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Photosynthesis (2)
Bio 2 Lecture 11
| Question | Answer |
|---|---|
| What is the purpose of the calvin cycle? | To make sugar (G3P) to store energy from the sun |
| Where does the calvin cycle occur? | In the stroma in the chloroplast |
| What are the requirements from the environment for the calvin cycle? | 1) CO2 gas used to build sugar 2) Rubisco enzyme to fix carbon 3) Energy to reduce CO2 |
| Where does ATP and NADPH come from? | ATP comes from PS2 and NADPH comes from PS1 |
| What are the 3 phases of the calvin cycle? | 1)CO2 fixation 2)Reduction 3)Regeneration |
| Generally, what happens in the 3 phases? | 1) C-fixation: Rubisco enxyme + RuBP + CO2--» PGA 2) Reduction of PGA to G3P (3C sugar) 3) Regeneration of initial reactant RuBP |
| What is Rubisco and what is it responsable for? | It's the most abundant enzyme. It's a large multienzyme complex that With RuBP and CO2 (O2 sometimes)to produce G3P. |
| When does photorespiration occurs? | When rubisco reacts with O2 to make CO2, which reduces the effeciency of photosynthesis to 80% because it makes the enzyme imperfect. |
| See notes for what happens in each phase of the cycle | slide 15 to 20 |
| How many ATP and NADPH are used in each of the phases? | Phases 1 and 2 use 6 ATP and 6 NADPH. Phase 3 uses 3 ATP. |
| In total, how many ATP and NADPH are used to generate a total of how many G3P? | 9 ATP total and 6 NADPH total to generate a total of 6 G3P. |
| What happens when ATP runs out in the calvin cycle? | NADPH accumulates, it fails to be released from NADP+ reductase, thus blocking the electrons from flowing down the ETC of PS1. |
| What is cyclical-photophosrylation? | PS 1's primary electron acceptor sends the electrons BACK to PS2 ETC causing a cyclical electron flow (called cyclical photo...) |
| What does cyclic electron flow generates? | Generates a surplus of ATP, satisfying the hugher demand in the Calvin Cycle |
| In what way is photosynthesis flawed? | Rubisco can bind to both O2 and CO2, and when it binds to O2, CO2 is produced instead of G3P. SO energy from light-dependent reactions is wasted when RuBP and O2 bind rubisco |
| What is it called when rubisco binds to O2 instead of CO2? | Photorespiration |
| SOO what are the 2 enzymatic activities of rubisco?? | 1) Binds CO2 in carbon fixation – under normal temperatures …makes sugar 2) Binds O2 in photorespiration – releases CO2 using energy but making no sugar |
| What conditions favor photorespiration? | 1) Hot and dry climate 2) High concentrations of oxygen 3) Low concentrations of CO2 4) Rubisco has a higher affinity for CO2 than for )2 when air temperatures are below 30 degrees |
| What is the problem with photosynthesis? | On hot dry days, plants close stomata to conserve water, which limits gas exchange |
| What are the 3 type of plants for carbon fixation? | C3, C4 and CAM plants |
| When are plants called C3? | IF the first stable fixed-carbon molecule from Calvin cycle contains 3 carbons, then the plants are called C3 plants. |
| What is the first carbon molecule made? | 3-carbon PGA |
| From what does a 3-carbon PGA result? | From the carbon fixation in the calvin cycle |
| What is the best climate for C3 plants? What's the % of C3 plant species? | Best adapted to moderate climatic conditions (below 25 to 30 degrees). About 85% of plant species are grouped as C3 plants (soybean for example) |
| C4 plants carry out photosynthetic reactions in 2 different cells, what are they called? | Mesophyll cells for light reactions and bundle sheat cells for the calvin cycle. |
| How does C4 plants avoid photorespiration? | By separating the light-dependent where (O2 is released) and light-independent reactions which uses rubisco |
| What does C4 plants fix? | They fix carbon to a 4-carbon molecule called oxaloacetate |
| For C4 plants, what is fixed in mesophyll cells and what is fized for bundle sheat cells? | 1) Meso: PEP carboxylase fixes CO2 to become a 4C molecule called oxaloacetate 2) Bun: The 4C is oxidized, releasing CO2 in bundle sheat cell to then bind with Rubisco in the Calvin cycle |
| Compare C3 and C4 plants :) See comparative table in notes for more | In C3, photorespiration is not supressed while it is for C4. For C3, photosynthesis happens when stomata are open while for C4 it's closed. 1st stable produc is 3C for C3 and 4C for C4. For C3, photosynthesis happens only in meso. cells and C4 in both |
| When does stomata open for CAM plants and CO2 is incorporated into what? | During the night and CO2 is incorporated into organic acids |
| When does light-dependent reactions occur and what do they create? | During the day, creating ATP and NADPH |
| What happens during the day for CAM plants? | The stomata is closed during the day and CO2 is released from organic acids and used in the Calvin cycle during the day |
| Sooo CO2 during night and day for CAM plants? | CO2 is stored at night and used during the day |
Created by:
Malayka
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