level of aggressiveness accordingly. Using additional video sequences, the students further quantified brood care behavior of N. pulcher social groups to understand why the dominant male tolerates male helper individuals in the group. This practical exam required a high de gree of concentration when observing behaviors, as well as developed analytical skills when manually calculating the statistical tests.
Practical 4 – Comparative and Functional Biosystematics (Syst ):
The goal of this exam was to reconstruct the phylogeny of mammals based on synapomor phic characters observed on skulls, as well as to study the rate of evolution of several skull shape measurements. Thanks to the incredible support of the Natural History Museum of the Burgergemeinde Bern, we were able to expose the students to original skulls from 8 mam mals, which they had to observe and measure carefully. The students then analyzed their data, complemented with data provided for an additional 16 species, using various phylogenetic methods such as the identification of synapomorphic characters, maximum parsimony or UPGMA (Unweighted Pair Group Method with Arithmetic Mean). Finally, the students used advanced statistical techniques to compare skull shape across species while taking skull size into account. A major hurdle in preparing this practical was that each of the 65 sets of skulls had to be measured multiple times individually before the IBO to ensure a fair marking scheme.
6. 1. 2 Preparing the Practical Exams In order to prepare diverse tasks and to share the workload broadly, each practical exam was organized in collaboration with a different institute of the University of Bern and one with the Natural History Museum of the Burgergemeinde Bern, an independent institution and long-term collaborator of the university. For each practical, the institute in charge named one or two main responsible persons that teamed up with a senior person from the Swiss Biology Olympiad and functioned as the organization team for this practical (see TABLE 3 . 1 ). This model allowed to pair the detailed knowledge in every subject with the experience in IBO exams the Swiss Biology Olympiad acquired over the years, while ensuring that the planned experiments could be organized with the available equipment and within the budget. A major challenge when organizing practical exams for an IBO is that most protocols estab lished for teaching purposes at universities are designed to demonstrate a particular biological effect, rather than to require the students to make their own interpretation. In order to assist the organization teams in developing high quality exams, each exam thus passed through several rounds of internal review with the goal to give vital feedback during the development, to help turning functioning protocols into practical exams in line with IBO rules and traditions, and to harmonize structure, organization and layout of the four exams. The review committee of the IBO 2013 consisted of the scientific project manager of the IBO 2013 (Prof. Daniel Wegmann) and the representatives of the Swiss Biology Olympiad implicated in the four exams (Thierry Aebischer, Adeline Colussi, Michael Jutzi), which brought together extensive experience regarding IBO exams both on national as well as international level. In a first step, each organization team developed feasible protocols in their subject and as sembled a list of necessary equipment. These proposals were then discussed in the review committee regarding their ability to function as an exam. Each team then developed a fully functioning protocol on their own. In a second round of review, the protocols were discussed regarding their difficulty and time requirements and several extensions or simplifications were worked out to match the demands of the IBO. Then, organization teams went ahead to write
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