How to write an excellent IB Biology Lab Report: a step by step guide

Your Biology IA is one of the best ways to boost your final score, especially if your on the upper boundary of a lower grade. Literally, it could push you up a grade. Here’s how to write one (in its logical sequence) worthy of full marks (I am using examples from my own IA that got close to full marks) :

The Title: An experimental study on…. – even though it is just the title, it should be as specific as possible. Try to include both the independent (the thing you’re changing) and dependent (the thing you are measuring e.g. time, height etc.) variables in your title. For example, An experimental study on the rate of reaction (dependent variable) of rennin (variable kept constant) on different percentage concentrations (independent variable, milk concentration is what we are changing) of full cream milk.  Note the use of both dependent and independent variables and the specificity of “full cream milk”.

The Research Question: Make this as specific as you possibly can. In itself it should be a one line brief on what your experiment is about- the examiner should be able to tell instantly what you are investigating, your independent and dependent variables. Are you looking for the effect of something on something else, the time taken for A to react with B etc.? If you are changing something, make sure you outline to what extent you are changing it. For example, 60 -100% milk concentrations, different colours of light (red, orange, yellow, green, blue, violet). What are the essential variables that need to be kept constant e.g. “….at a temperature of…”. State what you are measuring your dependent variable in, is it seconds? milliseconds? minutes and seconds? Be ultra specific. For example: What effect will the percentage concentration of full cream milk (measured from 60% to 100% concentration in 10% intervals) have on the rate of reaction of rennin and milk (measured in time taken in seconds to form clots) at a temperature of 35°C?

Background Theory: This should be where you essentially show the theory behind your investigation, and thus show your understanding of what you are doing. In this case, my practical had to do with enzymes, so in my background theory I made sure I explained how enzymes worked on its substrates, and in particular, how rennin worked on milk (I researched this, and put it as simply as possible in my own words, while still sounding smart). Because rennin also had a function in real life (clotting milk in mammals’ intestines to aid digestion) I made sure to include this too. Don’t forget to reference if you have used other sources! Harvard Style Referencing is loved by the IBO, and there are plenty of generators out there that can do it for you.

Hypothesis: Give a one line hypothesis stating what you think will happen (this should be in bold).  Keep in mind that it doesn’t have to totally work out in your experiment, it just has to make sense in line with the theory you have just explained.

Explain your hypothesis based on the theory directly under the statement you have just made. Link it back to the theory and explain it as logically as possible – show the examiner that you have made the link, and thus understand what is happening.

Apparatus used: a list of the apparatus and materials you used, including (in brackets) the error/limitations of any measuring equipment. Remember, this is half the limit of reading, so for a mercury thermometer it should be (±0.25C) and for burettes, (±0.006mL).

A table of all your variables (independent, dependent, controlled, and how they were achieved): It should be 2 columns, on the left, your variables, and on the right a (brief) explanation as to how you achieved it. This makes it super clear to your examiner exactly how you are controlling your variables, and is essentially a safety net if something doesn’t make sense in your method.

Method: a step by step, third person (impersonal) and past tense recount as to how you did the experiment. Again, be as specific as possible and get somebody else to read it and tell you whether it makes sense. Reading it aloud to yourself also helps.

Raw Data: presented in a table displaying units, repeat numbers and independent and dependent variables. Give your table a heading – Table showing…. and if necessary, label it “Table 1” for easy reference in your evaluation. (It may be useful to label all your graphs and tables with numbers so that you can make easy reference to them). All your headings for tables and graphs should be very specific as well. For example, Table 1: Table showing the time taken (in seconds) for different percentage concentrations of milk (60%- 100% in 10% increments) to react with the enzyme rennin at 35°C. If there are any anomalies in your data, highlight them clearly, and explain below your table why you consider them to be anomalous, and thus you are excluding them. If you have executed extra repeats for anything or done anything “unusual” explain why, and how this is contributing to the reliability, accuracy and overall quality of your investigation.

Observations: directly under your raw data, with at least 2 non-superficial observations you made. Crucial element to any investigation.

Processed Data: presented in (several) tables, if necessary. This should include averages, standard deviations, error calculations, if you are dealing with time and rate, rate calculations (1/t), average rate, standard deviation of rate, and so on and so forth. This is where you can really stretch out an investigation and find things to comment upon (an abnormally large standard deviation, any odd error calculations, any trends that are occurring?) Underneath each “table” of processed data you should include a worked example. E.g. worked example of averages, rate of reaction etc. Make sure you mention underneath your table if you have excluded anomalous data.

Presented Data: graphs! Make sure you LABEL your axis, BREAK your axis if necessary and make a reasonable scale that is suitable for your graph. Your graph should take up at least 3/4 of the graphing space. Error bars (and their explanation underneath the graph e.g. based on standard deviation, percentage error etc.) are crucial, because it gives you something to talk about in your evaluation! Note down any calculators or software e.g. Excel that you used to calculate error etc. or that you used to graph your data.


Conclusion: state the conclusion that you have made (in one sentence, bold), and then proceed to explain that conclusion based on theory.

Discussion: discuss any anomalous data, any methodology that may have led to that anomaly and provide several perspectives as part of your discussion (give plenty of reasons as to why you think your data was anomalous!). Include any information on any action you took to resolve those issues e.g. more repeats etc. Discuss variations in error, standard deviation, and again, make sure you DISCUSS, not list. Make sure you also make reference to your processed and presented data, that’s the whole point!

Evaluation: in a table format. On the left column, what you could have improved, on the right, an explanation as to how you could improve this in the future. They should be meaningful, and not superficial. Come up with at least 5. The IB wants you to recognise that you are not perfect and that with every investigation, there are things that can go wrong. They will give you marks for making mistakes, as long as you can identify them and identify solutions for the future. That is, you are better off performing a less than perfect investigation, and perfecting your evaluation and discussion.

(And finally,) Limitations: what were the limitations of your experiment? Time constraints? Limited supplies? – e.g. in my case, only one batch of rennin that could have been faulty and was also human engineered and thus may not have been a true representation of natural rennin. This is to show that you understand the factors that may have prevented you from performing a flawless investigation (which we all know, you did not). However, you must never blame the accuracy of your measuring tools – to scientists, this is a terrible excuse.

Related Articles: How to get a 7 in SL Biology

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One Response to How to write an excellent IB Biology Lab Report: a step by step guide

  1. IB Student says:

    Hey, I noticed that you have done the same lab experiment that I am doing right now, and I was wondering how you measured the product (the amount of insoluble casein/curdles in each concentration of milk) in your experiment. Thank you 🙂

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