Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: First Term
Week: 10
Age: 15 years
Duration: 45 minutes
Subject: Wood Work
Curriculum Theme: Vocational Studies
Previous Lesson: Determination of Moisture Content in Timber.
Topic: PROPERTIES OF TIMBER AND CHEMICAL COMPOSITION
Subject Matter: properties of timber, types of wood cells, chemical composition of wood, seasoning terms

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Define timber and list its key properties.
Identify and describe different types of wood cells.
State the main chemical components of wood.
Explain common terms related to timber seasoning.

Affective Domain:

Appreciate the importance of understanding timber properties in woodworking.
Show interest in the processes of wood treatment and preparation.

Psychomotor Domain:

Distinguish between different timber samples based on observable properties.
Sketch basic representations of wood cell structures.

Participate in group discussions about the uses and characteristics of various timber types.

Reference Materials

The following resources were used in planning this lesson:

Senior Secondary Education Curriculum for Wood Work.
State Unified Scheme of Work for Senior Secondary Schools.
Ugonabo, L. N. (2018). Comprehensive Wood Work for Senior Secondary Schools. Abuja: Learn Africa Plc.

Instructional Materials

The teacher will teach this lesson with the aid of:

Charts showing different timber properties.
Charts illustrating types of wood cells.
Samples of different timber species.
A hydrometer (for demonstrating moisture content principles).

Rationale for the Lesson

Understanding the properties and composition of timber helps pupils select the right type of wood for specific projects and ensures proper handling and storage. This knowledge is important for producing durable and high-quality woodwork items and for career paths in carpentry and construction.

Prerequisite/Previous Knowledge

Pupils should have prior knowledge of different types of wood and basic woodworking tools from previous lessons.

Lesson Content/Board Summary

PROPERTIES OF TIMBER AND CHEMICAL COMPOSITION

Properties of Timber

Timber is wood that has been prepared for use in construction or carpentry. Its properties determine its suitability for various applications.

The properties of timber are generally divided into physical and mechanical properties:

Physical Properties: These include colour, lustre, grain, texture, smell, density, moisture content, shrinkage, swelling, and thermal expansion.
Mechanical Properties: These relate to the timber’s strength and resistance to external forces, such as hardness, stiffness, elasticity, tensile strength, compressive strength, and shear strength.

Types of Wood Cells

Wood is made up of various types of cells, which contribute to its structure and properties.

The main types of wood cells include:

Tracheids: Long, narrow cells that provide support and transport water in softwoods.
Vessels (Pores): Larger, wider cells that efficiently transport water in hardwoods.
Parenchyma Cells: Storage cells found in rays and axial systems, storing food reserves.
Fibres: Thick-walled, elongated cells that provide strength and support in hardwoods.

Chemical Composition of Wood

Wood is primarily composed of organic polymers.

The main chemical components of wood are:

Cellulose: The most abundant component, a complex carbohydrate forming the primary structural material of cell walls (about 40-50%).
Hemicellulose: A group of branched polysaccharides that bind cellulose fibres together (about 15-25%).
Lignin: A complex polymer that provides rigidity and strength to the cell walls, acting as a binding agent (about 15-30%).
Extractives: Non-structural components such as resins, fats, waxes, tannins, and dyes, which contribute to wood’s colour, odour, and natural durability (about 5-10%).

Seasoning Terms

Seasoning is the process of drying timber to reduce its moisture content, which improves its stability and strength.

Important terms related to seasoning include:

Seasoning: The controlled removal of moisture from timber.
Moisture Content (MC): The amount of water present in timber, expressed as a percentage of its dry weight.
Fibre Saturation Point (FSP): The stage where all free water has left the cell cavities, but the cell walls are still saturated with bound water (typically around 25-30% MC).
Air Seasoning: A natural method of drying timber by exposing it to the air in a controlled stack.
Kiln Seasoning: An artificial method of drying timber in a controlled environment (kiln) using heat and humidity to speed up the process.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and asks them to mention different types of wood they know and where they are used. The teacher then introduces the topic, “Properties of Timber and Chemical Composition,” explaining that understanding wood’s characteristics is important for woodworking.
Pupils’ Activity: Pupils respond to the questions and listen attentively to the introduction.
Learning Point: Pupils are prepared for the lesson and understand its relevance.

Step 2: Presentation of Properties of Timber

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher displays charts showing various timber properties and uses actual timber samples to demonstrate physical properties like grain, texture, and density (by lifting different samples). The teacher explains both physical and mechanical properties of timber.
Pupils’ Activity: Pupils observe the charts and samples, listen to the explanations, and ask questions for clarification.
Learning Point: Pupils learn about the different properties of timber.

Step 3: Discussion on Types of Wood Cells

Time: 8 minutes
Teaching Skill: Explaining/Illustrating
Teacher’s Activity: The teacher uses a chart showing microscopic views of wood cells (tracheids, vessels, parenchyma, fibres) and explains the function of each cell type in softwoods and hardwoods. The teacher guides pupils to understand how cell structure influences timber properties.
Pupils’ Activity: Pupils observe the charts, listen to the explanations, and try to sketch simple cell structures if guided.
Learning Point: Pupils understand the cellular structure of wood.

Step 4: Explanation of Chemical Composition of Wood

Time: 7 minutes
Teaching Skill: Lecture/Questioning
Teacher’s Activity: The teacher explains the main chemical components of wood: cellulose, hemicellulose, lignin, and extractives. The teacher describes the role of each component in the wood’s structure and characteristics.
Pupils’ Activity: Pupils listen, take notes, and ask questions about the chemical components.
Learning Point: Pupils know the basic chemical make-up of timber.

Step 5: Elaboration on Seasoning Terms

Time: 7 minutes
Teaching Skill: Definition/Clarification
Teacher’s Activity: The teacher defines seasoning and explains its importance. The teacher then explains key terms such as moisture content, fibre saturation point, air seasoning, and kiln seasoning, showing how a hydrometer can be used to measure moisture content.
Pupils’ Activity: Pupils listen to definitions, understand the seasoning processes, and observe the hydrometer.
Learning Point: Pupils understand the purpose and methods of timber seasoning.

Step 6: Class Discussion/Activity

Time: 3 minutes
Teaching Skill: Group Discussion/Application
Teacher’s Activity: The teacher divides pupils into small groups and asks them to discuss why a carpenter needs to understand timber properties before starting a project. The teacher monitors and provides guidance.
Pupils’ Activity: Pupils discuss in groups and share their conclusions with the class.
Learning Point: Pupils apply their knowledge to practical scenarios.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define timber and list three of its physical properties.
Mention two types of wood cells and their functions.
State the three main chemical components of wood.
Explain the meaning of “seasoning” in woodworking.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 0 minutes
Teaching Skill: Summarization/Homework Assignment
Teacher’s Activity: The teacher summarizes the main points of the lesson, reinforcing the importance of timber properties, composition, and seasoning. The teacher assigns homework: “Research and write a short note on the advantages and disadvantages of air seasoning compared to kiln seasoning.”
Pupils’ Activity: Pupils listen to the summary and copy down the homework.
Learning Point: Pupils consolidate their learning and prepare for further study.

Lesson Keywords

Timber – Wood prepared for use in construction or carpentry.
Physical Properties – Characteristics like colour, density, grain, and texture.
Mechanical Properties – Characteristics like strength, hardness, and stiffness.
Wood Cells – Microscopic structures like tracheids, vessels, parenchyma, and fibres.
Cellulose – The main structural component of wood.
Lignin – The binding agent that provides rigidity to wood.
Seasoning – The process of drying timber to reduce its moisture content.
Moisture Content – The amount of water in timber, expressed as a percentage.
Fibre Saturation Point – The point where cell walls are saturated but no free water remains.

Differentiation

For pupils who grasp concepts quickly, the teacher can encourage them to research specific timber species and their unique properties. For pupils needing more support, the teacher can provide simplified diagrams of wood cells and a glossary of terms, offering individual guidance during activities.

Note for teachers using this lesson plan

Ensure that actual timber samples are available for pupils to touch and observe to enhance their understanding of physical properties. The hydrometer demonstration should be clear, explaining its purpose even if a working model is not available for individual pupil use. Encourage pupils to ask questions and relate the lesson to real-world applications of wood.