Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: First Term
Week: 10
Age: 15 years
Duration: 45 minutes
Subject: Biology
Curriculum Theme: Biology
Previous Lesson: Growth.
Topic: IRRITABILITY
Subject Matter: Cell reaction to environment, irritability as a characteristic of protoplasm, nastic tropic and taxis responses with examples, positive and negative responses.

Specific Objectives

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

Cognitive Domain:

Define irritability.
Differentiate between nastic, tropic, and taxis responses.
Identify positive and negative responses to stimuli.

Affective Domain:

Appreciate the importance of irritability for the survival of living organisms.
Show interest in observing and recording responses of plants and animals.

Psychomotor Domain:

Observe and record the nastic response of Mimosa pudica.
Set up simple experiments to demonstrate responses to light and gravity.

Collaborate effectively in group activities during experiments.
Share observations and discuss findings with peers.

Reference Materials

The following resources were used in planning this lesson:

Senior Secondary Education Curriculum for Biology.
State Unified Scheme of Work for Senior Secondary Schools.
Modern Biology for Senior Secondary Schools.

Instructional Materials

The teacher will teach this lesson with the aid of:

Mimosa pudica plant.
Potted seedlings (e.g., bean or maize).
Light source.
Boxes for directional light.
Ruler.
Charts illustrating different types of responses.

Rationale for the Lesson

This lesson helps pupils understand how living organisms react to changes in their environment, which is essential for their survival. It also enables pupils to observe and classify different types of responses in plants and animals, connecting biological concepts to real-world phenomena.

Prerequisite/Previous Knowledge

Pupils should have a basic understanding of living organisms and their general characteristics, including movement and nutrition.

Lesson Content/Board Summary

IRRITABILITY

Definition of Irritability

Irritability is the ability of living organisms to detect and respond to changes in their internal or external environment. These changes are called stimuli, and the reaction of the organism is called a response. Irritability is a fundamental characteristic of protoplasm.

Types of Responses to Stimuli

Responses in organisms can be broadly classified into three types:

Nastic Responses: These are non-directional movements of plant parts in response to a stimulus. The direction of the response is independent of the direction of the stimulus. Examples include the folding of Mimosa pudica leaves upon touch (thigmonasty) and the opening and closing of flowers.
Tropic Responses: These are directional growth movements of plant parts in response to an external stimulus. The direction of growth is determined by the direction of the stimulus.

The following are examples of tropic responses:

Phototropism: Growth response to light (e.g., shoots grow towards light).
Geotropism: Growth response to gravity (e.g., roots grow downwards, shoots grow upwards).
Hydrotropism: Growth response to water (e.g., roots grow towards water).
Thigmotropism: Growth response to touch (e.g., climbing plants coiling around a support).
Chemotropism: Growth response to chemicals (e.g., pollen tube growing towards ovule).

Taxis Responses: These are directional movements of whole organisms (usually motile microorganisms or animals) towards or away from a stimulus.

The following are examples of taxis responses:

Phototaxis: Movement towards or away from light (e.g., Euglena moving towards light).
Chemotaxis: Movement towards or away from chemicals (e.g., bacteria moving towards nutrients).
Thermotaxis: Movement towards or away from temperature changes.

Positive and Negative Responses

Responses can also be described as positive or negative:

Positive Response: When an organism moves or grows towards the stimulus. For example, shoots growing towards light (positive phototropism) or roots growing towards water (positive hydrotropism).
Negative Response: When an organism moves or grows away from the stimulus. For example, roots growing away from light (negative phototropism) or shoots growing away from gravity (negative geotropism).

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 recall some characteristics of living things. The teacher then introduces the topic “Irritability” by asking pupils how they react when they touch something hot or how plants respond to sunlight.
Pupils’ Activity: Pupils respond to the teacher’s questions and share their observations about responses in living organisms.
Learning Point: Pupils are prepared for the lesson and connect the topic to prior knowledge.

Step 2: Definition of Irritability

Time: 7 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher clearly defines irritability as the ability of an organism to respond to stimuli. The teacher explains that stimuli are changes in the environment and responses are the reactions to these changes. The teacher emphasizes that irritability is a characteristic of protoplasm.
Pupils’ Activity: Pupils listen attentively, take notes, and ask questions for clarification.
Learning Point: Pupils understand the definition of irritability, stimulus, and response.

Step 3: Types of Responses (Nastic, Tropic, Taxis)

Time: 10 minutes
Teaching Skill: Classification/Demonstration
Teacher’s Activity: The teacher introduces the three main types of responses: nastic, tropic, and taxis. The teacher uses charts to illustrate each type and prepares to demonstrate with the Mimosa pudica plant.
Pupils’ Activity: Pupils observe the charts and listen to the explanations. They prepare for the demonstration.
Learning Point: Pupils learn about the different categories of responses.

Step 4: Examples of Nastic Responses

Time: 5 minutes
Teaching Skill: Demonstration/Observation
Teacher’s Activity: The teacher gently touches the leaves of the Mimosa pudica plant to demonstrate its nastic response (folding of leaves). The teacher explains that this is a non-directional response to touch (thigmonasty).
Pupils’ Activity: Pupils observe the Mimosa pudica plant’s reaction and record their observations.
Learning Point: Pupils understand nastic responses through a practical example.

Step 5: Examples of Tropic Responses

Time: 8 minutes
Teaching Skill: Demonstration/Experimentation
Teacher’s Activity: The teacher explains phototropism and geotropism. Using potted seedlings and a light source/boxes, the teacher demonstrates or guides pupils to set up simple experiments to show shoots growing towards light and roots growing downwards.
Pupils’ Activity: Pupils observe the setup for the experiments and discuss expected outcomes. They record the principles demonstrated.
Learning Point: Pupils understand tropic responses and how to observe them.

Step 6: Positive and Negative Responses

Time: 5 minutes
Teaching Skill: Clarification/Examples
Teacher’s Activity: The teacher explains the concepts of positive and negative responses using the examples of phototropism and geotropism already discussed. For instance, shoots show positive phototropism and negative geotropism.
Pupils’ Activity: Pupils identify positive and negative responses for various stimuli and record them.
Learning Point: Pupils can classify responses as positive or negative based on direction relative to the stimulus.

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 irritability.
Mention two differences between nastic and tropic responses.
Give one example of a plant showing nastic movement.
Explain the terms “positive phototropism” and “negative geotropism.”

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 3 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the definition of irritability and the different types of responses (nastic, tropic, taxis), as well as positive and negative responses. The teacher gives pupils an assignment to find more examples of each type of response.
Pupils’ Activity: Pupils listen to the summary and copy down the assignment.
Learning Point: The lesson is concluded, and pupils are given an assignment to reinforce learning.

Lesson Keywords

Irritability – The ability of an organism to respond to stimuli.
Stimulus – A detectable change in the internal or external environment of an organism.
Response – The reaction of an organism to a stimulus.
Nastic – Non-directional plant movements independent of stimulus direction.
Tropic – Directional growth movements of plants in response to a stimulus.
Taxis – Directional movement of a whole organism towards or away from a stimulus.
Phototropism – Tropic response to light.
Geotropism – Tropic response to gravity.
Thigmonasty – Nastic response to touch.
Positive Response – Movement or growth towards a stimulus.
Negative Response – Movement or growth away from a stimulus.

Differentiation

For visual learners, charts and live demonstrations will be emphasized. Kinesthetic learners will benefit from setting up simple experiments. Advanced learners can research the underlying mechanisms of these responses (e.g., hormones in plants), while struggling learners will receive additional support through simplified explanations and one-on-one guidance during practical activities.

Note for teachers using this lesson plan

Ensure all instructional materials, especially the Mimosa pudica plant and potted seedlings, are available and in good condition before the lesson. Encourage active participation from pupils during demonstrations and discussions. Provide clear instructions for setting up experiments and observing results.