The Carbon, Nitrogen and Phosphorous Cycles

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Students will assess the dependence of all organisms on one another and the flow of energy and matter within their ecosystem.

Big Idea

The activities of human populations affect the biosphere.


5 minutes

Use the warm-up question as a review question from the previous lesson, Water Cycle.  Look for students to be able to demonstrate an understanding of the processes that are a part of the water cycle.

Number the steps of the water cycle in the order in which they occur, starting with the collection of water in lakes or oceans:

__            Through evaporation, water changes from a liquid to a gas.

__            Water is absorbed by plants growing in the soil and used for photosynthesis.

__            Water returns to Earth as precipitation.

__            Through condensation, water in the air changes from a gas to liquid.

Listen to students’ responses and correct any errors or misconceptions that are voiced.

Introduce New Material

20 minutes

Begin the introduction of new material with a discussion question:

Does human behavior benefit or harm the environment?

Allow students to engage in academic discourse around this question for 2-3 minutes.  Require students to identify specific examples that support their opinion.  Encourage discussion by asking students if they agree or disagree with statements made by other students. Inform the class that today’s lesson will focus on the roles of carbon, nitrogen, and phosphorus in the environment and the impact human behavior has on each of these biogeochemical cycles.

Inform students that the learning target for today’s lesson is that they can explain the cycling of carbon, nitrogen and phosphorus in the environment and the energy transfer that occurs in each cycle.

Display a visual diagram of the Carbon cycle and talk about each part of the cycle.  Instruct students to take notes using guided notes that you provide or using a note-taking plan that you have taught.

Ask students to recall the reactants needed for both photosynthesis and cellular respiration. This information was taught in a previous lesson so it should now serve as a review question.  Note whether most students are be able to identify the correct reactants.  If there is a general lack of understanding noted, take a few minutes to review both chemical reactions, noting the reactants and products of each reaction.

Emphasize the relationship between photosynthesis and cellular respiration, noting the interdependence of the biotic factors with abiotic factors in an ecosystem.  Point out the roles of photosynthesis, respiration, consumer groups, and pollution in the carbon cycle. 

Allow students to watch a short video clip, The Carbon Cycle. This informative clip can be found on a free teacher resource, Discovery  The clip is brief but full of important information that increases students’ understanding of the carbon cycle.  Before watching the clip, set the expectations for viewing and show students the question that they should be able to answer when the clip ends:

In what two ways is carbon trapped and delayed from being returned to the carbon cycle within a short time?

Giving students a preview of the question allows them to watch the video with a clear idea of what they are expected to know after watching the clip.

After the video ends, display the Check for Understanding question.  Pass out slips of scrap paper for students to use to write and submit their responses.  

Note: I find it helpful to recycle scrap paper for this type of use. I use a paper cutter to cut papers into thirds or fourths from old forms, copy errors and other documents for use throughout the year.

After the responses are collected, ask 1-2 students to share what they submitted in their written responses. This allows students to hear how their peers responded to the question and it serves as a formative assessment to see if students met the learning target planned for the video viewing.  Make sure to state the correct response so that students will know the correct answer to the question.

When time permits after class, take time to read through the student responses to determine how well all students were able to answer the question.  Based on the responses, decide whether the instructional strategy used was effective or not.  If most of the student responses are incorrect, then reassess and modify the instructional plan to better meet the learning needs of the students the next class session. The student work shows that most students were able to answer the question.

Provide information about the Nitrogen Cycle.  Display a visual diagram of the Nitrogen Cycle  and talk about each of the parts.  Instruct students to take notes using guided notes that you provide or using a note-taking plan that you have taught.

Allow students to watch a short video clip, The Nitrogen Cycle. Just as with the first clip, share the viewing expectations and inform students that there is a question that they should be able to answer when the clip ends:

Cite 2 factors upsetting the balance of the nitrogen cycle and explain what is caused by these factors.

After the video ends, display the Nitrogen Cycle Check for Understanding.  Pass out slips of scrap paper for students to use to write and submit their responses.  

The student work shows that some students are able to articulate that artificial fertilizers pollute waters and upset the nitrogen balance in the environment.  Another student's response indicates that electrical factories and cars pollutes air and release large amounts of N2 in the atmosphere.

Finish the lesson with the phosphorous cycle.  Show students a visual image of the cycle and talk about each of the parts of the cycle.  Emphasize that this cycle is different from the other cycles because it is the only cycle that does not cycle through the atmosphere.

Guided Practice

5 minutes

Distribute copy paper. Explain the word squares activity to students.  Display the instructions while modeling the paperfold:

Instruct students to fold their paper into fourths.  Explain that the folds should result in four equally divided parts. Instruct students to label each of the 4 sections of the paper:

1.     Term (Upper Left Corner):

2.     My Meaning, Textbook Meaning (Lower Left Corner)

3.     Picture/ Symbol ( Upper Right Corner)

4.     Sentence (Lower Right Corner)

Walk around to monitor students’ progress with the folding and labeling of the paper.

Provide an explanation of what should be included in each of the four sections.

Term- Write the term.  Define any root words, prefixes or suffixes associated with the term.

My meaning- Write your own definition of the word.

Textbook definition- Use your textbook or notes as a reference.

Sentence- Write a sentence using the term you are assigned.

Display the rubric that will be used to grade their work product.  Review each part of the rubric to ensure students understand what they are expected to do for the performance task.

Independent Practice

20 minutes

In advance of the lesson, create a set of terms specific to the three cycles. Cut and place the terms in a bag.  Allow students to randomly select a term from the bag.  Instruct students to work independently to complete the Word Square using the term they pulled from the bag.   

Provide markers and/or colored pencils for students’ use.  Instruct students to refer to the Word Square Grading Rubric to guide their completion of the performance task. The word square student work that is included shows how well students can be expected to complete the task and show understanding of the terms associated with the lesson. 



5 minutes

Give students an opportunity to share their completed work with the class.  By providing students a chance to share their finished work, the class benefits from seeing how other students approached the assignment.  The various creative images that students use might help the terms and definitions “stick” in a way that they had not considered.  Also, students improve their presentation and speaking skills when they have the chance to practice their skills in front of their peers in a non-threatening environment. 

Be sure to review the expectations for respective listening before the presentations begin.  Listen for how well students are able to define the term in their own words.  Listen for how students use the terms in sentences to assess how well their sentences convey that they understand the term.  Also, look for images that show that students have made a connection to the term in a way that signals content comprehension.