Nature of Science Practice – Cells

Here is a resource I will be using to help students learn and review the nature of science topics in Unit 4 – Cells (Topics 1.1, 1.2, 1.3, 1.4, 1.5).  This is an important topic for the Nature of Science, as the osmotic potential prescribed practical and Davson & Danielli have made multiple appearances on past exams – this is clearly an area to watch!



Here are some flashcards I put together on Quizlet identifying the scientists that are mentioned in the NOS. While it is unlikely that you would have a question asking you to name a specific scientist or the conditions under which their work took place, it is definitely helpful to be able to link names to topics and to their area of work.

Image from:

Famous Scientists. 2018.

A.4 Innate and learned behaviour

Looking for patterns, trends and discrepancies—laboratory experiments and field investigations helped in the understanding of different types of behaviour and learning.

Both laboratory experiments and field investigations have been essential in understanding animal behaviour and learning.  Both forms of investigation are necessary: lab experiments allow for the precise control and manipulation of variables, but provide an artificial setting; field investigations provide the natural setting required but can face challenges in controlling the boundaries of the experiment.

A classic 1950s lab study investigated mimicry in butterflies in the lab by providing caged birds with different species and recording their feeding behaviour (van Zandt Brower, 1958). This was based on the observed toxicity of monarch butterflies (Danaus plexippus) and its presumed mimic, the viceroy butterfly (Limenitis archippus). The butterflies were prevented from flying by folding the wings together and then presented to the birds. Control butterflies that did not mimic the coloration of the monarchs  were eaten in every trial by all birds. The monarch was not eaten in any of the trials and the butterfly that mimicked the coloration of the monarch (the Viceroy) was similarly avoided.  The study helped expand our understanding of mimicry and bird foraging behaviour in a very controlled setting.

In contrast, field studies have a range of challenges in ensuring that the behaviour observed is free of bias or manipulation by the presence of the observers. One recent interesting study investigates foraging behaviour of harbour seals in Alaska (Womble et al.). Dive duration and depth were inversely correlated with prey density, which depended on the habitat of the seals (glacial or terrestrial). As part of the investigation, seals had to be captured, sedated, weighed and fitted with data logging devices to record temperature, time and depth. They were then released and the data provided by the devices used to determine their foraging strategy. Obviously, there is some invasiveness in this method, but it does enable the researchers to then collect data on the natural feeding behaviour of the seals.  Field studies regularly involve such trade-offs. Similarly to lab experiments, they must also acknowledge the potential ethical concerns of these studies.

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Data from Womble et al. (2014; p1368)

Extension: Using the graph above, consider the following possible DBQ-style questions:

  1. State the average dive depth for both locations at hour 12. (1)
  2. Compare and contrast the data for terrestrial and glacial seals over the 24 hour period. (2)
  3. Using the data, evaluate the hypothesis that glacial seals spend more time foraging than terrestrial seals. (3).


Jane van Zandt Brower. “Experimental Studies of Mimicry in Some North American Butterflies: Part I. The Monarch, Danaus Plexippus, and Viceroy, Limenitis Archippus Archippus”. Evolution 12.1 (1958): 32–47. Web. Mar 15, 2016.

Womble, J.N. et al. “Linking marine predator diving behavior to local prey fields in contrasting habitats in a subarctic glacial fjord.” Marine Biology 161. (2014): 1361–1374. Web. Mar 15, 2016. Full-text available for download at: 

Language and Science

This is definitely a post for teachers!  We recently had some fantastic PD at school with Dr. Gini Rojas focusing on ELL: English Language Learning.  What was particularly useful were the range of strategies shared for developing and extending language skills in all classrooms – even IB Biology!

It does not take long for an IB teacher (or student) to realise that one of the keys to success is understanding the language of the exam, in particular determining exactly what it is that the question is asking.  Students need to be able to triangulate the Command Term, question and the number of marks, as well as interpret any additional information provided, in order to submit the appropriate response.  For English Language Learners, this can be especially challenging.

Based on a conversation with a colleague, I had a quick analysis of the word count of HL Paper 2 for  2014 (May TZ1 and TZ2 and November) and related it to the types of questions on the paper.  The results, while not definitive, do give some interesting indications of areas to focus on during class.

The figure below shows that the average number of words in the Data-Based Question section (DBQ) are considerably higher than the other two sections (Extended Response Questions – ERQ and Short Answer Questions – SAQ) of paper 2.  This is not surprising when you consider the additional information included with this question.

Word Count and Question Type
Word Count and Question Type
Ratio of word number to marks available.
Ratio of word number to marks available.

The second graph shows the average number of words per mark on the papers.  Again, the amount of words needed per mark are far greater for the DBQ than the other two sections. So what, if anything, does this “back of the envelope” calculation tell us about exams?

The DBQs require the least preparation in the sense that they are based on unseen information.  Often, the best way for students to prepare for them is to practice as many past DBQs as possible.  But looking at the language and format, there are definitely some areas that students can specifically work on in order to improve their marks. As they are worth 18 marks in HL P2, which equates to approximately 9% of their final IB Biology Grade, it is important that some thought is given here.

One of the most important things to understand are the Command Terms.  While they are no longer emphasised as much in the new syllabus, they are still the key to performing well on Paper 2 and 3. These are Tier 2 vocabulary words, meaning they have different meanings in different subjects.  Knowing the difference between “Explain” and “Evaluate” in a biology paper could be crucial.  Practicing with sentence starters linked to the command term is one way to do this, especially for EAL students. Matching Command Term to definition is an easy formative quiz topic as well.

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Sentence Starters for Compare and Contrast – Sweetwater District (2010)

Other useful tips include: highlighting and annotating the paragraphs to identify key information; writing a short summary of each graph’s data; paying attention to the number of marks available and looking for any key terms mentioned in the question (using an example; looking at all the data; based on the previous graph etc.)

There is much more to talk about here; I will try to put together another post before the exam season starts.  Please send any comments about how you prepare your students for DBQs; students feel free to ask any questions.


Sweetwater District-Wide Academic Support Teams. 2010. Academic Language Function Toolkit. Web. 8 March, 2016.


The Nature of Science and Assessment

The Grade 11 Semester 2 exams are almost upon us!  This will be the first formal assessment including the NOS this year, so it is important to think a little bit about how this might work and what exactly you need to know.

The Teacher Support Material says that  “NOS will be assessed in SL and HL examinations in all of the externally assessed components—papers 1, 2 and 3—in every session. NOS will not be examined in isolation. The questions will be put into subject-specific contexts. ” (2014)

What this tells us is that you are not expected to memorise dates, names, co-workers, detailed experimental procedures or who won Nobel Prizes.  What you need to be able to do is recognise how certain experiments changed the way we view biology and offer evidence of how biology works.

For example, you would not be expected to remember that in 1935, the English biochemists Hugh Davson and James Danielli proposed their model of membrane structure and that this was replaced in 1972 by the model devised by the Americans SJ Singer and Garth L. Nicholson. What you would need to remember is that this represents how biological knowledge changes over time and that as new evidence accumulates, theories which are no longer supported must be replaced by theories that reflect the experimental data. This is an example of the falsification of science and is a key aspect of the production of knowledge in the Natural Sciences.

In terms of your exam preparation, then, you should focus on the description of the NOS, which is displayed at the top of each blog post. You should understand in broad strokes how the particular individual or experimental technique mentioned relates to that statement.  You will also need to link the NOS to the syllabus content; for example, the Davson-Danielli NOS might need to be linked to the structure and function of the plasma membrane.

The idea here is that this should be approached form a process perspective, rather than focusing on content – you have enough to do of that as it is!


IB. Biology teacher support material: First assessment 2016. 2014. IBO; Cardiff. Print.