|Teacher Notes for “Photosynthesis and Cellular Respiration
– Understanding the Basics of Bioenergetics and Biosynthesis”1
In this activity, students analyze the relationships between photosynthesis, cellular respiration, and the production and use of ATP. Students also learn that some of the sugar molecules produced by photosynthesis provide input for cellular respiration and some of the sugar molecules are used as input for synthesizing other organic molecules. Thus, photosynthesis can result in increased plant biomass. Conversely, cellular respiration can decrease plant biomass. The final section challenges students to explain observed changes in biomass for plants growing in the light vs. dark.
In accord with the Next Generation Science Standards2:
This activity helps students to prepare for Performance Expectations:
HS-LS1-5, "Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy."
HS-LS1-7, "Use a model to illustrate that cellular respiration is a chemical process whereby the bonds of food molecules and oxygen molecules are broken and the bonds in new compounds are formed resulting in a net transfer of energy."
HS-LS2-5, "Develop a model to illustrate the role of photosynthesis and cellular respiration in the cycling of carbon among the biosphere, atmosphere…
Students learn the following Disciplinary Core Ideas:
LS1.C: "The process of photosynthesis converts light energy to stored chemical energy by converting carbon dioxide plus water into sugars plus released oxygen. The sugar molecules thus formed contain carbon, hydrogen, and oxygen; their hydrocarbon backbones are used to make amino acids and other carbon-based molecules… Cellular respiration is a chemical process whereby the bonds of food molecules and oxygen molecules are broken”, carbon dioxide and water are formed, and the energy released is used in the production of ATP from ADP and P. Then, the hydrolysis of ATP molecules provides the energy needed for many biological processes.
Students engage in recommended Scientific Practices, including constructing explanations, interpreting data, and developing and using models.
This activity can be used to illustrate the Crosscutting Concepts, “Energy and matter: Flows, Cycles and Conservation” and “Cause and Effect: Mechanism and Prediction”.
Each student or pair of students will need a piece of paper that they can tear or cut into 16 rectangles and label as directed on page 2 of the Student Handout. If you prefer, you can print copies of the last page of these Teacher Preparation Notes and have students cut the pieces and then write the names of the molecules in the pieces from the first column. For some students, you may want to simplify the activity on page 2 of the Student Handout by omitting the numbers in front of the molecular formulae. Also, if you have not used the introductory activities described on the top of the next page, you may prefer to omit the \/ symbol for coupled equations and
instead have your students represent cellular respiration as
C6H12O6 + 6 O2 + ~29 ADP + ~29 P 6 CO2 + 6 H2O + ~29 ATP + ~29 H2O
Instructional Suggestions and Background Information
Before your students begin this activity, they should have a basic understanding of photosynthesis and cellular respiration. For this purpose I recommend the analysis and
How do biological organisms use energy? (http://serendip.brynmawr.edu/exchange/bioactivities/energy)
Using Models to Understand Photosynthesis (http://serendip.brynmawr.edu/exchange/bioactivities/modelphoto)
To maximize student participation and learning, I suggest that you have your students work in pairs (or individually or in small groups) to complete groups of related questions and then have a class discussion after each group of related questions. In each discussion, you can probe student thinking and help them to develop a sound understanding of the concepts and information covered before moving on to the next group of related questions.
To help students understand the big picture and consolidate their understanding of photosynthesis and cellular respiration, I recommend that you use a modified version of storyboarding3 with this activity, as follows:
Before students begin the Student Handout, students work in pairs and use their background knowledge to respond to the Introductory Photosynthesis and Cellular Respiration Storyboard (shown on page 8 of these Teacher Notes). This will help to activate students’ memory of relevant concepts and information. I recommend that you review these initial storyboards to learn more about your students’ knowledge and any misconceptions they may have; this storyboard is intended for formative assessment only.
As students increase their understanding of photosynthesis and cellular respiration during the activity, they can modify their Introductory Storyboards.
After completing the activity presented in the Student Handout, students complete the Follow-up Storyboard (shown on page 9 of these Teacher Notes) without looking at their earlier storyboard or the Student Handout. After they complete the Follow-up Storyboards, students should have prompt feedback so they can improve the accuracy and completeness of their storyboards; you can accomplish this in a class discussion where students compare their storyboards. This type of active recall with feedback helps to consolidate student understanding and retention of the concepts learned during the activity.4
A key for the Student Handout and a key for the storyboards are available upon request to Ingrid Waldron (firstname.lastname@example.org). The following paragraphs provide additional instructional suggestions and background information.
For background information on photosynthesis and cellular respiration, please see the Student Handout and Teacher Preparation Notes for the two introductory analysis and discussion activities listed above and the overview, “Cellular Respiration and Photosynthesis – Important Concepts, Common Misconceptions, and Learning Activities” (http://serendip.brynmawr.edu/exchange/bioactivities/cellrespiration).
You may want to introduce this activity by discussing with students whether cells can directly use sunlight to provide the energy needed for the processes of life. Then you could discuss whether cells can directly use glucose to provide the energy needed for the processes of life. This context will help students understand why plants need photosynthesis, cellular respiration, and hydrolysis of ATP to provide energy for the processes of life.
The figure on page 1 of the Student Handout shows glucose as the sugar produced by photosynthesis. Photosynthesis directly produces a three-carbon sugar glyceraldehyde-3-phosphate which is used to synthesize glucose and fructose. Some of the glucose and fructose are used to make sucrose which is transported to other parts of the plant.
As you know, hydrolysis refers to a chemical reaction in which a molecule is split into smaller molecules by reacting with water. Students may be less familiar with this term and may need help to recall this definition. This figure shows the hydrolysis of ATP. (There appears to be some disagreement about the details of where the atoms in the water molecule end up, but there is general agreement about what the products are.) For simplicity, the Student Handout represents Pi + H+ as P.
The Student Handout does not mention that the hydrolysis of ATP usually occurs after the ATP has bound with a substrate molecule, e.g. a motor protein or one of the reactants in a synthesis reaction. In this way, the exergonic hydrolysis of ATP is coupled with the endergonic change in conformation of the motor protein or the synthesis reaction.
Question 4 helps students to understand two important points:
All organisms (including plants) need to carry out cellular respiration to produce ATP, since ATP provides energy in the form needed to carry out many cellular processes (e.g. pumping substances into and out of cells and synthesis of organic molecules).5
All organisms need a source of organic molecules for cellular respiration, but plants use photosynthesis to make organic molecules, whereas animals eat food to get organic molecules.
After discussing question 8, you may want to have the students compare and contrast the diagram of photosynthesis and cellular respiration that they have developed in their answers to questions 5-7 with the diagram shown in the figure on page 1 of the Student Handout.
Page 3 of the Student Handout introduces the concept that the sugar molecules produced by photosynthesis are used not only for cellular respiration, but also for the synthesis of other organic molecules in plants. (Organic molecules are complex, carbon-containing molecules found in living organisms.) This figure provides some additional information about how glucose is used to synthesize a variety of organic molecules. Obviously, nitrogen and phosphorus from soil water will also be needed to synthesize amino acids, nucleotides, and phospholipids.