Class 11 Biology Transport In Plants Means of transport

Means of transport


  • The movement of molecules from regions of higher concentration to regions of lower concentration is called diffusion.
  • Movement by diffusion is passive.
  • Diffusion rates are affected by the gradient of concentration, the permeability of the membrane separating them, temperature, and pressure.


Fig. Diffusion 

Facilitated diffusion

  • Facilitated diffusion is the passive transport of molecules along their concentration gradient across a biological membrane with the help of special proteins.
  • The proteins form channels in the membrane for molecules to pass through.
  • The porins are proteins that form huge pores in the membrane allowing molecules up to the size of small proteins to pass through. Example- pores in the outer membranes of the plastids, mitochondria and some bacteria.
  • Aquaporins are integral membrane proteins that form water channels, which rotate and release the extracellular molecule bound to the transport protein inside the cell.
  • Some carrier or transport proteins allow diffusion only if two types of molecules move together.


Fig. Facilitated diffusion 

  • In a symport, both molecules cross the membrane in the same direction
  • In an antiport, both the molecules move in opposite directions.
  • When a molecule moves across a membrane independent of other molecules, the process is called uniport.


Fig. Uniport, symport, antiport 

Active transport

  • The movement of molecules against a concentration gradient, from the region of lower concentration to the region of higher concentration, with the help of ATP is called active transport.
  • Active transport is an up-hill transport.


Fig. Active transport

Share these Notes with your friends  

< Prev Next >

You can check our 5-step learning process