Using the Nature of Science in Class

With my current grade 11s, we have not spent much time on the nature of science in class.  Although resources are provided in their notes, we have focused more on experiments and content.  Having just finished our second unit and the end of unit test, I developed this resource as an introductory activity that students worked on in groups of three.

The resource is adapted from one of the many wonderful templates provided at the #TMSouthHistorians blog: https://tmsouthhistorians.wixsite.com/tmsouthhistorians/copy-of-blog-resources and often shared through @Jmosley_history – this is the A-B Starter.

 

I chose NOS prompts from topics 5.1, 5.2, 5.3, 10.3, 4.1, 2.1, 2.2, 2.3, 2.4, 2.5 and 8.1, which make up the first two units I teach – Diversity of Life and Chemistry of Life.  I had the students work together with no resources to begin with and try to identify links to the syllabus topics, TOK and to using the five categories of NOS to help organise the different ideas.  I tried to emphasise that they didn’t need to try and memorise new content but to discuss how these link to the knowledge they already have.  The task seemed to work well and got them more engaged than if we were just learning the content of the statements.  I hope to eventually develop templates for each unit that I teach.

 

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5.2 Natural selection

Use theories to explain natural phenomena—the theory of evolution by natural selection can explain the development of antibiotic resistance in bacteria. (2.1)

Evolution occurs at both the micro and macro levels.  Macroevolution is the eye-catching form, where we see species changing into dramatically new ones. This process though takes time and is not directly observable. 

Microevolution, while less “glamorous” is no less interesting. Indeed, it has applications that are amongst the most serious concerns in health, medicine and agriculture. This is the ability of populations of bacteria, protists, fungi, insects or plants to evolve resistance to antibiotics, drugs, pesticides and other chemicals used to control them. 

The resistance of bacteria to antibiotics has occurred at an incredible rate, as the image below shows:

Image from CDC.gov

What is particularly concerning about this is shown in the following graph – the number of antibiotics being developed approved continues to decline, which leaves fewer options for treatment.

Understanding the process of evolution is critical to estimating the number and type of new drugs that are needed to combat them.  It is thus necessary to understand that antibiotic use represents a very strong selection pressure. Given the reproductive potential of bacteria (more offspring are born than can survive) and the variation that is possible (through both mutation and horizontal gene transfer) it should therefore come as no surprise that populations rapidly evolve resistance.  Evolution and natural selection are thus not the dated musings of a 19th-century naturalist, but of critical importance to health problems of the 21st-century: in the US alone, over 2 million illnesses and 23,000 deaths per year are directly attributed to evolved resistance.

From an assessment perspective, antibiotic resistance in bacteria is a great example to use when responding to and extended response question on evolution/natural selection.

Sources:

“About Antimicrobial Resistance | Antibiotic/Antimicrobial Resistance | CDC “. Centers for Disease Control and Prevention. Cdc.gov., 2016. Web. 11 Dec. 2016.

“Microevolution”. Understanding Evolution. University of California Museum of Paleontology.Evolution.berkeley.edu. 2016. Web. 11 Dec. 2016.

5.1 Evidence for Evolution

Looking for patterns, trends and discrepancies—there are common features in the bone structure of vertebrate limbs despite their varied use.

This Nature of Science statement fits neatly into the syllabus content for this topic.  One of the applications for 5.1 is – “Comparison of the pentadactyl limb of mammals, birds, amphibians and reptiles with different methods of locomotion.” (IBO, p67). Thus understanding the importance of the pentadactyl limb as an example of a homologous structure should allow you to understand it as an example of seeking patterns, trends and discrepancies.

All amphibians, birds, reptiles and mammals descended from a common ancestor that had a tetrapod (4-legged) body plan and lived some 360 million years ago. However, as the different vertebrate groups then radiated outwards, this basic structure became adapted for different functions, some more radically than others.  Snakes have lost their legs, birds developed their forelegs into wings and whales and icthyosaurs returned to the water, with fore limbs adapted for paddling. However, despite these differences in function, an analysis of anatomy shows the same underlying structure.

The pattern is the repeated form of bone and limb structure (1 long bone-2 shorter bones-smaller bones-5 digits); the trend is that this developed among all four tetrapod classes and the discrepancies are the evolution of different functions and forms (wings-flying; flippers-swimming; arms-grasping etc. )

Homologous Tetrapod Limbs (University of California Museum of Palaeontology)

 

As Stephen Jay Gould wrote, “Why should a rat run, a bat fly, a porpoise swim and I type this essay with structures built of the same bones unless we all inherited them from a common ancestor? (Gould, 258).

 

Gould, Stephen Jay. Hen’s Teeth and Horses Toes. New York, Penguin. 1990. Print.

“Homologous Tetrapod Limbs (4 Of 6)”. Evolution.berkeley.edu. University of California, Museum of Paleontology, 2016. Web. 24 May 2016.

IBO. Biology guide: First assessment 2016. Cardiff, IBO. 2014. Print.

5.4 Cladistics

Falsification of theories with one theory being superseded by another—plant families have been reclassified as a result of evidence from cladistics.

The use of DNA sequences to classify organisms has been an important breakthrough in classification. Previously, species were classified primarily on morphology (physical characteristics), which works some of the time but is less useful in other situations. Thus seemingly unrelated organisms have been grouped more closely together and those that were thought to be very closely related have been found to be more distant.  Carl Woese used gene sequencing to not only overturn the existing dogma of the 5-Kingdom system, but to also propose that Archaea are more closely related to humans (eukaryotes) than to other prokaryotic bacteria. This was a major paradigm shift  in microbiology and has since been recognised as “…one of the 20th century’s landmark achievements in biology…” by Dr. Nigel Goldenfeld (“Carl Woese | Carl R. Woese Institute For Genomic Biology”).

In another example, the Figwort family of flowering plants, underwent a dramatic recent reclassification.   The figworts were a large family classified under the family Scrophulariaceae and included the popular snapdragons and foxgloves. Using three genes found in the chloroplast, researchers were able to determine that there were significant differences in lineage and so an entire family had to be reclassified into six families. See Olmstead et al. (2001), full text available online, for the full scientific story.

Butter-and-eggs, or Linaria vulgaris, is a close relative of the snapdragon, and no longer in the Scrophulariaceae

The monkey flower is a traditional snapdragon to many people, but is now in a more obscure family – the Phrymaceae.

Cladogram representing changes to the classification of the snapdragons. Olmstead et al. (2001).

Sources:

n.a. ” Carl Woese | Carl R. Woese Institute For Genomic Biology”. Igb.illinois.edu. University of Illinois, 2016. Web. 25 Apr. 2016.

Essig, F. “Whatever Became of the Snapdragon Family?”. BotanyProfessor. Botanyprofessor.blogspot.  April 5, 2012. Web. April 25, 2016.

Olmstead, Richard G., Claude W. dePamphilis, Andrea D. Wolfe, Nelson D. Young, Wayne J. Elisons, and Patrick A. Reeves. Disintegration of the Scrophulariaceae.
Am. J. Bot. February 2001 88:348-361. Web. Accessed April 25, 2016.

5.3 Classification

Cooperation and collaboration between groups of scientists—scientists use the binomial system to identify a species rather than the many different local names.

This is one of my favourite topics (as a former zoologist) and one that lends itself to a number of different activities with students. To emphasise how different languages classify organisms in very different ways, I ask the students to come up to the board and write the name “elephant” (or another readily identifiable animal) in their mother tongue.  Here’s what we come up with today:

How many ways to say elephant?

Out of 11 students in the HL class, we had 8 different mother tongues represented in the picture above: Shona, English, German, Khmer, Chinese (Mandarin), Vietnamese, Urdu and Japanese.  This provides a clear indication of the need for a uniform system of classification.  It can also be augmented by a side discussion about, to continue the trend, elephant grass, elephant seal, elephant shrew, etc.

The next part of the lesson allows us to focus on the Khmer language (a good opportunity to link to our host-country). In Khmer, the word for tiger is ខ្លា (Klah)  and the word for sun-bear is ខ្លាឃ្មំ (klah kmoom). We discuss how this intimates a very close relationship between the two species.  But how close?

Binomial classification of the tiger and the sun bear.

A binomial classification then reveals that the two animals are indeed closely related to the level of the Order, but then separate into different Families, Genus and Species.  This makes it very apparent to the students that scientists can use the binomial system to improve communication and understanding of the classification and relationships between living organisms. Thus both the Nature of Science and the required content are covered in this lesson.  An additional extension could be to name a common name in English and then have students translate it into their mother tongue.  Jellyfish is a good example, as it is nonsensical when translated into many languages (not to mention it is not a fish!)

How do other IB Biology teachers teach classification?  How do others use language to frame the lesson?  I would love to hear from you.