Summary

In this activity, students will read a ChemMatters article about the science of algal blooms to learn how the blooms affect ecosystems. While developing their understanding, students will create a mathematical model to predict algal growth.

Grade Level

High School

NGSS Alignment

This activity will help prepare your students to meet the performance expectations in the following standards:

• HS-LS2-1: Use mathematical and/or computational representations to support explanations of factors that affect carrying capacity of ecosystems at different scales.
• Scientific and Engineering Practices:
  • Using Mathematics and Computational Thinking
  • Developing and Using Models

Objectives

By the end of this activity, students should be able to:

• Explain how algae blooms affect an ecosystem.
• Model algae bloom growth using exponential growth.
• Use a model to predict at what time an algal bloom will occur.
• Apply mathematical modeling to other chemistry concepts.
• Generate a correctly formatted graph to present a set of data.

Chemistry Topics

This activity supports students’ understanding of:

• Quantitative Chemistry
• Mathematical Modeling
• Graphing
• Interdisciplinary

Time

Teacher Preparation: 20-25 minutes
Lesson: 45-50 minutes

Materials

• The April 2018 ChemMatters article, “Toxic Shorelines: The Science of Algal Blooms”
• Modeling Algae Growth Worksheet

Safety

• No specific safety precautions need to be observed for this activity.

Teacher Notes

• This activity was created as part of the 2023 Chemists Celebrate Earth Week (CCEW) Lesson Plan Contest. CCEW is celebrated the week of April 16–22, 2023 with the theme, “The Curious Chemistry of Amazing Algae.” Through this theme, students, teachers and all those interested are encouraged to explore Algae. Emerging as one of the most promising long-term, sustainable sources of food, feed, and other co-products, algae are extremely important both now and for our future.
• To start this activity (before providing students with the worksheet, article, and instructions), it’s helpful to activate prior knowledge to see how much the students already know about the topic. I spend about 10 minutes doing this.
• To start a discussion, use questions such as those below:
  • “Has anyone ever seen algae growing in a fish tank or water supply?” Perhaps use a picture to show, there are a lot on the CDC website that can be used to provide students with a visual of what algae looks like. The purpose of the discussion is just simply to give students a visual for algae and what it can look like in different environments (salt vs freshwater).
  • “Is there a difference between algae and seaweed?” Seaweed is a type of algae. Seaweed is much larger than algae, often referred to as “macroalgae”, and is exclusively multicellular. The activity is going to focus on unicellular algae so distinguishing between the two is important to direct the discussion. Unicellular organisms (algae) contain only one type of cell that is able to perform process in order to survive. Multicellular organisms contain more than one type of cell that are able to perform different life process inside the organism. For example, liver cells are specific to performing functions of the liver in the human body contrasted with muscle cells. For more information, check out this infographic that compares algae with seaweed.
  • "What does algae provide for the organisms living in the lake?” Algae are a source of food serving as primary producers in food chains. Algae produce more than half of the oxygen in the atmosphere because most species of algae are autotrophs, able to undergo photosynthesis. The discussion will help students understand that algae are important for ecosystems despite some of the negative connotations associated with algal blooms.
  • “Is it possible for algae to harm an ecosystem (and if so, how)?” Students may have heard of algal blooms before, and this discussion leads into the topic of the article. The CDC has a good resource for the different types of algal blooms and how these can be of public health concern. It may be something to use at either the beginning of end of the activity to show students what causes blooms, how to recognize them, and why they are a growing concern.
• Another helpful option is to use Google Images to find and show images of algae and algal blooms to initiate student interest and discussion.

• After the discussion, provide students with resources (the ChemMatters article and student worksheet). There are three parts (A, B, and C). The first part (A) has students read the article and answer questions based on information from the text. In part B, students learn how to apply a mathematical model to a set of data. In part C, students research and extend the learning with the ideas presented in the article.

• Part A: There are several ways to complete Part A, depending on the dynamics of your class. Here are some sample ideas:
  • Whole group read-aloud where students take turns reading paragraphs of the article, followed by either class discussion or small group discussion of the following questions.
  • Students silently read and answer the questions, followed by either a whole group class discussion or small group discussion of the following questions.

• Part B: This part of the activity is focused on mathematical modeling. Depending on the dynamics of your classroom and the background knowledge of the students, this can be completed according to teacher preference. Here are some suggestions:
  • Idea #1: Teacher asks students to answer questions #5 and #6. Teacher gives students hints to fill out table 7. Teacher monitors student work on the table (walk around room, use google doc, etc.) and calls on volunteers to fill out table. Teacher models for students how to graph the data in question #8. Students use either printed worksheet or excel to create graph. Level of support provided depends on student background knowledge/needs in your classroom. Teacher explains how to come up with equation for question #9. Start with base of 2 and explain the exponents to see if students can match the exponents to their table. For example, 2¹ = 2, 2² = 4, 2³ = 8… and ask what would 2¹⁰ be, or what would 2^x be? Have students attempt question #10. Explain that they are solving for the exponent in this problem. If they have taken Algebra II, they may be familiar with shortcut “change of base formula” but if not, I would suggest having students perform trial and error Have students try questions #11 – 15 on their own. Monitor progress, go over as needed. The students should have a general idea on how to fill out the table in question #13 and graph question #14 since this was modeled in prior questions. Provide additional support as needed.
  • Idea #2: Break the students into small groups (2-3 students per group). Direct them to try their best to answer the questions. I would pull the class together to discuss the first table/graphing questions (#7 and #8) to make sure the students are on the right track with understanding the data table and graphing. Direct them to continue working in groups. Have a whole group discussion of the questions once the majority of class completes part B.
  • Idea #3: Break the class into groups (2-3 students per group). Make sure there are an even number of groups. For example, 20 students would give 10 groups (2 students in each group). Now that you have your groups, split the groups so that half are working on Questions #8/#9 and the other half Questions #13/14. Check in with groups as they are working and provide helpful hints as needed. Once groups finish those questions, pair up opposite groups and have them compare/contrast their models in Question #15. If students finish early, have them work on the other questions.
  • Note that for all options, it may be helpful to show/explain that where the answers from questions 5 and 6 go in the table, so students are able to figure out the pattern and get the idea of how to apply the mathematical reasoning of an exponential function.
  • For the graphing questions, its suggested to use Microsoft Excel or Google Sheets to give students practice with plotting data through those programs. If not, a graph template is provided as part of the student handout. A review on independent vs. dependent variable may be needed so students know what variable to place where on the graph. The AACT Graphing Simulation is a good resource for students to reference if needed.

• Part C: This part of the activity requires students to engage with the ChemMatters article again. Teachers can follow the ideas provided for implementing Part A for this section as well.
  • Idea #1: Whole group read-aloud where students take turns reading paragraphs of the article, followed by either class discussion or small group discussion of the following questions.
  • Idea #2: Students silently read and answer the questions, followed by either a whole group class discussion or small group discussion of the following questions.
  • Idea #3: Have students go out to the CDC website to answer the questions about algal blooms. Students report out findings with class at end of session.

• A complete Answer Key is available for teacher reference.