Reading a Graph Caption in a Science Report
A science report includes this caption: 'Figure 3: Mean plant height (cm) after four weeks, by light exposure. Bars show the mean of 20 plants per group; error bars show the range. Groups A and B received 6 and 12 hours of light respectively; Group C received 18 hours.' The graph shows Group A at 14 cm, Group B at 22 cm, and Group C at 19 cm, with error bars of ±3 cm. A classmate writes: 'Plants grow taller with more light. Group C shows that 18 hours is best.' The report's conclusion says: 'Height increased between 6 and 12 hours of light but did not increase further at 18 hours.'
1. Evaluate the classmate's claim using the caption and the data, including the role of the error bars.
Read the worked answer
The classmate's first sentence is only partly right. Height rose from 14 cm (Group A, 6 hours) to 22 cm (Group B, 12 hours), but fell to 19 cm at 18 hours (Group C). So 'more light means taller plants' does not hold across the whole range.
The second sentence is wrong. Group C did not produce the tallest plants; Group B did, at 22 cm. Group C at 19 cm is lower.
The error bars matter. Each mean has a range of ±3 cm, so Group B spans roughly 19–25 cm and Group C spans roughly 16–22 cm. Those ranges overlap, which means the difference between B and C may not be meaningful. The report's cautious conclusion - height increased between 6 and 12 hours but not further at 18 - is better supported than the classmate's confident ranking.
The lesson: read the caption for what the numbers represent, and check overlap before declaring one group the winner.
2. The caption says 'Groups A and B received 6 and 12 hours of light respectively'. Explain what 'respectively' tells the reader and what error would follow from misreading it.
Read the worked answer
'Respectively' pairs two lists in order: the first group named (A) matches the first value (6 hours), and the second group (B) matches the second value (12 hours). So A = 6 hours and B = 12 hours.
If a reader ignored 'respectively' and paired them the other way, they would conclude A = 12 hours and B = 6 hours. That reverses the whole trend: the graph would then appear to show height falling from 6 to 12 hours (22 cm at 6 hours down to 14 cm at 12 hours), which contradicts the report's conclusion that height increased over that range.
This is a common trap in science and social studies texts: 'respectively' is a small word carrying the whole mapping between two lists. Whenever you see it, draw the pairs explicitly before interpreting any data.