Biol 160: Lab 4 Name: __________________________

Rev. 10/2011 1

Lab #4: Cellular Respiration and Photosynthesis in Plants OBJECTIVES

In this laboratory exploration, you will • Use oxygen and carbon dioxide probes to measure the production or consumption of these gases

by plant leaves. • Use the data to make conclusions about the rate of cellular respiration and photosynthesis in the

light. INTRODUCTION ♦ Recall that plant cells, like animal cells, use their mitochondria to produce energy in the form of ATP. This process is known as cellular respiration. We can measure rates of respiration in several ways, all of which come from the basic equation of cellular respiration:

C6H12O6 + 6O2 6 H2O + 6 CO2 + energy (ATP + heat) (glucose) (oxygen) (water) (carbon dioxide) Thus, if we wanted to know how much respiration was occurring in an organism, we could measure any of the following:

• Rates of the disappearance (consumption) of glucose • Rates of the disappearance (consumption) of oxygen • Rates of the production of water • Rates of the production of carbon dioxide • Rates of the production of ATP

Because we are measuring cellular respiration in living organisms, it is not easy to measure the

consumption of glucose or the production of water molecules or energy. Also, remember that some of the energy produced is captured as ATP and some is lost as heat. If we want to measure respiration, the easiest things to measure, is either the consumption of oxygen or the production of carbon dioxide. In this laboratory exploration, we will concentrate on the consumption or production of these two gases. ♦ As animals, we acquire the sugars we use in our mitochondria by ingestion (eating!). Most plants, however, produce their own sugars using carbon dioxide and sunlight in a process known as photosynthesis. We can measure rates of photosynthesis in several ways, all of which come from the basic equation of photosynthesis:

light energy + 6 H2O + 6 CO2 C6H12O6 + 6O2 (water) (carbon dioxide) (glucose) (oxygen) Thus, if we wanted to know how much photosynthesis was occurring in an organism, we could measure any of the following:

• Rates of the appearance (production) of glucose • Rates of the appearance (production) of oxygen • Rates of the disappearance (consumption) of water • Rates of the disappearance (consumption) of carbon dioxide • Rates of the consumption of light energy

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Of these possibilities, again the easiest to measure is the appearance of oxygen or the

disappearance of carbon dioxide. For this lab exploration, we will measure the concentration of both these gases to estimate the rate of photosynthesis and respiration. Remember, however, that plants are made of cells and so they must also undergo cellular respiration. Therefore, we will be measuring both respiration and photosynthesis by measuring changes in oxygen levels under light conditions. Based on what you know about photosynthesis and respiration, which would you expect to be more prevalent in a plant under light conditions compared to dark conditions? What would you expect to happen to oxygen levels in light compared to dark conditions? These are questions you will address as part of this exploration. Fill out these questions FIRST to help you review cellular respiration and photosynthesis in plants. 1. Do plants have mitochondria? 2. Why do you think plants do cellular respiration? To produce ___________________. 3. Do you think plants perform cellular respiration in the light? 4. Do you think plants perform cellular respiration in the dark? 5. Why do you think plants photosynthesize? To produce _____________________. 6. Do you think plants photosynthesize in the light? Why? 7. Do you think plants photosynthesize in the dark? Why? 8. Critical Thinking: What are two possible ways a plant might use the product you identified in #5? 9. Critical Thinking: If plants don’t photosynthesize in the dark (at night), where would they get their ATP energy from during the night? 10. Given your answers to #8 and #9 above, do you hypothesize that the rate of photosynthesis during optimal conditions in the daytime will be (the same as / greater than / less than) the rate of cellular respiration? 11. Given your hypothesis in #10, what do you predict will happen to the oxygen concentration in the light? Explain why. 12. Given your hypothesis in #10, what do you predict will happen to the carbon dioxide concentration in the light? Explain why.

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NOW: Propose and enter into Tables 1 and 2, below, the appropriate hypotheses and predictions for our experiments, testing whether photosynthesis and/or respiration occur in a plant in light and/or dark conditions. Remember that a hypothesis is a testable, tentative explanation of what will occur in your experiment. In this case, your hypothesis should explain what you think will happen to the rates of photosynthesis and respiration under each condition (light vs dark). In contrast, a prediction is much more specific; it describes what you will see or measure in your experiment if your hypothesis is supported.

Table 1: Our question: Is the rate of photosynthesis in the light (the same as / greater than / less than) the rate of cellular respiration?

Hypothesis:

Prediction:

Table 2: Our question: How does a plant obtain ATP energy in the dark?

Hypothesis:

Prediction:

MATERIALS (per group) LabQuest Vernier O2 Gas Sensor Vernier CO2 Gas Sensor BioChamber 2000 Spinach Ring Light Apparatus PROCEDURE 1. Work in groups of 4. To work efficiently, split up the work! 2. Get a Biochamber 2000 and a Labquest. The Biochamber 2000 has both a CO2 Gas Sensor and an O2 Gas Sensor. Make sure the switch on the CO2 Gas Sensor is set to low (0-10,000 ppm) setting. The O2 sensor must remain upright during the entire experiment!

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3. Connect the CO2 and O2 sensors to the Labquest by attaching the white wires from the sensors to any of the USB ports on the Labquest. The Labquest is smart enough to auto-detect which port has which sensor hooked up to it. 4. Each Labquest has a stylus that can be used as a computer mouse. If you are used to the iPod touch, notice that the Labquest only picks up a signal from the stylus if you hold it down (more firmly) than you would for an iPod or iPhone. If it does not pick up your signal, hold it down a little longer or a little firmer. You don’t need to push really hard, just harder than you would for an iPod or iPhone. 5. To change the Units to ppt (parts per thousand) on the Labquest, do the following:

• Use the stylus to hold on “Sensors” until it notices the stylus. • Hold on Change Units • Hold on CO2 • Hold on “ppt” (parts per thousand) instead of ppm (parts per million) or %

Repeat this process to select ppt as the units for the O2 Gas Sensor. Now both the CO2 and O2 Gas Sensor should read as ppt. 6. To set the timer on the Labquest, do the following:

• Hold on the data collection box (anywhere on the far right side of the home screen). • Change Rate to 15

o Hold on box o arrow back to delete numbers and then type “15”

• Change length (time of run) o type “15” in numbers box o change to “min” in the units box (change from “s”)

7. Weigh out 40 grams of spinach and place the spinach into the BioChamber 2000. Place the lid with the CO2 and O2 Gas Sensors on the BioChamber 2000. Make sure the lid fits snugly so no air can escape. 8. Place the BioChamber 2000, probes and the LabQuest handheld into a dark cabinet for 5 minutes to equalize. After 5 minutes start data collection by pressing the Start button on the LabQuest. 9. After 15 minutes the data collection will end. Take the apparatus out of the cabinet and sketch copies of the CO2 and O2 vs. time graphs on the Data Sheet at the end of this lab. 10. Perform a linear regression to calculate the rate of cellular respiration and/or photosynthesis for the CO2 Gas Sensor.

• Hold on Analyze • Hold on Curve Fit • Hold on CO2 Gas. • Hold on Choose fit • Hold on Linear • The linear-regression statistics are displayed to the right of the graph for the equation in the form y

= mx + b. “m” is the slope, which is the rate of change (This is the CO2 (ppt) per second.) Record this value in Table 3.

• Select OK.

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11. Repeat #10 for the O2 graph. 12. Turn the ring light on and place the BioChamber 2000 in the center of the light. The lamp should be on over the BioChamber 2000 for 5 minutes prior to beginning data collection. 13. After 5 minutes start data collection by pressing the Start button on the LabQuest. When prompted, select Discard to start a fresh graph. Data will be collected for 15 minutes and stop automatically. Sketch both CO2 and O2 graphs on the Data Sheet at the end of this lab. 14. Repeat steps 8 and 9 to determine the rate (slope) of cellular respiration and/or photosynthesis. 15. Complete the questions on the Data Sheet. Clean up 1. Remove the plant leaves from the respiration chamber and return them to the container in the front of the classroom. Clean and dry the chamber portion of the BioChamber 2000. Neatly wrap up all cords and put the lid, with the CO2 probe and O2 probe back on the BioChamber and return it to the cart. 2. Turn off the LabQuest by holding down the power button and tap Discard to completely turn off the machine. Plug the LabQuest back into its charging dock and make sure the stylus lanyard is not blocking the power connector.

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Data  Sheet  -­‐  Lab  #4:    Cellular  Respiration  and  Photosynthesis  in  Plants  

GRAPHS Darkness

O2 Gas vs. Time CO2 Gas vs. Time Light

O2 Gas vs. Time CO2 Gas vs. Time

DATA

Table 3

Leaves O2 rate of

production/consumption (ppt/s)= m value

CO2 rate of production/consumption

(ppt/s) = m value

In the dark

In the light

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INTERPRETING THE DATA AND CONSTRUCTING AN ARGUMENT Revisit the hypotheses and predictions you made in Tables 1 and 2. Using your data, answer the

following questions to construct your argument:

1. Do you support or reject your hypothesis explaining the rates of photosynthesis and respiration occurring in the light? Explain your reasoning and support it with specific evidence. If you reject your hypothesis, write a corrected hypothesis below.

2. Do you support or reject your hypothesis explaining how a plant obtains energy in the dark?

Explain your reasoning and support it with specific evidence. If you reject your hypothesis, write a corrected hypothesis below.

Additional Questions: 3. Were either of the rate values for CO2 a positive number? If so, what is the biological significance of

this?

4. Were either of the rate values for O2 a negative number? If so, what is the biological significance of this?

5. Do you have evidence that cellular respiration occurred in leaves? Explain.

6. Do you have evidence that photosynthesis occurred in leaves? Explain.

7. List three factors that might influence the rate of oxygen production or consumption in leaves. Explain how you think each will affect the rate.

8. How would test the influence of ONE of those factors?