Ecosystem health depends on balance between the growth and consumption of its organisms. This balance is found in its food web organization. In this lesson students will learn about the make-up of food webs, with an emphasis on primary producers. Specifically they will explore connections between primary production and nutrient availability through experimentation with diatoms (a single celled, primary producer). Nutrient limitation on primary production will be seen in real time as students grow diatoms under three different nutrient concentrations. Data collection and analysis will connect student observations with larger relationships between nutrients, primary production and food webs.

  • Student understands the importance of primary producers to food webs.
  • Student understands that primary producers occur on land as well as in marine environments.
  • Students understand that nutrients are one factor which determines how much primary producers can grow.
  • Animals are the only important part of food webs.
  • All primary producers are found on land.
  • Primary producers only need sunshine and water to grow.
  • This lesson will give students the opportunity to grow diatoms in the classroom under three different nutrient concentrations. The students will collect daily data on diatom growth for the three treatments by doing cell counts. Finally class data will be plotted and analyzed to determine the impact of different nutrient concentrations on diatoms.
    • This lesson is intended for a 7th grade life science classroom. It can be taught as a standalone activity but connects well with the Genetic Mutation unit authored by Sarah Lerch and Felicia Ryder which explores diatoms in more detail. It is helpful, although no essential, for students to understand photosynthesis and primary production prior to this lesson.
    • Assessment of student progress towards learning goals is focused on gauging student comprehension through class discussions, notebook entries, and data analysis.
    • Five E learning method used. All lessons are divided into engage, explore and explain sections. Student notebooks are also provided with each lesson within the unit. These notebooks are structured around students hypothesizing, gathering evidence and analyzing that evidence over the course of the lesson.
    • CA Next Generation Science Standards MS-L2-1.
    • CA Next Generation Science Standards MS-L2-4.

    Diatom Growth Activity

    Student doing Cell Counts
    (Photo Credit: Erik Jepsen
    UC San Diego Publications)

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    Lesson Specifics
    • Grade Level: 7th grade
    • Time Frame: 7 days

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