Notes on xylem: features, definition and adaptations

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Definition of Xylem

Xylem is a plant transport tissue that carries water from the roots to the rest of the plant

  • sieve tube elements
  • companion cells
  • Living parenchyma cells
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Xylem Vessels

- Are long cells with thick walls that are impregnated with lignin

- As the cell develops, the lignin waterproofs the walls of cells

  •  As a result, cells die and their end walls and contents decay
  • = dead cells with no contents
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- Strengthens vessel walls

- Prevents vessel from collapsing

  • This keeps vessels open even at times when water may be in short supply
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Lignin Thickening

- Ligning thickening forms patterns in the cell wall

- Patterns may be:

  • spiral
  • annular (rings)
  • reticulate (network of broken rings)

- This prevents the vessel from being too rigid and allows flexibility of the stem or branch

- In some places, ligninfication incomplete

  • leaves pores in wall of vessel, called pits or bordered pits
  • These allow water to leave one vessel and pass into another adjacent vessel, or pass into the living parts of plant
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Adaptations of xylem to its function

Xylem tissue can carry water and minerals from roots to the very top of plant because:

  • made from dead cells- forming continuous column
  • narrow tubes- water column does not break easily and capillary action effective
  • pits in lignified pools- allow water to move sideways from one vessel to another
  • patterns with deposited lignin- xylem can stretch as grows and stem can bend

Flow of water not impended because:

  • no end walls
  • no cell contents
  • no nucleus or cytoplasm
  • lignin thickening prevents walls from collapsing
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