Old IBDP Biology Practicals for the New IBDP Biology Syllabus... what works?
After six years of teaching IBDP Biology I know the old syllabus and the seven old required practicals very well...so well that I wrote a blog post about each one. In classic IBDP fashion the syllabus has changed, as it does every seven years. In the new syllabus (first exam 2025) there are no longer any required practicals, but many laboratory skills are still included and 40 hours of practical work are also still a key part of the syllabus. So, what can we save from the old syllabus? A reliable and useful lab is not easy to come by, so in this post I will go through each of the old lab practicals and describe how they do or do not fit into the new syllabus.
Old Practical 1: Microscopy
In the old syllabus this lab required that students demonstrate the following skill: "Skill: Use of a light microscope to investigate the structure of cells and tissues, with drawing of cells. Calculation of the magnification of drawings and the actual size of structures and ultrastructures shown in drawings or micrographs. (Practical 1)."
The good news is this lab is still part of the new syllabus, although some components have been added in. It is now part of Subtopic A2.2 Cell Structure on page 39 of the new Subject Guide: "Microscopy Skills: Student should have experience making temporary mounts of cells and tissues, staining, measuring sizes using eyepiece graticules, focusing with coarse and fine adjustments, calculating actual size and magnification, producing a scale bar and taking photographs"
I have modified my old Practical 1 lab sheet into a new microscopy lab, which you can download for your own use here. It doesn't yet include anything about eyepiece graticules as we still need to find some that work with our school microscopes, hopefully for next year.
Old Practical 2: Osmolarity
This lab practical was an important component of Topic 1, focusing on cell membrane transport, the specific description from the IBO stated "Skill: Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions. (Practical 2)". I used to use potato cores to analyze the movement of water and ions across cell membranes in different solutions.
The good news is this lab is very much still a part of the syllabus in Subtopic D2.3 Water Potential on page 94 of the new Subject Guide. There are however, more details given about the analysis of the data and for this reason this lab is now later in my course than it was before. The new subject guide describes it as "D2.3.4—Changes due to water movement in plant tissue bathed in hypotonic and those bathed in hypertonic solutions Application of skills: Students should be able to measure changes in tissue length and mass, and analyse data to deduce isotonic solute concentration. Students should also be able to use standard deviation and standard error to help in the analysis of data. Students are not required to memorize formulae for calculating these statistics. Standard deviation and standard error could be determined for the results of this experiment if there are repeats for each concentration. This would allow the reliability of length and mass measurements to be compared. Standard error could be shown graphically as error bars."
I will be using a very similar lab protocol to what I used with the old syllabus, I will simply be adding more analysis tasks such as calculation of standard deviation and standard error using the entire classes data set as well as graphing the data using error bars.
Old Practical 3: Enzyme Reactivity
This is an excellent lab practical, I used to always do this lab using lactase pills since it made a nice connection to the example of lactose intolerance included in the old syllabus. The description from the IBO of the old practical is "Skill: Experimental investigation of a factor affecting enzyme activity. (Practical 3)". This lab is also still in the new syllabus, with some modifications. It is part of subtopic C1.1 Enzymes & Metabolism on page 65 of the new syllabus. In my new version of this lab I would include more graphing and interpretation of graphs as well as secondary data to compare with students primary data.
While keeping the lab pretty much the same to include a choice of manipulating temperature, pH and substrate concentration I would add secondary data to the data analysis, ideally from scientific journal articles. This is a particularly useful skill as students prepare for their IA, using both primary and secondary data to answer a research question is an excellent skill to develop well in advance of the IA. The example of lactose intolerance and production of lactose-free milk is no longer a required example, so while I will probably use that enzyme this year since I still have some there is no reason to continue using it (and sneaking it into Morocco in my luggage) in the future. Any enzyme will do.
Old Practical 4: Photosynthetic Pigments
I always enjoyed the chromatography part of this lab, but found the spectroscopy component much more challenging to both run in class (spectrophotometers are expensive!) and to help my students understand. The old practical was described in the Subject Guide as "Skill: Separation of Photosynthetic Pigments by Chromatograph. (Practical 4)".
Luckily, the chromatography part of this lab is still part of the syllabus in Subtopic C1.3 Photosynthesis on page 70 of the new subject guide. In the future I will attempt both paper and thin-layer chromatography in my class as students are still required to calculate Rf values for different photosynthetic pigments and identify them by colour as well as by calculated Rf value.
I am happy to say that the Spectroscopy component of this practical has been significantly changed. Now students are required to understand the differences between absorption and action spectra and how these are affected by differing quantities of carbon dioxide, light intensity or temperature and plotting these graphs themselves. This requires much more understanding than the old syllabus implied, which will help students to connect these ideas better. It will require significant adaption of the lab before I can use the spectroscopy component, but it will be worth it.
Old Practical 5: Mesocosms
This was always the very first practical of my IBDP Biology course, I used it as a way to assess students planning and collaboration skills and we turned mesocosm survival into a little bit of a competition with home-made cookies for the team with the longest surviving mesocosm. In the old syllabus it was described as "Skill: Setting up sealed mesocosms to try and establish sustainability (Practical 5)".
It is now part of Subtopic D4.2 Stability & Change which I plan to teach later in the course, at least in this first round of teaching the new syllabus. It can be found on page 104 of the new guide and says "D4.2.4 - Use of a model to investigate the effect of variables on ecosystem stability. Mesocosms can be set up in open tanks but sealed glass vessels are preferable because entry and exit of matter can be prevented but energy transfer is still possible. Aquatic or microbial ecosystems are likely to be more successful than terrestrial ones. NOS: Care and maintenance of the mesocosms should follow IB experimental guidelines."
Interestingly, the new syllabus does not outline it as an Application of Skills, but clearly states that mesocosms can (should?) be set up. Regardless, I love this lab and will be keeping it in my PSOW, although I will be adding some parameters around a more formal investigation into factors affecting ecosystem stability, maybe having each group use the same species of plants, but different amounts of water or light.
Old Practical 6: Ventilation Rate
In the past I have used this practical as a way to help students better understand the challenges of working with human subjects before they choose their IA topics. The large samples sizes required and many confounding variables as well as ethics involved are important concepts to teach before students decide to take on an IA which requires humans for data collection, which is usually a very popular choice. The old syllabus describes this practical as "Monitoring of ventilation in humans at rest and after mild and vigorous exercise (Practical 6)".
This practical, like several of the others discussed in this post has been included, but heavily modified. You can now find it in Subtopic B3.1 Gas Exchange and it is described as: "B3.1.6—Measurement of lung volumes. Application of skills: Students should make measurements to determine tidal volume, vital capacity, and inspiratory and expiratory reserves." (pg. 57 of the new subject guide). So the effect of exercise is now completely gone, and more data collection is required. Luckily all of these variables can be measured with an air bag or spirometer, we have purchased some digital vernier spirometers this year that I am excited to try.
I think this lab will now require some control group/base data collection of these different variables along with maybe some demographic data about subject height, weight, smoking status, physical activity etc. so that we can still learn about consent forms and investigations involving human subjects. I do not plan to include the effect of exercise any longer, but I will encourage students to find another factor to investigate such as age or height and their effect on one of these required values (tidal volume, vital capacity, inspiratory reserves & expiratory reserves). It will definitely take some trial and error to figure out, but I think it will still be a great lab.
Old Practical 7: Potometers
The last of the old practicals was only for HL students and was one that my students always found a bit challenging to set up correctly and to understand. However, once they were able to think of the water movement as a continuous column through the potometer, the stem, the leaves and then the stomata it really was a great lightbulb moment. In the old syllabus the instructions for this lab were "Skill: Measurement of transpiration rates using potometers (Practical 7)".
This is the only one of the old required practicals that is completely absent from the new syllabus. That being said, if you really like this lab and it helps your students learn it can still be tied into several subtopics. It fits with B3.1.9 Transpiration as a consequence of gas exchange in a leaf (students should be aware of the factors affecting the rate of transpiration), B3.2.7 Transport of water from roots to leaves during transpiration and D2.3.10 Contributions of solute potential and pressure potential to the water potential of cells with walls (including xylem vessels). While I won't be teaching this concept until next year my current plan is to use magnetic water molecules from 3D molecular designs, a great animation from Science & Plants for Schools along with some demonstrations of the cohesive and adhesive properties of water rather than this lab. Since stomatal density is now required I would rather take the time to do that as a full lab instead.
While teaching a brand new syllabus can be overwhelming it is really nice that some of these tried and true labs can still be used, albeit with modifications. I hope that you found this post useful and that your first year teaching the new IBDP Biology syllabus is going well.
Thanks for reading teachers, wanderers and curious souls of all kinds.
The Roaming Scientist
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