Year 9 Science · Unit 1 · Lesson 7
Challenge Worksheet
Learning Goals
Find the mistake
A student wrote this explanation of the body's response to infection
"When a pathogen enters your body, the first line of defence includes phagocytes that immediately swallow the invader. If the pathogen gets past the first line, the second line responds with antibodies produced by B cells, which destroy the pathogen. Fever is a second-line response that directly kills bacteria by overheating them. Pus is made mostly of dead red blood cells that have rushed to the infection site to fight the pathogen. Once all pathogens are cleared, your immune system forgets the infection completely and responds from scratch next time."
1. This explanation contains four errors. Identify all four mistakes. List each one clearly.
2. Choose any two of the errors you identified and rewrite those sentences correctly. Use precise scientific language.
3. Explain why two of the four errors you found are easy mistakes to make. What aspect of how the immune system works makes these misconceptions understandable? Use scientific reasoning in your answer.
4. A healthy Year 9 student gets a splinter and develops a small abscess. Using the correct version of the immune response (not the student's flawed version), write a step-by-step account of what is happening from the moment the splinter pierces the skin until the abscess resolves. Include at least one first-line defence and at least three second-line responses (such as inflammation, phagocytosis by neutrophils and macrophages, fever, and complement).
Wrap Up
In one sentence, explain the key difference between what the first line and the second line of defence do when a pathogen enters the body.