domain-bilingual-v2 — discriminative confusable retrieval gate (corpus + query drafts)

datasets/domain-bilingual-v2/corpus/cell-energy-calvin-cycle.md

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+---
+title: The Calvin cycle
+language: en
+source: openai-codex-synthetic
+---
+
+# The Calvin cycle
+
+## Role in cellular energy
+
+The Calvin cycle is the light-independent carbon-fixation pathway of photosynthesis. It runs in the **stroma of chloroplasts**, where enzymes use the chemical energy of **ATP** and the reducing power of **NADPH** to convert inorganic carbon dioxide into carbohydrate. It is “light-independent” because its reactions do not require photons directly, although they depend on ATP and NADPH supplied by the photosynthetic energy system.
+
+The pathway is historically associated with **Melvin Calvin**, **Andrew Benson**, and **James Bassham**, who traced carbon atoms using radioactive carbon-14. In many plants it is called the **C3 pathway** because the first stable product has three carbon atoms.
+
+## Carbon fixation by RuBisCO
+
+The defining enzyme of the Calvin cycle is **RuBisCO**: ribulose-1,5-bisphosphate carboxylase/oxygenase. In its carbon-fixing role, RuBisCO attaches **CO₂** to the five-carbon acceptor **ribulose-1,5-bisphosphate** (**RuBP**). The unstable six-carbon intermediate immediately yields two molecules of **3-phosphoglycerate** (**3-PGA**).
+
+This carboxylation step is the entry point for atmospheric carbon into organic metabolism. Unlike pathways that break down sugar for energy, the Calvin cycle uses energy input to build reduced carbon compounds that can later support sucrose, starch, cellulose, and other plant molecules.
+
+## Reduction and sugar output
+
+After fixation, 3-PGA is phosphorylated by **ATP** and reduced by **NADPH** to form **glyceraldehyde-3-phosphate** (**G3P**), also called triose phosphate. G3P is the main carbohydrate product exported from the cycle. It is not yet glucose, but two G3P molecules can be used by plant metabolism to assemble a six-carbon sugar.
+
+For every **3 CO₂** fixed, the cycle produces one net G3P molecule while consuming **9 ATP** and **6 NADPH**. The remaining carbon skeletons stay in the cycle so that the CO₂ acceptor can be rebuilt.
+
+## Regeneration of RuBP
+
+Most G3P molecules are rearranged through a series of enzyme-catalysed steps to regenerate **RuBP**, allowing RuBisCO to continue carbon fixation. This regeneration phase also requires ATP.
+
+Overall, the Calvin cycle is the central anabolic route by which photosynthetic cells turn CO₂ into usable carbohydrate, coupling carbon fixation to ATP consumption and NADPH oxidation.

datasets/domain-bilingual-v2/corpus/cell-energy-chemiosmosis.md

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+---
+title: Chemiosmosis and ATP synthase
+language: en
+source: openai-codex-synthetic
+---
+
+# Chemiosmosis and ATP Synthase
+
+## The proton-motive force
+
+Chemiosmosis is the coupling of an electrochemical proton gradient to ATP production. The stored energy is called the **proton-motive force** (PMF), often written as Δp. It has two parts: a membrane voltage, **Δψ**, and a proton concentration difference, **ΔpH**. Together they make one side of an energy-transducing membrane more positive and more acidic than the other.
+
+In mitochondria, this membrane is the **inner mitochondrial membrane**; in chloroplasts, it is the **thylakoid membrane**. In both settings, ATP synthase does not create the gradient by itself. Instead, it uses the existing proton-motive force as its immediate energy source. Protons move down their electrochemical gradient through ATP synthase, and that downhill movement is what powers the uphill phosphorylation of **ADP + inorganic phosphate (Pi)** to form **ATP**.
+
+Peter Mitchell proposed this chemiosmotic mechanism in the 1960s, explaining how a membrane gradient could link energy capture to ATP formation.
+
+## ATP synthase as a rotary enzyme
+
+ATP synthase is a membrane protein complex commonly called **F₀F₁-ATP synthase**. The **F₀** portion sits in the membrane and forms the proton channel. The **F₁** portion projects from the membrane and contains catalytic sites where ATP is made.
+
+As protons pass through F₀, they bind and release from subunits in the rotating **c-ring**. This rotation turns the central **γ (gamma) stalk**, which extends into the F₁ head. The γ stalk forces the three catalytic **β subunits** of F₁ through different conformations: loose, tight, and open. This binding-change mechanism, associated with Paul D. Boyer, allows ADP and Pi to bind, ATP to form tightly, and ATP to be released.
+
+John E. Walker’s structural work helped show how the enzyme’s architecture supports this rotary catalysis.
+
+## The direct link to ATP formation
+
+The key point is that ATP synthase is driven by **proton flow down the proton-motive force**, not by direct electron transfer, light absorption, carbon fixation, or glucose splitting. Those processes may supply energy to cells in other steps, but the immediate driver of ATP synthase is the PMF across a membrane.
+
+When the gradient is strong, proton flow turns the enzyme and favors ATP production. When the gradient collapses, ATP synthase can no longer efficiently phosphorylate ADP. Thus, chemiosmosis explains how a membrane-stored electrochemical gradient is converted into the chemical bond energy of ATP.

datasets/domain-bilingual-v2/corpus/cell-energy-electron-transport.md

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+---
+title: The electron transport chain
+language: en
+source: openai-codex-synthetic
+---
+
+# The electron transport chain
+
+## Location and purpose
+
+The electron transport chain, or ETC, is a set of protein complexes and mobile electron carriers embedded in the inner mitochondrial membrane. Its defining role is to pass high-energy electrons from reduced carriers such as NADH and FADH₂ to a final electron acceptor, while using the released energy to pump protons across the membrane.
+
+In mitochondria, protons are moved from the matrix into the intermembrane space. This unequal distribution creates an electrochemical proton gradient: the intermembrane space becomes more acidic and positively charged relative to the matrix. The ETC therefore does not directly “make sugar” or split glucose; its central job is membrane-based electron transfer coupled to proton pumping.
+
+## Carriers and complexes
+
+Electrons enter the chain mainly through Complex I, also called NADH dehydrogenase, when NADH is oxidised. Complex I transfers electrons to ubiquinone, also known as coenzyme Q, and pumps protons across the inner membrane.
+
+FADH₂-associated electrons enter through Complex II, succinate dehydrogenase. Complex II passes electrons to ubiquinone but does not pump protons. This difference matters because electrons entering through Complex I contribute more strongly to the proton gradient.
+
+Reduced ubiquinone carries electrons within the membrane to Complex III, the cytochrome bc₁ complex. Complex III transfers electrons to cytochrome c, a small mobile protein on the outer side of the inner membrane, and contributes further proton movement into the intermembrane space.
+
+Cytochrome c delivers electrons to Complex IV, cytochrome c oxidase. Complex IV transfers electrons to molecular oxygen, producing water, and pumps additional protons across the membrane.
+
+## Building the gradient
+
+The ETC’s proton pumping is directional and organised. For a pair of electrons from NADH, Complex I, Complex III, and Complex IV together move multiple protons from the matrix to the intermembrane space. A common accounting is about 10 protons translocated per NADH: 4 by Complex I, 4 by Complex III, and 2 by Complex IV. Electrons entering through FADH₂ bypass Complex I, so fewer protons are pumped.
+
+The resulting proton gradient stores energy across the inner mitochondrial membrane. This stored energy is the immediate product of the electron carriers’ activity and links oxidation of electron carriers to later ATP production.

datasets/domain-bilingual-v2/corpus/cell-energy-glycolysis.md

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+---
+title: Glycolysis
+language: en
+source: openai-codex-synthetic
+---
+
+# Glycolysis
+
+## Core Role in Cellular Energy
+
+Glycolysis is the cytosolic pathway that splits one six-carbon glucose molecule into two three-carbon pyruvate molecules. It is the first stage of glucose breakdown in many cells and provides a small, immediate net yield of ATP without requiring oxygen directly. Because it occurs in the cytosol, glycolysis does not depend on membrane-bound energy-converting structures.
+
+The pathway is also called the Embden–Meyerhof–Parnas pathway. Its central purpose is controlled chemical rearrangement: glucose is phosphorylated, cleaved, oxidized, and converted into pyruvate while conserving some released energy in ATP and reduced electron carriers.
+
+## ATP Investment and Payoff
+
+Glycolysis contains ten enzyme-catalyzed steps, commonly grouped into two phases.
+
+In the energy-investment phase, the cell spends 2 ATP to activate glucose. Key enzymes include **hexokinase** or **glucokinase**, which phosphorylates glucose, and **phosphofructokinase-1 (PFK-1)**, a major regulatory enzyme that commits the sugar to glycolytic breakdown.
+
+In the energy-payoff phase, the two three-carbon intermediates are processed to produce ATP and NADH. **Glyceraldehyde-3-phosphate dehydrogenase** reduces **NAD+** to **NADH**, capturing high-energy electrons. ATP is formed by substrate-level phosphorylation, especially through **phosphoglycerate kinase** and **pyruvate kinase**.
+
+For each glucose molecule, the net glycolytic yield is:
+
+- **2 pyruvate**
+- **2 ATP net**  
+- **2 NADH**
+- **2 water molecules**
+
+Although 4 ATP are produced in the payoff phase, 2 ATP were used earlier, so the net ATP gain is only 2.
+
+## Pyruvate as the Product
+
+The defining endpoint of glycolysis is pyruvate, not carbon dioxide or a fully oxidized waste product. Pyruvate retains much of the original chemical energy of glucose and can be used in different downstream pathways depending on cell type and conditions.
+
+Glycolysis is therefore best understood as a rapid, cytosolic glucose-splitting process: it converts glucose into pyruvate while producing a modest net supply of ATP and NADH for cellular energy metabolism.

datasets/domain-bilingual-v2/corpus/cell-energy-light-reactions.md

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+---
+title: The light-dependent reactions
+language: en
+source: openai-codex-synthetic
+---
+
+# The light-dependent reactions
+
+## Purpose and location
+
+The light-dependent reactions are the chloroplast processes that convert absorbed light into the chemical energy carriers **ATP** and **NADPH**. They occur in the **thylakoid membrane**, a folded membrane system inside chloroplasts, with the **thylakoid lumen** on one side and the **stroma** on the other.
+
+These reactions use two linked photosystems: **Photosystem II (PSII)** and **Photosystem I (PSI)**. Their pigments, including chlorophyll a, chlorophyll b, and carotenoids, capture photons and pass excitation energy to special chlorophyll pairs called **P680** in PSII and **P700** in PSI.
+
+## Water splitting at Photosystem II
+
+The sequence begins at **Photosystem II**. When P680 absorbs light, it loses high-energy electrons to an electron acceptor. The missing electrons are replaced by electrons taken from water by the **oxygen-evolving complex**, a protein complex containing a manganese-calcium cluster.
+
+For every two water molecules split, the reaction produces:
+
+- 4 electrons for the photosynthetic electron transport chain
+- 4 protons released into the thylakoid lumen
+- 1 molecule of oxygen gas, **O₂**
+
+Thus, the oxygen released by photosynthesis comes directly from **water**, not from carbon dioxide.
+
+## Electron flow and proton movement
+
+Electrons from PSII move through a chain of thylakoid carriers, including **plastoquinone (PQ)**, the **cytochrome b6f complex**, and **plastocyanin (PC)**. As electrons pass through cytochrome b6f, additional protons are moved from the stroma into the thylakoid lumen.
+
+This electron flow builds a proton concentration difference across the thylakoid membrane. The lumen becomes more acidic than the stroma, storing energy as an electrochemical gradient.
+
+## ATP and NADPH formation
+
+The proton gradient is used by **chloroplast ATP synthase** to convert ADP and inorganic phosphate into **ATP** on the stromal side of the membrane. At the same time, electrons reaching **Photosystem I** are re-energized by light absorbed at P700.
+
+The excited electrons from PSI pass to **ferredoxin**, then to **ferredoxin–NADP⁺ reductase (FNR)**. FNR reduces **NADP⁺** to **NADPH** using electrons and protons from the stroma.
+
+Together, PSII, PSI, water splitting, electron transport, and ATP synthase form the light-dependent reactions: a light-powered system that produces **ATP, NADPH, and O₂** in the thylakoids.

datasets/domain-bilingual-v2/corpus/cell-energy-photorespiration.md

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+---
+title: Photorespiration
+language: en
+source: openai-codex-synthetic
+---
+
+# Photorespiration
+
+## RuBisCO as Oxygenase
+
+Photorespiration is the wasteful side reaction that occurs when RuBisCO, the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase, reacts with oxygen gas instead of carbon dioxide. In the productive Calvin cycle, RuBisCO attaches CO2 to ribulose-1,5-bisphosphate (RuBP), creating molecules that enter carbon fixation and can ultimately support sugar production. In photorespiration, the same active site accepts O2, so RuBP is oxygenated rather than carboxylated.
+
+This oxygenase reaction produces one molecule of 3-phosphoglycerate, which can still rejoin Calvin-cycle metabolism, and one molecule of 2-phosphoglycolate, which cannot be used directly for sugar synthesis. The 2-phosphoglycolate must be recycled through a salvage pathway involving the chloroplast, peroxisome, and mitochondrion. During this recycling, plants lose previously fixed carbon as CO2 and consume cellular energy, including ATP and reducing power, without making additional carbohydrate.
+
+## Contrast with the Calvin Cycle
+
+The Calvin cycle is a carbon-gaining pathway: RuBisCO uses CO2, RuBP is regenerated, and ATP and NADPH help convert fixed carbon into energy-rich carbohydrate intermediates. Photorespiration is carbon-losing: RuBisCO uses O2, part of the substrate is diverted into phosphoglycolate repair, and CO2 is released back to the cell and atmosphere.
+
+Thus the crucial distinction is RuBisCO’s substrate choice. Carboxylase activity supports carbon fixation. Oxygenase activity competes with that fixation and reduces photosynthetic efficiency. This is why photorespiration is often described as “wasteful,” even though it is a real metabolic pathway that plants must run to recover carbon from toxic or unusable phosphoglycolate.
+
+## Conditions and Biological Importance
+
+Photorespiration is especially common in C3 plants such as wheat, rice, and soybean when leaves are hot, dry, or CO2-limited. Under these conditions, stomata may close to conserve water, internal CO2 drops, and O2 becomes more likely to occupy RuBisCO’s active site. The result is less net carbon gain for the same investment of ATP and NADPH.
+
+Some plants reduce this problem. C4 plants such as maize and sugarcane concentrate CO2 near RuBisCO, while CAM plants such as pineapple separate CO2 uptake from daytime carbon fixation. These adaptations do not change what photorespiration is: the oxygenase activity of RuBisCO that opposes the Calvin cycle’s productive carboxylation.

datasets/domain-bilingual-v2/corpus/cell-energy-respiration.md

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+---
+title: Cellular respiration overview
+language: en
+source: openai-codex-synthetic
+---
+
+# Cellular respiration overview
+
+Cellular respiration is the catabolic pathway that oxidises glucose completely to carbon dioxide and water while conserving part of the released energy as ATP. In aerobic eukaryotic cells, its main stages are glycolysis in the cytosol, pyruvate oxidation and the Krebs cycle in the mitochondrial matrix, and the electron transport chain on the inner mitochondrial membrane.
+
+The overall reaction is commonly summarized as:
+
+**C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + ATP + heat**
+
+## Carbon flow: glucose to carbon dioxide
+
+Respiration begins when one molecule of glucose, a six-carbon sugar, is converted by glycolysis into two molecules of pyruvate. This stage produces a small amount of ATP directly and transfers high-energy electrons to **NAD⁺**, forming **NADH**.
+
+Each pyruvate then enters the mitochondrion and is converted by the **pyruvate dehydrogenase complex** into **acetyl-CoA**. This link reaction releases one CO₂ per pyruvate, so two CO₂ are produced per glucose before the Krebs cycle begins.
+
+In the **Krebs cycle**, also called the citric acid cycle or TCA cycle, each acetyl-CoA combines with **oxaloacetate** to form citrate. Through a series of enzyme-catalysed steps in the mitochondrial matrix, the two-carbon acetyl group is fully oxidised. Per glucose, the cycle releases four additional CO₂, produces two ATP or GTP by substrate-level phosphorylation, and loads electrons onto **NADH** and **FADH₂**.
+
+## Electron flow: carriers to oxygen
+
+By the end of glycolysis, pyruvate oxidation, and the Krebs cycle, the carbon atoms of glucose have been released as six CO₂ molecules. Most usable energy, however, is stored temporarily in reduced electron carriers: approximately ten NADH and two FADH₂ per glucose.
+
+These carriers deliver electrons to the **electron transport chain**. As electrons pass through membrane protein complexes, their energy is used to help establish a proton gradient across the inner mitochondrial membrane. **Oxygen** is the final electron acceptor; it combines with electrons and protons to form water.
+
+## ATP yield and purpose
+
+The proton-motive force generated by electron transport drives oxidative phosphorylation, producing most of the ATP made during aerobic respiration. In many eukaryotic cells, complete oxidation of one glucose yields about **30–32 ATP**, depending on shuttle systems and membrane efficiency. The essential outcome is the controlled oxidation of glucose to CO₂ and H₂O, coupled to ATP production.

datasets/domain-bilingual-v2/corpus/china-lit-hongloumeng.md

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+---
+title: 红楼梦
+language: zh
+source: openai-codex-synthetic
+---
+
+# 红楼梦
+
+## 作品定位与成书
+
+《红楼梦》是清代曹雪芹创作的章回体长篇小说，又名《石头记》。通行本一百二十回，前八十回通常认为出自曹雪芹之手，后四十回与程伟元、高鹗整理本关系密切。小说以贾、史、王、薛四大家族为背景，集中书写宁国府、荣国府由富贵鼎盛走向衰败的过程。
+
+## 贾府兴衰与主要人物
+
+贾府的繁华以贾母、贾政、王夫人、王熙凤等人物维系，又因奢靡、权势依附、内部腐败而逐渐崩塌。元春省亲和大观园的营建显示家族声势，抄检大观园、获罪抄家则揭示盛极而衰。王熙凤精明强干却贪权弄术，贾探春敏锐能干而难改大势，贾琏、贾珍等人物表现出贵族子弟的败坏。
+
+## 宝黛爱情与核心主题
+
+贾宝玉厌恶功名利禄，珍重少女才情；林黛玉敏感聪慧，以诗才和真情回应宝玉。二人的“木石前盟”与薛宝钗所代表的“金玉良缘”形成冲突，最终以黛玉病逝、宝玉出家象征理想爱情的破灭。小说通过金陵十二钗的命运，表现青春、爱情、女性悲剧与封建礼教的压迫，是中国古典小说中人物群像、心理描写和家族兴衰叙事的高峰。