📚 The Carbon Cycle | 碳循环
Carbon is one of the most important elements for life on Earth. It is present in all living organisms, in the atmosphere as carbon dioxide, in the oceans, and locked inside rocks and fossil fuels. The carbon cycle describes how carbon atoms move continuously between the atmosphere, living things, oceans, and the Earth's crust. Understanding this cycle helps us see how human activities, such as burning fossil fuels, can disrupt the natural balance and contribute to climate change. In the Edexcel IGCSE Science syllabus, the carbon cycle is a core concept linking biology, chemistry, and environmental science.
碳是地球上对生命最重要的元素之一。它存在于所有生物体中，以二氧化碳的形式存在于大气中，也存在于海洋以及锁在岩石和化石燃料里。碳循环描述了碳原子如何在大气、生物、海洋和地壳之间不断移动。理解这个循环能帮助我们看清人类活动（例如燃烧化石燃料）会如何打破自然平衡并加剧气候变化。在 Edexcel IGCSE 科学课程中，碳循环是连接生物学、化学和环境科学的核心概念。
1. What is the Carbon Cycle? | 什么是碳循环？
The carbon cycle is a biogeochemical cycle by which carbon is exchanged among the biosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is not created or destroyed; it simply changes form and location. The cycle consists of several key processes that either remove carbon dioxide from the atmosphere or release it back.
碳循环是一个生物地球化学循环，碳在地球的生物圈、岩石圈、水圈和大气圈之间进行交换。碳不会凭空产生或消失，它只是改变形态和位置。该循环由几个关键过程组成，这些过程要么从大气中移除二氧化碳，要么将其释放回大气。
The main reservoirs of carbon include the atmosphere (as CO₂), living organisms (organic compounds), oceans (dissolved CO₂ and carbonates), fossil fuels (coal, oil, natural gas), and sedimentary rocks (limestone). The movement between these reservoirs happens over timescales ranging from days to millions of years.
碳的主要储存库包括大气（二氧化碳）、生物体（有机化合物）、海洋（溶解的二氧化碳和碳酸盐）、化石燃料（煤、石油、天然气）以及沉积岩（石灰岩）。碳在这些储存库之间的移动发生在从几天到数百万年的不同时间尺度上。
2. Key Processes in the Carbon Cycle | 碳循环中的关键过程
Four main biological and chemical processes drive the carbon cycle: photosynthesis, respiration, decomposition, and combustion. Each plays a distinct role in moving carbon between organic and inorganic forms. In addition, geological processes such as the formation of fossil fuels and the weathering of rocks operate over much longer periods.
碳循环由四个主要的生物和化学过程驱动：光合作用、呼吸作用、分解作用和燃烧。每个过程在碳的有机形态和无机形态之间移动碳原子时都扮演着独特角色。此外，诸如化石燃料的形成和岩石风化等地质过程，则以更长的周期运作。
Together these processes maintain a dynamic equilibrium. When this equilibrium is disturbed, for example by the large-scale burning of fossil fuels, the concentration of atmospheric CO₂ rises, which has a direct impact on the global climate.
这些过程共同维持着动态平衡。当这种平衡被打破，比如大规模燃烧化石燃料时，大气中二氧化碳浓度就会上升，这直接影响全球气候。
3. Photosynthesis: Capturing Carbon | 光合作用：固定碳
Photosynthesis is the process by which green plants, algae, and some bacteria use sunlight to convert carbon dioxide and water into glucose and oxygen. This process removes CO₂ from the atmosphere and stores carbon in organic molecules. It is the primary way carbon enters the living portion of the cycle.
光合作用是绿色植物、藻类和某些细菌利用阳光将二氧化碳和水转化为葡萄糖和氧气的过程。这一过程从大气中移除二氧化碳，并将碳储存在有机分子中。这是碳进入生物圈循环部分的主要途径。
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
The glucose produced provides energy for the plant and becomes the building block for other organic compounds such as cellulose, proteins, and lipids. Forests, grasslands, and phytoplankton in the oceans act as major carbon sinks through photosynthesis.
生成的葡萄糖为植物提供能量，并成为纤维素、蛋白质和脂质等其他有机化合物的构建基础。森林、草原和海洋中的浮游植物通过光合作用起着巨大的碳汇作用。
4. Respiration: Releasing Carbon | 呼吸作用：释放碳
Respiration is carried out by all living organisms, including plants, animals, and decomposers. During aerobic respiration, glucose reacts with oxygen to release energy, producing carbon dioxide and water as waste products. This process returns carbon to the atmosphere.
呼吸作用由所有生物体进行，包括植物、动物和分解者。在有氧呼吸中，葡萄糖与氧气反应释放能量，同时产生二氧化碳和水作为废物。这一过程将碳返还到大气中。
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy)
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O（+ 能量）
While photosynthesis dominates during the day in plants, respiration happens continuously. On a global scale, respiration and photosynthesis roughly balance each other in natural ecosystems, keeping atmospheric CO₂ levels relatively stable before human interference.
植物在白天以光合作用为主，但呼吸作用时刻都在进行。在全球范围内，自然生态系统中呼吸作用和光合作用大体保持平衡，在没有人类干预时使大气中二氧化碳浓度相对稳定。
5. Decomposition | 分解作用
When plants and animals die, decomposers such as bacteria and fungi break down their organic matter. This process releases carbon dioxide back into the atmosphere through respiration of the decomposers. At the same time, some carbon is converted into humus, enriching the soil.
植物和动物死亡后，细菌和真菌等分解者会分解其有机物质。该过程通过分解者的呼吸作用将二氧化碳释放回大气。同时，一部分碳转化为腐殖质，使土壤变得肥沃。
Microorganisms play a vital role in decay. The rate of decomposition depends on temperature, moisture, and the availability of oxygen. In waterlogged or acidic conditions, decay is slow, and organic material may accumulate to form peat, which can eventually turn into coal over geological time.
微生物在腐烂过程中至关重要。分解速率取决于温度、湿度和氧气的供应。在积水或酸性条件下，腐烂缓慢，有机物质会积累形成泥炭，经过漫长的地质年代最终可能转变为煤。
6. Combustion | 燃烧
Combustion is a chemical reaction in which a fuel reacts rapidly with oxygen, releasing heat and light. When fossil fuels or biomass burn, the carbon stored in them combines with oxygen to form carbon dioxide, which enters the atmosphere. This is a major source of the recent increase in atmospheric CO₂.
燃烧是一种化学反应，燃料与氧气快速反应，释放出热和光。当化石燃料或生物质燃烧时，储存在其中的碳与氧结合生成二氧化碳，并进入大气。这是近年来大气中二氧化碳增加的主要来源。
Incomplete combustion can also produce carbon monoxide (CO) and soot (carbon particles), which pose health and environmental risks. However, in the context of the carbon cycle, complete combustion is the dominant pathway for returning geologically stored carbon to the atmosphere.
不完全燃烧还会产生一氧化碳（CO）和炭黑（碳颗粒），这会带来健康和环境风险。但在碳循环的语境中，完全燃烧是将地质储存的碳返还大气的主要途径。
7. Formation of Fossil Fuels | 化石燃料的形成
Fossil fuels such as coal, oil, and natural gas are formed from the remains of ancient plants and microorganisms. Over millions of years, layers of sediment bury the organic matter, and high pressure and temperature transform it into energy-rich compounds with high carbon content. This process locks carbon away underground.
煤、石油和天然气等化石燃料是由远古植物和微生物遗骸形成的。在数百万年里，沉积物层掩埋了有机物质，高压和高温将其转变为富含能量的高碳化合物。这一过程将碳锁在了地下。
Coal originates mainly from forest vegetation in swampy environments, while oil and natural gas come from marine plankton settled on the sea floor. These fossil carbon stores remained largely untouched until humans began extracting and burning them on a massive scale.
煤主要来源于沼泽环境中的森林植被，而石油和天然气则来自沉积在海底的海洋浮游生物。这些化石碳储存库在人类开始大规模开采和燃烧之前，基本上未被触动。
8. Ocean Uptake and Release | 海洋吸收与释放
The oceans play a crucial role in the carbon cycle. Carbon dioxide from the atmosphere dissolves in surface waters. Some of this dissolved CO₂ is used by marine organisms for photosynthesis, and some reacts with water to form carbonic acid, bicarbonate, and carbonate ions. This removes CO₂ from the atmosphere.
海洋在碳循环中起着关键作用。大气中的二氧化碳溶解在表层海水中。部分溶解的二氧化碳被海洋生物用于光合作用，还有一些与水反应生成碳酸、碳酸氢根和碳酸根离子。这从大气中移除了二氧化碳。
Marine organisms like corals, mollusks, and plankton also use carbonate ions to build calcium carbonate shells and skeletons. When these organisms die, their shells sink and may eventually form limestone rock, sequestering carbon for millions of years. However, warmer oceans hold less dissolved CO₂, meaning global warming can reduce ocean uptake.
珊瑚、软体动物和浮游生物等海洋生物还会利用碳酸根离子构建碳酸钙外壳和骨骼。当这些生物死亡后，外壳下沉，最终可能形成石灰岩，将碳封存数百万年。然而，温暖的海洋能容纳的溶解二氧化碳更少，这意味着全球变暖会削弱海洋的吸收能力。
9. The Role of Carbon Stores (Sinks) | 碳库（碳汇）的作用
A carbon sink is any reservoir that absorbs more carbon than it releases. Major natural sinks include forests, soils, and the oceans. These sinks help regulate the amount of CO₂ in the atmosphere and are essential for maintaining climate stability.
碳汇是指吸收碳多于释放碳的任何储存库。主要的天然碳汇包括森林、土壤和海洋。这些碳汇有助于调节大气中二氧化碳的含量，对维持气候稳定至关重要。
The Amazon rainforest, for instance, stores vast amounts of carbon in its trees and soil. Peat bogs and permafrost regions also hold enormous carbon stocks. When these sinks are damaged or destroyed by deforestation or warming, they can turn into carbon sources, releasing stored CO₂.
例如，亚马逊雨林在树木和土壤中储存了大量的碳。泥炭沼泽和永久冻土区也蕴藏着巨大的碳储量。当这些碳汇因森林砍伐或气候变暖而遭到破坏时，它们就会转变为碳源，释放出储存的二氧化碳。
10. Human Impact on the Carbon Cycle | 人类对碳循环的影响
Human activities have dramatically altered the carbon cycle. The burning of fossil fuels for electricity, transport, and industry releases billions of tonnes of CO₂ each year. Deforestation reduces the number of trees available to absorb CO₂ and often involves burning, which directly emits more carbon dioxide.
人类活动显著改变了碳循环。用于发电、交通和工业的化石燃料燃烧每年释放数十亿吨二氧化碳。森林砍伐减少了能够吸收二氧化碳的树木数量，而且砍伐过程常常伴随焚烧，直接排放更多二氧化碳。
Agriculture contributes through livestock respiration and methane emissions, as well as the use of machinery that runs on fossil fuels. Cement production also releases CO₂ when limestone is heated. These combined effects have pushed atmospheric CO₂ levels to their highest in at least 800,000 years.
农业通过牲畜呼吸和甲烷排放，以及使用以化石燃料为动力的机械，也会加剧这一问题。水泥生产在加热石灰石时同样释放二氧化碳。这些效应的叠加已使大气二氧化碳浓度达到至少80万年来的最高水平。
11. The Greenhouse Effect and Climate Change | 温室效应与气候变化
Carbon dioxide is a greenhouse gas. It traps heat in the Earth's atmosphere by absorbing infrared radiation emitted from the surface, preventing it from escaping into space. This natural greenhouse effect is necessary for life, keeping our planet warm enough. However, increased CO₂ from human activities enhances this effect, leading to global warming.
二氧化碳是一种温室气体。它通过吸收地表发出的红外辐射，阻止热量散逸到太空，从而将热量截留在地球大气中。这种天然的温室效应是生命所必需的，它使我们的星球保持温暖。然而，人类活动增加的二氧化碳增强了这一效应，导致全球变暖。
Consequences of the enhanced greenhouse effect include rising sea levels, more frequent extreme weather events, melting ice caps, and disruption to ecosystems. Understanding the carbon cycle is vital to predicting and mitigating these impacts. International efforts such as the Paris Agreement aim to reduce carbon emissions and restore balance.
增强的温室效应带来的后果包括海平面上升、更频繁的极端天气事件、冰盖融化和生态系统遭到破坏。理解碳循环对于预测和缓解这些影响至关重要。《巴黎协定》等国际合作旨在减少碳排放、恢复平衡。
12. Maintaining Balance | 维持平衡
Restoring a healthy carbon balance requires both reducing emissions and protecting natural sinks. Afforestation and reforestation increase the number of trees that photosynthesise. Switching to renewable energy sources such as wind, solar, and hydroelectric power cuts fossil fuel use.
恢复健康的碳平衡需要既减少排放又保护天然碳汇。植树造林和再造林增加了进行光合作用的树木数量。转向风能、太阳能和水电等可再生能源，可以减少化石燃料的使用。
Carbon capture and storage technologies are being developed to trap CO₂ from power plants and store it underground. At an individual level, reducing energy consumption, eating less meat, and supporting sustainable farming all contribute to a smaller carbon footprint. Education about the carbon cycle empowers people to make informed decisions for a sustainable future.
碳捕获与封存技术正在发展中，以便从发电厂捕集二氧化碳并将其储存在地下。在个人层面，减少能源消耗、少吃肉、支持可持续农业，都有助于减少碳足迹。关于碳循环的教育让人们能够做出明智的决定，为可持续发展的未来贡献力量。
Published by TutorHao | Edexcel IGCSE Science Revision Series | aleveler.com
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