3 (2 reviews)
4 The link worked for me
Reviewed by: Janet (Dutton, MT) on 3/25/2022 1:24:34 PM
The lesson was timely (ew pandemic) and worked well for students.
This activity is a hands-on simulation using Skittles and mini-marshmallows to show how natural selection can act as a mechanism to increase the presence of antibacterial resistance in a population. Students simulate the effect of hand sanitizer on a population of bacteria, collect, record, graph and analyze their data. The bacteria that are affected by the selective pressure decrease and the population of bacteria evolves to be one that is largely populated by bacteria that are unaffected by the selective pressure. To begin the lesson students are given background information about natural selection and discuss how this can relate to their lives. Then students are given Skittles and mini-marshmallows and simulate the effect of hand sanitizer on bacteria. Since most of the “bacteria” are soft marshmallows they are caught more easily by a toothpick (the hand sanitizer) than the hard shelled Skittles. After a specified period of time the round ends and the remaining “bacteria” reproduce by fission for the next generation. The process continues for three generations. Possible follow-up lessons include watching videoclips and reading about antibiotic resistance having student role play scenarios to illustrate how antibiotic resistance happens in our world.
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. Clarification Statement: Emphasis is on using simple probability statements and proportional reasoning to construct explanations. Assessment Boundary: none
This resource is explicitly designed to build towards this performance expectation.
Comments about Including the Performance Expectation As written, the activity does not have students construct an explanation. The activity helps students gain an understanding of the Disciplinary Core Idea of natural selection for this Performance Expectation, but more needs to be done to have them construct an explanation. Writing a Darwinian Explanation (see the tip for Aligning to the Practice below for a more detailed explanation) or an explanation in the Claim/Evidence/Reasoning format would help students achieve this goal. The model presented seems to be absolute. The toothpicks (representing the hand sanitizer) are 100% effective against the marshmallows (normal bacteria) and 0% effective against the skittles (drug resistant bacteria). The result of this model is eventually having a population that is nothing but skittles (drug resistant bacteria) so that the entire population is 100% resistant to the toothpicks (hand sanitizer). If this were how things worked in real life, it would make no difference whether a person continued to take the full prescription of his or her antibiotics because the antibiotics (toothpicks) have no effect on the skittles. In real life, the antibiotics can still kill the drug-resistant bacteria, it just isn’t as effective as it is against normal bacteria. This difficulty with the activity could be turned into a strength if teachers noted the problem with the simulation and asked students how they could refine the simulation to better fit the actual phenomena. Another suggestion would be to use harder gumdrops like Dots instead of skittles. Gum drops can be grabbed with a toothpick, but it’s harder to grab a gumdrop with a toothpick than it is to grab a skittle. You could also use hard and soft gumdrops rather than marshmallows and skittles. This change would more closely model antibiotics resistant bacteria.
This resource was not designed to build towards this science and engineering practice, but can be used to build towards it using the suggestions provided below.
Comments about Including the Science and Engineering Practice The multiple choice homework questions ask students to explain, but they are not a fully constructed scientific explanation. One way to have students fully address the practice would be to have them write a Darwinian Explanation that describes the variation in the population at the start of the simulation, the selective advantage, which variation is more likely to reproduce and pass on their genes and what the variations are like in the end population. An example would be: There were more marshmallow bacteria at the beginning of the activity than Skittles bacteria. When the hand sanitizer was added most of the marshmallow bacteria died and the Skittles survived. Since they were alive they could reproduce and make offspring that were Skittles bacteria. Over generations there were mostly Skittles bacteria in the population although a few marshmallow bacteria were present. An alternate way to formulate an explanation is to have students make a claim, back it with evidence from the simulation and then state reasoning that ties the evidence to the claim.
This resource is explicitly designed to build towards this disciplinary core idea.
Comments about Including the Disciplinary Core Idea You may want to include more questions about harmful, beneficial and neutral traits. Writing a scientific explanation with the tips mentioned above would be very helpful to students to tie the practice of constructing an explanation using models or representations to the disciplinary core idea of natural selection.
This resource appears to be designed to build towards this crosscutting concept, though the resource developer has not explicitly stated so.
Comments about Including the Crosscutting Concept The addition of hand sanitizer (cause) led to the increase in the population of “skittles” bacteria (effect). The selective advantage influences the effect of the cause since a hard shell on the “skittles” bacteria was responsible for their survival while the soft outside of the marshmallow influenced the number that were killed by the hand sanitizer. A teacher could add questions explicitly asking about cause and effect in the simulation. This could include "The hand sanitizer caused what type of effect on the variation in the population of bacteria?"