Photosynthesis: 18 flashcards
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1. What is the overall chemical equation for photosynthesis?
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$$6CO_2 + 6H_2O + light \ energy \rightarrow C_6H_{12}O_6 + 6O_2$$
2. In which organelle does photosynthesis occur in plant cells?
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The **chloroplast**.
3. Name the two main stages of photosynthesis and where each occurs in the chloroplast.
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1. **Light-dependent reactions** – occur in the **thylakoid membranes**. 2. **Light-independent reactions (Calvin cycle)** – occur in the **stroma**.
4. What is the role of chlorophyll in photosynthesis?
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Chlorophyll **absorbs light energy** (mainly red and blue wavelengths) and uses it to drive the light-dependent reactions, converting light energy into chemical energy.
5. What are the products of the light-dependent reactions?
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**ATP**, **NADPH**, and **oxygen gas (O₂)** (released as a byproduct from the splitting of water).
6. What is the primary purpose of the Calvin cycle (light-independent reactions)?
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To **fix carbon dioxide** (CO₂) into organic molecules, ultimately producing **glucose** (C₆H₁₂O₆) using the ATP and NADPH from the light-dependent reactions.
7. What molecule is split during the light-dependent reactions to release oxygen?
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**Water (H₂O)** – this process is called **photolysis**.
8. What are the two main types of chlorophyll found in plants?
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**Chlorophyll a** and **chlorophyll b**.
9. What is the role of NADPH in the Calvin cycle?
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NADPH provides **reducing power** (electrons and hydrogen ions) to convert 3-PGA into G3P, a key intermediate in glucose synthesis.
10. What is the function of stomata in photosynthesis?
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Stomata are small pores on the leaf surface that allow **CO₂ to enter** and **O₂ to exit** the leaf, facilitating gas exchange for photosynthesis.
11. What is the role of the electron transport chain in the light-dependent reactions?
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It is a series of proteins in the thylakoid membrane that **transfers electrons** from water to NADP⁺, using the energy to pump protons and generate ATP via chemiosmosis.
12. What is the primary product of the Calvin cycle that is used to make glucose?
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**Glyceraldehyde-3-phosphate (G3P)** – two G3P molecules combine to form one glucose molecule.
13. How many turns of the Calvin cycle are required to produce one molecule of glucose?
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**Six turns** – each turn fixes one CO₂ molecule, and glucose has six carbons.
14. What is the role of the enzyme RuBisCO in the Calvin cycle?
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RuBisCO catalyzes the **fixation of CO₂** to ribulose-1,5-bisphosphate (RuBP), the first step of the Calvin cycle.
15. What is the main difference between C3 and C4 photosynthesis?
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C3 plants use the Calvin cycle directly, while C4 plants first fix CO₂ into a four-carbon compound (oxaloacetate) in mesophyll cells, then release CO₂ in bundle sheath cells for the Calvin cycle, reducing photorespiration.
16. What is photorespiration and why is it considered wasteful?
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Photorespiration occurs when RuBisCO fixes **O₂ instead of CO₂**, leading to a process that consumes ATP and releases CO₂ without producing sugar, reducing photosynthetic efficiency.
17. What is the role of the thylakoid membrane in the light-dependent reactions?
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It houses the **photosystems** (PSII and PSI), the electron transport chain, and ATP synthase, providing the structure for light absorption, electron transport, and ATP synthesis.
18. What is the primary function of the Calvin cycle in terms of carbon?
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To **convert inorganic CO₂ into organic carbon** (G3P), which can be used to synthesize glucose and other carbohydrates.
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