Year 7 Science · Unit 1 · Lesson 20

Unit Review + Working Scientifically

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Name
Date
Class

Learning Goals

Warm Up

Predict + reason

Scenario

A student is investigating whether the amount of light affects the growth rate of duckweed (Lemna minor) over 7 days. They set up three identical containers: one placed in bright light, one in dim light, and one in total darkness. They count the number of duckweed fronds in each container every day. All other conditions — water type, water volume, temperature, starting number of fronds, and container size — are kept the same.

(a) Write a hypothesis for this investigation using the "If … then … because …" structure.

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(b) Identify the independent variable in this investigation and name one controlled variable.

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Your Turn

Because… chain

The Q-H-M-R-D-C structure shows how a scientific investigation unfolds. Fill in the missing steps in the chain below.

A scientific question is identified: "How does light intensity affect duckweed growth?"
→
A method is planned: variables are listed, replicates are set up, safety is considered.
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Results are analysed: patterns, trends, and possible errors are identified in the data.
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Overall: a conclusion is reached that directly answers the original question using the results.

Show What You Know

1. A student changes both light intensity and water temperature in the same duckweed experiment. Explain why this makes it impossible to draw a valid conclusion about light intensity.

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2. In the duckweed investigation, a student sets up only one container per light condition (no replicates). Explain why replicates are important and what could go wrong without them.

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Wrap Up

In one sentence, what is the most important rule for designing a fair test?

HSCScience · Year 7 Science · Unit 1 · Lesson 20 · Apply Worksheet