5. Plant Respiration and Photosynthesis



5. Plant Respiration and Photosynthesis Do plants perform cellular respiration in addition to photosynthesis? Do plants affect carbon dioxide concentration (in a closed system) differently in light versus dark environments? ObjectivesMeasure change in carbon dioxide in a closed system. Explain the role of carbon dioxide in respiration and photosynthesis in plants.Materials and EquipmentData collection systemAluminum foil (30 cm x 30 cm sheet)Carbon dioxide gas sensor with sampling bottleFresh spinach leaves, 1-2CFL or LED light source (800 lumens)SafetyFollow these important safety precautions in addition to your regular classroom procedures:Use caution when working with a hot light bulb.Procedure1.Select Sensor Data in SPARKvue. 2.Connect the carbon dioxide gas sensor to your device.3.Choose the graph template.4.Seal the empty sampling bottle with the carbon dioxide sensor. Calibrate the sensor.3457575138430Figure 1: Photosynthesis setupFigure 1: Photosynthesis setup5.Obtain one or two fresh spinach leaves. Remove the stems and use paper towels to gently absorb excess moisture from the leaves.6.Set the bottle on its side over the piece of foil. Arrange the leaves face-up to rest flat inside the bottle, as shown in Figure 1. Do not overlap leaves.Note: Use the blunt end of a pencil to position leaves inside the bottle.7.Place the carbon dioxide sensor in the sampling bottle so the rubber stopper makes an airtight seal.Part 1 – In Light 1.Position the light source above the sampling bottle so that it is directly above the leaves (not the sensor probe) as shown in Figure 1.2.Make a prediction: What do you think will happen to the carbon dioxide level in the bottle while the leaves are exposed to bright light? Record and explain your prediction in Table 1.3.Turn on the light. Allow the system to rest for one minute with the light on.4.Select Start to begin collecting data. Record the initial carbon dioxide (CO2) concentration in Table 2.5.After about 5 minutes (300 seconds), stop collecting data. Record the final CO2 concentration and time elapsed in Table 2.Note: Do not open the bottle until the entire investigation is complete.Part 2 – In Darkness1.Keep the sample bottle on its side with the sensor in firmly in place. Wrap the foil around the bottle and cover all sides to prevent light from entering the bottle. Keep the light source on.2.While you allow the system to rest for one minute, make a prediction: What do you think will happen to the carbon dioxide level in the bottle while the leaves are in the dark? Record your and explain your prediction in Table 1.3.Start collecting data. Record the initial CO2 concentration in Table 2.4.After 5 minutes, stop collecting data. Record the final CO2 concentration and time elapsed in Table 2.5.Show both runs in SPARKvue and scale the display. Sketch your results in Graph 1. Include numbers, labels, and units on the x- and y-axes. Add a key to identify each run.6.Calculate the change in carbon dioxide concentration for each run. Use the following equation and enter the result in Table 2.Change in CO2 Concentration = Final CO2 Concentration - Initial CO2 Concentration7.Calculate the rate of CO2 concentration change for each run. Use the following equation and enter the result in Table 2.Rate of CO2 Concentration Change = Change in CO2 concentration ÷ TimeData CollectionTable 1: Predictions of CO2 concentration in the presence and absence of lightLight ConditionPredictionLightDarkTable 2: Change in CO2 concentration in the presence and absence of lightLight ConditionInitial CO2 Concentration (ppm)Final CO2 Concentration (ppm)Time Elapsed (s)Change in CO2 Concentration (ppm)Rate of CO2 Concentration Change (ppm/s)LightDarkGraph 1: Carbon dioxide levels of spinach leaves in the light and in the darkQuestions and Analysis1.Why do you think it is important for the leaves to be flat, facing up, with the bottle on its side?2.What happens to the concentration of carbon dioxide gas when the spinach leaf is in bright light? Support your answer with data from this investigation. 3.What happens to the concentration of carbon dioxide gas when the spinach is in darkness? Support your answer with data from this investigation.4.Plant cells contain both chloroplasts and mitochondria. Explain whether photosynthesis, respiration, or both processes occur when the bottle is in light and when the bottle is in darkness.5.Draw a model that illustrates how plants and animals play a role in the carbon cycle. Use another piece of paper if necessary. 6.Oxygen is another gas that relates to photosynthesis. If you were to repeat this investigation using an oxygen sensor, would you expect the same results? Explain your answer. ................
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