Pits, Biology


  • Depressions in secondary cell wall is called pit.
  • A pit present on the free cell wall surface without its partner is called Blind pit.
  • It consists of 2 parts - Pit chamber and Pit membrane.
  • Pit chamber / pit cavity is depression in wall where secondary wall is absent.
  • Opening of pit chamber into cell is called pit pore / aperture.
  • Pit membrane is formed of (PCW + middle lamella + PCW) it is "trilaminar".
  • Pit membrane also called closing membrane.
  • Pit membrane is permeable due to permeability of primary cell wall.
  • Pits are of 2 types (depending upon the shape of the pit chamber.)


(i) Simple pit

  • Pit chamber has uniform width.
  • Diameter of lumen remains the same.
  • Found in vessels, tracheids & sclerenchyma.

(ii) Bordered pit

  • Pit chamber is flask-shaped.
  • Diameter of lumen is increases from inner to outer side.
  • A disc-shaped thickening called Torus is present in the middle of pit chamber on pit membrane.
  • It controls diffusion, it prevents rupturing of pit membrane when unequal pressure is present on its both sides.

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Posted Date: 10/5/2012 6:03:42 AM | Location : United States

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