What is lignin in biology?

All vascular plants possess lignin in their cells, cell walls, and intercellular spaces. Lignin is what provides food its fiber content, giving vegetables their delicious crunch and giving trees their woody appearance. The word "lignin" is very self-explanatory since it derives from the Latin word for "wood". Lignin helps plants stay upright by strengthening the cell walls and preventing them from collapsing, which is essential for the transportation of liquids throughout the plant (just think of trees). Lignin enables waste to be transported out of the plant and permits liquids to climb up the plant.

• Structure: A few different precursors of lignols were used to create the very heterogeneous polymers that make up lignin. The variety and strength of crosslinking between these lignols give rise to heterogeneity. Coniferyl alcohol sinapyl alcohol and paracoumaryl alcohol are the three main types of lignols that crosslink each other to form lignin.
• Function: It provides support to vascular plants as it is present in tissues, such as xylem tracheids, vessel elements, and sclereid cells. Lignin fills the voids in the cell wall between cellulose, hemicellulose, and pectin components.

In plant stems, lignin is an essential component of the water and aqueous nutrition transport system. Lignin is more hydrophobic in nature, whereas polysaccharide components of plant cell walls are very hydrophilic and so it is permeable to water. Lignin's ability to crosslink polysaccharides prevents the cell wall from absorbing water. Therefore, lignin enables the plant's vascular tissue to transmit water effectively. All vascular plants contain lignin, while bryophytes do not, supporting the concept that lignin's initial use was limited to water transport.

Since it is covalently connected to hemicellulose, it crosslinks.