phloem

• What is the function of the phloem?

  • to transport organic compounds (assimilates), particularly sucrose, from the source (eg. leaf) to the sink (eg. roots). The transport of these compounds can occur up and down the plant
• What is the phloem made up of?

  its bulk is made up of sieve tube elements which are the main conducting cells and companion cells

  • Other cell types of phloem tissue also include parenchyma for storage and strengthening fibres
• What is the function of the sieve plates with pores?

  allows for the continuous movement of the organic compounds
• What is the function of the cellulose cell wall?

  strengthens the wall to withstand the hydrostatic pressure that move the assimilates
• Why does the phloem have no nucleus, vacuole or ribosomes in mature cells ?

  to maximise the space for translocation of the assimilates
• Why does the phloem have thin cytoplasm?

  reduces friction to facilitate the movement of the assimilates
• What do companion cells do?

  • Each sieve tube element has a companion cell associated with it as companion cells control the metabolism of their associated sieve tube member
  • They also play a role in loading and unloading of sugars into the phloem
• Why do companion cells have large numbers of mitochondria?

  to provide ATP for the active transport of assimilates into or out of the companion cells
• Plasmodesmata?

  channels in the cell wall

  allows organic compounds to move from the companion cells into the sieve tube elements
• How is the structure of the phloem related to its function?

  has sieve tube elements that transport sugars around the plants

  companion cells designed for the active transport of sugars into tubes,

  plasmodesmata allows for the flow of substances between cytoplasm of different cells
• What are plasmodesmata?

  microscopic channels through the cellulose cell walls, linking the cytoplasm of adjacent cells, thus allowing for the flow of substances