Class: Senior Secondary School 1 (SSS 1)
Term: 2nd Term
Week: 3
Age: 15 years
Duration: 45 minutes
Subject: Carpentry And Joinery
Curriculum Theme: Entrepreneurship Trade Subjects
Previous Lesson: Maintenance of Bench Vice, Cramps and Hammers.
Topic: TIMBER – Growth and Structure of Timber
Subject Matter: growth of timber, structure of timber, annual rings, sapwood and heartwood

Specific Objectives

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

Cognitive Domain:

Define timber and explain how it grows.
Identify and explain the main components of timber structure.
Differentiate between sapwood and heartwood.
Describe the significance of annual rings.

Affective Domain:

Appreciate the natural process of timber growth.
Show interest in learning about the properties of different timber types.

Psychomotor Domain:

Sketch a cross-section of a timber log.
Label the key parts of a timber structure on a diagram.

Collaborate with peers to discuss and understand timber characteristics.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Carpentry and Joinery (Senior Secondary Education)
State Unified Scheme of Work for Senior Secondary Schools
Basic Technology for Senior Secondary Schools 1 by F.O. Okoro
https://www.nigeriancurriculum.gov.ng/sss/carpentry
https://www.wood-database.com/wood-articles/wood-growth-and-structure/

Instructional Materials

The teacher will teach this lesson with the aid of:

Actual timber samples (logs or cross-sections)
Charts showing the cross-section of a timber log with labelled parts
Whiteboard/blackboard and markers/chalk
Diagrams of timber structure

Rationale for the Lesson

This lesson helps pupils understand how timber grows and its internal structure. Knowing this basic information is important for selecting and working with wood effectively in carpentry and joinery, as the structure influences the properties and uses of timber.

Prerequisite/Previous Knowledge

Pupils are expected to have a general understanding of trees and their uses from Basic Technology or everyday observations.

Lesson Content/Board Summary

TIMBER – Growth and Structure of Timber

Growth of Timber

Timber is wood obtained from trees. Trees grow primarily through cell division in the cambium layer, located just beneath the bark. This process adds new layers of wood each year, increasing the tree’s diameter and height. The roots absorb water and nutrients, while the leaves produce food through photosynthesis, supporting the overall growth of the tree.

Structure of Timber

The internal structure of timber can be observed in a cross-section of a log. The main components are:

Pith: The small, central core of the tree, consisting of soft tissue. It is the original stem around which the tree grows.
Medullary Rays: Thin, radial lines of cells extending from the pith towards the bark. They store food and transport sap horizontally across the trunk.
Cambium Layer: A thin layer of living cells between the sapwood and the bark. It is responsible for the annual growth in girth, producing new wood cells inwards and new bark cells outwards.
Bark: The outermost protective layer of the tree trunk. It protects the inner wood from insects, diseases, and weather.

Annual Rings

Annual rings, also known as growth rings, are concentric circles visible in the cross-section of a tree trunk. Each ring represents one year of growth. The lighter, wider part of the ring (earlywood or springwood) indicates rapid growth, while the darker, narrower part (latewood or summerwood) indicates slower growth. Counting these rings can determine the age of the tree.

Sapwood and Heartwood

The timber within a tree trunk is divided into two main zones:

Sapwood:

It is the outer layer of wood, usually lighter in colour.
It contains living cells and is responsible for transporting water and nutrients from the roots to the leaves.
It is generally less durable and more susceptible to insect attacks and decay because of its high moisture and nutrient content.

Heartwood:

It is the inner, older, and usually darker core of the tree.
It consists of dead cells and no longer participates in water transport.
It is typically denser, harder, and more durable than sapwood due to the accumulation of extractives (resins, gums, tannins) that provide natural resistance to decay and insects.

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, checks attendance, and reviews the previous lesson briefly. The teacher then introduces the new topic by asking pupils about their knowledge of trees and how they grow, and what wood is used for.
Pupils’ Activity: Pupils respond to questions and listen attentively.
Learning Point: Pupils are engaged and their prior knowledge is activated, linking it to the new lesson.

Step 2: Explanation of Timber Growth

Time: 8 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains how trees grow, focusing on the role of the cambium layer, and how new wood is formed annually. The teacher uses diagrams or simple sketches on the board to illustrate.
Pupils’ Activity: Pupils listen, observe the diagrams, and ask questions for clarification.
Learning Point: Pupils understand the basic process of timber growth.

Step 3: Introduction to Timber Structure

Time: 7 minutes
Teaching Skill: Illustration/Explanation
Teacher’s Activity: The teacher presents a cross-section of a timber sample or a chart showing the internal structure of a log. The teacher points out and explains the pith, medullary rays, cambium layer, and bark.
Pupils’ Activity: Pupils observe the timber sample/chart and listen to the explanations.
Learning Point: Pupils can identify and describe the basic components of timber structure.

Step 4: Focusing on Annual Rings

Time: 7 minutes
Teaching Skill: Explanation/Visualisation
Teacher’s Activity: The teacher further explains annual rings, their formation, and how they indicate the age and growth conditions of the tree. The teacher uses the timber sample to show clear examples of annual rings.
Pupils’ Activity: Pupils observe the annual rings on the timber sample and understand their significance.
Learning Point: Pupils understand what annual rings are and how they are formed.

Step 5: Differentiating Sapwood and Heartwood

Time: 8 minutes
Teaching Skill: Comparative Analysis/Discussion
Teacher’s Activity: The teacher explains and differentiates between sapwood and heartwood, highlighting their characteristics, functions, and practical implications for carpentry. The teacher uses the timber sample to show the colour and texture differences.
Pupils’ Activity: Pupils observe, listen, and participate in a short discussion about the differences and uses of sapwood and heartwood.
Learning Point: Pupils can distinguish between sapwood and heartwood and understand their properties.

Step 6: Practical Activity – Sketching Timber Structure

Time: 5 minutes
Teaching Skill: Practical Application/Demonstration
Teacher’s Activity: The teacher guides pupils to sketch a simple cross-section of a timber log in their notebooks, encouraging them to label the parts discussed: pith, annual rings, medullary rays, sapwood, heartwood, cambium, and bark.
Pupils’ Activity: Pupils draw and label the structure of timber in their notebooks.
Learning Point: Pupils develop psychomotor skills and reinforce their understanding through drawing.

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.
Mention three main parts of the internal structure of timber.
What are annual rings, and what do they indicate?
State two differences between sapwood and heartwood.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key learning points of the lesson, reiterating the importance of understanding timber growth and structure in carpentry. The teacher assigns homework: “Draw a detailed diagram of a timber cross-section and label all its parts.”
Pupils’ Activity: Pupils listen to the summary and copy the homework.
Learning Point: The lesson is reinforced and pupils are given an activity to consolidate learning.

Lesson Keywords

Timber – Wood obtained from trees, used as a building material.
Growth – The process by which a tree increases in size and mass.
Structure – The internal arrangement of parts within a timber log.
Annual rings – Concentric circles in a tree trunk, each representing one year of growth.
Sapwood – The outer, living, and lighter-coloured wood that transports water and nutrients.
Heartwood – The inner, dead, and usually darker core of the tree, providing strength and decay resistance.
Pith – The small, soft central core of a tree trunk.
Cambium – The thin layer of cells responsible for a tree’s annual growth in girth.

Differentiation

For pupils who grasp concepts quickly, the teacher can ask them to research different types of timber and how their growth patterns affect their properties. For pupils needing more support, the teacher can provide pre-drawn diagrams of timber structure for them to label, or work in small groups to discuss the concepts using the physical timber samples.

Note for teachers using this lesson plan

Ensure that actual timber samples are available for pupils to observe and touch, as this enhances understanding of the abstract concepts. Encourage questions and active participation. Emphasize the practical relevance of understanding timber structure for future carpentry work.