📚 Mastering Ecosystems for GCSE AQA Science | GCSE AQA 科学：生态系统考点精讲
Ecosystems are a core topic in GCSE AQA Science, covering how living organisms interact with each other and their environment. This revision guide breaks down key concepts such as food chains, energy flow, nutrient cycles, and sampling techniques. Mastering these will help you excel in both Combined Science and Biology exams.
生态系统是 GCSE AQA 科学的核心主题，涵盖生物体之间以及它们与环境之间的相互作用。本复习指南逐一剖析食物链、能量流动、物质循环和抽样方法等关键概念。掌握这些内容将助你在组合科学和生物学考试中取得好成绩。
1. What is an Ecosystem? | 什么是生态系统？
An ecosystem is a self-sustaining unit made up of a community of living organisms interacting with the non-living components of their environment. Energy flows through the ecosystem while matter is recycled.
生态系统是一个自我维持的单元，由生物群落与其环境中的非生物成分相互作用构成。能量在生态系统中流动，而物质被循环利用。
The biotic (living) part includes all plants, animals, fungi, and microorganisms. The abiotic (non-living) part includes factors like sunlight, water, temperature, soil, and air.
生物部分包括所有植物、动物、真菌和微生物。非生物部分包括阳光、水、温度、土壤和空气等因素。
Examples of ecosystems range from a small pond to a large woodland. In each case, organisms are adapted to survive in their particular habitat.
生态系统的例子小到一个池塘，大到一片林地。在每一种生态系统中，生物都适应在其特定生境中生存。
2. Key Ecological Terms | 关键生态术语
Species: A group of similar organisms that can interbreed to produce fertile offspring.
物种：一组可以相互交配并产生可育后代的相似生物。
Population: All the individuals of the same species living in a particular area at a given time.
种群：在特定时间和区域内生活的同一物种的所有个体。
Community: All the populations of different species living together in a habitat.
群落：生活在同一生境中的所有不同物种的种群总和。
Habitat: The physical environment where an organism lives, providing food, shelter, and mates.
生境：生物生活的物理环境，为其提供食物、庇护所和配偶。
Niche: The role of a species within its ecosystem, including what it eats, where it lives, and how it interacts.
生态位：物种在生态系统中扮演的角色，包括它的食物、栖息地以及它与其他生物的相互作用方式。
3. Abiotic and Biotic Factors | 非生物因素与生物因素
Abiotic factors are non-living physical and chemical conditions that affect the distribution and abundance of organisms. Key examples include light intensity, temperature, water availability, oxygen levels, and soil pH.
非生物因素是影响生物分布和数量的非生命理化条件。主要例子包括光照强度、温度、水分可用性、氧气浓度和土壤酸碱度。
Biotic factors are living interactions that influence organisms. These include competition for resources, predation, disease, and symbiotic relationships such as mutualism and parasitism.
生物因素是影响生物的生命活动间的相互作用，包括对资源的竞争、捕食、疾病以及互惠共生和寄生等共生关系。
For instance, a high light intensity allows plants to photosynthesise more, supporting more herbivores. Conversely, a low soil pH can limit plant growth, reducing the entire food web.
例如，高光照强度使植物能进行更多光合作用，从而支持更多食草动物。相反，低土壤 pH 会限制植物生长，缩减整个食物网。
4. Food Chains and Food Webs | 食物链和食物网
A food chain shows a single linear pathway of energy transfer from one organism to another. It always begins with a producer, such as a green plant or alga, which captures sunlight through photosynthesis.
食物链显示了能量从一种生物传递到另一种生物的单一线性路径。它始终以生产者开始，例如能通过光合作用捕获阳光的绿色植物或藻类。
The arrow in a food chain points in the direction of energy flow: from the eaten to the eater. A simple example: grass → rabbit → fox.
食物链中的箭头指向能量流动的方向：从被吃者到吃者。一个简单的例子：草 → 兔 → 狐。
A food web is a network of interconnected food chains, showing more realistic feeding relationships in an ecosystem. If one species is removed, the entire web can be affected.
食物网是相互连接的食物链形成的网络，展示了生态系统中更真实的取食关系。如果移除一个物种，整个食物网都可能受到影响。
5. Energy Flow and Trophic Levels | 能量流动和营养级
Each step in a food chain is called a trophic level. Producers occupy the first trophic level, primary consumers the second, secondary consumers the third, and so on.
食物链中的每一步被称为一个营养级。生产者占据第一营养级，初级消费者占据第二级，次级消费者占据第三级，依此类推。
As energy passes from one trophic level to the next, about 90% is lost to the environment, mostly as heat from respiration. Only around 10% is converted into new biomass and passed on.
当能量从一个营养级传递到下一个时，大约有 90% 散失到环境中，主要是呼吸作用释放的热量。只有约 10% 转化为新的生物量并被传递下去。
This inefficiency explains why food chains rarely exceed four or five trophic levels — there simply isn’t enough energy to support additional levels.
这种低效性解释了为什么食物链很少超过四到五个营养级——根本没有足够的能量支持更多的层级。
6. Pyramids of Biomass | 生物量金字塔
A pyramid of biomass represents the total dry mass of living material at each trophic level, typically measured in grams per square metre (g/m²). The pyramid is usually upright, meaning the producer level has the greatest biomass.
生物量金字塔表示各营养级生物体的总干重，通常以克每平方米 (g/m²) 为单位。金字塔通常呈正立形，即生产者级别的生物量最大。
The biomass decreases at each higher level because energy is lost, so fewer organisms can be supported. This shape clearly visualises the inefficiency of energy transfer.
由于能量散失，每个更高的营养级生物量都会减少，从而能支持更少的生物。这种形状清晰地展示了能量传递的低效性。
In some aquatic ecosystems, the pyramid of biomass can appear inverted over a short period due to rapid turnover of phytoplankton, but the pyramid of energy is always upright.
在一些水生生态系统中，由于浮游植物周转极快，生物量金字塔短期内可能看似倒置，但能量金字塔始终是正立的。
7. The Carbon Cycle | 碳循环
The carbon cycle describes how carbon is recycled between the atmosphere, living organisms, oceans, and rocks. It is driven by processes like photosynthesis, respiration, decomposition, and combustion.
碳循环描述了碳如何在大气、生物体、海洋和岩石之间循环。它由光合作用、呼吸作用、分解作用和燃烧等过程驱动。
Photosynthesis removes CO₂ from the atmosphere: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Respiration releases CO₂ back into the air as organisms break down glucose.
光合作用从大气中移除 CO₂：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。呼吸作用在生物体分解葡萄糖时将 CO₂ 释放回空气中。
Decomposers break down dead organic matter, returning carbon to the soil and atmosphere. The burning of fossil fuels and deforestation release large amounts of stored carbon, unbalancing the cycle.
分解者分解死亡的有机物，将碳归还到土壤和大气。化石燃料的燃烧和森林砍伐会释放大量储存的碳，打破循环的平衡。
8. The Water Cycle | 水循环
The water cycle is the continuous movement of water on, above, and below Earth’s surface. Energy from the sun powers evaporation from oceans, lakes, and rivers, as well as transpiration from plants.
水循环是水在地球表面、上空和地下的持续运动。来自太阳的能量驱动了海洋、湖泊和河流的水分蒸发，以及植物的蒸腾作用。
Water vapour rises, cools, and condenses to form clouds. Precipitation (rain, snow, hail) returns water to the land, where it runs off into bodies of water or infiltrates the ground to become groundwater.
水蒸气上升、冷却并凝结形成云。降水（雨、雪、冰雹）将水送回陆地，水流经地表汇入水体或渗入地下形成地下水。
This cycle ensures a constant supply of freshwater essential for life. Human activities like deforestation reduce transpiration and can disrupt local water cycles.
这一循环保障了生命必需的淡水持续供应。砍伐森林等人类活动减少了蒸腾作用，可能破坏当地水循环。
9. Interdependence and Competition | 相互依赖与竞争
All organisms in an ecosystem are interdependent — they rely on each other for food, shelter, pollination, seed dispersal, and nutrient cycling. Removing one species can destabilise the whole system.
生态系统中的所有生物都是相互依赖的——它们彼此依靠以获取食物、庇护所、传粉、种子传播和养分循环。移除一个物种可能破坏整个系统的稳定。
Competition occurs when organisms require the same limited resource. Intraspecific competition happens between members of the same species, while interspecific competition occurs between different species.
当生物需要相同的有限资源时，就会发生竞争。种内竞争发生在同一物种的成员之间，而种间竞争则发生在不同物种之间。
Predator-prey relationships show cyclical fluctuations. As prey numbers increase, predators have more food and their numbers rise, which then reduces prey numbers, leading to a decline in predators — the cycle repeats.
捕食者-猎物关系表现出周期性波动。当猎物数量增加时，捕食者食物充足数量上升，导致猎物数量下降，捕食者也随之减少——如此循环往复。
10. Adaptations and Sampling | 适应性与抽样方法
Organisms possess adaptations — structural, behavioural, or physiological traits — that help them survive in their environment. For example, a polar bear has thick fur and blubber for insulation; a cactus has spines to reduce water loss.
生物具有适应性——结构上、行为上或生理上的特征——帮助它们在其环境中生存。例如，北极熊有厚厚的皮毛和脂肪保暖；仙人掌有刺以减少水分流失。
Ecologists use sampling techniques to estimate the distribution and abundance of species. Random sampling with quadrats avoids bias, while systematic sampling using a transect line reveals changes across a gradient.
生态学家使用抽样方法来估计物种的分布和丰度。用样方进行随机抽样可避免偏差，而使用样线进行系统抽样可揭示沿某个梯度发生的变化。
To estimate population size, count the number of organisms in several randomly placed quadrats, then use the formula:
要估计种群数量，需计算几个随机放置的样方中的生物数量，然后使用以下公式：
Estimated population = (Total count in all quadrats ÷ Total area of quadrats) × Total habitat area
估计种群数量 = (所有样方中的个体总数 ÷ 样方总面积) × 总生境面积
Repeating the process and averaging the results improves reliability. Always state the units clearly, such as individuals per square metre.
重复此过程并取平均值可提高可靠性。始终明确标注单位，例如每平方米的个体数。
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