🌿 CHAPTER 10 – PHOTOSYNTHESIS (COMPLETE FLASHCARDS)
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67 Terms
🔑 Key Definitions
Q: What is photosynthesis?
A: The process where light energy is used to convert CO₂ and H₂O into carbohydrates and O₂; occurs in plants, algae, and cyanobacteria.
Q: What is the electromagnetic spectrum?
A: The range of all types of electromagnetic radiation, including visible light used in photosynthesis.
Q: What is wavelength?
A: The distance between peaks in a wave; shorter wavelength = higher energy.
Q: What is a photon?
A: A particle of light energy. When absorbed, it can excite electrons from ground state (low energy) to excited state (high energy).
Q: What is a pigment?
A: A molecule that absorbs specific wavelengths of light (e.g., chlorophyll).
Q: What is an absorption spectrum?
A: A graph showing the wavelengths absorbed by a pigment.
Q: What is an action spectrum?
A: A graph showing the rate of photosynthesis versus light wavelength.
Q: What is chlorophyll a?
A: The main pigment in photosynthesis; absorbs red and blue light, reflects green.
Q: What is chlorophyll b?
A: An accessory pigment that helps broaden the range of light absorbed.
Q: What are accessory pigments?
A: Pigments like chlorophyll b, carotenoids, and phycobilins that absorb light wavelengths not absorbed by chlorophyll a.
Q: What is a reaction center?
A: A chlorophyll a molecule in a photosystem that donates an excited electron to an acceptor.
Q: What is a mesophyll cell?
A: Leaf cell where photosynthesis mainly occurs.
Q: What are chloroplasts?
A: Organelles in plant cells that perform photosynthesis.
Q: What is the stroma?
A: The fluid-filled area inside a chloroplast surrounding the thylakoids.
Q: What are thylakoids?
A: Flattened membrane sacs in chloroplasts that contain photosynthetic pigments.
Q: What is a photosystem?
A: A protein-pigment complex that captures light energy for photosynthesis (includes Photosystem I and II).
Q: What is photophosphorylation?
A: ATP synthesis using light energy and a proton gradient in chloroplasts.
Q: What is ferredoxin?
A: An electron carrier that helps reduce NADP+ in Photosystem I.
Q: What is ATP synthase?
A: An enzyme that uses the H+ gradient to make ATP from ADP + Pi.
Q: What is NADP+ reductase?
A: An enzyme that reduces NADP+ to NADPH using electrons from Photosystem I.
Q: What is the Calvin cycle?
A: A light-independent pathway that fixes CO₂ into carbohydrates using ATP and NADPH.
Q: What is rubisco?
A: Ribulose bisphosphate carboxylase/oxygenase – the enzyme that fixes CO₂ in the Calvin cycle.
Q: What is ribulose bisphosphate (RuBP)?
A: A 5-carbon sugar that binds CO₂ in the first step of the Calvin cycle.
Q: What is 3-phosphoglycerate (3PG)?
A: The first stable 3-carbon product of the Calvin cycle.
Q: What is glyceraldehyde-3-phosphate (G3P)?
A: A 3-carbon sugar produced in the Calvin cycle; can be used to make glucose or starch.
Q: What is phosphoglycolate?
A: A 2-carbon compound produced during photorespiration when rubisco binds O₂.
Q: What is oxaloacetate?
A: A 4-carbon compound formed during CO₂ fixation in C4 and CAM plants.
Q: What is malate?
A: A 4-carbon compound that transports CO₂ from mesophyll to bundle sheath cells in C4 plants.
Q: What is phosphoenolpyruvate (PEP)?
A: A 3-carbon compound that combines with CO₂ in C4 and CAM pathways.
Q: What is photorespiration?
A: A process where rubisco adds O₂ to RuBP instead of CO₂, decreasing photosynthetic efficiency.
Q: What is thioredoxin?
A: A protein activated by light that regulates Calvin cycle enzymes via redox reactions.
Q: What are stomata?
A: Pores in the leaf that allow gas exchange.
Q: What are C3 plants?
A: Plants that fix CO₂ directly into 3PG using rubisco; prone to photorespiration in hot, dry conditions.
Q: What are C4 plants?
A: Plants that fix CO₂ into oxaloacetate using PEP carboxylase in mesophyll cells, then deliver CO₂ to bundle sheath cells.
Q: What are CAM plants?
A: Plants that fix CO₂ at night using PEP carboxylase and store it as malate; perform the Calvin cycle during the day.
Q: What is PEP carboxylase?
A: An enzyme that fixes CO₂ in C4 and CAM plants; unaffected by O₂.
Q: What are autotrophs?
A: Organisms that make their own food via photosynthesis.
Q: What are heterotrophs?
A: Organisms that consume other organisms for food.
💡 Key Concepts
Q: What is the relationship between wavelength, energy, and color of sunlight?
A: Shorter wavelengths = higher energy. Blue/violet has more energy than red. Pigments absorb specific wavelengths for photosynthesis.
Q: What is the summary equation for photosynthesis?
A:
6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
Q: Describe energy flow in a photosystem.
A: Light excites pigments in antenna complexes → energy passed to reaction center → excited electron transferred to electron transport chain.
Q: What are the events in non-cyclic electron transport?
A:
Light hits PSII → electrons from water split → O₂ released
Electrons move through ETC → ATP made
Electrons reach PSI → excited again → reduce NADP+ to NADPH
Q: What are the events in cyclic electron transport?
Q: What are the events in cyclic electron transport?
Q: What is the final electron acceptor in photosynthesis?
A: NADP+, which becomes NADPH.
Q: What experiment showed O₂ comes from H₂O, not CO₂?
A: Ruben & Kamen used radioactive ¹⁸O in water; showed labeled O₂ came from H₂O.
Q: Trace the electron pathway in the thylakoid membrane.
A: H₂O → PSII → ETC → PSI → NADP+ → NADPH
Q: What is the chemiosmotic gradient in chloroplasts?
A: Protons (H⁺) accumulate in the thylakoid lumen → diffuse through ATP synthase → drive ATP synthesis.
Q: Difference between light-dependent and light-independent reactions?
A:
Light-dependent: Use light to make ATP & NADPH (in thylakoid).
Light-independent: Use ATP & NADPH to fix CO₂ (in stroma).
Q: When are H₂O, O₂, and NADPH used/produced?
A:
H₂O: Used in light reactions
O₂: Produced from splitting H₂O
NADPH: Produced in light reactions, used in Calvin cycle
Q: What are the three steps of the Calvin cycle?
A:
CO₂ fixation (RuBP + CO₂ → 3PG)
Reduction of 3PG → G3P
Regeneration of RuBP
Q: How many ATP and NADPH are needed to make one glucose?
A: 18 ATP and 12 NADPH per glucose (6 turns of the cycle).
Q: How did Calvin & Benson determine the CO₂ fixation steps?
A: Used ¹⁴CO₂ with Chlorella; tracked radioactive carbon in intermediates over time.
Q: What is the first stable product of the Calvin cycle?
A: 3-phosphoglycerate (3PG)
Q: What are the fates of G3P?
A:
Exported to cytoplasm → hexoses → sucrose
Remains in chloroplast → glucose → starch
Q: What’s the difference between C3, C4, and CAM plants?
A:
C3: Fix CO₂ with rubisco; photorespiration occurs
C4: Use PEP carboxylase in mesophyll → deliver CO₂ to bundle sheath
CAM: Fix CO₂ at night (malate); Calvin cycle during day
Q: In what environments would you find C3, C4, or CAM plants?
A:
C3: Cool, moist environments
C4: Hot, dry environments (e.g. corn, sugarcane)
CAM: Very dry areas (e.g. cactus, pineapple)
Q: How does light stimulate the Calvin cycle?
A:
Increases stromal pH
Activates enzymes via thioredoxin-mediated reduction
Q: Why is rubisco both a carboxylase and an oxygenase?
A: It can fix CO₂ (carboxylase) or O₂ (oxygenase); O₂ fixation leads to photorespiration.
Q: What is photorespiration and why is it inefficient?
A: Rubisco fixes O₂ → makes phosphoglycolate → converted to 3PG but loses CO₂; reduces net CO₂ fixation.
Q: What organelles are involved in photorespiration?
A: Chloroplasts, peroxisomes, and mitochondria.
Q: Why is PEP carboxylase more efficient than rubisco?
A: PEP carboxylase only fixes CO₂, even when O₂ levels are high.
Q: What are advantages and disadvantages of C4 plants?
A:
Advantage: Avoid photorespiration in hot, dry conditions
Disadvantage: Use more ATP for CO₂ concentration
Q: Give examples of C3, C4, and CAM plants.
A:
C3: Wheat, barley, soybeans
C4: Corn, sugarcane
CAM: Cactus, pineapple
Q: How does the Calvin cycle link photosynthesis and respiration?
A: G3P from the Calvin cycle is used for respiration or biosynthesis throughout the plant.
Q: What are the energy losses in photosynthesis?
A: Only ~5% of solar energy is stored as chemical energy; losses due to reflection, heat, inefficient absorption, and respiration.