Lesson Note on Excretory System: Excretory Organs and Structures for SSS 2

Class: Senior Secondary School 2 (SS2 / SSS2)
Term: First Term
Week: 7
Age: 16 years
Duration: 45 minutes
Subject: Biology
Curriculum Theme: Regulation and Control
Previous Lesson: Respiratory System: Mechanism in Higher and Lower Animals.
Topic: EXCRETORY SYSTEM
Subject Matter: Contractile vacuoles, flame cells, Malpighian tubules, kidneys, stomata, lenticels.

Specific Objectives

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

Cognitive Domain:

• Define excretion and state its importance.
• Identify various excretory organs in different organisms.
• Describe the function of contractile vacuoles, flame cells, Malpighian tubules, and kidneys.
• Explain how stomata and lenticels are involved in plant excretion.

Affective Domain:

• Appreciate the diversity of excretory mechanisms in living organisms.
• Develop an interest in comparing physiological processes across different life forms.

Psychomotor Domain:

• Draw and label diagrams of excretory structures in insects and mammals.
• Observe and identify excretory structures in provided specimens or diagrams.

Social Domain:

• Collaborate with peers to discuss observations and share findings.
• Participate actively in classroom discussions regarding excretion.

Reference Materials

The following resources were used in planning this lesson:

• Senior Secondary Schools Education Curriculum
• State Unified Scheme of Work
• Essential Biology for Senior Secondary Schools by M.C. Michael

Instructional Materials

The teacher will teach this lesson with the aid of:

• Textbook
• Posters or charts showing excretory systems of different organisms (e.g., Amoeba, Planaria, insect, mammal)
• Dissected cockroach and rat (if available and appropriate for demonstration)

Rationale for the Lesson

This lesson helps pupils understand how living organisms remove waste products from their bodies, a process essential for survival. It enables them to compare different excretory structures and mechanisms in various organisms, linking biological functions to structural adaptations.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of living organisms, their classification, and general life processes like feeding, respiration, and growth.

Lesson Content/Board Summary

EXCRETORY SYSTEM

Definition of Excretion

Excretion is the process by which living organisms remove metabolic waste products and excess substances from their bodies. These wastes, if accumulated, can be toxic and harmful.

Excretory Organs in Lower Organisms

• Contractile Vacuoles: These are specialized organelles found in freshwater protozoans like Amoeba and Paramecium. They collect excess water and some metabolic wastes from the cytoplasm and expel them from the cell, helping in osmoregulation.
• Flame Cells (Protonephridia): These are part of the excretory system in simple invertebrates such as flatworms (e.g., Planaria). They are ciliated cells that beat to drive waste fluids through a tubular system, eventually exiting the body through excretory pores.

Excretory Organs in Insects

• Malpighian Tubules: These are the main excretory and osmoregulatory organs in insects (e.g., cockroach) and other terrestrial arthropods. They are blind-ended tubules that absorb solutes, water, and wastes from the hemolymph and empty into the digestive tract, where wastes are eliminated with faeces.

Excretory Organs in Mammals

• Kidneys: These are the primary excretory organs in mammals (e.g., rat, human). They filter blood to remove metabolic wastes, regulate blood volume and pressure, and maintain electrolyte balance. The kidneys produce urine, which is then transported to the bladder for storage before being expelled.
• Other excretory organs in mammals include the skin (sweat glands remove water, salts, urea), lungs (exhale carbon dioxide and water vapour), and liver (detoxifies substances and excretes bile pigments).

Excretion in Plants

Plants generally produce fewer waste products than animals because their metabolic rates are lower. They also reuse many waste products. However, they do have mechanisms for excretion:

• Stomata: These are tiny pores found mainly on the surface of leaves. They allow for the exchange of gases (oxygen, carbon dioxide) and the release of excess water vapor through transpiration.
• Lenticels: These are porous tissues found on the surface of woody stems and roots. They facilitate gas exchange between the internal tissues and the atmosphere, and also allow for the release of some water vapor.
• Other methods include storing waste products in non-living parts of the plant (e.g., bark, old leaves) and shedding these parts.

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 what happens to the waste products generated in their bodies after they eat food or breathe.
Pupils’ Activity: Pupils respond by mentioning urination, defecation, sweating, and breathing out. They try to link these to waste removal.
Learning Point: Pupils are introduced to the concept of waste removal from the body.

Step 2: Explanation of Excretion

Time: 5 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines excretion and explains why it is important for living organisms to remove metabolic wastes.
Pupils’ Activity: Pupils listen attentively and copy the definition of excretion into their notebooks.
Learning Point: Pupils understand the meaning and significance of excretion.

Step 3: Excretion in Lower Organisms

Time: 10 minutes
Teaching Skill: Illustration/Discussion
Teacher’s Activity: The teacher explains and illustrates the function of contractile vacuoles in protozoans and flame cells in flatworms using diagrams or charts.
Pupils’ Activity: Pupils observe the diagrams, ask questions, and take notes on these simple excretory structures.
Learning Point: Pupils learn about excretory mechanisms in simple organisms.

Step 4: Excretion in Insects

Time: 5 minutes
Teaching Skill: Demonstration/Observation
Teacher’s Activity: The teacher introduces Malpighian tubules as the excretory organs in insects and, if possible, guides pupils to observe them in a dissected cockroach or a detailed diagram.
Pupils’ Activity: Pupils observe the structures shown or discussed and record their observations about Malpighian tubules.
Learning Point: Pupils identify and understand the role of Malpighian tubules in insect excretion.

Step 5: Excretion in Mammals

Time: 5 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher discusses kidneys as the main excretory organs in mammals, showing a diagram of the mammalian excretory system (e.g., rat or human).
Pupils’ Activity: Pupils observe the diagram of the kidney and its associated structures, comparing it with the insect system.
Learning Point: Pupils understand the basic function and structure of mammalian kidneys.

Step 6: Excretion in Plants

Time: 5 minutes
Teaching Skill: Explanation/Questioning
Teacher’s Activity: The teacher explains how stomata and lenticels contribute to excretion in plants, linking them to gas exchange and transpiration.
Pupils’ Activity: Pupils listen, ask questions, and note down the roles of stomata and lenticels in plant excretion.
Learning Point: Pupils learn about the different ways plants excrete waste products.

Step 7: Evaluation/Review

Time: 5 minutes
Teaching Skill: Questioning/Assessment
Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. Define excretion.
2. Name two excretory organs found in lower organisms.
3. What are Malpighian tubules, and in which organisms are they found?
4. Mention two ways plants excrete waste products.

Pupils’ Activity: Pupils answer orally and in writing.
Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 5 minutes
Teaching Skill: Summarization/Assignment
Teacher’s Activity: The teacher summarizes the key points of the lesson, emphasizing the diversity and importance of excretory systems. The teacher then assigns homework: “Draw and label the excretory system of an insect and a mammal.”
Pupils’ Activity: Pupils listen to the summary and copy down the homework.
Learning Point: Pupils consolidate their understanding and are given a task to reinforce learning.

Lesson Keywords

• Excretion – The process of removing metabolic waste products from the body.
• Contractile vacuoles – Organelles in protozoans that expel excess water and wastes.
• Flame cells – Ciliated cells in flatworms that drive waste fluids through tubules.
• Malpighian tubules – Excretory and osmoregulatory organs in insects.
• Kidneys – Primary excretory organs in mammals that filter blood and produce urine.
• Stomata – Pores on plant leaves for gas exchange and transpiration.
• Lenticels – Porous tissues on woody stems for gas exchange.

Differentiation

The teacher will provide additional diagrams and simplified explanations for struggling learners. Advanced learners will be encouraged to research the detailed mechanisms of specific excretory organs, such as the nephron in the mammalian kidney.

Note for teachers using this lesson plan

Teachers should prepare clear diagrams or charts of the various excretory structures. If actual dissections are not feasible, high-quality videos or interactive simulations can be used to show the structures of Malpighian tubules and mammalian kidneys. Encourage pupils to compare and contrast the different excretory mechanisms based on the environment and complexity of the organism.