Year 10 Science · Unit 4 · Lesson 10
Challenge Worksheet
Learning Goals
Read the graph
Study the scatter plot below. It shows the mean annual sea surface temperature (SST) of a Great Barrier Reef monitoring site against the number of mass coral bleaching events recorded in each five-year period. Answer the questions using the data shown.
Mean Sea Surface Temperature vs Mass Bleaching Events (Great Barrier Reef, 1992 to 2022)
Illustrative data based on AIMS Long-Term Monitoring Program and Bureau of Meteorology sea surface temperature records.
(a) Describe the relationship shown in the scatter plot. Name the type of correlation and explain what it means in everyday words.
(b) The six recorded mean sea surface temperatures were 26.7, 26.9, 27.0, 27.2, 27.4 and 27.5 degrees C. Calculate the mean and the range. Show your working and include units.
(c) A student concludes: "This graph proves that rising sea surface temperature causes coral bleaching." Explain why this conclusion overstates what the data shows, and rewrite it more accurately.
Evaluate the investigation
A student's depth study
A student investigated whether bushfire frequency in south-east Australia is linked to maximum summer temperature. She downloaded the number of major bushfires for three years and the single hottest day of each of those years from one weather station, then drew a line of best fit through the three points and concluded that hotter summers cause more bushfires.
(a) Identify two limitations of this investigation that reduce confidence in the conclusion.
(b) Suggest two specific improvements to the method that would make the investigation more valid and reliable.
(c) Scientists say that to move from correlation toward establishing causation you need more than a relationship in the data. Name the three things scientists look for, and explain how a biological or physical mechanism strengthens a causal claim.
Wrap Up
In one sentence, what was the main idea of this lesson?
For teacher or self-marking use. Accept reasonable wording that shows the same understanding.
Warm Up, Read the graph
(a) The plot shows a positive correlation: as mean sea surface temperature increases, the number of mass bleaching events also increases. In everyday words, warmer water over a five-year period tends to go with more bleaching events. Award 1 mark for "positive correlation" and 1 mark for a correct plain-language description.
Page 2 questions
(b) Mean = (26.7 + 26.9 + 27.0 + 27.2 + 27.4 + 27.5) / 6 = 162.7 / 6 = 27.12 degrees C (accept 27.1 degrees C). Range = maximum minus minimum = 27.5 - 26.7 = 0.8 degrees C. Award 1 mark for the mean working, 1 mark for the correct mean with unit, and 1 mark for the range with unit.
(c) The graph only shows a correlation, not causation. With this data alone the student cannot rule out other factors or prove the direction of cause and effect, and six points is a small sample. A more accurate conclusion: "Between 1992 and 2022, higher mean sea surface temperature was associated with (correlated with) a greater frequency of mass coral bleaching events; this is consistent with the known mechanism that heat stress expels zooxanthellae, but correlation alone does not prove causation." Award marks for: identifying correlation vs causation (1), a valid reason the claim is too strong (1), and an accurate rewritten conclusion (1).
Go Deeper, Evaluate the investigation
(a) Any two of: only three data points (sample far too small to draw a line of best fit); data from a single weather station (not representative of the whole region); using only the single hottest day rather than a seasonal average; ignores other causes of bushfires such as fuel load, drought, wind, and ignition source. Award 1 mark each.
(b) Any two of: use many more years of data (e.g. 30+ years); use data from multiple weather stations or a regional average; use a seasonal average maximum temperature rather than one day; include and control for confounding variables such as rainfall or fuel load; source data from a credible body such as BOM and the relevant fire authority. Award 1 mark each.
(c) To support causation scientists look for: (1) a correlation between the variables, (2) temporal precedence (the cause occurs before the effect), and (3) elimination of alternative explanations (confounding variables ruled out). A plausible mechanism strengthens a causal claim because it explains how the cause produces the effect (for example, heat stress denatures coral proteins and expels zooxanthellae), making it far less likely the relationship is coincidental. Award 1 mark per criterion, up to 2, plus 1 mark for the mechanism explanation.