In this high school unit on evolution, students initially investigate the case of young girl with a life-threatening infection of pan-resistant bacteria. This case sparks questions that lead them to investigate the growing prevalence of such cases and the discrepancies between antibiotic use in their communities and CDC recommendations. They expand their investigations to look at population changes occurring in a population of birds (juncos) which exhibit noticeable differences in physical and behavioral traits from the past 60 years.
Individual bacteria that have an advantageous trait variation, like fewer pores, have a better chance of surviving exposure to antibiotics, than those without that variation.
New simulation will add the following features: amount of antibiotics, dosage frequency, variations of bacteria (# of pores) and bacteria reporduction frequency.
In this next investigation, you will use a model that has many of the same mechanisms in it that it had before. One change to the simulation is the way that the individual bacteria can vary in the starting population. Bacteria don’t just vary based on color; they also vary slightly in the structure of their cell membranes.
How do you think trait variations among bacteria might be related to which bacteria have a better chance of surviving in Addie or in your Petri dishes when antibiotics are introduced?
Home-learning Instructions: Fill out the table of your assigned generation. Then complete the graphs for the rows indicated. Please use colors to designate your percentages of bacteria with each variation (purple, green, brown, and red).
Individual bacteria with trait variations that allow them to survive exposure to antibiotics, reproduce. Over time this leads to a shift in the distribution of traits in bacteria populations, so that those variations become more prevalent over time.
How could the model you made today in class today be used to help answer questions about Addie's condition?
The same interactions and outcomes in the simulation were also at work in Addie's body and also at work in our community over the past ninety years. Bacteria populations became more resistant to being killed by antibiotics as trait distributions in the population that granted them a competitive advantage for survival became more prevalent over many generations of exposure to antibiotics.
How did the bacteria population become more resistant in Addie and in our community? Review lessons/IMTs
Key Components and Interactions: Look across the three systems from Lesson 9 and pull out the general component and interaction.
Scientists often compare models and evaluate the strengths and weaknesses of each. We have spent some time developing a model for how bacteria populations have changed over time to become more resistant to antibiotics. Now, it is time to compare our model to that of two scientists before: Charles Darwin and Jean Baptiste de Lamarck.
Think back to all you’ve done to learn about the evolution of bacteria and the spread of antibiotic-resistant bacteria in this unit.