GCSE CIE Biology: Carbon Cycle Key Points | GCSE CIE 生物：碳循环考点精讲

📚 GCSE CIE Biology: Carbon Cycle Key Points | GCSE CIE 生物：碳循环考点精讲

Understanding the carbon cycle is essential for GCSE CIE Biology students. The carbon cycle describes how carbon atoms move between the atmosphere, living organisms, oceans, and the Earth’s crust. This cycle involves key processes such as photosynthesis, respiration, decomposition, and combustion. In this revision guide, we break down the key concepts and processes you need to know for your exam, including the impact of human activities on the carbon cycle.

对于GCSE CIE生物学生来说，理解碳循环至关重要。碳循环描述了碳原子如何在大气、生物体、海洋和地壳之间移动。该循环涉及光合作用、呼吸作用、分解和燃烧等关键过程。在本复习指南中，我们分解了你需要掌握的关键概念和过程，包括人类活动对碳循环的影响。

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

The carbon cycle is a biogeochemical cycle through which carbon is exchanged between the biosphere, geosphere, hydrosphere, and atmosphere. Carbon exists in different forms, such as carbon dioxide (CO₂) in the atmosphere, organic molecules in living organisms, fossil fuels underground, and dissolved carbon in oceans. The cycle is crucial for maintaining Earth’s temperature and supporting life.

碳循环是一种生物地球化学循环，碳元素在生物圈、岩石圈、水圈和大气圈之间进行交换。碳以不同形式存在，例如大气中的二氧化碳（CO₂）、生物体内的有机分子、地下的化石燃料以及海洋中溶解的碳。该循环对于维持地球温度和维持生命至关重要。

The main reservoirs of carbon include the atmosphere (as CO₂), living organisms (biomass), soil and detritus, oceans (dissolved CO₂ and carbonates), and fossil fuels (coal, oil, natural gas).

主要的碳库包括大气（以CO₂形式）、生物体（生物质）、土壤和碎屑、海洋（溶解的CO₂和碳酸盐）以及化石燃料（煤、石油、天然气）。

2. Key Processes in the Carbon Cycle | 碳循环的关键过程

There are four key processes that move carbon between reservoirs: photosynthesis, respiration, decomposition, and combustion. Photosynthesis removes CO₂ from the atmosphere and converts it into organic carbon. Respiration and decomposition release CO₂ back into the atmosphere. Combustion of fossil fuels and biomass also returns carbon to the atmosphere quickly.

有四个关键过程推动碳在不同库之间移动：光合作用、呼吸作用、分解和燃烧。光合作用从大气中吸收CO₂并将其转化为有机碳。呼吸作用和分解将CO₂释放回大气。化石燃料和生物质的燃烧也快速地将碳返回到大气中。

1. Photosynthesis: CO₂ is fixed into glucose by plants and algae.
2. Respiration: All living cells break down glucose, releasing CO₂.
3. Decomposition: Microorganisms break down dead matter, releasing CO₂ and returning minerals to soil.
4. Combustion: Burning of organic material and fossil fuels releases stored carbon as CO₂.

1. 光合作用：CO₂被植物和藻类固定为葡萄糖。
2. 呼吸作用：所有活细胞分解葡萄糖，释放CO₂。
3. 分解：微生物分解死物，释放CO₂并将矿物质归还土壤。
4. 燃烧：有机物质和化石燃料的燃烧以CO₂形式释放储存的碳。

3. Photosynthesis: Carbon Fixation | 光合作用：碳的固定

During photosynthesis, autotrophs such as green plants, algae, and cyanobacteria take in carbon dioxide and water. Using sunlight energy absorbed by chlorophyll, they produce glucose (C₆H₁₂O₆) and release oxygen (O₂). The overall equation is:

在光合作用过程中，自养生物如绿色植物、藻类和蓝细菌吸收二氧化碳和水。利用叶绿素吸收的太阳光能量，它们产生葡萄糖（C₆H₁₂O₆）并释放氧气（O₂）。总方程式为：

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

This process removes carbon dioxide from the atmosphere and converts inorganic carbon into organic forms, which can then be passed along the food chain when primary consumers eat plants.

这一过程从大气中去除二氧化碳，并将无机碳转化为有机形式，随后当初级消费者食用植物时，可以沿着食物链传递。

Photosynthesis is the primary way carbon enters the living component of the cycle, making it a carbon sink on a global scale. The carbohydrates produced provide energy and building blocks for all heterotrophic life.

光合作用是碳进入循环中生物成分的主要途径，使其在全球范围内成为一个碳汇。产生的碳水化合物为所有异养生物提供能量和构建材料。

4. Respiration: Carbon Release | 呼吸作用：碳的释放

All living organisms carry out respiration to release energy from organic molecules like glucose. Aerobic respiration uses oxygen and produces carbon dioxide and water. The overall equation is the reverse of photosynthesis:

所有生物体进行呼吸作用，释放有机分子如葡萄糖中的能量。有氧呼吸利用氧气，产生二氧化碳和水。总方程式与光合作用相反：

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP)

Respiration returns carbon to the atmosphere as CO₂. This process occurs in both plants (during darkness and daytime) and animals, as well as in decomposers like fungi and bacteria. Even plant cells respire at all times, though net CO₂ absorption during the day may mask this release.

呼吸作用将碳以CO₂的形式返回大气。这一过程发生在植物（在夜间和白天）和动物体内，也发生在真菌和细菌等分解者中。尽管植物在白天净吸收CO₂可能掩盖了这一释放，但植物细胞始终在进行呼吸作用。

Respiration is essential for maintaining the balance of atmospheric gases; without it, CO₂ would gradually be depleted from the air.

呼吸作用对于维持大气气体的平衡至关重要；没有它，大气中的CO₂将逐渐枯竭。

5. Decomposition and the Role of Decomposers | 分解作用和分解者的角色

When organisms die and produce waste, decomposers such as fungi and bacteria break down the organic material. They secrete enzymes that digest complex organic compounds into simpler substances. Through their own respiration, they release CO₂ into the atmosphere. This process recycles nutrients and carbon.

当生物死亡并产生废物时，分解者（如真菌和细菌）分解有机物质。它们分泌酶，将复杂的有机化合物消化成较简单的物质。通过自身的呼吸作用，它们向大气中释放CO₂。这一过程回收了养分和碳。

Not all carbon is immediately released; some remains in the soil as humus, forming an important carbon reservoir. Under certain conditions, detritus may be buried and over millions of years transform into fossil fuels.

并非所有的碳都被立即释放；一部分作为腐殖质保留在土壤中，形成重要的碳库。在特定条件下，碎屑可能被掩埋并经过数百万年转化为化石燃料。

The rate of decomposition depends on temperature, moisture, and oxygen availability. In waterlogged or acidic soils, decomposition is slow, leading to carbon accumulation.

分解速率取决于温度、湿度和氧气供应。在涝渍或酸性土壤中，分解缓慢，导致碳的积累。

6. Combustion of Fossil Fuels and Biomass | 化石燃料和生物质的燃烧

Fossil fuels such as coal, oil, and natural gas were formed from the remains of ancient organisms subjected to heat and pressure over geological time. When we burn these fuels for energy, the carbon that was locked away for millions of years is rapidly released as CO₂ into the atmosphere. The equation for combustion of a hydrocarbon such as methane is: CH₄ + 2O₂ → CO₂ + 2H₂O.

化石燃料（如煤、石油和天然气）是由远古生物的遗骸在地质时间尺度内经受高温高压而形成的。当我们燃烧这些燃料获取能量时，被锁存了数百万年的碳以CO₂的形式迅速释放到大气中。碳氢化合物（如甲烷）的燃烧方程式为：CH₄ + 2O₂ → CO₂ + 2H₂O。

Similarly, burning biomass (wood, crop residues) also releases CO₂, but it is generally considered carbon-neutral over the short term because the plants recently absorbed that CO₂ through photosynthesis. However, deforestation reduces the number of trees available for CO₂ absorption, exacerbating atmospheric CO₂ levels.

同样，燃烧生物质（木材、作物残余物）也会释放CO₂，但通常认为在短期内是碳中和的，因为这些植物近期通过光合作用吸收了等量的CO₂。然而，森林砍伐减少了能够吸收CO₂的树木数量，从而加剧了大气CO₂浓度。

7. Fossilisation and Long-term Carbon Storage | 化石作用与长期碳储存

When organisms die in anaerobic or acidic conditions (such as in peat bogs or ocean sediments), decomposition may be incomplete. Over millions of years, the preserved organic matter can be transformed into fossil fuels. This process sequesters carbon from the short-term cycle into long-term geological storage.

当生物在厌氧或酸性条件下死亡（例如在泥炭沼泽或海洋沉积物中），分解可能不完全。经过数百万年，保存的有机物质可以转化为化石燃料。这一过程将碳从短期循环中隔离出来，进入长期地质储存。

Additionally, some marine organisms use carbonate ions (CO₃²⁻) to build shells and skeletons made of calcium carbonate (CaCO₃). When they die, their remains settle on the ocean floor and eventually form sedimentary rocks such as limestone. This is another long-term carbon store.

此外，一些海洋生物利用碳酸根离子（CO₃²⁻）构建由碳酸钙（CaCO₃）组成的壳和骨骼。当它们死亡后，遗骸沉积在海底，最终形成沉积岩（如石灰岩）。这是另一种长期碳储存库。

Weathering of rock and volcanic activity can also release this carbon back into the atmosphere over very long timescales.

岩石的风化和火山活动也可以在很长的时间尺度上将这部分碳释放回大气。

8. Oceans as a Carbon Sink | 海洋作为碳汇

The oceans play a vital role in the carbon cycle by absorbing CO₂ from the atmosphere. Carbon dioxide dissolves in seawater producing carbonic acid (H₂CO₃), which can dissociate into bicarbonate (HCO₃⁻) and carbonate ions. This process helps regulate atmospheric CO₂ levels.

海洋在碳循环中起着至关重要的作用，它吸收大气中的CO₂。二氧化碳溶于海水生成碳酸（H₂CO₃），碳酸可以解离成碳酸氢根离子（HCO₃⁻）和碳酸根离子。这一过程有助于调节大气中的CO₂水平。

However, increased atmospheric CO₂ leads to ocean acidification, which harms calcifying organisms. Despite being a carbon sink, this capacity is not unlimited and is affected by rising temperatures.

然而，大气中CO₂的增加导致海洋酸化，危害钙化生物。尽管海洋是碳汇，但其吸收能力并非无限，并受到温度上升的影响。

Phytoplankton in the upper oceans also perform photosynthesis, removing CO₂ and incorporating carbon into marine food webs.

表层海洋中的浮游植物也进行光合作用，移除CO₂并将碳融入海洋食物网。

9. Human Impact on the Carbon Cycle | 人类对碳循环的影响

Human activities have significantly disrupted the carbon cycle. The two main contributors are the burning of fossil fuels and deforestation. Burning fossil fuels releases vast amounts of CO₂, increasing the greenhouse effect and global warming. Deforestation, especially of tropical rainforests, reduces the removal of CO₂ by photosynthesis and often involves slash-and-burn agriculture, which emits additional CO₂.

人类活动已显著扰乱碳循环。两个主要因素是化石燃料的燃烧和森林砍伐。燃烧化石燃料释放大量CO₂，增强温室效应并导致全球变暖。砍伐森林，尤其是热带雨林，减少了光合作用对CO₂的清除，且常涉及刀耕火种农业，进一步释放CO₂。

Increased atmospheric CO₂

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GCSE CIE Biology: Carbon Cycle Key Points | GCSE CIE 生物：碳循环 考点精讲