  • Osmosis – movement of water molecules (dependent on solute concentrations)
  • Facilitated diffusion – movement of large or charged molecules via membrane proteins (e.g. ions, sucrose, etc.)

Active Transport

Active transport involves the movement of materials against a concentration gradient (low concentration  high concentration)

Because materials are moving against the gradient, it requires the expenditure of energy (e.g. ATP hydrolysis)

There are two main types of active transport:

  • Primary (direct) active transport – Involves the direct use of metabolic energy (e.g. ATP hydrolysis) to mediate transport
  • Secondary (indirect) active transport – Involves coupling the molecule with another moving along an electrochemical gradient

Types of Membrane Transport

types of transport