Year 9 Science · Unit 1 · Lesson 4
Challenge Worksheet
Learning Goals
Design a mini-experiment
A scientist wants to test: "Does handwashing with soap reduce the bacterial count on hands more than washing with water alone?" Plan the investigation below.
| What I will change (independent variable) | |
| What I will keep the same (controlled variables, list at least 3) | |
| What I will measure (dependent variable) | |
| My prediction (if … then … because …) | |
| How I would know if my prediction is wrong | |
| One limitation of this experiment |
1. Soap works by disrupting the lipid (fat) membranes of bacteria and viruses. Using this information and your knowledge of the first line of defence, explain why handwashing with soap is more effective than water alone at protecting the body from infection.
2. The skin microbiome contains millions of beneficial bacteria that compete with pathogens. A patient undergoing a course of broad-spectrum antibiotics kills many of these skin bacteria. Predict and explain the consequence for their first-line defences.
Wrap Up
In one sentence, what was the main idea of this lesson?