Ace the Certified Arborist Test 2026 – Branch Out and Leaf Your Mark!

The reason cellulose and lignin are indigestible to many insects and some pathogens lies in their structural complexity and robust nature. Cellulose is a polysaccharide made up of long chains of glucose molecules, forming a strong, fibrous structure that provides rigidity and strength to plant cell walls. Lignin, on the other hand, is a complex organic polymer found in the secondary cell walls of many plants, providing additional structural support and contributing to the waterproofing and durability of the plant tissues.

Insects and pathogens often lack the necessary enzymes to break down these compounds effectively. Many herbivorous insects, while able to digest other simpler carbohydrates, do not have the enzymes required to degrade cellulose efficiently. Similarly, the lignin structure is highly resistant to microbial degradation, making it difficult for pathogens to access the nutrients within the plant cells. Therefore, these components play a crucial role in protecting trees from herbivory and disease.

The other choices do not accurately represent the indigestible nature of tree cells. Xylem and phloem are vascular tissues crucial for transporting water, nutrients, and sugars but are not characterized by indigestibility in the same way. Chloroplasts and mitochondria are organelles involved in photosynthesis and energy production,