Lignin

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Lignin

Lignin (pronounced /ˈlɪɡnɪn/) is a complex organic polymer that is found in the cell walls of many plants, giving them rigidity and resistance to decay.

Etymology

The term "lignin" comes from the Latin word lignum, meaning "wood". This is because lignin is a major component of wood and is responsible for much of its strength and durability.

Definition

Lignin is a class of complex organic polymers that form key structural materials in the support tissues of vascular plants and some algae. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity and do not rot easily.

Related Terms

  • Cellulose: Another component of plant cell walls, which is a complex carbohydrate that provides structure.
  • Polymer: A large molecule composed of many repeated subunits.
  • Vascular plants: Plants that have specialized tissues for conducting water, minerals, and photosynthetic products through the plant.
  • Algae: A simple, non-flowering, and typically aquatic plant of a large group that includes the seaweeds and many single-celled forms.

Function

Lignin fills the spaces in the cell wall between cellulose, hemicellulose, and pectin components, especially in vascular and support tissues: xylem tracheids, vessel elements and sclereid cells. It is covalently linked to hemicellulose and thereby crosslinks different plant polysaccharides, conferring mechanical strength to the cell wall and by extension the plant as a whole.

Importance

Lignin plays a crucial part in conducting water in plant stems. The polysaccharide components of plant cell walls are highly hydrophilic and thus permeable to water, whereas lignin is more hydrophobic. The crosslinking of polysaccharides by lignin is an obstacle to water absorption to the cell wall. Thus, lignin makes it possible for the plant's vascular tissue to conduct water efficiently.

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