Photosynthesis, Part 1-Modeling Photosynthesis

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Students will model the process of photosynthesis in order to visualize how photosynthetic organisms use sunlight to combine inorganic molecules to form energy storing organic molecules and release oxygen that is vital to most living things.

Big Idea

It's cool to be able to make your own food.


5 minutes

Warm-Up: Does the process of photosynthesis use light.  And if so, for what?

This warm-up question’s intent is to activate prior knowledge about the reactants and products of photosynthesis.  Although photosynthesis has not yet been formally taught, it has been mentioned several times in other science topics, such as the Characteristics of living things, and the Carbon Cycle.  Look for students to identify that light is the energy source for the chemical process.  


Introduce New Material

10 minutes

Provide an overview of the vocabulary that will be explicitly taught:

  • exergonic reaction,
  • endergonic reaction,
  • hydrolysis,
  • dehydration synthesis,
  • aerobic,
  • anaerobic,
  • glycolysis. 

Instruct students to add these terms to the Vocabulary Map, which students maintain as a reference set of biology terms that have Greek or Latin roots, or prefixes and suffixes.  Provide students a brief explanation of the function and process of photosynthesis.  Write the chemical equation for photosynthesis and identify the molecules that are reactants and those that are products.

Ask, "Is photosynthesis is an endergonic or exergonic reaction?"  State the term, endergonic reaction.  Emphasize “en” and ask students to tell you what “en” sounds like it might mean.  Look for someone to tell you that “en”  sounds like it means “in". Ask students by a show of hands to indicate if they think that photosynthesis is  an endergonic reaction.  Give 2-3 students an opportunity to explain why or why not.  Look for them to correctly state that energy is stored in the form of food (or glucose) during photosynthesis so it is an endergonic reaction. 

Repeat this explicit vocabulary instruction process for the term, exergonic.  Students should be able to correctly identify that "ex'" might mean "exit" or "out".

Using this type of processing helps students practice the type of deductive reasoning that is useful whenever they encounter words that they do not know. 



Guided Practice

10 minutes

Distribute the modeling photosynthesis hand-out, markers and colored pencils.  Write or project the chemical equation for photosynthesis on the board and instruct students to do the same on their own papers. Write the equation using both chemical formulas and the atomic structures.

Explain that both equations show the chemical reaction for photosynthesis. The first equation uses chemical formulas and the second using structural formulas.  Show students how H2O are the same.  The structural equation will be helpful later when students model photosynthesis using atomic model during Independent Practice.  Using colored pencils/crayons, color the molecules, following the color assignments indicated for each molecule on the student hand-out.

The coloring of the different molecules helps students identify the different molecules that are a part of photosynthesis.  Check for understanding by asking students to tell you how many reactants are needed for photosynthesis and how many products are formed.  Follow by asking them to name the three reactants and the two products of photosynthesis. Use the board or projector to model the same task as the students.

After coloring the molecules on both sides of the equation, identify and number the reactants #1, #2 and # 3 so that students will be able to easily see that there are 3 reactants for this reaction.  Instruct students to number the three reactants on their papers.  Follow by numbering the two products, #1 and #2.  It is a good practice to teach students, “When I write, you should write, as well”.  I explain to students that those things that I write are typically important points that I write to emphasize key points.

Walk around to check that students are indicating the correct information on their modeling sheets.

Independent Practice

20 minutes

Distribute atomic model sets and instructions to groups of two students. Briefly review what is contained in the atomic model sets. Inform students that the performance task is to use the molecular model kit to simulate the processes of Photosynthesis. Remind students they can use the chemical equation that is found on the hand-out as a reference. 

Instruct them to begin by constructing 6 carbon dioxide molecules and 6 water molecules (the reactants) for photosynthesis. Inform them that all other parts of the model must be put away before they construct one molecule of glucose through the process of photosynthesis. If done correctly, students should have exactly 6 O2 molecules remaining (O=O).  Instruct students to raise their hand once they have constructed their molecule of glucose, and have them explain the process to you, as the instructor.  Look for them to show you what remains after glucose is formed. 

Be sure to have both members of each group of two contribute to the explanation.  It is very important to listen for students’ correct use of the relevant vocabulary as they provide explanations for the reaction. If they fail to include that photosynthesis is an endergonic reaction, query them to find out if they know that it is an endergonic reaction and why it is an endergonic reaction.

Complete the practice by instructing students to complete the "What I should know" review.  Student responses to these questions are a useful way for students to identify their understanding of the content.  Walk around the room to observe and guide students as they complete this component of the task. Equally important, if not more so, is student self-identification of their attainment of the learning target for the day’s lesson. 

I like to end hands-on activities with written responses because students sometime fail to make the connection between the purpose of the hands-on activity as it relates to learning a new concept.  By having to respond to questions, they are guided to the desired connections as they respond to questions that make it clear as to what they should have gained from the activity.  

The student work sample shows that the learning target was met based on the student's ability to identify the reactants and products of photosynthesis, as well as explain how the products were created.

Lesson Close

5 minutes

Project the photosynthesis diagram.  Work whole group to identify the missing numbered parts of the picture.  Students should be able to identify each of the missing parts by name.

Formative Assessments are not always completed independently. We can learn a lot by observing and listening while students are working together to complete a closing formative assessment.   Listening and observing the number of students who are able to contribute to the group activity helps me know is there is understanding among the group or if understanding only exits in pockets of students in the room.  I will plan where to begin the next day based on a general sense of the level of understanding in the class.