Lab 10.pdf

LABORATORY EXERCISE 10 Photosynthesis and Respiration Learning Objectives ● Understand how light impacts plant metabolism. ● Understand the reactions of photosynthesis and respiration. ● Identify the organelles responsible for photosynthesis and respiration. Introduction All living organisms, bacte...

LABORATORY EXERCISE 10 Photosynthesis and Respiration Learning Objectives ● Understand how light impacts plant metabolism. ● Understand the reactions of photosynthesis and respiration. ● Identify the organelles responsible for photosynthesis and respiration. Introduction All living organisms, bacteria, archaea, plants, fungi, and animals, require energy to function. A common form of energy used by all living organisms is adenosine triphosphate (ATP). ATP is made by a series of energy transformations of adding a phosphate to ADP. Regardless of the organism being classified as an autotroph or heterotroph, the original energy source of which all life depends is the sun. Photosynthetic plants make sugar by transforming and storing sunlight energy into chemical energy. The energy contained in photons of light are transformed into chemical energy by creating covalent bonds that hold glucose together. Molecules of beta-glucose connect via a beta 1,4 glycosidic bond to form cellulose, the principal polysaccharide that forms plant structure. The process of photosynthesis involves the use of light energy to convert carbon dioxide and water into sugar, oxygen, and other organic compounds. This process is summarized by the following reaction: Photosynthesis: 6 H2O + 6 CO2 + light energy → C6H12O6 + 6 O2 When plants cannot photosynthesize yet require energy to power cellular reactions, glucose is oxidized to create ATP by the process of cellular respiration. Cellular respiration refers to the process of converting the chemical energy of organic molecules into a form immediately usable by organisms. Glucose may be oxidized completely during cellular respiration if sufficient oxygen is available. This process is summarized by the following equation: Aerobic cellular respiration: C6H12O6 + 6 O2 → 6 H2O + 6 CO2 + energy Photosynthesis takes place in a plant cell’s chloroplast. A chlorophyll pigment absorbs the energy of sunlight, and through the process of photosynthesis converts light energy to chemical energy. The process of photosynthesis can be divided into two type of reactions: 1. Light-dependent reactions (PSII and PSI) 2. Light-independent reactions (Calvin Cycle reactions) The light dependent reactions capture the photons of light in reaction centers. The kinetic motion of the photons (light energy) is transferred to water molecules, whose electrons are displaced (electrochemical energy). This breaks the covalent bonds of individual water molecules, reshuffles the distribution of remaining electrons between two separate water molecules, and forms gaseous oxygen (O2) and two hydrogen ions as a result. This last part is nicknamed “splitting water”, and it is the event by which animals are provided “usable” air. For the plant, the displaced, high-energy electrons are used to create ATP. O2 sensor Figure 10.1. Exercise set-up. Note specific position of CO2 and O2 sensors. Procedure 1. Set the CO2 gas sensor to the Low (0–10,000 ppm) setting. Connect the CO2 gas sensor and the O2 gas sensor to LabQuest. Discard any “old” data that Labquest may have retained. 2. Tap the CO2 sensor display box and change the unit to part per thousand (ppt). Repeat the process to select ppt as the units for the O2 gas sensor. 3. Obtain several leaves from the resource table and if damp, gently blot them dry between two pieces of paper towel. 4. Place the leaves into the respiration chamber. Wrap the respiration chamber in aluminum foil so that no light can enter the chamber. 5. Place the O2 gas sensor into the BioChamber 250 as shown in Figure 10.1. Insert the sensor snugly. The O2 Gas Sensor should remain vertical throughout the experiment. Place the CO2 gas sensor into the neck of the BioChamber 250. 6. Wait 7 minutes for a baseline to establish before starting data collection. As your chamber establishes a baseline, write a hypothesis describing what you expect. Hypothesis: 7. At TIME zero, tap the O2 sensor display on the LabQuest. Select ZERO instrument. The O2 display should read 0.00 ppt. SECOND, tap the CO2 sensor display. Select mg/m3 value. Read and record the value, then change the display value back to ppt. Record the ppt value. Collect data every 2 min for a period of 30 min. When collecting the final data point for the CO2 sensor, collect both a ppt and mg/m3 value. When finished, remove the aluminum foil from around the respiration chamber. 8. Turn the lamp on. Place the lamp as close to the leaves as reasonable. Do not let the lamp touch the tissue culture flask. Wait 4 minutes before beginning data collection. As your chamber equilibrates, write a hypothesis describing what you expect. Hypothesis: 9. At TIME zero, tap the O2 sensor display on the LabQuest. Select ZERO instrument. The O2 display should read 0.00 ppt. SECOND, tap the CO2 sensor display. Select mg/m3 value. Read and record the value, then change the display value back to ppt. Record the ppt value. Collect data every 2 min for a period of 30 min. When collecting the final data point for the CO2 sensor, collect both a ppt and mg/m3 value. When finished, remove your leaves from the chamber. 10. Plot the release/consumption of the CO2 and O2 vs. Time for both the dark and light experiment (i.e. you should have 2-4 graphs). 11. Draw a smooth-fit line through your data points (i.e. a linear regression) to calculate the rate of respiration/photosynthesis for the CO2 gas sensor and O2 gas sensor. X is time and Y is carbon dioxide concentration or oxygen concentration Record the absolute value of the slope, m, as the rate of respiration/photosynthesis for the CO2 gas sensor and O2 gas sensor in Table 10.1. 12. Analyze your data and write a summary indicating if your hypotheses were supported. Data Table 10.1 Leaves In the dark In the light O2 rate of production/consumption (ppt/min) CO2 rate of production/consumption (ppt/min) Table 10.2 Raw Data O2 and CO2 ppt values Dark TIME (min) 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 O2 Sensor (ppt) Light CO2 Sensor (ppt) O2 Sensor (ppt) CO2 Sensor (ppt)