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# Modeling Algae Growth Mark as Favorite (2 Favorites)

ACTIVITY in Interdisciplinary, Measurements, Graphing. Last updated April 11, 2023.

### 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, 2
^{1}= 2, 2^{2}= 4, 2^{3}= 8… and ask what would 2^{10}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.

- 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, 2

__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.

### For the Student

**Part A: Reading Activity **

**Directions**

Read the article, “Toxic Shorelines: The Science of Algal Blooms”, by Rebecca Heisman on page 15 of the April/May 2018 *ChemMatters* issue. Stop at the subsection “A pollution problem.” Discuss the following questions with your classmates.

- Why are algae important to the earth’s ecosystems?
- How might algal blooms harm an ecosystem?
- Examine the algal bloom severity graph on page 16 of the article. Of the years listed on the graph, what year had the highest severity? What factors do you think affect the algal bloom index?
- What is the name of the species of algae that are harmful to freshwater supplies? Examine the picture on page 16 of the article. Would you predict this species of algae to be unicellular or multicellular? Explain.

**Part B: Mathematical Modeling **

**Directions**

Read each statement and answer the following questions:

- If conditions are right, algal blooms take off at a rapid pace. For simplicity, let’s say that a freshwater supply starts off with ONE algae cell in the lake. The algae cell divides. How many algae cells are now in the lake?
- If the number of algae cells from question 5 divide, how many cells are there in total now?
- Continue the pattern for three more cellular divisions. Report your total numbers of algae after each cell division in the table below.

Number of algae cell divisions |
0 |
1 |
2 |
3 |
4 |
5 |

Total number of algae |
1 |

- Graph the data provided in the table above.
- Decide on an appropriate title. Write at the top of the graph.
- Label the x-axis (independent variable) and y-axis (dependent variable).
- Decide on an appropriate scale for your x- and y-axes.

- How would you describe the mathematical relationship in the table above? Can you derive an equation that fits the model? Use your equation to predict how many algae would be present in the freshwater lake after 10 cellular divisions.
- The Environmental Protection Agency (EPA) provides guidance for states to consider when developing water quality standards. The EPA recommends that a swimming advisory be issued if the microcystin level in recreational water exceeds 8 mg/L. Let’s say that the 8 mg/L threshold is exceeded when the algal bloom reaches 1,048,576 cells. How many cell divisions did this take? (
*Hint: Use your formula from question 8. You are solving for the exponent. You can do trial/error or if you know how to solve with logarithms, apply that math knowledge*). - Let’s say each algae cell divides twice a day. After how many days since the first algae cell appeared in the lake, would the EPA recommend issuing the swimming advisory?
- Do you think algae cells will continue to grow and reproduce at an exponential rate? Why or why not?
- The common pleco is a type of fish that eats algae in aquarium and ponds. Let’s say there are enough pleco in the freshwater to consume one algae cell after each division. In other words, only one of the two algae cell survives after each cellular division. Fill out the table to show the number of total number of algae after each cell division. How is this model different from the mathematical relationship in question 7?

Number of algae cell divisions |
1 | 2 | 3 | 4 | 5 |

Total number of algae |
1 | 2 |

- Graph the data provided in the table above.
- Decide on an appropriate title. Write at the top of the graph.
- Label the x-axis (independent variable) and y-axis (dependent variable).
- Decide on an appropriate scale for your x- and y-axes.

- Compare and contrast how the data is graphed in Question #8 and Question #14?

**Part C: Research **

**Directions**

Continue reading pages 16, 17, and 18 of the article, “Toxic Shorelines: The Science of Algal Blooms”, by Rebecca Heisman and discuss the following questions with your classmates.

- What nutrients cause algae to thrive?
- How does pollution contribute to algal blooms?
- What actions can be taken to control algae blooms?
- How do algae blooms impact you?