Introduction to transport in plants

• what is transport like in plants?

  • generally passive - water moves up stem by transpiration (driven by evaporation of water from leaf by sun)
  • water moves into roots due to water potential gradient
• why do plants need a transport system to meet their metabolic demands?

  • green parts of plants make their own glucose and oxygen by photosynthesis - but many internal and underground parts of plants do not photosynthesise
  • they need oxygen and glucose transported to them and the waste products of cell metabolism removed
  • hormones made in one part of a plant need transporting to the areas where they have an effect
  • mineral ions absorbed by the roots need to be transported to all cells to make the proteins required for enzymes and the structure of the cell
• why do plants need a transport system depending on their size?

  • plants need very effective transport systems to move substances both up and down from the tip of the roots to the topmost leaves and stems
• why do plants need a transport system due to their surface area to volume ratio?

  • leaves are adapted to have a relatively large SA:V ratio for the exchange of gases with the air
  • the size and complexity of multicellular plants means that when the stems, trunks, and roots are taken into account they still have a relatively small SA:V ratio
  • they cannot rely on diffusion alone to supply their cells with everything they need