In a “March Madness” game of survival of the fittest, will your microbe and its genes survive the test of changing conditions on Planet Earth and beyond? Students choose genes from a “toolbox” and pit their microbe against their classmates’, using critical thinking and argument writing to determine the microbe with the best chance of success. Based on PolarTREC expedition “Microbialites in Lake Joyce, Antarctica.”
By the completion of this lesson, students will:
-demonstrate that environmental pressures drive evolution
-form compelling arguments predicting what kinds of genes would useful, given the environment
-theorize the genetic resources necessary to survive in an extraterrestrial environment, thus gaining understanding of the work of astrobiologists
Students can/should read the article from the Antarctic Sun about the Microbialites in Lake Joyce expedition to gain background about using the Dry Valley lakes as an analog for understanding ancient microbial environments. It would be helpful for students to have a basic understanding of evolution and/or cell biology prior to completing this lesson.
Describe the steps needed to complete the lesson.
A Warm Up: Discuss or do a quickwrite: How can we learn about the possibility of life on another planet without actually going to there ourselves?
Answer: Study similar places on Earth and what lives there.
The TED-Ed video- “Why Extremeophiles Bode Well for Life Beyond Earth” may also be a good introduction.
Explain that microbes dominate our planet. For a long time, single-celled organisms were the only living thing here. We estimate that life on other planets is likely to be single celled as well. How did these life forms survive for billions of years?
Theorize what genes would be needed to survive the test of time and changing conditions. Students will select traits from a list and write their choices in LARGE print on the “Gene Choices” page so it can easily be seen from the back of the class. Make sure that students realize that…
• No ONE gene will eliminate them from a round – their microbe just has to be the Best Fit. For example, if the environment is cold, and they have no genes for tolerating that, but they have everything else to suit that environment, then maybe they will still be better off than their competitors.
• Many genes are needed for photosynthesis – if they choose to photosynthesize, they also need to be able to take in carbon dioxide AND iron – it’s a big commitment.
• They are limited to 15 points for their microbe in order to simulate that the size of the genome is a limiting factor.
• One microbe CAN potentially “breathe” more than one gas. It happens in real life, and therefore it can happen in this game too, but it will cost points.
Randomly select environmental qualities for the first round using the Environmental Conditions, best printed on different colors of paper to correspond to each dimension. Post these conditions on the board for all to see and refer back to. Then, each pair of students will decide which of their two microbes are best suited to survive. Remind them that their genes don’t have to be a perfect match, they just have to be more competitive in that particular environment. The winner will advance on to the next round.
Repeat step 4 but only change one of the environmental conditions (indicating slow changes over a long period of time), this time with a group of 4 students choosing which of their two remaining microbes will advance on to the next round.
Pause the rounds here so that students can complete the first table on the Argument Writing Chart, outlining why their chosen microbe is the best fit for its environment. Give students time to discuss their claims, evidence and reasoning before each student writes their ideas on the page. The teacher can model an example of a trait (that would be evidence), and the reasons for it.
Continue the rounds with increasingly larger groups of students deciding on which of their microbes advances on to the next round, until the last environmental change occurs and the last microbe (winner) is voted on.
Instruct students to turn back to their Argument Writing Chart, discuss and write about why the winner is best suited for the environment it is found in.
One could extend this lesson to include pressures in terms of cellular metabolic functions – that in extreme conditions, microbes with large genomes lose the ability to simultaneously carry on complex processes AND still have enough energy for the reproductive process.
Students can be evaluated based on the strength of their Argument Writing Charts.
List relevant books, maps, posters, websites, videos, etc. that serve are additional resources for the lesson. If known, include resource authorship, dates, publishers, ISBN number, website URL, and any other information necessary for finding the additional resources.
Describe how student understanding, learning, and achievement are evaluated for this lesson. List any related documents (e.g. surveys, rubrics) when submitting the lesson and send them separately.
Lesson by PolarTREC teacher Lucy Coleman (lucyecoleman [at] gmail.com) collaborating with researcher Megan Krusor and fellow teacher Sang Bae.
Next Generation Science Standards
MS-LS4 - Analyze and interpret data for patterns in the fossil record that document the existence, diversity, extinction, and change of life forms throughout the history of life on Earth under the assumption that natural laws operate today as in the past.
MS-LS4-4 - Construct an explanation based on evidence that describes how genetic variations of traits in a population increase some individuals’ probability of surviving and reproducing in a specific environment
Common Core Standards
Write arguments to support claims with clear reasons and relevant evidence.
Introduce claim(s), acknowledge alternate or opposing claims, and organize the reasons and evidence logically.
Support claim(s) with logical reasoning and relevant evidence, using accurate, credible sources and demonstrating an understanding of the topic or text.
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