The Next Generation Science Standards promote teaching methods that are use seven, Cross Cutting Concepts (click for a link to more information about the NGSS). While thematic approaches to biology teaching have been around for a long time (just look in the opening chapter of just about any biology textbook), the CCCs are distinct in that 1) they range across all the sciences (including physical sciences and earth/space science), and 2) they will be implemented (with increasing complexity and sophistication) throughout a child’s K-12 education. According to the writers of the standards, this will provide students with the “mental tools to help engage in and come to understand the phenomena” they encounter when learning science (NGSS release, April 2013, p. 2).
I agree with this proposition, and to help biology teachers get up to speed on what these concepts involve, I’m sharing the following thoughts. I’ll start with a brief description of each of the cross cutting concepts. I’ll follow that with an application of the CCCs to one topic in biology…the biology of spiders. Why spiders? I was lucky enough to spend some time at the American Museum of Natural History, where I visited their special exhibit about spiders. Inspired by the exhibit (and by a recent workshop I attended at the California Academy of Sciences about the NGSS, I thought I would try my hand at applying the CCCs to that one topic. Here goes.
2. An Overview of the CCCs
- Pattern: A pattern is a repeated form or event. Patterns don’t occur randomly: when they do, scientific thinkers (including educators, learners, and practicing scientists) can look for a cause. Patterns can also be used to classify and organize objects and events.
- Cause and Effect: A cause is something “that acts, happens, or exists in such a way that some specific thing happens as a result; the producer of an effect” (dictionary.com). Events have causes, and a goal of science is to explain how events come about. At the same time, an important part of science is seeing what effect a phenomenon’s presence has. How, for example, is a system different when a certain phenomenon is present? How does the system change when the phenomenon is absent? Finally, a habit of mind cultivated by scientific thinkers is to carefully distinguish between causes and correlations, particularly with regard to making sure that correlations only get causal status when earned through observation and experimentation.
- Scale, Proportion, and Quantity: Phenomena occur at different scales of time, size, and energy. When trying to understand something, a common scientific move is to measure it: how big is it? How long does it take? How much energy does it require (or release)? Similarly, to understand a scientific representation, one needs to ask (and get your students to ask) the same questions. For example, when presenting a diagram showing protein synthesis, students have trouble contextualizing where this process is happening, and how small the various pieces involved (mRNA, ribosomes, proteins) are. This CCC encourages us to explicitly teach this.
- Systems and System Models: Any biological phenomenon is part of some open system, and embedded in a larger system. All systems have features like boundaries, inputs, processes and outputs. To understand biological processes, students need to be able to create conceptual models of systems, and demonstrate an understanding of how changing the system’s dynamics (inputs or processes) changes the system’s behavior and outputs.
- Energy and Matter: This concept focuses on tracking flows of energy and matter through systems, differentiating between cyclic and linear flows, and describing how energy and matter are conserved.
- Structure and Function: In the living world, evolution has resulted in structures at a variety of levels and physical scales that are adapted to fulfilling a particular function (promoting survival and reproduction). In the world of human design, objects have been fashioned to fulfill specific personal and collective goals. In both cases, structure determines function.
- Stability and change: In any natural or a built system, what keeps that system stable, even as energy and matter flow through it? In Biology, this typically shows up in adaptations that maintain homeostasis. On the other hand, how can that system change over time, which might involve adaptation on an organismal timescale, biological development, or (on a much larger timescale) evolutionary adaptation.
3. The CCCs applied to Spiders (inspired by the Spider Exhibit at the American Museum of Natural History, New York).
- The presence of certain anatomical traits (two body sections (cephalothorax and abdomen), four pairs of legs, a pedicel (thin waist between the two sections), and tarsi (tiny claws at the end of the legs)), along with some physiological traits (production of venom in most spiders, silk production) is the pattern that makes a spider a spider.
- Different arrays of traits lets us classify smaller groupings (such as tarantulas), all the way down to the level of specific species (each of which has a unique pattern).
- Pattern also showed up in species-specific markings. This, of course, leads to the question of why that pattern exists. Some of these questions show up in “Structure and Function” below.
Cause and Effect:
- How venom causes paralysis in prey. What’s the mechanism, on a cellular/biochemical level, by which this happens?
- How spider silk works. What chemical processes keep the venom as a liquid inside, until it makes contact with air, which causes it to solidify?
Scale, Size, and Proportionality:
- Scaling the models of spider parts to the reality of their size. There was a model of spinnerets that represented them as the size of a cow’s udders.
- Scaling processes: neurotoxins operating at a sub-microscopic scale, interacting with neurotransmitters and receptors in the spider’s prey’s nervous system.
- Thinking about why spiders are relatively small animals (compare their range of size to the range of size of vertebrates). This isn’t about the tracheal system that keeps insects small; spiders have book lungs. Is this about the limits of an exoskeleton? I left the exhibit with this question unanswered.
Systems and System Models:
- A spider is, like any organism, an open system, sustained by flows of matter and energy (more on that below).
- Within the spider are other systems that play various roles in sustaining life (e.g. circulatory, respiratory, etc.).
- Each of those systems, in term, could be broken down into subsystems, all the way down to the cellular level (systems for protein synthesis, cell signaling, gene activation, etc.)
- Moving up, the spider is a part of an ecosystem. As a predator, the spider is part of a food web, itself sustained by flows of energy from the sun, to producers, to primary consumers (insects, small animals) that the spider consumes.
- Ecosystems are embedded in larger systems, each with their own inputs, processes, outputs. This includes biogeochemical cycles (carbon,nitrogen, water, etc.), and even the Earth as a planet receiving energy from the Sun, and so on.
Energy and Matter:
- As open systems (see above), spiders are maintained by flows of energy and matter. Incoming matter includes flows of oxygen, water, and food. Incoming energy is the chemical bond energy in the spider’s prey. Energy is transformed into ATP to sustain the spider’s life processes.
- Incoming matter might be funneled toward cellular respiration, and oxidized to carbon dioxide and water; or transformed into the body structures that make up the spider.
- When the spider dies, the chemical bond energy in its body will be utilized by scavengers and decomposers to sustain their life processes, simplifying spider molecules into the simpler substances that can re-enter biogeochemical cycles like the carbon cycle.
Structure and Function:
- Fangs are structured to inject venom.
- At a much smaller scale (more about that below), venom molecules are structured to paralyze the nervous system of the spider’s prey.
- Urticating Hairs: These are hairs on the abdomen with little spikes. Spiders can fling these at their predators with their hind legs. The hairs embed themselves in the predator’s skin, eyes, and respiratory tract.
- Spinnerets have spigots with valves for release of silk, and control of its thickness. Each spinneret is controlled by muscles that allow for precise positioning of the silk.
- Species-specific markings allow for mate recognition and act as reproductive isolating mechanisms (two spectacular examples are the Happy Faced Spider or the Peacock Spider).
- Orb webs for capturing prey
Stability and Change:
- A spider is a stable system. On any short timescale, it will continue to look more or less the same, even as many if not most of the atoms and molecules within it are constantly renewed. This is a typical feature of living things, and it’s explained by the system of genetically controlled protein synthesis and cellular development common to all living things. New atoms and molecules come in and get converted into parts of the same spider-stuff (on both an individual and a species level) because DNA directs the synthesis of enzymes that continue to lay down the same spider molecules to sustain the right spider-tissues in the right places. The same thing happens in you, me, and every other living organism. Stability is dynamically maintained through homeostasis.
- In terms of change, spiders, like all multicellular creatures, go through a developmental process. Through this process, the spider developed from a zygote, to a baby spider, to an adult spider. And like all organisms, spiders have evolved through time. This also relates to DNA, mutations in DNA, and the subsequent process of natural selection, which will edit out unfavorable variations, and promote favorable ones.
Originally, my intention was to make myself a test subject in a teacher’s thought-experiment. What would it be like to bring a bunch of my students to this exhibit, and Instead of putting together a scavenger-hunt, fill-in-the-blanks worksheet (a move I’ve made before), I would try something different. Since, in the relatively near future (2020?), students will have been well-indoctrinated in using the CCCs (after all, by 2020 my 9th graders would have used them all through middle school, assuming that middle school teachers were getting on board with the NGSS), I would tell my students to observe and experience all they can, and then report back with an analysis of Spiders, using as many of the CCCs as possible. Would it work? Is that too open ended?
Well, my experience was that “if it sounds too easy, it probably won’t work.” In terms of my own experience, I was able to pull off the assignment, but only by drawing on half of a lifetime of thinking about Biology. In terms of a student assignment, most of my students would have been able to find things to write about related to Structure and Function. Cause an Effect might also have been accessible to some of my students, as would Scale. But I think the rest of what I wrote above is very general, and comes from my expert lens of experiencing this kind of museum exhibit. I probably would have written much the same thing in almost any field trip experience that focused on a particular organism.
But who knows what kids will be able to do in five years if this paradigm is implemented in a significant way? I think that with some training, my students could start to think about Systems and System Models, or Stability and Change in more sophisticated, nuanced ways. And if Systems and System Models drives students to apply levels of biological organization (tissues, organs, organ systems, etc.), and Stability and Change gets them to reflect on themes related to genetics (Stability), and evolution (change), or to think about homeostasis (organisms responding to change), then that’s not a bad thing.
NGSS, here we come!