Photosynthesis Investigation

When and how does photosynthesis occur?

Part 1a: Light Experiment

How does the amount of exposure to light affect the amount of photosynthesis vs. respiration in a spinach plant?

Follow the steps below and complete the Photosynthesis Light and Dark Investigation assignment page.

Hypothesis: Look at your Introduction to Photosynthesis and Introduction to Respiration notes, in particular the equations. Using this information, write a hypothesis for this investigation on your assignment page

Materials: 

• Spinach leaves

• Photosynthesis chamber with lamp

• Vernier O2 and CO2 probes

• Chromebook with 2 USB ports & Vernier graphicalanalysis.app

Procedure: 

1. To use the “Vernier graphical analysis Chrome,” click graphicalanalysis.app. 

2. Spread a medium-sized handful of spinach around the photosynthesis chamber. 

3. Close the chamber, plug in the O2 and CO2 probe sensors, and turn on the lamp.

4. In the App, click the untitled tab & new experiment. Click Sensor Data Collection, USB, and Go Direct USB. Enable both sensors by clicking each Go Direct USB. 

5. For the O2 and CO2 change the y tabs with the appropriate values, making sure that the CO2 sensor is in PPM and that the O2 sensor is in PPT (press O2 on the left).

6. Press the "COLLECT" button at the top of the screen.  

7. Record the O2 and CO2 values for 0, 100, and 300 seconds on your data table. 

8. Turn off lamp, return leaves to container, restock bin with sensors and chamber.

RUN a 2nd trial if time: turn off lamp for 3 minutes between trials and do directions 4-8.

Part 1b: Dark Experiment

Materials: 

• Spinach leaves

• Photosynthesis chamber with aluminum foil

• Vernier O2 and CO2 probes

• Chromebook with Vernier graphicalanalysis.app

Procedure: 

1. To use the “Vernier graphical analysis Chrome,” click graphicalanalysis.app. 

2. Plug O2 and CO2 sensors into Chromebooks.

3. Adjust settings to include the data tables and change oxygen from % to ppt.

4. Put spinach leaves in container (double layer) and seal shut.

5. Let the sensors calibrate (sit there) for 2 minutes.

6. Place foil completely over the container to not let light in.

7. Start collection and record data at 0, 100, and 300 seconds.

8. Make a double point-line graph and write a full 4-point scientific conclusion.

9. Clean-up: Return spinach leaves, restock bin (keep foil flat-using for other classes)

Complete the Photosynthesis Light and Dark Investigation assignment page.

Part 1c: Photosynthesis Investigation Debrief

Photosynthesis formula:

• 6CO2 + 6H2O ---(add light energy and chlorophyll)---> C6H12O6 + 6O2

Respiration formula:

• C6H12O6 + 6O2 ---(uses enzymes to release energy)---> 6CO2 + 6H2O 

Look at the inputs (left side) and outputs (right side) of the above equations.

Is more photosynthesis or respiration is happening in the following situations?

• Increasing levels of CO2 (carbon dioxide)?

• Decreasing levels of CO2?

• Stable levels of both CO2 and O2 (oxygen)?

Look at your data and graphs. What was happening in light and dark for you? 

If not complete, finish the Photosynthesis Light and Dark Investigation page.

Extension: For the bean experiment:

1. Reset the graph (upper left untitled button) but keep the oxygen in ppt

2. Place the beans in the container  (NO FOIL)

3. Collect for 300 seconds

4. When finished take beans out and put back in cup

5. Have someone breathe into container and measure O2 and CO2 for comparison to the other experiments

Part 2: Why So Blue, Plants?

Recall from previous science classes that pH is a measure of how acidic or basic a substance is.

Bromothymol blue (BTB) is a pH indicator that changes colors as follows. 

The teacher will demonstrate what happens when respiration happens in a pH indicator solution (the teacher blows air into a cup of  BTB).

• The process of photosynthesis gives off oxygen (O2). 

• The process of respiration gives off carbon dioxide (CO2).

• CO2 makes things acidic. 

• If there is more photosynthesis happening than respiration, the pH indicator will turn blue.

• If there is more respiration happening than photosynthesis, the pH indicator will turn yellow.

Complete the following investigation and write answers on your Photosynthesis Investigation assignment sheet.

Photosynthesis Investigation

Question: How does the amount of exposure to light affect the amount of photosynthesis vs. respiration in a moss plant?

Hypothesis: Write your hypothesis on the Photosynthesis Investigation assignment sheet.

Materials:

• Beaker that can hold 150 mL of water

• 30 drops of Bromothymol blue (BTB) solution

• Straw, clear plastic wrap and safety goggles for turning solution green

• 3 vials with lids

• Enough moss plants to fill three vials

• Tape and pencil or pen to label vials

Procedure:

1. Two table groups work together to label 3 different vials with period, tables, and hours of light (0, 8 and 24).

2. Add 150 mL of water and 30 drops of BTB solution to beaker.

3. Cover beaker with plastic wrap, poke a hole in the plastic wrap with a straw, put goggles on and blow into the straw until the solution turns green.

4. Place 2-4 moss plants in each vial and fill each vial with green solution.

5. Choose locations that have 0, 8, and 24 hours of light each day and place one vial in each location.

6. After at least one day, observe, measure and record the color of each vial.

7. Repeat steps 1-6 three more times with the other pairs of table groups.

8. Clean-up: Dump liquid, throw away straw and plastic wrap and restock bin.

Data: Write your data on the Photosynthesis Investigation assignment sheet.

Graph: Create a graph on the Photosynthesis Investigation assignment sheet.

Conclusion: Write your conclusion on the Photosynthesis Investigation assignment sheet.

Part 3: Flower Dissection

Follow the guidelines in the "Plants" lesson to dissect a flower.