Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 1st Term
Week: 5
Age: 15 years
Duration: 45 minutes
Subject: Wood Work
Curriculum Theme: Vocational Studies
Previous Lesson: West African Timber Types and Uses.
Topic: STRUCTURE OF WOOD CELLS AND TIMBER CHARACTERISTICS
Subject Matter: structure of wood cells, timber sources, timber characteristics, timber growth

Specific Objectives

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

Cognitive Domain:

Define a wood cell.
Describe the basic structure of wood cells.
Identify various sources of timber.
State the key characteristics of timber.
Explain the process of timber growth.

Affective Domain:

Appreciate the natural process of timber growth.
Value the importance of understanding timber characteristics for proper selection and use.

Psychomotor Domain:

Identify components of a wood cell on a diagram or chart.
Distinguish between different types of timber based on their characteristics.

Participate actively in class discussions about timber properties.
Collaborate with peers to identify different timber types.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Wood Work (Senior Secondary Education)
State Unified Scheme of Work for Wood Work SSS 1
Wood Work for Senior Secondary Schools by E.A. Adenuga and O.J. Olawore

Instructional Materials

The teacher will teach this lesson with the aid of:

Charts showing the structure of wood cells.
Posters illustrating different timber sources and types.
Samples of different timber types (e.g., Iroko, Mahogany, Pine).

Rationale for the Lesson

This lesson helps pupils understand the fundamental structure of wood and how trees grow into timber. Knowing timber characteristics enables them to select the right type of wood for various projects and appreciate its properties in daily life.

Prerequisite/Previous Knowledge

Pupils are expected to have basic knowledge of trees and their uses from their earlier primary and junior secondary classes.

Lesson Content/Board Summary

STRUCTURE OF WOOD CELLS AND TIMBER CHARACTERISTICS

1. Structure of Wood Cells

Wood is made up of millions of tiny cells. These cells are mostly elongated and arranged parallel to the trunk’s axis. The primary components include the cell wall and the lumen (the hollow space within the cell).

The growth of wood occurs through cell division in the cambium layer, leading to the formation of annual rings.

2. Timber Growth

Timber grows from trees through a process involving several layers:

Bark: The outermost protective layer.
Cambium Layer: A thin layer beneath the bark where new wood and bark cells are produced, causing the tree to grow in girth.
Sapwood: The living wood nearest the bark, responsible for transporting water and nutrients.
Heartwood: The older, inactive, and usually darker central wood, which provides structural support.
Pith: The small, soft core at the centre of the tree.
Annual Rings: Concentric rings formed each year due to seasonal growth, indicating the age of the tree.

3. Timber Sources

Timber is wood that has been processed into planks and beams for construction and other uses. It is obtained from various types of trees, broadly classified as:

Hardwoods: These come from deciduous trees (shed leaves annually) and are generally dense and durable. Examples include Iroko, Mahogany, Teak, Opepe, Oak.
Softwoods: These come from coniferous trees (evergreen, cone-bearing) and are generally lighter and easier to work with. Examples include Pine, Cedar, Spruce, Fir.

4. Timber Characteristics

The following are important characteristics of timber that influence its use and quality:

Colour: Varies greatly (e.g., light yellow, reddish-brown, dark brown) and can indicate species and age.
Grain: The pattern formed by the wood fibres, which can be straight, wavy, interlocked, or spiral.
Texture: Refers to the relative size and uniformity of the wood cells (fine, medium, coarse).
Density/Weight: The mass per unit volume. Denser timbers are generally stronger.
Hardness: Resistance to indentation or scratching.
Durability: The ability to resist decay, insect attack, and wear over time.
Strength: The ability to withstand forces such as compression, tension, and bending.
Workability: Ease with which timber can be cut, planed, nailed, and finished.
Moisture Content: The amount of water present in the wood, which affects its stability and strength.
Defects: Natural or acquired imperfections that can affect timber quality, such as knots, shakes, and warps.

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 name items in the classroom or at home that are made of wood. The teacher then introduces the topic by explaining that wood, or timber, is a natural material with a specific structure and properties.
Pupils’ Activity: Pupils respond by naming wooden items like tables, chairs, doors, and roofs.
Learning Point: Pupils are introduced to the topic and its relevance.

Step 2: Presentation of Wood Cell Structure

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher uses charts to explain the basic structure of wood cells, describing the cell wall, lumen, and how these cells are arranged. The teacher also briefly explains the role of the cambium layer in cell division and wood formation.
Pupils’ Activity: Pupils observe the charts, listen attentively, and ask questions for clarification.
Learning Point: Pupils understand the microscopic structure of wood.

Step 3: Explanation of Timber Growth

Time: 7 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher explains the process of timber growth, detailing the different layers of a tree trunk (bark, cambium, sapwood, heartwood, pith) and the formation of annual rings. The teacher can draw a simple cross-section of a tree on the board.
Pupils’ Activity: Pupils listen and copy the diagram/notes from the board.
Learning Point: Pupils learn how trees grow and form timber.

Step 4: Discussion of Timber Sources

Time: 7 minutes
Teaching Skill: Question and Answer/Discussion
Teacher’s Activity: The teacher defines timber and discusses its primary sources, categorising them into hardwoods and softwoods. The teacher provides examples of each and asks pupils to mention other types of timber they know.
Pupils’ Activity: Pupils contribute by naming different types of timber and differentiating between hardwoods and softwoods.
Learning Point: Pupils identify various sources and types of timber.

Step 5: Elaboration on Timber Characteristics

Time: 7 minutes
Teaching Skill: Explanation/Analysis
Teacher’s Activity: The teacher explains the various characteristics of timber, such as colour, grain, texture, density, hardness, durability, strength, and workability. The teacher uses timber samples to demonstrate some of these properties.
Pupils’ Activity: Pupils observe the timber samples, listen to the explanations, and ask questions about specific characteristics.
Learning Point: Pupils understand the properties that define timber quality and suitability.

Step 6: Class Activity/Recap

Time: 4 minutes
Teaching Skill: Collaborative Learning
Teacher’s Activity: The teacher divides pupils into small groups and gives each group a few timber samples (if available) or pictures. Each group discusses and identifies the possible characteristics of the timber.
Pupils’ Activity: Pupils work in groups to identify and discuss the characteristics of the given timber samples/pictures.
Learning Point: Pupils apply their knowledge to practical identification of timber.

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 a wood cell.
Mention three layers involved in timber growth.
List two sources of timber.
State three characteristics of good timber.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 3 minutes
Teaching Skill: Summarisation
Teacher’s Activity: The teacher summarises the key points of the lesson, reiterating the importance of understanding wood cell structure, timber growth, sources, and characteristics for practical applications in woodworking. The teacher gives pupils an assignment to draw a cross-section of a tree trunk showing its growth layers.
Pupils’ Activity: Pupils listen to the summary and note down the assignment.
Learning Point: Pupils consolidate their learning and are given follow-up tasks.

Lesson Keywords

Wood Cell – The basic structural unit of wood.
Cambium – The growth layer in a tree that produces new wood and bark cells.
Sapwood – The outer, living wood of a tree that transports water and nutrients.
Heartwood – The inner, darker, and denser part of a tree trunk that provides structural support.
Hardwood – Timber from deciduous trees, generally dense and durable (e.g., Iroko).
Softwood – Timber from coniferous trees, generally lighter and easier to work (e.g., Pine).
Grain – The pattern of fibres in wood.
Durability – The ability of timber to resist decay and insect attack.

Differentiation

For pupils who grasp concepts quickly, the teacher can challenge them to research specific timber defects and their implications. For those needing more support, the teacher can provide simplified diagrams and allow peer-to-peer explanations.

Note for teachers using this lesson plan

Teachers should ensure they have adequate visual aids and, if possible, actual timber samples to make the lesson more engaging and practical for the pupils. Encourage pupils to relate the lesson to real-life applications of timber.