Transportation in Plants: Meaning and Definition, Xylem and Phloem (For CBSE, ICSE, IAS, NET, NRA 2022)

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Meaning and Definition of Transportation

  • The process involving the movement of water along with necessary nutrients to all parts of the plant for its survival.
  • Transportation involves transporting water, minerals, and food to all parts of the plant body.
  • It is a vital process in plants.
  • Xylem and Phloem act as the circulatory system that transports blood throughout the human body.
Transportation in Plants

Xylem

  • The water and mineral salts from the roots up to other parts of the plant is carried out by Xylem.
  • Lignin is the woody material having tough walls.
  • Transpiration stream is the process involved.
  • Mature xylem consists of:
    • Elongated dead cells.
    • Arranged end to end to form continuous vessels (tubes) .
    • There is no cytoplasm and are impermeable to water.
  • Xylem provides mechanical support.
  • It is in the center of the vascular bundle, deep in the plant.
  • Dead cells are the only (parenchyma is the only living cells present in the xylem) .

Phloem

  • It is responsible for transporting sucrose and amino acids.
  • This transportation occurs between the leaves and other parts of the plant.
  • Translocation is the process involved.
  • It consists of living cells arranged end to end.
  • It contains cytoplasm which goes through holes from one cell to the next.
  • They contain living cells (fibers are the only dead cells in the phloem) .
  • It doesn՚t provide mechanical support.

Transportation Occurs in Three Levels

  • Substance transportation from cell to another.
  • Within phloem and xylem, there is a long-distance transportation of sap.
  • Solute and water release along with uptake by individual cells.

Means of Transportation in Plants

Diffusion Facilitated Diffusion Active Transport

Diffusion

  • There is a passive movement of a substance from cell-to-cell or from one plant part to the cell.
  • Movement of molecules is in a random manner and it is a slow process.
  • The movement of substance is from higher concentration to lower concentration region.
  • The rate of diffusion depends on:
    • Temperature
    • Pressure
    • A gradient of concentration.

Facilitated Diffusion

  • It is a passive process that comprises antiport, uniport, and symport.
  • As compared to larger substances a smaller substance must be diffused faster.
  • The uniport protein carries single solute across the membrane.
  • The Symport proteins transfer two different solutes simultaneously in the same direction.

Active Transport

  • The energy of ATP is used to drive the pump.
  • A phosphate to a gateway molecule is donated which is responsible for pumping the desired molecule across the membrane.