Year 9 Science · Unit 1 · Lesson 4

First Line of Defence

Foundation Worksheet

Name
Date
Class

Learning Goals

Warm Up

Sort it!

Write each item from the pool into the correct category box, Physical Barrier or Chemical Barrier.

Skin (keratinised dead cells) Stomach acid (HCl, pH 2) Cilia in the respiratory tract Lysozyme in tears Mucous membranes Sebum (skin oil) Eyelashes and blinking Earwax Lactoferrin in breast milk Skin microbiome (beneficial bacteria)

Physical Barrier

Chemical Barrier

Your Turn

Fill the gap

Choose the correct word from the word bank to complete each sentence. Two words will NOT be used.

skin mucus cilia lysozyme stomach acid barrier pathogen antibody vaccine

The first line of defence acts as a that stops a from entering the body in the first place. The outer layer of is made of tough, dead, keratinised cells that most pathogens cannot penetrate. When pathogens are breathed in, sticky produced by membranes in the respiratory tract traps them. Then tiny hair-like sweep the trapped pathogens up toward the throat so they are swallowed. In the stomach, at around pH 2 kills most pathogens before they can reach the intestines. In tears and saliva, the enzyme breaks down the cell walls of bacteria, destroying them chemically.

Show What You Know

1. A patient in hospital has severe burns covering 30% of their skin. Explain why they are at much greater risk of infection than a healthy person.

Recall 2 marks

2. Name two first-line defences found in the respiratory tract and briefly describe how each one works.

Recall 2 marks

Wrap Up

In one sentence, what was the main idea of this lesson?

HSCScience · Year 9 Science · Unit 1 · Lesson 4 · Foundation Worksheet