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, S₂ & 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).