Nutrient Cycling: Nitrogen and Phosphorus in Ecosystems

Environmental Science Grades High School 9:22 Video
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Lesson Description

Explore the vital roles of nitrogen and phosphorus in ecosystems through the nitrogen and phosphorus cycles, understanding how these nutrients become biologically available and the impact of human activities.

Video Resource

Nitrogen & Phosphorus Cycles: Always Recycle! Part 2 - Crash Course Ecology #9

CrashCourse

Duration: 9:22
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Key Concepts

  • Nitrogen Cycle: The process by which nitrogen is converted between various chemical forms.
  • Phosphorus Cycle: The biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere.
  • Nutrient Availability: The forms of nitrogen and phosphorus that can be utilized by plants and other organisms.
  • Human Impact: The effects of synthetic fertilizers on nutrient cycles and ecosystems.

Learning Objectives

  • Students will be able to describe the steps involved in the nitrogen cycle and the role of nitrogen-fixing, nitrifying, and denitrifying bacteria.
  • Students will be able to explain the phosphorus cycle and its dependence on the lithosphere rather than the atmosphere.
  • Students will be able to analyze the impacts of synthetic fertilizers on nitrogen and phosphorus cycles and propose solutions to mitigate negative effects.

Educator Instructions

  • Introduction (5 mins)
    Begin by engaging students with a question about a time they needed something that was readily available but inaccessible (e.g., clean water after a natural disaster). Relate this to the concept of nutrients being abundant but not always biologically available, as introduced in the Crash Course video.
  • Video Viewing (13 mins)
    Play the Crash Course Ecology #9 video: Nitrogen & Phosphorus Cycles. Instruct students to take notes on the key processes and organisms involved in each cycle.
  • Nitrogen Cycle Discussion (15 mins)
    Lead a class discussion on the nitrogen cycle, focusing on the roles of nitrogen-fixing bacteria, nitrifying bacteria, and denitrifying bacteria. Use diagrams to illustrate the different forms of nitrogen and the transformations between them. Emphasize the importance of bacteria in making nitrogen available to plants.
  • Phosphorus Cycle Discussion (15 mins)
    Lead a class discussion on the phosphorus cycle, emphasizing its reliance on the lithosphere and the slow process of weathering. Compare and contrast the phosphorus cycle with the nitrogen cycle. Discuss the role of decomposers in releasing phosphates back into the soil and water.
  • Human Impact Analysis (15 mins)
    Discuss the impact of synthetic fertilizers on the nitrogen and phosphorus cycles. Explore the consequences of excessive nutrient runoff, such as eutrophication and algal blooms. Brainstorm potential solutions to mitigate these negative effects, such as reducing fertilizer use, implementing buffer zones, and improving wastewater treatment.
  • Wrap-up and Assessment (7 mins)
    Administer the multiple choice and fill-in-the-blank quizzes to assess student understanding of the key concepts. Review the correct answers and address any remaining questions.

Interactive Exercises

  • Cycle Diagram Creation
    Students work in small groups to create visual diagrams of the nitrogen and phosphorus cycles, labeling the key components, processes, and organisms involved. Groups present their diagrams to the class and discuss the similarities and differences between their approaches.
  • Fertilizer Impact Simulation
    Use an online simulation or a hands-on model to demonstrate the effects of fertilizer runoff on aquatic ecosystems. Students can manipulate variables such as fertilizer concentration and observe the resulting changes in water quality and aquatic life.

Discussion Questions

  • How would the absence of nitrogen-fixing bacteria impact terrestrial ecosystems?
  • What are the long-term consequences of disrupting the natural phosphorus cycle with excessive fertilizer use?
  • How can we balance the need for agricultural productivity with the environmental impacts of synthetic fertilizers?
  • Compare and contrast the roles of bacteria and plants in the nitrogen and phosphorous cycles.

Skills Developed

  • Critical Thinking: Analyzing the interconnections within ecosystems.
  • Scientific Communication: Clearly explaining complex scientific processes.
  • Problem-Solving: Identifying and evaluating solutions to environmental challenges.

Multiple Choice Questions

Question 1:

Which of the following is NOT a form of nitrogen that plants can directly assimilate?

Correct Answer: Nitrogen Gas

Question 2:

What is the primary role of nitrogen-fixing bacteria in the nitrogen cycle?

Correct Answer: Converting nitrogen gas into ammonia

Question 3:

Which process returns nitrogen gas to the atmosphere?

Correct Answer: Denitrification

Question 4:

The phosphorus cycle primarily relies on which sphere of the Earth?

Correct Answer: Lithosphere

Question 5:

How do plants obtain phosphorus?

Correct Answer: Absorbing dissolved phosphates from the soil

Question 6:

What is a major environmental consequence of excessive fertilizer runoff?

Correct Answer: Eutrophication and algal blooms

Question 7:

Which of the following human activities has the LEAST impact on the nitrogen and phosphorous cycles?

Correct Answer: Organic Farming

Question 8:

What enzyme is used by nitrogen fixing bacteria to split the strong nitrogen triple bond?

Correct Answer: Nitrogenase

Question 9:

What process causes inorganic phosphates to dissolve into water from rocks?

Correct Answer: Weathering

Question 10:

What do denitrifying bacteria metabolize to create nitrogen gas?

Correct Answer: Nitrogen Oxides

Fill in the Blank Questions

Question 1:

The process by which bacteria convert nitrogen gas into ammonia is called nitrogen _________.

Correct Answer: fixation

Question 2:

___________ bacteria convert ammonia into nitrates and nitrites.

Correct Answer: Nitrifying

Question 3:

___________ bacteria convert nitrogen oxides back into nitrogen gas.

Correct Answer: Denitrifying

Question 4:

The Earth's crust is also known as the ___________.

Correct Answer: lithosphere

Question 5:

The process of rocks being broken down by water is called __________.

Correct Answer: weathering

Question 6:

Excessive nutrients in a body of water often lead to a process called ___________.

Correct Answer: eutrophication

Question 7:

___________ are often formed in aquatic and marine ecosystems from dead organisms collecting and layering for long periods of time.

Correct Answer: Sedimentary Rocks

Question 8:

The enzyme ___________ is unique to nitrogen-fixing bacteria and can break the triple bond between Nitrogen atoms.

Correct Answer: nitrogenase

Question 9:

___________ is the process of dead material being broken down into ammonia.

Correct Answer: Decomposition

Question 10:

Fritz Haber is infamous for the synthesis of nitrogen into ammonia for fertilizers and __________.

Correct Answer: chemical weapons

Educational Standards

EN.LS2.4:[Standard] Use a mathematical representation to support claims for the cycling of matter and the flow of energy among organisms in an ecosystem. EN.LS2.6:[Standard] Evaluate the claims, evidence, and reasoning that the complex interactions in ecosystems maintain relatively consistent numbers and types of organisms in stable conditions, but changing conditions may result in a new ecosystem. EN.LS2.7:[Standard] Design, evaluate, and refine a solution for reducing the impacts of human activities on the environment and biodiversity.* EN.ESS3.4:[Standard] Evaluate design solutions for a major global or local environmental problem that reduces or stabilizes the impacts of human activities on natural systems.*

Teaching Materials

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