It scored 23/24, (EXAMPLE HERE) the mark that was lost was in the “Evaluation” section. Hopefully it’ll be a decent exemplar for you all. Here’s a quick guide I’ve sketched out for a rough layout of an IA (this is also on my Chemistry IA page). We’ve omitted the conclusion given how straightforward it is.
Introduction: Explain the real life significance of the topic. Why should scientists care? The basis of the investigation should be linked immediately to a recognisable real world issue (hence your investigation may have results of some benefit to the scientific community). One thing I might suggest depending on the nature of the RQ is putting a null hypothesis too (but of course science is not quite as binary as that, but if it is simple enough, it could work).
Methodology: I recommend planning early. Spend as much time planning it as you possibly can – a well planned experiment will be one that is difficult to be critiqued. Consider exactly why you chose your independent and dependent variables and the values of the former. Justify this with research. The controlled variables must be explicitly linked to your dependent variable (e.g. this fluctuation affected X, which affected recordings of the dependent variable). Limitations should be pointed out. Limitations are not weaknesses. A limitation with an experiment that finds the relationship between sodium ion concentration and the rate of neurogenesis in the hippocampus of the brain is that its results are not applicable to other parts of the nervous system. Weaknesses like using high uncertainty apparatus should be addressed in the evaluation.
Analysis: I would point out that if your standard deviation is high for a particular set of values, look for an anomalous point, check the SD without it and if necessary, remove it using a reduction in SD as justification for doing so. Try to explain what R squared is as well if you can.
Evaluation: Link your strengths and weaknesses directly to the independent/dependent variable and the reliability of your data and therefore the certainty of your conclusion.Also, the strengths of the experiment should also be explained clearly. I typically go for a 3-4 rule, explaining 3 strengths and 4 weaknesses.
Lastly, explain everything as clearly as you can. Link your arguments to concepts you have covered as part of the course and if possible, go beyond the course and introduce more complex Biology to substantiate your central thesis.