Biology · Year 10 · Infection and Response · Spring Term

Types of Pathogens

Classifying viruses, bacteria, protists, and fungi and understanding their basic characteristics and modes of infection.

• National Curriculum Attainment Targets
• GCSE: Biology - Infection and Response
• GCSE: Biology - Communicable Diseases

About This Topic

Pathogens and disease transmission covers the biology of communicable diseases caused by viruses, bacteria, protists, and fungi. Students learn how these pathogens spread through air, water, and direct contact, and how they cause damage to host cells. This topic is a vital part of the GCSE 'Infection and Response' unit, providing the context for public health measures and personal hygiene.

In line with the cultural context of the UK curriculum, this topic also touches on the global history of disease and how international travel and trade have influenced the spread of infections. Understanding the life cycles of pathogens like the malaria protist or the tobacco mosaic virus is essential. This topic comes alive when students can physically model the patterns of transmission and use peer explanation to evaluate the effectiveness of different prevention strategies.

Key Questions

1. Justify why viral infections are often harder to treat than bacterial infections.
2. Differentiate between the structural features of bacteria and viruses.
3. Explain how different types of pathogens cause disease in their hosts.

Learning Objectives

• Classify given microorganisms as viruses, bacteria, protists, or fungi based on their structural characteristics.
• Compare and contrast the modes of infection and reproduction for bacteria and viruses.
• Explain how protists and fungi cause disease, providing specific examples of host interactions.
• Analyze the structural differences between bacteria and viruses to justify why viral infections are often harder to treat.

Before You Start

Cells: Structure and Function

Why: Students need to understand basic cell structures, including the presence or absence of a nucleus and cell wall, to differentiate between bacteria, protists, and fungi.

Basic Biological Molecules

Why: Knowledge of DNA and RNA is foundational for understanding the genetic material within viruses and its role in infection.

Key Vocabulary

Pathogen	A microorganism, such as a bacterium, virus, or fungus, that can cause disease.
Virus	An infectious agent with a simple structure, typically consisting of genetic material (DNA or RNA) surrounded by a protein coat. Viruses can only replicate inside the living cells of other organisms.
Bacteria	Single-celled microorganisms with a cell wall and cell membrane, but lacking a nucleus. Bacteria can reproduce independently and can cause disease through toxins or by damaging host tissues.
Protist	A diverse group of eukaryotic microorganisms, some of which are pathogenic. Examples include amoebas and Plasmodium, which causes malaria.
Fungi	Eukaryotic organisms that include yeasts, molds, and mushrooms. Some fungi are pathogenic, causing infections like athlete's foot or thrush.

Watch Out for These Misconceptions

Common Misconception

Students often believe that all bacteria are harmful.

What to Teach Instead

Remind students that many bacteria are useful, such as those in the gut or used in food production. Focusing on 'pathogenic' bacteria helps distinguish the harmful ones from the beneficial ones.

Common Misconception

The idea that viruses and bacteria are the same thing.

What to Teach Instead

Highlight that bacteria are living cells that can reproduce on their own, while viruses are much smaller and must live inside a host cell to replicate. Using a scale diagram helps show the massive size difference.

Active Learning Ideas

Simulation Game: The Outbreak Game

Students are given 'status' cards (susceptible, infected, or immune). They move around the room and 'transmit' the disease through handshakes, tracking how quickly the infection spreads through the population.

30 min·Whole Class

Gallery Walk: Pathogen Profiles

Set up stations for diseases like Salmonella, Gonorrhoea, Malaria, and Rose Black Spot. Students move around to identify the pathogen type, symptoms, and methods of prevention for each.

35 min·Small Groups

Think-Pair-Share: Global Health History

Students discuss how historical events, such as the expansion of the British Empire, affected the global spread of diseases like smallpox or cholera, and how this shaped modern public health policies.

25 min·Pairs

Real-World Connections

• Public health officials at the UK Health Security Agency track outbreaks of bacterial infections like E. coli and viral infections like influenza, using this classification to guide treatment and prevention strategies.
• Medical researchers develop antiviral drugs, like those for HIV or COVID-19, by understanding the unique replication mechanisms of viruses, which differ significantly from how antibiotics target bacteria.
• Mycologists study pathogenic fungi, such as Candida albicans, to develop antifungal treatments used in hospitals to combat serious infections in immunocompromised patients.

Assessment Ideas

Quick Check

Present students with images or brief descriptions of four different microorganisms. Ask them to identify each as a virus, bacterium, protist, or fungus and provide one key characteristic that led to their classification.

Discussion Prompt

Pose the question: 'Why can doctors prescribe antibiotics for a bacterial throat infection but not for a viral cold?' Facilitate a class discussion where students explain the fundamental differences in how bacteria and viruses cause illness and reproduce.

Exit Ticket

On an index card, have students draw a simple diagram illustrating how a virus infects a host cell and, in a separate box, draw a simple diagram showing how a bacterium reproduces. Ask them to label one key difference between the two processes.

Frequently Asked Questions

How do bacteria and viruses cause disease differently?

Bacteria cause disease by reproducing rapidly inside the body and producing toxins that damage tissues. Viruses live and reproduce inside cells, eventually causing the cells to burst and die. This cellular damage is what makes the host feel ill.

What are the best hands-on strategies for teaching disease transmission?

Simulations are the most powerful tool for this topic. By using 'glow germ' lotions or water-transfer activities, students can see how easily invisible pathogens spread. This makes the abstract concept of 'transmission' visible and helps them understand why interventions like handwashing or social distancing are so effective in real-world scenarios.

How is malaria spread and prevented?

Malaria is caused by a protist and is spread by female Anopheles mosquitoes, which act as vectors. It can be prevented by stopping the mosquitoes from breeding and using mosquito nets or repellent to avoid being bitten.

Why are viral diseases difficult to treat?

Viruses live inside the body's cells, which makes it difficult to develop drugs that destroy the virus without also damaging the body's own tissues. Antibiotics do not work on viruses because they target bacterial structures that viruses don't have.