I was recently completing a biology past paper the Scottish SQA 2017 Advanced Higher Biology Qualifications. The question is as follows:


To solve this, I did:

EPT Index = 100*(striped stonefly + net spinning caddisfly + flathead mayfly)/(total number of taxa) = 100*(6+6+3)/(44)=34.09%

So, I answered C, however, the answer is B. What mistake have I made?

  • $\begingroup$ Do not post questions as graphics. They are unindexable and unreadable by people with sight problems. $\endgroup$
    – David
    Apr 24, 2018 at 22:19
  • $\begingroup$ The point of the question was to determine if you know what taxa are. You don't; remedying that might give you the right answer. $\endgroup$
    – swbarnes2
    May 24, 2018 at 19:00

1 Answer 1


Well, you made a mistake: The numbers in the second table are irrelevant to the question as it is not about taxa but about individuals. And the ETP number is calculated from number of EPT taxa (and not individuals).

The correct answer was 3*100/7 = 42.9% ==> B good quality of water.


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