Scientists Say: Lignin

This hardy polymer gives trees their strength

a photo of a tree is taken looking upward along the trunk, through leaves against a sunny blue sky

Trees don’t have bones — they get their strength from a polymer called lignin. This sturdy substance adds rigidity to trees and other plants. It also helps plants conduct water from their roots to their leaves.

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Lignin (noun, “LIG-nehn”)

Lignin is one of three polymers that make up the cell walls of plant cells. Polymers are chainlike substances made up of smaller, repeating molecules.

Lignin helps give plants their sturdy structure. It resists decay and adds rigidity to the walls of plant cells. The woody parts of plants contain more lignin than the leafy parts. That’s why the woody parts are tougher and more rigid. And when a tree dies, the parts that take the longest to break down are the wood and bark.

Besides structural support, lignin helps plants carry water and the nutrients in that water. Much of a plant’s xylem tissue — which slurps water from the plant’s roots to its shoots — consists of lignin. Lignin repels water, allowing the liquid to glide through the xylem’s straw-like tubes without getting stuck.

Lignin’s water-repelling and rot-defying properties stem from its molecular building blocks. Lignin consists of branching networks of smaller molecules called phenols.

Lignin can include hundreds or thousands of these phenols. Networked together, they form polymers with bulky, 3-D forms. That shape differs from other common plant polymers, such as cellulose, which typically are long and thin. Lignin’s structure allows it to fill in gaps between the other materials that make up cell walls. Filling these gaps helps to strengthen cell walls.

In a sentence

Scientists used chemistry to break lignin’s networked molecules down into their subunits and make tape adhesive.

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Katie Grace Carpenter is a science writer and curriculum developer, with degrees in biology and biogeochemistry. She also writes science fiction and creates science videos. Katie lives in the U.S. but also spends time in Sweden with her husband, who’s a chef.

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