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Practical 5: Mesocosm Building Challenge!

Practical 5 is the 5th of the six required practicals in the SL IBDP Biology course (last exam May 2024) and it is one of my favourites. I love to start my course with this practical! It's a great opportunity for students to collaborate, problem-solve and apply their knowledge of Biology in a new way. The planning and organization required allows me to identify which students are likely to need further support with time management and I can also identify the natural leaders in the group.

In case you are not certain what a mesocosm is, it is similar to a terrarium in that it is often a small transparent container of pebbles, soil, plants and sometimes insects in a glass jar. The key difference is that the goal of a terrarium is often decorative or serves as a demonstrative tool rather than an analytical tool. Some terrariums are open to the air, but all mesocosms are sealed.

Mesocosms allow for the observations of nature under controlled conditions. The IBO does not specify that the mesocosms built by students must be terrestrial, although most of my students choose to build terrestrial ones. In fact, building an aquatic or even microbial mesocosm can be easier (as long as you can find the materials). The key is that students need to aim for a sustainable mini-ecosystem, much easier said than done!

Even though this lab will not be part of the new IBDP Biology syllabus as a required practical it is included in Subtopic D4.2 Stability & Change. You can see the extract from the new syllabus (page 104) here:

In the old syllabus it was called Practical 5 and could be found on page 60, where it says "Skill: Setting up sealed mesocosms to try and establish sustainability (Practical 5)" as part of Subtopic 4.1, Species, Communities & Ecosystems. This is a pretty open practical, which I love about it as it gives students a chance to figure it out and a chance for you as the teacher to observe their ATLs as they attempt to do so. Here are some pictures of Mesocosm building with my class from two years ago. It's hard to believe that these students have graduated and are now off studying or exploring.

I take an entire class block for mesocosm building and include some simple supplies, including soil, rocks and any containers from previous years (the students need to clean them out first). It easily takes up an hour of my required 40 hours in the PSOW and is a really fun day. Once we finish building the mesocosms students place them on a table in the IB Study room by some windows so they can add some colour to the space, advertise my class and students can check on the health of their mesocosm over time.

Some tips for mesocosm building:

  • Give students at least a week to gather their materials and allow them to work in pairs, this makes it easier for them to source the materials they will need

  • Be prepared for a mess, borrow a broom, dustpan and mop from you school cleaning staff if you don't have one in your room (and make the students clean up after themselves!)

  • Try to schedule the set up block when you don't have class afterwards, since our schedule is tumbling I try to schedule this before morning break or lunch, sometime students take longer than expected, usually the disorganized and unprepared groups

  • Circulate and listen to your students as they build, this is great formative data and you can give them some tips as needed

  • Make it an assignment, you can see the assignment I give to my students below, rubrics included!

Practical 5 Mesocosm
Download DOCX • 18KB

I have always turned my mesocosm practical into a little competition, we see which mesocosm(s) can survive the longest. Here are the winners from the group two years ago, we ended up having several that were still alive after over a year! Students love to check in on their mesocosms and see the changes that are happening over time, did they include enough moisture or too much? Did all of their plants survive, or did some take over? You can see in the survivors from this group that many did not stay the same, they changed significantly over time.

I hope this post was helpful and that you and your students enjoy this lab as much as my class always does. It's one of my favourite labs of the course! If you would like information about the other required practicals I have blog posts about Practical 1: Microscopy, Practical 2: Osmolarity lab, Practical 3: Enzymes & Practical 4: Chromatography of Plant Pigments. Luckily, most of these labs fit well with the new syllabus, so we can keep using them!

Thanks for reading teachers, travelers & curious souls of all kinds.

The Roaming Scientist



Hi, thanks for stopping by!

I'm the kind of teacher who is always trying something new, new labs, new Apps, new scaffolds and even new countries to live and teach in. I'm looking forward to share what I learn with you all through my weekly blog posts. 

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