Year 9 Science · Unit 1 · Lesson 7

Midunit Synthesis, Checkpoint (L01–L06)

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Learning Goals

Identify the odd item out from groupings spanning L01–L06 and explain the reasoning
Apply concepts of pathogen entry, first-line failure, and second-line response to a real clinical scenario
Explain what pus is and how it forms during infection

Warm Up

Odd one out

Circle the item that does not belong in each group. Then explain why it doesn't fit in the answer column.

#	Group	Your answer (odd one + reason)
1	Bacteria Virus Prion Phagocyte
2	Skin Mucus Cilia Inflammation
3	Droplet Direct contact Vector Fever
4	Complement proteins Phagocytes Lysozyme Fever

Your Turn

Clinical scenario

A 14-year-old student was working in the garden and a thorn pierced the skin on their left hand. Two days later, the area around the wound is red, hot, swollen, and painful. A pus-filled abscess is beginning to form. The student visits a GP who explains that bacteria have entered and the immune system is responding.

(a) How did the pathogen enter? Which specific first-line defence was breached, and why is skin normally effective at keeping pathogens out?

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(b) Identify two other first-line defences that were either not present at the wound site or failed to stop the bacteria. Briefly explain why.

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(c) The wound is red, hot, and swollen. Name the second-line response causing each of these three signs and explain what is happening at the cellular level.

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(d) What is pus made of? Name its main components and explain why its formation indicates that second-line defences are actively fighting the infection.

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Wrap Up

In one sentence, explain why a wound becoming red and swollen is actually a sign that the immune system is working, not failing.