Year 8 Science · Unit 4 · Lesson 6
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Learning Goals
Read the graph
Effect of fertiliser concentration on plant height after 4 weeks
Data: simulated classroom investigation, modelled on plant nutrition literature.
(a) Describe the overall trend in plant height as fertiliser concentration increases from 0 to 10 g/L. Use the words "increases," "peaks," and "decreases" in your answer.
(b) At which fertiliser concentration was plant growth greatest? What is this concentration called in science?
(c) Using your science knowledge, suggest why plant growth decreases at high fertiliser concentrations (8 and 10 g/L).
Correlation ≠ causation
A viral news headline
"Scientists prove that eating chocolate increases exam scores! A new study of 1 200 students found that those who ate more chocolate each week scored significantly higher on maths tests. Chocolate lovers rejoice."
(a) What type of correlation does this headline describe — positive, negative, or no correlation? Define your chosen term.
(b) The headline says "proves." Explain why this is scientifically incorrect. Why does correlation not prove causation in this case?
(c) Identify a confounding variable that could explain why students who eat more chocolate also score higher. (Hint: think about what else might be different between high-chocolate and low-chocolate students.)
1. Explain the difference between interpolation and extrapolation. Which is more reliable, and why?
2. Describe what a non-linear trend looks like on a graph, and give one example of a non-linear relationship from science.
Wrap Up
In one sentence, what was the main idea of this lesson?