How It Works: How Pathogens Cause Disease
Part of Pathogens and Disease Transmission — GCSE Biology
This how it works covers How It Works: How Pathogens Cause Disease within Pathogens and Disease Transmission for GCSE Biology. Types of pathogens, how diseases spread, transmission methods, and prevention strategies It is section 12 of 18 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 12 of 18
Practice
18 questions
Recall
20 flashcards
How It Works: How Pathogens Cause Disease
Pathogens cause harm in two main ways: by directly damaging host cells, and by releasing toxic substances called toxins. Bacteria multiply rapidly inside the body and may produce toxins that interfere with cell function — for example, the Salmonella bacterium produces toxins that irritate the gut lining, causing vomiting and diarrhoea. Viruses take a different approach: they invade host cells, hijack the cellular machinery, and force the cell to produce thousands of viral copies. When the new viruses burst out, they destroy the host cell. This cell destruction is what causes symptoms such as tissue damage, inflammation, and fever.
The key to pathogen success is reaching a target tissue in sufficient numbers. The infectious dose — the minimum number of pathogens needed to establish an infection — varies by pathogen. Norovirus can cause illness with as few as 20 viral particles, while Salmonella typically needs millions of bacterial cells. This explains why some diseases spread extremely easily while others require close, prolonged contact.
Understanding these mechanisms explains why different treatments work for different pathogens: antibiotics disrupt bacterial structures (cell walls, ribosomes) that do not exist in host cells, so they can kill bacteria selectively. Viruses lack these structures entirely, which is why antibiotics are completely ineffective against viral infections.