Lesson 2: Wood: Decay, Pests, and Photodegradation

How do microscopic organisms like fungi and macroscopic pests like termites turn a solid structural beam into a safety hazard?

Why does sunlight, which seems harmless, physically break down the "glue" that holds wood fibers together?

How can environmental conditions like moisture and heat accelerate these degradation processes?

Lignin: The natural "glue" that binds wood fibers together; it is the primary target of UV photodegradation.
Fungal Decay: The breakdown of wood cells by secreted enzymes from brown, white, or soft rot fungi.
Cellulose: The organic compound that provides structural strength to wood, which termites consume as food.
Photodegradation: The chemical alteration of wood surfaces caused by UV radiation, leading to graying and cracking.
Warping/Discoloration: Early physical signs of moisture-induced wood degradation.

HS-PS1-2: Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.

HS-LS2-3: Construct and revise an explanation based on evidence for the cycling of matter and flow of energy in aerobic and anaerobic conditions (relevant to fungal rot).

HS-ETS1-3: Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics.

Scientific Analysis: Identifying independent and dependent variables in wood degradation experiments (e.g., moisture level vs. rate of decay).

Synthesis of Technical Texts: Comparing different modes of material failure (biological vs. chemical) to determine the best preventative measures.

Description
Day 1: The Fungal and Moisture Threat. Focus on how rainwater saturates wood, causing swelling, shrinking, and leaching of preservatives. Students will explore the three main types of rot (brown, white, and soft) and how they drastically reduce structural strength.
Day 2: Insect Infestation and Structural Hollowing. Investigation into wood-boring pests. Students will analyze the differences between termite damage (inside-out hollowing), carpenter ant tunneling, and powderpost beetle boring.
Day 3: Sunlight and Prevention. A study of UV photodegradation and "The Silent Threat" of surface cracking. The lesson concludes with engineering methods to prevent failure, such as waterproof coatings, regular maintenance, and moisture-resistant material choice.


Purpose
To provide students with a deep understanding of why wood, while a versatile building material, requires constant environmental protection and inspection to prevent catastrophic failures like deck, balcony, or roof collapses.

DOK Level
Level 2: Skill/Concept (Differentiating between types of rot and insect damage).
Level 3: Strategic Thinking (Analyzing how moisture acts as a catalyst for multiple types of wood failure simultaneously).

Real-World Connections
2007 UK Floods: Analyzing how wood soaked in water for extended periods lost its structural support and rotted.
Historic Preservation: Investigating why old wooden structures gray and crack over time when exposed to the elements.

Culturally Relevant Connections
Regional Pests: Discussing how termite types and prevalence differ by geography (e.g., Formosan termites in the South vs. local varieties).
Tropical Resilience: Evaluating traditional building methods in high-humidity environments (like the Caribbean) to combat moisture-induced rot.

Misconception: "Wood rot is just a cosmetic issue." Correction: Fungal enzymes physically dismantle wood cells, leading to a complete loss of load-bearing capacity and potential collapse.

Misconception: "Pressure-treated wood is immune to all damage." Correction: While resistant, moisture can still cause swelling/shrinking, and UV light still breaks down lignin.

Scaffolded Lab: Provide a "Signs of Decay" checklist for students to use when inspecting local wood samples.

Visual Aids: Compare high-magnification images of healthy wood cells vs. wood cells destroyed by fungal enzymes.

Project Choice: Students can choose to research a specific pest or a specific protective coating (e.g., stains, sealants).

Failure Analysis Report: Students are given a scenario of a collapsed balcony and must determine if the cause was likely rot, pests, or UV-induced surface failure based on physical evidence.

Prevention Plan: Design a 10-year maintenance schedule for a standard wooden deck to prevent the three main types of degradation.

Presentation: "Wood Degradation Over Time."

Technical Text: "Identification and Analysis of Factors contributing to Construction Material Deterioration."

Case Study: "Impact of the 2007 UK Floods on Wooden Infrastructure."

Speaker: An arborist or a professional pest control inspector focusing on structural damage.