Lignin is a complex organic polymer found in the cell walls of plants, especially in wood and bark. It provides structural support, helping plants stand upright and resist decay. Lignin is what makes trees strong and durable, allowing them to grow tall and withstand harsh weather conditions. In addition to its structural role, lignin plays a part in the plant's defense against pests and diseases. When plants are damaged, lignin can help seal wounds and prevent the entry of harmful organisms. This makes lignin an important component in the overall health and longevity of plants.