Making The Connection: Photosynthesis and Cellular Respiration

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SWBAT illustrate a model and develop a narration to explain the cycling of carbon through the chemical reactions of photosynthesis and cellular respiration.

Big Idea

Students will make the connection between plants and animals and be able to describe the inter-dependence using chemical reactions as evidence.

Video Introduction: Connecting To See The Big Picture

1 minutes

This video clip discusses the need for the students to see the "BIG picture" of how photosynthesis and cellular respiration function in the macro-scale of the Carbon Cycle.  

Hook - Connecting Photosynthesis and Cellular Respiration

10 minutes

Students will need to determine if each statement describes photosynthesis, cellular respiration, or both.  Students will record their responses on their paper to reference during our pair-share and class discussion.

  1. Releases energy (CR)
  2. Needs light to occur (P) 
  3. Gives off carbon dioxide (CR)
  4. An exothermic reaction (CR)
  5. An endothermic reaction (P)
  6. Animals use this reaction (P)
  7. Plants use this reaction (Both)
  8. Needs chlorophyll (P)
  9. All living things do this at night (CR)
  10. Makes glucose (P)
  11. Waste products are carbon dioxide and water (CR)
  12. Waste product is oxygen (P)
  13. Occurs in the mitochondria (CR)
  14. Occurs in the chloroplast (P)
  15. Makes most of the oxygen we breathe (P) 

Students will share their answers with their neighbor and identify two statements that were most confusing.  The class will discuss these "hang-up" statements in detail to ensure clarification before the lesson moves forward.

Student Misconception: Many students do not think that plants undergo cellular respiration because they forget that plants can undergo two chemical reactions in different organelles.  To clarify ask students, "Where does the cellular respiration occur?"  Most students will respond with the mitochondria.  Then ask students, "Do plants have mitochondria?"  Again, most students will answer, "yes".  Then you get to see the light bulbs illuminate as they realize that plants can undergo BOTH photosynthesis and cellular respiration!

Guided Practice - Visualizing the Connections

25 minutes

This laboratory demonstration activity was set-up in the previous lesson and needed to react for 24 hours before the final observations could be made.

This activity can be completed as a student-led lab or a class demonstration depending on the amount of available time in the teacher's lesson plans and the availability of laboratory resources. This lab exercise will exemplify the inter-relationship between plants and animals using water snails and water plants (elodea or anacharis).  The class demonstration is designed to support students understanding by illustrating the cycling of carbon through the processes of photosynthesis and cellular respiration.  

Due to the limited time in the class schedule, this activity was prepared as a class demonstration in the previous lesson and the students will make observations, analyze the data, and develop a conclusion in today's lesson.  

As a reminder, the set-up of the lab demonstration was as follows:

  • Test Tube #1: 2 pieces of water plant and 1 water snail
  • Test Tube #2: 1 water snail
  • Test Tube #3: 2 pieces of water plant
  • Test Tube #4: No living organisms (the control)

Each test tube was filled 3/4 full of water and 10 drops of Bromothymol Blue (BTB) solution (an indicator) was added.  Each student volunteer used a straw to gently blow bubbles (exhale carbon dioxide) into their test tube until a color change is observed. In yesterday's preparation, the students observed all four test tubes turned a yellow color to indicate the acidic pH values of the test tubes' water.  Science Note: BTB will turn yellow if the solution's pH is less than 6 and will remain blue if the ph is 7 or above.

All four test tubes were left on the window sill for 24 hours so the plants could undergo photosynthesis and cellular respiration, while the water snails underwent cellular respiration.

The teacher will display each of the four test tubes to the class so that each student has the opportunity to view test tubes against the white paper background.  The white paper is necessary so that students can observe the color change, even if it is very slight.  Students will use their Making the Connections Between Plants and Animals Lab Sheet to record their observations in the data table.  Students will work with their lab partner (groups of 2-3) to respond to the lab analysis questions and to develop their lab conclusion.  

The lab conclusion should always contain the following components:

  1. What did you do? (quick summary of the procedure)
  2. What happened? (observations and evidence)
  3. What did it mean? (claims and conclusion statement)

Students are encouraged to make claims and provide supporting evidence in each of our science laboratory investigations.  These are the same skills that are being practiced in their math and language arts classes in support of the Common Core Standards.

Making the Connection Class Demonstration - Student Response #1 - This student work sample shows a basic understanding of the demonstration process but does not demonstrate a strong analysis of the data in regards to the relationship of CO2 (cellular respiration) and O2 (photosynthesis).

Making the Connection Class Demonstration - Student Response #2 and #3 - These student work samples demonstrate a more advanced understanding of the demonstration process by providing a more detailed analysis of the data in regards to the relationship of CO2 (cellular respiration) and O2 (photosynthesis).


Independent Practice: Connecting To The Carbon Cycle

15 minutes

Students will use their Cellular Respiration Lecture Notes from the previous lesson and their Photosynthesis Lecture Notes from a prior lesson in the beginning of the Cell Energy Unit to connect their understanding of photosynthesis and cellular respiration.  Students will design a model that depicts the photosynthesis and cellular respiration as the processes cycle carbon through the biosphere (living organisms), the atmosphere (gases), the hydrosphere (water), and the geosphere (solid rocks/land).  Students have spent the last few lessons attempting to understanding the detailed process of the chemical reactions of photosynthesis and cellular respiration.  Now students need to conceptualize the big picture in an effort to understand how these two chemical processes fit into the carbon cycle.  Students will also need to reference prior knowledge from earth science classes to visualize how the photosynthesis, cellular respiration, and the carbon cycle interact with the "spheres" on Earth.  This activity requires a macro-understanding of Biology and students will need a little extra support from the teacher to to think on a big scale!

In addition, students will develop a narration that accompanies the illustrated model to describe how the carbon molecules are converted as it cycles through each part of the ecosystem: in living organisms, gases, dissolved in water, and converted into rocks.  

Sample of Student Diagram and Narration: Most of the students enjoyed the artistic component of sketching the Carbon Cycle Diagram.  As you can see from this example, many of my students struggled with the ability to make the connection between the processes of photosynthesis and cellular respiration as they relate to the Carbon Cycle.  As a result of this gap in comprehension, the students participated in a whole-class review of the Carbon Cycle diagram and brainstormed how plants (photosynthesis) and animals (cellular respiration) fit into the biogeochemical cycle of carbon.  


Close - Connecting With Our Partners

5 minutes

Each student will receive a Study Guide Handout that will support their understanding of photosynthesis and cellular respiration as they prepare for an upcoming assessment.  Students will review the handout and create two questions to ask their neighbor as a review.  Students are able to take the handouts home to study and are encouraged to review their lecture notes as well!

Sample Student QuestionsSome students took the assignment a step further and wanted to try to stump their partner with their questions.  These partner discussions were rich in student learning and based in Biology curriculum.  Students were overheard debating the chemical processes of photosynthesis and cellular respiration and using the book's diagrams as a source to settle their disputes.  The scientific student discourse made this lesson a success!