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Symbiosis. Many would say this word describes two living things that benefit each other. While this is a common understanding of the term, in biology, symbiosis has a slightly more broad definition. Symbiosis (as defined by Western science), is an intimate association between two or more organisms, typically a very specialized association that has evolved over millions of years. For example, many people are familiar with the mutually beneficial association between clownfish and anemones. However, there also exists a clownfish parasite that eats the fish’s tongue and mooches off its food. This too is symbiosis; there must be a close relationship, but not everyone necessarily benefits.

SymbiosisThere are 3 main types of symbiosis. Categorizing a relationship into these 3 types depends on who gets something out of the deal.

  • (+/+) mutualism (what most people think of when they hear symbiosis)
  • (+/o) commensalism
  • (+/-) parasitism

The plus (+), minus (-), and zero (o) symbols represent the impact on each of the organisms involved. A plus means that the organism benefits from the relationship, a minus means they are negatively affected by it, and a zero means they are not significantly affected by it either way.

You may have noticed that there are more possible combinations of pluses, minuses, and zeros not listed above. Below are the rest of them, though these are debated as to whether they are truly forms of symbiosis or not. This is because they are too broad or unspecific; just because a seagull may benefit from eating your french fries does not mean they have a close evolutionary relationship with potatoes.

(+/-) predation/herbivor
(-/o) amensalism
(-/-) competition
(o/o) neutralism

When I first heard about symbiosis in school, I was ecstatic. Not only was I learning about amazing coadaptations, but every symbiotic relationship could be satisfyingly placed into one of those neat little categories, or so I thought. It turned out that the more I learned, the more I researched in the lab, and the more I talked to other scientists, the messier these categorizations became (we will explore some of these “exceptions to the rule” in the lesson below). These counterexamples were important because I realized something that to me was quite profound, and something that I think we should teach every student: your textbook is lying to you. 

Textbooks and other learning tools can be helpful, but they are also biased and simplified. As an educator, I want my students to learn earlier than I did that biology is messy and breaks the rules. Below are a couple activities you can use to guide students through this concept, best for students who have already been introduced to the idea of symbiosis.

Activity 1

Symbiosis is a great topic for a card sorting activity (you can find an example at https://learn.islandwood.org/ab-sorting/).

  • Make cards with different symbiotic relationships (examples below), along with some context regarding the nature of the relationship with text and/or pictures. Students may also brainstorm ideas and create the cards themselves. Some examples can be classic or “easy” relationships to sort, others can be a bit trickier or in some of the “contested” categories of symbiosis. Students will sort the cards into the 3 main categories of symbiosis (mutualism, commensalism, parasitism). This is best done in groups to facilitate discussion, but students can also complete their sorts individually and then compare afterwards.

Below are some classic examples to get started:

  • Epiphytes on trees (o/+)
  • Barnacles and whales (+/o)
  • Clownfish and anemones (+/+)
  • Bees and flowers (+/+)
  • Lichen/algae and fungus (+/+)
  • Wasps and caterpillars (+/-)
  • Dogs and fleas (+/-)

These are some much more contested relationships that will be explored in the next activity:

  • Water buffalo and oxpeckers (?)
  • Tapeworms and humans (?)
  • Leaf cutter ants (?)
  • Bacteria and humans (?)

Hopefully, the card sort will spark active discussion. There may be disagreement as to how things should be categorized, and that’s great, because it means students will have to dig deeper into their reasoning. During and after the sort, ask students to justify how they sorted their cards, and ask students with different answers to figure out why they disagree. Then, you can open it up to a large group discussion with the next activity to further challenge student thinking.

Activity 2

The following are case studies of classic symbiotic relationships that are more complicated than they may first appear. Each case includes 1) theme or lesson to discuss, 2) the example relationship, and 4) an explanation of the nuance behind why it is a contested example. You might have students re-sort their cards from activity 1 after they have discussed these case studies.

OxpeckerTheme 1: Categorization is subjective and depends on the observer

Example: Oxpecker and Bison. A supposed poster child of mutualism, the oxpecker bird receives nutrition by eating insects and other pests off of the skin of bison, giving it some relief and health benefits.

Nuance: Scientists have found that the oxpeckers are in fact not eating parasites, but instead picking at the bison's wounds and drinking their blood, perhaps making the birds a parasite themselves. (P.S. the same goes for remoras and sharks; watch a video about this at https://youtu.be/yzDWWzDenZQ)


tapeworm adTheme 2: Defining the nature of symbiotic relationships means defining values of good and bad

Example: Tapeworms. These are a well known parasite that live in the intestines of vertebrates such as ourselves, where they absorb food through their skin and deprive the host of nutrients.

Nuance: Tapeworms were used in the early 1900s as a weight loss treatment. While this practice is no longer recommended for a number of reasons, tapeworms were at one point seen as a helpful remedy--a mutualistic companion. Nothing about their nature changed, it was simply our perception of them that shifted. This really highlights the impact of societal norms on the perception of the natural world. Weight loss can be a sensitive subject for some people, so be sure that you present this example with care and compassion, and do not use it if you know any of your students would be uncomfortable. The use of leeches for medical purposes is a similar example that can be used as a substitute to illustrate the same point.

Theme 3: Symbiosis is not always simple partnership between two organisms

Example: Leaf cutter ants. Also known as attine ants, these insects cut leaves off of plants and bring them back to their colony. Without further observation, this may appear to be a simple case of herbivory, one of the contested cases of symbiosis listed at the top of this article.

Nuance: This example of symbiosis actually involves at least 6 different organisms, as diagrammed below—and this doesn’t even include the plants the ants eat! A red arrow on the diagram represents a negative or parasitic relationship, and a green arrow represents a positive or mutualistic one.


Diagram by Michael Poulsen


Microbes are great at breaking the rules. There are many surprising examples of bacteria switching between mutualism and parasitism with their hosts, or acting as both a parasite and a partner at the same time. This (https://courses.lumenlearning.com/boundless-microbiology/chapter/microbial-symbioses/) is a great resource to get started, but I highly recommend further exploring the world of symbiotic microbes with your students!


Categories can be useful--they make complicated concepts more simple, universal, and easier to understand--but there are often exceptions. In biology, the exceptions are sometimes the most interesting things to study. Really, every example of symbiosis could be more carefully examined. Is one organism both a benefit and a detriment to another? If it’s mutualism, does one organism benefit more? What environmental factors might change the nature of this relationship? How did this relationship evolve and how might it continue to change?

This uncertainty is not proof that science is broken, it’s proof that science works. To me, science is about continuing to learn, and it cannot be successful unless it is routinely questioned, retried, and modified. When a discovery breaks the scientific norm, it should be a moment of triumph and growth for the field. When this happens, it is also a chance for us to question our own assumptions and biases. It is critical that educators challenge the idea that relationships are defined and finite no matter the discipline. We will always have something to learn from the natural world, and we should always be thinking about how we can better understand and protect it. Now that is symbiosis.

Science has a closely held secret: it is full of failures.

Failed experiments. Failed hypotheses. The experience of failure is a rite of passage, a cornerstone in every scientist’s career. To be explicit, I am referring to the day-to-day mistakes every human (scientists included) make, not blatant unethical research methods. Failure is common, and expected. Yet despite its prevalence, few scientists discuss or bring to light their mistakes. Shrouded in secrecy and shame, these mistakes are tucked away.

This perpetuates a sinister misunderstanding of science; that science, and by default, scientists are the peak of perfection in our society. As a result, young scientists are taught to fear failure, to be ashamed, and to even hide failed experiments and hypotheses. This is the fundamental breakdown between the reality of scientific research and public understanding of science.

As science educators, we serve as the conduit between science and the general population. With this unique position, we have the power to connect, disconnect or reconnect the general population with science. It is how we do this that has a lasting impact on our students. We often integrate a culture of error in our teaching, framing our mistakes as learning opportunities, yet this seems to get lost in science. Why is this? I can’t think of a better time or subject to teach failure. Through science we can teach failure as expected, respected and valued.

Failure is to be expected
Failure occurs at every level of science, but is not often seen. More often than not we only see the end results of an experiment rather than the countless failed attempts and accidental discoveries in between leaving us to assume that the entire scientific study was as flawless as the end result. This could not be further from the truth. Developing an expectation of failure is essential for young scientists to understand the scientific method.

Expecting failure more accurately reflects the reality of a non-linear scientific method. We are taught that the scientific method is a one-way road that occurs step by step when in actuality the scientific method is a complex web of steps, missteps, and redirections. When something does not go as planned it is reevaluated and immediately remediated. Bringing this process to light both in scientific communities and in the classroom promotes transparency, ethical practices, and culture of error.

Failure is valued
Failure is the ultimate teacher. By pointing out our mistakes, and providing a pathway to improvement, failure teaches us how to be the best versions of ourselves. Failed experiments and methods provide us with the greatest learning opportunities in science. Unabashedly sharing our failures and mistakes with the world allows others to prevent making similar mistakes, resulting in the advancement of science as a whole. Openly presenting the details and missteps of every failure provides insight into how and why something went wrong. At its core, science is the pursuit of explaining reality, the hows and whys of the world. It is logical then to assume that every failure is not merely a roadblock but a stepping stone bringing us closer to a more accurate understanding.

Failures can result in the accidental discoveries of cures, theories, and technologies. Take Alexander Fleming’s accidental discovery for example: a failed sterilization technique and consequently contaminated experiment resulted in the discovery of penicillium mold that fought the flu virus he had been culturing. This resulted in the discovery of the antibiotic Penicillin, which saved countless lives. Many scientific discoveries have been the direct result of failures, mistakes and imperfect methods. Why should then be so afraid of failure if it has brought about so many successes?

Failure is respected
Respect for failure comes in multiple forms. From recognizing to addressing mistakes, we must respect what failure is telling us. Is this failure informing our practice? Is it pointing to an accidental discovery? Is it telling us that we are looking in the wrong direction? Each failure has a message, one we must listen to with respect if we want to grow from it.

Not only must the failure itself be respected as an opportunity to learn but the scientist who made said mistake must be too. The fear of failure comes directly from the fear of our peers’ reaction. Establishing a culture of error in our scientific communities allows our failures to be shared without hesitation, resulting in healthier, and happier scientists, and students. Respecting failure allows to us to work free of judgment or fear of failure.

Learning from failure is respected in many communities. Why would the scientific community be any different? A fundamental perspective shift must occur in our scientific communities and it starts in early science education. If we teach students to expect and value the inevitable failures of science, we have taught them to respect failure. Only after we have established respect for failure can we successfully establish a far-reaching culture of error in the sciences.

Teaching failure
microscopehelpIn teaching these practices early we can allow students to embrace science as a plastic, ever-changing subject. Breaking down the fear of failure in young scientists is essential for student growth and scientific advancement. We can teach failure by being open and vulnerable with our students when we make mistakes. Modeling the ability to adapt and reframe failures as learning opportunities is arguably the most important step in creating a culture of error. When failure occurs we must celebrate with our students. We should embrace this failure and seek to learn all we can from it.

Recognizing failures as learning opportunities requires a critical look into scientific history. Students should be shown the colorful history of accidental scientific discoveries, where apparent failure turned into unimaginable success. Instead of only teaching the end result of scientific studies, teach the in-between. Show the uncomfortable, the messy and frustrating side of science by drawing back the curtain. This result in a better understanding of the non-linear scientific methods, confident students, and who knows, maybe another accidental discovery.


Anyone who has ever tried to mention a popular culture reference in front of Gen-Zer knows the look: eyebrows raised, shame and speculation etched in their face, eyes rolling. But breaking down this barrier can lead to great success in accessing higher-level thinking and discussions of how the latest Internet trend or meme reflects on our society and perspective of the world. Take the latest sensation for example: Yanny vs. Laurel. The seven-second video, which is currently making its way across all social media platforms, is raising many debates. Does it say Yanny or does it say Laurel. People have STRONG opinions on what they hear. After a weekend of debating with my friends over what the video is saying (being only hear Laurel I can’t fathom how anyone could possibly hear Yanny!) I started thinking about using this video to discuss perspectives, with an equity lens, with students.

On the Monday of my next teaching week, sitting in a circle with my eleven students and two adult chaperones, I asked the students to define ‘perspective’. After a quick turn and talk, they gave answers such as “someone’s view” or “different ways to look at something”. I then asked them, ‘can someone’s perspective be wrong?’ The students thought silently for a moment before one raised her hand saying “I don’t think so... For example, if I pointed at water and said it’s blue and someone else said to me it looks brown, we could both be right, we just have different viewpoints... perspectives.” My follow up question: what effects/changes someone’s perspective? The answers included past experiences, your eyesight, your height, your race, your gender, your hearing.

I then asked them if they had heard about the Yanny vs. Laurel debate - about half of them had, while the other half knew what I was talking about but hadn’t heard the actual recording yet. I explained that I would play the recording and I wanted them to silently listen to if they heard ‘Yanny’ or ‘Laurel’. After a playing the video a couple times with the background squeaks of students restraining themselves from yelling out, I asked them what they heard. All at once each of them shouted out their answers and looked in shock at their friends who had heard something different. A few chaotic moments later we had collected ourselves enough to vote by a show of hands what we had heard it was nearly equally between ‘Yannys’ and ‘Laurels’. I then posed the question, why are we hearing different things when we’re listening to the same recording. “We have different perspectives!” one kid yelled out.
“We have different experiences that impact how we hear it!” yelled another.
“Okay, but I really don’t get how you hear Laurel” said a third – a great transition to my next question: “I hear Laurel, while half of the group hears Yanny. We’re all very sure in what we hear. Does that mean that some of us are wrong about what we are perceiving the recording to say?”
The question was followed by a few seconds of silent think time before one student finally said, “well no, our perspectives are personal and just because I hear one thing, doesn’t mean that someone else has to hear the same thing. We can both still be right”. Bingo.

We then spent some time talking about the science of why we hear what we hear – some current theories in the scientific community include if your ears are used to listening to higher pitched sounds you hear Yanny, and lower pitched, Laurel. We discussed that the video has been recorded so many times over that our brains are struggling to get rid of background stimulations in the video, which changes how we hear it. Another theory is that our ears are unable to distinguish between the sound waves of Yanny and Laurel, as they are so similar in shape in this low resolution recording. This too provided a fun conversation with students - our brains are crazy things.

Kaplan shoeDon’t have access to the Yanny vs. Laurel video? The internet is full of other strange photos to use in the classroom. Simply google ‘The Dress’ and you can Kaplan Dressweed through the 3,860,000,00 results, including many photos and a wikipedia page discussing the 2015 viral photo. The question: is the dress blue and black or white and gold? Another photo that can be used to spark a discussion of perspectives is the pink/white vs. grey/teal shoe debate.

Throughout the rest of the week I noticed students thinking about perspectives on their own. On one occasion a student squished an ant and another asked them, “from the ant's perspective what was it trying to do before you killed it? How would you feel if you were the ant?” leading to a very interesting student-led discussion. Another time a student wondered aloud what the perspective of their classmate might be during a team building activity.

We are living in a world where are students are constantly connected and engaging in and with the internet; I challenge you to embrace opportunities it presents rather than fight it - see what happens. You may just be surprised.


When conducting student-led investigations in the field, the variety of questions, tools, and methods that students use can make summative assessment difficult for the instructor.  Though debriefing the experience can be a great way to find evidence of student learning, there may be students who tend not to contribute in group discussions.  Journal work, though comprehensive in some students, may be lacking in others.  I have found that requiring my students to present their research to the rest of the group not only provides excellent evidence of learning, but also gives my students the opportunity to share their work, ask and answer questions of each other, and be applauded for their achievement. 

Presentations  allow students to take ownership of their work and feel proud of their achievement, while allowing them to learn from one another through sharing knowledge and asking questions. Often, I find that student presentations level the playing field, giving every student the opportunity to share, question, and think about one another’s work in a safe environment.  Lastly, it provides an avenue for students to feel a sense of accomplishment at the end of their investigation.

Here are a few tips for incorporating research presentations into your student-led investigations.

  1. Explain and Scaffold the experience.

    Let students know at the beginning of the investigation that they will be presenting their research to the rest of the group once they are finished.  This will entail two responsibilities: to present their work, and to listen and ask questions of their peers.  Explain that this is an opportunity to share their hard work with one another, ask each other questions, and hear what their teammates have been working on.  Address concerns on nervousness by giving a few guidelines. For example, I allow my students to present individually, in pairs, and occasionally in groups of three.  Encourage them to be creative and fun in their presentations! 

  2. Name the steps.
    Be explicit about what you want your students to present.  I require five components in my students’ presentations:
    1. Their question
    2. Their methods & tools
    3. Their results: data, what they found
    4. Their conclusion: what did they learn from their results?
    5. Next steps: what might have affected the accuracy or usefulness of their data, what they learned about using their tools/method, follow-up questions, etc.

      These should align with the steps they are following to complete their investigation, and so can be modified based on the instructor’s style in facilitating investigations.

  3. Give students the opportunity to prepare.
    Set aside a few minutes at the end of the investigation to give students time to prepare for their presentation. Encourage them to make their presentations unique! If some students are ready to present before others, instruct them to start thinking of good questions to ask their peers.

  4. Create a visual reminder.
    List each component of the presentation on a whiteboard or butcher paper and place it where the presenters can easily reference it.  If students lose their train of thought or freeze up, gently remind them what to say next, for example: “excellent question! What method did you use to begin answering it?”  Some students will give the entire presentation without a hitch, while others might benefit from a more conversational presentation, with prompts from the instructor. 

  5. Encourage questions.
    One of the most fruitful and interesting aspects of these presentations are the questions students ask of one another. These can lead to excellent discussions, follow-up lessons or activities, and insight for the instructor on students’ thinking. Be explicit about when it is time for student questions, particularly if you prompt students during their presentations.  Ask follow-up questions!

Student-led investigation presentations are versatile, fun, and interesting, and can be used in a variety of contexts.  They are excellent summative assessment tools, great teambuilding exercises, and a way to challenge your students to think critically, support one another, and be supported in a different way.

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