Investigating Photosynthesis with Algae (Part 2/2)

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Objective

Students will determine the rate of respiration and photosynthesis of algae.

Big Idea

What a bright idea! Light energy is trapped and converted into chemical energy during photosynthesis.

What Students will Learn in this Lesson

1 minutes

In today's lesson students will complete a lab to determine when photosynthesis and respiration occurs in algae. This lab helps students understand the connections between photosynthesis and respiration.  This is the second day of a two day lesson.  Here is an overview of what students will learn today.

Hook/Check for Understanding

3 minutes

Use the following assessment probe and ask students to predict when the processes of photosynthesis and respiration occur. The probe is designed to reveal whether students recognize that plants respire continuously.

During a class discussion, five students were talking about when plants carry out the processes of photosynthesis and respiration.  Here is an except of what they said:

Mike:  "Photosynthesis and respiration occur when it is light and when it is dark outside. 

Rachel: "Photosynthesis occurs when the sun is out; respiration occurs at night."

George: "Photosynthesis occurs when it is light; respiration occurs when it is light and when it is dark."

Tina: "Photosynthesis occurs both when it is light and when it is dark; respiration only happens when it is dark."

Stacy:  "Photosynthesis occurs in the day; plants don't carry out the process of respiration."

In your lab notebooks, make a +/- chart to determine what each student believe. With whom do you agree the most? Highlight that portion of the chart.  Explain why you agree with that statement and not the others below the chart.  

based on Keeley, Page. 2001. Light and Dark. Uncovering Student Ideas in Life Science. NSTA Press: Arlington, VA. 

 

Student Designed Lab: The effects of colored light on rate of photosynthesis

30 minutes

Using the lab proposal that students wrote yesterday, students will conduct an experiment to determine the effects of colored light on the rate of photosynthesis. After conducting the lab, students will input data into LoggerPro. Then they will use a regression line to calculate the rate of photosynthesis under different lighting conditions. Students will evaluate which type of light allows for the highest rate of photosynthesis. Students will explain their results at the bottom of their lab proposal.  

Student Lab: Determining the rates of photosynthesis and cellular respiration

30 minutes

In this activity, students will use algae as their model organism.  They will measure the rate of respiration and photosynthesis by monitoring carbon dioxide and oxygen levels over time.  

For this lab each student group will need the following equipment: 

  • Labquest
  • computer
  • Logger Pro
  • Vernier O2 Gas Sensor
  • Vernier CO2 Gas Sensor
  • Aluminum foil
  • 12-inch ring fluorescent lamp setup
  • BioChamber 2000
  • utility clamp
  • ringstand
  • algae culture

Collection of Data: Dark Chamber

  • Students should wrap the entire BioChamber with aluminum foil (including the lid) so that no light will reach the algae.
  • They should cover the bottom of the chamber with a mat of algae and 200 mL of algal medium.
  • Next, they should set the CO2 Gas Sensor has to the Low (0–10,000 ppm) setting and connect the CO2 Gas Sensor to Channel 1 and the O2 Gas to Channel 2 of the Vernier Labquest.
  • Students should prepare the computer for data collection by opening the file “31C Photo (CO2 and O2)” from the Biology with Vernier folder of Logger Pro.
  • Next, they should secure the lid on the chamber and insert the sensors into the holes.
  • Students should wait five minutes for the sensors to equilibrate, then click on the collect button to begin the 15-minute data collection.

Analysis of Data

  • After all data has been collected, they should determine the rate of respiration.
  • Students should click anywhere on the CO2 graph. Then they should select the Autoscale icon.
  • Students should vove the cursor to the point where the data values begin to increase.
  • They should hold down the left mouse button and drag the cursor to select the region of increasing CO2 gas concentration.
  • Students should select on the Linear Fit button to perform a linear regression.
  • A box will appear with the formula for a line of best fit.
  • Students should record the slope of the line, m, as the rate of respiration in Table 1 on provided handout.
  • Students should repeat preceding steps for the O2 graph, selecting the region of decreasing O2 concentration.

Collection of Data: Light Chamber

  • Students should store your data by choosing Store Latest Run from the Experiment menu.
  • Next, they should assemble the lamp so that it encompasses the Biochamber 2000. Important: they should not turn the lamp yet.
  • Next, they should Remove the aluminum foil from the respiration chamber and invert the chamber to remove the algal mat, solution, and accumulated gases.
  • Then, they should cover the bottom of the chamber with algal mat and solution.
  • Students should secure the lid on the chamber and insert the sensors into the holes.
  • Next, they should place the chamber inside the bulb and turn on the lamp.
  • Finally, they should repeat the procedure used previously to collect. 

Analysis of Data

  • After all data has been collected, students should determine the rate of respiration.
  • They should click anywhere on the CO2 graph. Then select the Autoscale icon.
  • They should move the cursor to the point where the data values begin to increase.
  • Students should hold down the left mouse button and drag the cursor to select the region of increasing CO2 gas concentration.
  • Students should next select on the Linear Fit button to perform a linear regression. A box will appear with the formula for a line of best fit.
  • Students should record the slope of the line, m, as the rate of respiration in Table 1 on the provided handout
  • Finally, students should repeat preceding steps for the O2 graph, selecting the region of decreasing O2 concentration.

Reporting the results

  • Students should label each curve by choosing Text Annotation from the Analyze menu
  • They should print a graph showing their photosynthesis and respiration data.
  • Finally, they should clean and dry the chamber. 

based on Redding, Kelly and David Mastermind. 2007. Photosynthesis and Respiration. Biology with Vernier. Vernier Software and Technology: Beaverton, OR

Putting It All Together

15 minutes
Bring the class back together and have several groups share their findings.  As a class consider the following questions:  
  • Were either of the rate values a positive number? If so, what is the biological significance of this?
  • Were either of the rate values a negative number? If so, what is the biological significance of this?
  • What evidence shows that cellular respiration occurred in the algae? Explain your answer using claims, evidence, reasoning.
  • What evidence also shows that that photosynthesis occurred in the algae? Explain your answer using claims, evidence, reasoning.. 
  • List five factors that might influence the rate of carbon dioxide production or consumption in the algae. Explain how you think each will affect the rate? 

Have students record their responses in their lab notebooks. 

Next have students revisit the assessment probe to which they responded at the beginning of the period.  Have students modify their responses as necessary and support their new explanation with data from today's experiment. (Note: See student assessment probe revision.)

Homework:  How might you repeat this experiment to determine if you would find similar results with complex plants?