Section 2 The Calvin Cycle - PDF Free Download

Section 2 The Calvin Cycle Objectives Summarize the main events of the Calvin cycle. Describe what happens to the compounds that are made in the Calvin cycle. Distinguish between C 3, C 4, and CAM plants. Summarize how the light reactions and the Calvin cycle work together to create the continuous cycle of photosynthesis. Explain how environmental factors influence photosynthesis.

Section 2 The Calvin Cycle Carbon Fixation The ATP and NADPH produced in the light reactions drive the second stage of photosynthesis, the Calvin cycle. In the Calvin cycle, CO 2 is incorporated into organic compounds, a process called carbon fixation.

Section 2 The Calvin Cycle Carbon Fixation, continued The Calvin cycle, which occurs in the stroma of the chloroplast, is a series of enzyme-assisted chemical reactions that produces a three-carbon sugar. Most of the three-carbon sugars (G3P) generated in the Calvin cycle are converted to a five-carbon sugar (RuBP) to keep the Calvin cycle operating. But some of the three-carbon sugars leave the Calvin cycle and are used to make organic compounds, in which energy is stored for later use.

Section 2 The Calvin Cycle

Section 2 The Calvin Cycle The Calvin Cycle

Section 2 The Calvin Cycle Alternative Pathways The C 4 Pathway Some plants that evolved in hot, dry climates fix carbon through the C 4 pathway. These plants have their stomata partially closed during the hottest part of the day. Certain cells in these plants have an enzyme that can fix CO 2 into four-carbon compounds even when the CO 2 level is low and the O 2 level is high. These compounds are then transported to other cells, where the Calvin cycle ensues.

Section 2 The Calvin Cycle Alternative Pathways, continued The CAM Pathway Some other plants that evolved in hot, dry climates fix carbon through the CAM pathway. These plants carry out carbon fixation at night and the Calvin cycle during the day to minimize water loss.

Section 2 The Calvin Cycle

Section 2 The Calvin Cycle Factors That Affect Photosynthesis Light Intensity The rate of photosynthesis increases as light intensity increases, because more electrons are excited in both photosystems. However, at some point all of the available electrons are excited, and the maximum rate of photosynthesis is reached. The rate then stays level regardless of further increases in light intensity.

Section 2 The Calvin Cycle Factors That Affect Photosynthesis, continued Carbon Dioxide Levels As with increasing light intensity, increasing levels of carbon dioxide also stimulate photosynthesis until the rate levels off.

Section 2 The Calvin Cycle Factors That Affect Photosynthesis, continued Temperature As temperature increases, the rate of photosynthesis increases to a maximum and then decreases with further rises in temperature. The rate peaks at a certain temperature, at which many of the enzymes that catalyze the reactions become ineffective. Also, the stomata begin to close, limiting water loss and entry of carbon dioxide.

Section 2 The Calvin Cycle Environmental Influences on Photosynthesis

Multiple Choice 1. Which of the following is a reactant in the Calvin cycle? A. O 2 B. CO 2 C. H 2 O D. C 6 H 12 O 6

Multiple Choice, continued 1. Which of the following is a reactant in the Calvin cycle? A. O 2 B. CO 2 C. H 2 O D. C 6 H 12 O 6

Multiple Choice, continued 2. Which of the following statements is correct? F. Accessory pigments are not involved in photosynthesis. G. Accessory pigments add color to plants but do not absorb light energy. H. Accessory pigments absorb colors of light that chlorophyll a cannot absorb. J. Accessory pigments receive electrons from the electron transport chain of photosystem I.

Multiple Choice, continued 3. Oxygen is produced at what point during photosynthesis? A. when CO 2 is fixed B. when water is split C. when ATP is converted into ADP D. when 3-PGA is converted into G3P

Multiple Choice, continued The diagram below shows a portion of a chloroplast. Use the diagram to answer the question that follows. 4. Which of the following correctly identifies the structure marked X and the activities that take place there? F. stroma Calvin cycle G. stroma light reactions H. thylakoid Calvin cycle J. thylakoid light reactions

Multiple Choice, continued 5. light reactions : ATP :: Calvin cycle : A. H + B. O 2 C. G3P D. H 2 O

Multiple Choice, continued The diagram below shows a step in the process of chemiosmosis. Use the diagram to answer the question that follows. 6. What is the substance identified as Y in the image? F. H + G. NAD + H. NADPH J. ADP synthase

Short Response Chloroplasts are organelles with areas that conduct different specialized activities. Where in the chloroplast do the light reactions and the Calvin cycle occur?

Short Response, continued Chloroplasts are organelles with areas that conduct different specialized activities. Where in the chloroplast do the light reactions and the Calvin cycle occur? Answer: The light reactions of photosynthesis occur along the thylakoid membrane. The Calvin cycle occurs in the stroma, surrounding the thylakoids.

Extended Response The reactions of photosynthesis make up a biochemical pathway. Part A What are the reactants and products for both the light reactions and the Calvin cycle? Part B Explain how the biochemical pathway of photosynthesis recycles many of its own reactants, and identify the recycled reactants.

Extended Response, continued Answer: Part A The reactants for the light reactions of photosynthesis are sunlight, water, NADP +, and ADP. The products are oxygen, ATP, and NADPH. The reactants for the Calvin cycle are ATP, NADPH, CO 2, and RuBP. The products are NADP +, ADP, and organic compounds. Part B ADP/ATP, NADP + /NADPH, and electrons are recycled during photosynthesis. RuBP, which reacts with CO 2 in the Calvin cycle, is regenerated at each turn of the cycle.