The Carbon Cycle | 碳循环

📚 The Carbon Cycle | 碳循环

Carbon is the backbone of life on Earth, cycling continuously between the atmosphere, oceans, rocks, and living organisms. Understanding the carbon cycle is essential for grasping how ecosystems function and how human activities are driving unprecedented global changes.

碳是地球生命的支柱，在大气、海洋、岩石和生物体之间持续循环。理解碳循环对于掌握生态系统如何运作以及人类活动如何引发前所未有的全球变化至关重要。

1. Overview of the Carbon Cycle | 碳循环概述

The carbon cycle describes the movement of carbon atoms through various reservoirs: the atmosphere, biosphere, hydrosphere, and lithosphere. It involves both short‑term biological processes, such as photosynthesis and respiration, and long‑term geological processes, including sedimentation and volcanic activity.

碳循环描述了碳原子在各个库（大气圈、生物圈、水圈和岩石圈）之间的移动过程。它包括短期的生物过程（如光合作用和呼吸作用），也包括长期的 geological 过程（如沉积作用和火山活动）。

The global carbon cycle can be divided into a fast cycle operating over days to centuries, driven by living organisms, and a slow cycle driven by tectonic forces and rock weathering over millions of years. Both are tightly interconnected and determine atmospheric CO₂ concentrations.

全球碳循环可以分为由生物驱动的快速循环（数天到数百年）和由板块构造与岩石风化驱动的缓慢循环（数百万年）。两者紧密相连，共同决定大气二氧化碳浓度。

2. Photosynthesis: Fixing Carbon into Organic Matter | 光合作用：将碳固定为有机物

Photosynthesis is the primary process by which carbon dioxide is removed from the atmosphere and converted into glucose. Autotrophs, mainly plants, algae, and cyanobacteria, use light energy to combine CO₂ with water, producing glucose and oxygen.

光合作用是二氧化碳从大气中被移除并转化为葡萄糖的主要过程。自养生物（主要是植物、藻类和蓝藻）利用光能将 CO₂ 与水结合，产生葡萄糖和氧气。

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

In CIE and IB syllabuses, you are expected to link this equation to the light‑dependent and light‑independent stages and to understand that glucose can be used for respiration or converted into starch, cellulose, lipids, and amino acids, storing carbon in biomass.

在 CIE 和 IB 的考纲中，你需要将这个方程式与光反应和暗反应阶段联系起来，并理解葡萄糖既可用于呼吸作用，也可以转化为淀粉、纤维素、脂质和氨基酸，以生物量的形式储存碳。

3. Respiration: Returning Carbon Dioxide to the Atmosphere | 呼吸作用：将二氧化碳释放回大气

All living organisms carry out respiration to release energy from organic compounds. Aerobic respiration breaks down glucose in the presence of oxygen, producing CO₂ and water as by‑products.

所有生物都进行呼吸作用以从有机化合物中释放能量。有氧呼吸在有氧条件下分解葡萄糖，产生二氧化碳和水作为副产物。

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

Decomposers, such as bacteria and fungi, respire when breaking down dead organic matter. This process is a major pathway returning carbon from the biosphere to the atmosphere, connecting the carbon cycle with energy flow through ecosystems.

分解者（如细菌和真菌）在分解死亡有机物时进行呼吸作用。这一过程是将碳从生物圈送回大气的主要途径，将碳循环与生态系统中的能量流动连接起来。

4. Decomposition and the Role of Microorganisms | 分解作用及微生物的角色

Decomposition is the breakdown of dead plant and animal material by saprotrophic organisms. These decomposers secrete enzymes that digest complex organic molecules externally, then absorb the simpler products for respiration, releasing CO₂.

分解作用是指死去的动植物材料被腐生生物分解的过程。这些分解者分泌酶，在体外消化复杂的有机分子，然后吸收较简单的产物进行呼吸作用，释放出 CO₂。

Conditions such as temperature, moisture, and oxygen availability influence decomposition rates. In waterlogged or anaerobic environments, decomposition is slow and may lead to the accumulation of partially decomposed organic matter, forming peat or fossil fuels over geological timescales.

温度、湿度和氧气可用性等条件影响分解速率。在水涝或缺氧环境中，分解缓慢，可能导致部分分解的有机物积累，在 geological 时间尺度上形成泥炭或化石燃料。

5. Combustion: Rapid Release of Stored Carbon | 燃烧：储存碳的快速释放

Combustion of organic materials, whether natural (wildfires) or human‑induced (burning fossil fuels, biomass), rapidly oxidises carbon‑containing compounds and releases CO₂ into the atmosphere. This transfers carbon that had been locked away in biomass or fossil fuels back into the active carbon cycle.

有机材料的燃烧，无论是自然发生的（野火）还是人为的（燃烧化石燃料、生物质），都会迅速氧化含碳化合物并将 CO₂ 释放到大气中。这将原本锁定在生物量或化石燃料中的碳重新转移到活跃的碳循环中。

In exams, you should distinguish between combustion of recent biomass, which is part of the short‑term cycle, and fossil fuel combustion, which injects carbon that has been sequestered for millions of years into the modern atmosphere, causing a net increase in atmospheric CO₂.

在考试中，你应该区分近期生物质的燃烧（属于短期循环的一部分）和化石燃料的燃烧，后者将已封存数百万年的碳注入现代大气，导致大气 CO₂ 浓度净增加。

6. Oceanic Absorption and the Biological Pump | 海洋吸收与生物泵

Oceans are a major carbon sink, absorbing about one‑quarter of anthropogenic CO₂ emissions. CO₂ dissolves in seawater and reacts with water to form carbonic acid, which dissociates into bicarbonate (HCO₃⁻) and carbonate (CO₃²⁻) ions.

海洋是一个主要的碳汇，吸收了大约四分之一的人为 CO₂ 排放。CO₂ 溶解在海水中并与水反应生成碳酸，碳酸进一步解离为碳酸氢根离子 (HCO₃⁻) 和碳酸根离子 (CO₃²⁻)。

Marine organisms incorporate carbonate ions into shells and skeletons made of calcium carbonate (CaCO₃). When they die, these structures sink and can become buried in sediments, effectively locking carbon away in the lithosphere—this is the biological carbon pump.

海洋生物将碳酸根离子结合到由碳酸钙 (CaCO₃) 构成的壳和骨骼中。当它们死亡时，这些结构沉入海底并可能埋藏在沉积物中，从而有效地将碳锁定在岩石圈中——这就是生物碳泵。

7. Sedimentation and the Formation of Fossil Fuels | 沉积作用与化石燃料的形成

Over millions of years, the remains of marine organisms and terrestrial plants can be buried under layers of sediment. Heat, pressure, and anaerobic conditions transform this organic matter into fossil fuels: coal from ancient plant material, oil and natural gas from marine microorganisms.

经过数百万年，海洋生物和陆地植物的遗骸可能被埋藏在沉积层之下。热量、压力和缺氧条件将这些有机物质转化为化石燃料：煤由远古植物材料形成，石油和天然气则来自海洋微生物。

Limestone is another important long‑term carbon reservoir, formed from the compressed calcium carbonate skeletons of marine organisms. Together with fossil fuels, these geological formations store the vast majority of Earth’s carbon.

石灰岩是另一个重要的长期碳库，由海洋生物的碳酸钙骨架压缩而成。这些地质构造与化石燃料一起储存了地球上绝大多数的碳。

8. Human Impact: Disrupting the Natural Balance | 人类影响：打破自然平衡

Human activities have dramatically altered the carbon cycle since the Industrial Revolution. The burning of fossil fuels for energy, cement production, and deforestation releases massive amounts of CO₂, exceeding the capacity of natural sinks to absorb the excess.

自工业革命以来，人类活动极大地改变了碳循环。为获取能源而燃烧化石燃料、水泥生产以及森林砍伐释放了大量 CO₂，超出了自然碳汇吸收多余碳的能力。

Deforestation not only releases carbon stored in biomass but also reduces the number of trees available to photosynthesise, diminishing a crucial carbon sink. Agriculture, particularly livestock farming, also adds methane (CH₄), a potent greenhouse gas, further intensifying global warming.

森林砍伐不仅释放了储存在生物量中的碳，还减少了可进行光合作用的树木数量，削弱了这个关键的碳汇。农业，特别是畜牧业，还会释放强效温室气体甲烷 (CH₄)，进一步加剧全球变暖。

9. The Greenhouse Effect and Enhanced Global Warming | 温室效应与加剧的全球变暖

Carbon dioxide, along with methane and water vapour, is a greenhouse gas. These gases trap infrared radiation re‑radiated from the Earth’s surface, maintaining the planet’s habitable temperature. This natural greenhouse effect is essential for life.

二氧化碳与甲烷和水蒸气一样，属于温室气体。这些气体捕获从地球表面重新辐射的红外线，维持地球适宜居住的温度。这种天然的温室效应对生命至关重要。

However, the enhanced greenhouse effect caused by soaring CO₂ levels from human activities is trapping excess heat, leading to global warming, climate change, rising sea levels, and extreme weather events. IB and CIE exams frequently ask you to analyse data showing the correlation between CO₂ concentration and global temperature rise.

然而，由人类活动导致 CO₂ 水平飙升所引发的增强温室效应正在捕获过多热量，导致全球变暖、气候变化、海平面上升和极端天气事件。IB 和 CIE 考试经常要求你分析显示 CO₂ 浓度与全球气温升高相关性的数据。

10. Carbon Footprints and Mitigation Strategies | 碳足迹与缓解策略

A carbon footprint measures the total greenhouse gas emissions caused directly and indirectly by an individual, organisation, or product, expressed as carbon dioxide equivalents (CO₂e). It includes emissions from energy use, transport, diet, and consumption of goods.

碳足迹衡量个人、组织或产品直接和间接造成的温室气体排放总量，以二氧化碳当量 (CO₂e) 表示。它包括能源使用、交通、饮食和商品消费产生的排放。

Mitigation strategies include transitioning to renewable energy sources (solar, wind, hydro), improving energy efficiency, reforestation and afforestation, carbon capture and storage technologies, and adopting sustainable agriculture. At the personal level, reducing meat consumption, using public transport, and minimising waste can lower one’s carbon footprint.

缓解策略包括转向可再生能源（太阳能、风能、水力）、提高能源效率、重新造林和造林、碳捕获与封存技术以及采用可持续农业。在个人层面，减少肉类消费、使用公共交通和减少浪费可以降低自己的碳足迹。

11. Investigating Carbon Cycle Processes | 探究碳循环过程

In a school laboratory, you can investigate the carbon cycle through simple experiments. For example, using hydrogencarbonate indicator to detect CO₂ changes during respiration or photosynthesis in aquatic plants, or measuring oxygen production in varying light conditions.

在学校实验室中，你可以通过简单的实验来探究碳循环。例如，使用碳酸氢盐指示剂检测水生植物在呼吸作用或光合作用过程中 CO₂ 的变化，或在不同的光照条件下测量氧气的产生量。

Field studies, such as measuring soil respiration rates using a CO₂ sensor or analysing the carbon content of different soil samples, link theoretical knowledge with practical skills. IB internal assessments often encourage such hands‑on investigations of carbon flux.

实地研究，如使用 CO₂ 传感器测量土壤呼吸速率或分析不同土壤样品的碳含量，将理论知识与实践技能联系起来。IB 内部评估经常鼓励此类对碳通量的动手探究。

12. Exam Tips and Common Pitfalls | 考试技巧与常见误区

A common mistake is confusing the fast and slow carbon cycles. Remember that photosynthesis and respiration drive the short‑term cycle, while sedimentation, fossilisation, and weathering are part of the long‑term cycle. Do not label fossil fuel combustion as part of the ‘natural’ short‑term cycle.

一个常见的错误是混淆快速碳循环和缓慢碳循环。请记住，光合作用和呼吸作用驱动短期循环，而沉积作用、化石化和风化作用属于长期循环。不要将化石燃料的燃烧标记为“自然”短期循环的一部分。

Be precise with terminology: carbon is ‘sequestered’ in sinks, ‘fixed’ by producers, ‘released’ by respiration, and ‘combusted’ by burning. When interpreting graphs, note the difference between annual fluctuations in CO₂ due to seasonal plant growth and the long‑term upward trend caused by human emissions.

术语使用要精确：碳在碳汇中被“封存”，被生产者“固定”，通过呼吸作用“释放”，并通过燃烧而“燃烧”。在解读图表时，注意由于季节性植物生长导致的 CO₂ 年度波动与人类排放引起的长期上升趋势之间的差异。

Finally, in data‑response questions, link your answers back to specific processes in the carbon cycle. Use the correct equation for photosynthesis or respiration to support your explanation of changing gas concentrations.

最后，在数据回答题中，将你的答案与碳循环中的具体过程联系起来。使用正确的光合作用或呼吸作用方程来支持你对气体浓度变化的解释。

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The Carbon Cycle | 碳循环