Certified Arborist Practice Exam

Which tree cells are indigestible to many insects and some pathogens?

1. Phloem and Xylem

2. Cambium and Cork

3. Epidermis and Cortex

4. Cellulose and Lignin

The correct answer is: Cellulose and Lignin

Cellulose and lignin are indeed the correct answer when discussing tree cells that are indigestible to many insects and some pathogens. These two components are fundamental structural elements of plant cell walls. Cellulose is a complex carbohydrate that forms the primary structure of the cell walls, providing rigidity and strength, while lignin is a complex polymer that adds additional hardness and resistance to decay. Insects and certain pathogens often struggle with breaking down cellulose and lignin due to their complex structures. Many insects have evolved specific enzymes to digest cellulose, but the efficiency of this process can vary significantly between species. Pathogens like fungi can degrade cellulose, but lignin is much more challenging for them to break down, which limits their ability to attack and decompose woody tissues. Understanding these components is essential for an arborist, as they play a significant role in the overall health and longevity of trees, influencing how trees respond to damage, disease, and the presence of pests.