Types of cell wall, Biology

TYPES OF CELL WALL

Cell wall differentiated into the following layers :

1. Primary Cell Wall       2. Secondary Cell wall             3. Tertiary Cell wall

1.       PRIMARY CELL WALL (10 CELL WALL)

  • The first formed cell wall is known as primary cell wall, laid inner to the middle lamella.
  • The primary cell was is comparatively thin and permeable.
  • It consists of hemicellulose 50%, cellulose 20%, lipid 20%, Protein 1-2%, water 60%
  • Macrofibrils of cellulose are randomly distributed.
  • Found in all types of plant cell (meristematic & soft parenchymatous tissues like mesophyll, cortex, pith, fruit)
  • Microfibril are loose wavy & short. Lignin, Pectin is also present.
  • The primary cell wall of the yeast & the fungi is composed of the chitin.

2.       SECONDARY CELL WALL (20 CELL WALL)

  • The secondary cell wall is thick, permeable & lies near the plasma membrane or the tertiary cell wall.
  • It is composed of 3 layers S1, S& S3 (S2= thickest and S3 thinnest layer)
  • Chemically the secondary cell wall is composed of compactely arrange macrofibrils of the cellulose, hemicellulose, pectin & lignin. Hemicellulose 25%, cellulose 20-40%, Lipid - protein = negligible amount, Hydration = 30%
  • Formed by apposition / accretion (growth occur due to accretion) intussusception
  • To have a uniform thickness Intussusception method is better than apposition.
  • Thickness 3-10 mm, uniform thickness absent.
  • At places the thickning is absent it form pits.
  • It collenchyma it provides elasticity & allow for limited growth.
  • Macrofibrils arranged in a regular pattern (parallel to long axis)
  • Present in Sclerenchyma, Vessels, Tracheids. Absent in Meristem.
  • Thickening is of purely cellulose in collenchyma cells, cotton fibres, flax fibres.

3.       TERTIARY CELL WALL

  • In certain plant cells another cell wall found beneath the secondary cell wall which is known as tertiary cell wall.
  • It consists of xylan and hemicellulose. (Xylan is the polymer of xylulose.)
  • Tertiary cell wall found in tracheids of gymnosperms (Tension wood).

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Posted Date: 10/5/2012 4:40:32 AM | Location : United States







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