aqa BIOL2 PLANTS

XYKE

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  • Created by: melissa
  • Created on: 16-04-12 17:30

Xylem

The majority of water in a plant is transported up the xylem

  • thick muscular wall
  • as they mature,waterproof lignin is produced and cells die
  • the end walls break down which allows the cell to form a continuous tube

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Xylem

How is the xylem cell adapted for its function?

function= water transport from the roots

  • total lack of cell contents
    • nothing to stop the flow of water
  • No end walls
    • unimpeded water flow
  • a diameter of between 0.001 and 0.2 mm
    • water will rise by capillary action
  • lignified walls
    • waterproof
  • pits
    • allow water to move out to go to other cells
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Root

Water movement across a root

Pure water enters by osmosis

2 pathways:

appoplast: non-living part of the cell- cellulose cell wall

symplast: living part of the cell- cytoplasm

appoplast pathway

appoplast pathway

  • water is pulled along due to the cohesive properties of water
  • water molecules form hydrogen bonds between one another and thus stick together (cohesive force)
  • when the water reaches the endodermis, it comes across a water repellent substance called suberin in the walls of the endermal cells.
  • This strip is called the casparian strip.
  • The water molecules are then forced to enter the cytoplasm of the endodermal cell as it is the only root to the xylem

The significance of this:

  • water and minerals must pass through the cell membrane and therefore is under control of the living cell
  • it could also be a protective measure against the entry to pathogens
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