Photosynthesis: Problem Solving Lab

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Students will be able to experiment to see how changing the amount of light changes the amount of oxygen produced.

Big Idea

More reactants=more products!

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Purpose of Lesson:

 The purpose of this lesson is to apply learning on photosynthesis to a lab situation and give students a chance to work authentically through the scientific method.  

Major Strategy to Watch for:

Conclusion writing -  Writing to show evidence.

Ready. Set. Engage!

5 minutes

Learning Goal: Apply understanding of photosynthesis to a lab situation.

Opening Question: How will changing the amount of sunlight change the way photosynthesis works?

Students record their opening question on their learning goal sheet and are ready to start class 3 min after the bell has rung.  I reward students who get started early with ROCK STAR SCIENTIST tickets.  

Follow the links to learn more about the beginning of class strategies and ROCK STAR scientist tickets.   

Understand and Describe the Problem

10 minutes

The purpose of this section is to introduce the problem to the lab and have students write the purpose and hypothesis.  

I start this section by going back to the photosynthesis equation. I have students locate the products and reactants.

Then I ask students, "Ok let's say it is a cloudy day.  How is that going to change the equation?  How will it change the reactants?  How will it change the products?  What if it is a sunny day what will happen?

Once we've had this discussion I tell the students we are going to do a lab today to answer that question.  However, it is very difficult to tell how much sugar the plant has made because it stores it.  That's why in this experiment we are going to measure the amount of oxygen produced. 

Here's the question we are going to answer today, "How will changing the amount of light effect the amount of oxygen produced?"

Once students have the question they write the title, purpose, and hypothesis of the lab.  

Obtain a Plan

15 minutes

The purpose of this section is to explain the Virtual Experiment Photosynthesis website and the procedure to the students.  

Once they are done with the beginning aspects of the lab report, I display the simulation on my screen.  I show them how they can move the light forward from 200 cm to 100 cm.  They look at how distance changes the amount of light on the plant.  I then show them how to go into the simulation and record and read the bubble count.  Then we write the procedure.

  1. Count and record the bubbles per min for 200 cm.
  2. Count and record the bubbles per min for 150 cm.
  3. Count and record the bubbles per min for 100 cm.

Data Table:  Bubbles per minute

Distance from light (cm)

Count (bubbles/min)







 At this point students are ready to log into their computers and do the lab.  

Carry out Plan

15 minutes

The purpose of this section is to do the lab and analyze the results.  

When students have their title, purpose, hypothesis, and procedure done they are ready to do the lab. Students now go to the Photosynthesis Virtual Lab and I walk around and help them with the controls of the simulation. Then I let the students work and explore. Here is a video of a student explaining the lab.  


Depending on how much time is left in the class, I sometimes do a graph of this data.  Students have not really graphed yet this year so I do the graph and have them make one with me. In a couple of units, students will be making a variety of different graphs and so this is a good introduction. Also, the data tends to make a really nice graph!

Evaluate / Revise the Answer

12 minutes

Now that the students are done with their experiment, it is time to communicate the answer.  I do a short mini lesson here on Writing to Demonstrate.  (This is the partner to the strategy they learned earlier - Writing to Learn).  These two anchor charts stay on my wall all year so that students can always ground their writing in the purpose.  

I tell the students that in this case, we are going to use a very scripted form of writing.  That is because in lab reports it is the data and precision that are important.  In my lab reports I have the students use a three sentence conclusion.  An anchor chart for this also goes on the wall for easy access. 

In this lab I found.........

I know this because.......

This makes sense because.......


Over the years I have tried different forms of conclusions, longer, more in depth, and I've just found the most success with these three sentences.  In my opinion, it is enough writing to get the evidence and thinking across and not enough that it frightens my reluctant writers.  

 I ask the students to use these three sentence starters to write their conclusions.  Since this is the first conclusion we have written I will read aloud the sentence starter and then give different options of how to finish it.  It is important to tell the students over and over that they need to give actual data, otherwise they will consistently write-"I know this because of the data."  This is an absolute no- no in my class because it shows little thinking and understanding.  


3 minutes

Closing Statement: "Today we applied out learning to a lab situation.  Tomorrow we will be using our knowledge to make videos about photosynthesis."

Closing Question: "Do you think plants photosynthesize at night?  Why or why not."

Closure depends greatly on timing and is not as easy to plan in advance as opening.  You can find more information about how I manage closure here.