Lesson Notes By Weeks and Term v4 - SHS 3

Lesson Video

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Performance objectives

• Define antigens and their role in the immune response.
• Differentiate between exogenous and endogenous antigens.
• Describe the steps of the immune response.
• Identify common diseases caused by pathogens with antigens.
• Discuss the importance of the immune response in staying healthy.

Lesson summary

This lesson introduces the body's remarkable defense system, the immune system, and how it responds to invaders. In Ghana, we are constantly exposed to various microorganisms that cause diseases like malaria, typhoid, cholera, and influenza. Understanding how our bodies fight these invaders is fundamental to appreciating health, hygiene, and the science behind vaccinations and treatments. We will explore the concept of "antigens" – the molecular signals that trigger our body's army – and classify them to better understand how our immune system recognizes and neutralizes threats, from a common cold virus to the parasite that causes malaria.

Lesson notes

Introduction: The Body's Defence Force

Think of the human body as the nation of Ghana and the immune system as the Ghana Armed Forces. Its job is to patrol the country (your body), identify any unauthorised intruders (pathogens like bacteria, viruses), and eliminate them to maintain peace and order (health). This entire process of identification and elimination is called the immune response. The "uniform" or "flag" that our body's army uses to identify an invader is called an antigen. Concept 1: Distinguishing 'Self' from 'Non-Self'

The first and most crucial task of the immune system is to know the difference between the body's own cells ('self') and foreign invaders ('non-self'). 'Self' Markers: Almost every cell in your body has special protein markers on its surface called Major Histocompatibility Complex (MHC) markers. Think of these as a national ID card or a Ghanaian passport. Immune cells constantly check these MHC markers. If a cell has the correct 'ID card', the immune system leaves it alone. 'Non-Self' Recognition: When a bacterium, virus, or even a splinter enters the body, it lacks these specific 'self' MHC markers. The immune system immediately recognizes it as 'non-self' or foreign and mounts an attack. This is also why organ transplants can be rejected – the recipient's immune system sees the new organ's cells as 'non-self' because their MHC markers are different. Concept 2: What is an Antigen? Definition: An antigen (from antibody generator) is any substance, usually a protein or polysaccharide on the surface of a cell or virus, that is recognised as foreign by the immune system and triggers an immune response. Analogy: If a pathogen is an enemy soldier, its antigen is the specific uniform, flag, or insignia that allows your body's army to identify it as the enemy. The immune system doesn't react to the whole soldier, but specifically to that uniform. Concept 3: Classification of Antigens

Based on their origin, we can group antigens into three main types. This is a key concept for understanding different diseases.

Evaluation guide

• Explore the immune response in relation to the introduction of antigens.
• Managing Talk for Learning : Teacher leads a discussion with the class on ways they think the
• body responds to the invasion of foreign and harmful materials. Engage in a discussion on immune
• response and the meaning of the term “antigens”