Final answer:
Lignin in trees provides high compressive strength, enabling them to reach tall heights and withstand mechanical forces, like wind. It also waterproofs and protects vascular tissues, contributing to the tree's longevity and protection from decay and predators.
Step-by-step explanation:
Lignin is a crucial component that allows trees and other vascular plants to grow tall and withstand the force of gravity. Forming part of the secondary cell wall, lignin is a complex polymer with phenolic subunits, providing plants with high compressive strength. As trees grow, the lignin lays down inside the primary cell wall, creating rigid structures that are incompressible. This rigidity prevents cells from expanding, which is why it appears after the cell stops growing. Notably, lignin is also hydrophobic and aids in waterproofing tissues, making vascular transport more efficient.
Lignin's structural role is like the rebar in reinforced concrete, offering both tensile and compressive strength to a tree's trunk, enabling it to resist various mechanical forces such as those from wind. This function allows trees to reach great heights, access unfiltered sunlight, and increase their evolutionary success by outcompeting shorter plants. Moreover, due to the strength and resistance to degradation, lignin contributes to wood's longevity and the survival of the species over time. The natural resistance of lignin to being broken down by most organisms also protects plants from herbivores and pathogens, further enhancing its protective role.