Ecosystems: Key Concepts and Exam Essentials | 生态系统：核心概念与考点精讲

📚 Ecosystems: Key Concepts and Exam Essentials | 生态系统：核心概念与考点精讲

Ecosystems are dynamic communities of organisms interacting with their physical environment. Understanding how energy flows and matter cycles within an ecosystem is fundamental to GCSE OCR Science. This revision guide breaks down the key concepts, from biotic and abiotic factors to human impacts, to help you prepare for your exams.

生态系统是由生物体组成的动态群落，与它们的物理环境相互作用。理解生态系统内能量流动和物质循环的原理是 GCSE OCR 科学的基础。本复习指南将拆解关键概念，从生物与非生物因素到人类影响，助你备考。

1. What is an Ecosystem? | 什么是生态系统？

An ecosystem consists of all the organisms living in a particular area (the community) along with the non-living (abiotic) components of their environment. The hierarchy of organisation starts with an individual organism, then population (all individuals of the same species in an area), community (all populations of different species), and ecosystem (community plus abiotic factors). The habitat is the place where an organism lives within the ecosystem.

一个生态系统由生活在特定区域的所有生物（群落）及其环境中的非生物（非生命）组成部分构成。组织层次从个体开始，然后种群（同一物种的所有个体），群落（不同物种的所有种群），生态系统（群落加上非生物因素）。栖息地是生态系统中生物居住的地方。

2. Biotic and Abiotic Factors | 生物因素与非生物因素

Biotic factors are the living influences on an ecosystem, such as competition for resources, predation, and disease. Abiotic factors are non-living physical and chemical conditions: temperature, light intensity, moisture, soil pH, oxygen levels, and mineral nutrients. These factors determine which species can survive and thrive in a habitat.

生物因素是生态系统中生活的影响因素，如对资源的竞争、捕食和疾病。非生物因素是非生命的物理和化学条件：温度、光照强度、水分、土壤 pH、氧气水平和矿物质营养。这些因素决定了哪些物种可以在栖息地中生存和繁衍。

The table illustrates common biotic and abiotic factors. Both groups are constantly interacting; for example, a change in temperature (abiotic) can affect predator activity (biotic).

上表展示了常见的生物和非生物因素。两组因素不断相互作用；例如，温度变化（非生物）可影响捕食者活动（生物）。

3. Feeding Relationships: Food Chains and Webs | 摄食关系：食物链与食物网

Producers (usually green plants or algae) photosynthesise to make their own food. Primary consumers eat producers; secondary consumers eat primary consumers; tertiary consumers eat secondary consumers. Decomposers (bacteria and fungi) break down dead remains and return nutrients to the soil. A food chain shows a simple linear feeding relationship. A food web is a network of interconnected food chains, showing the real complexity of who eats whom in an ecosystem.

生产者（通常是绿色植物或藻类）通过光合作用制造自己的食物。初级消费者吃生产者；次级消费者吃初级消费者；三级消费者吃次级消费者。分解者（细菌和真菌）分解死去的残骸，将养分归还土壤。食物链展示简单的线性摄食关系。食物网是由相互连接的食物链组成的网络，显示生态系统中谁吃谁的实际复杂性。

4. Energy Flow and Trophic Levels | 能量流动与营养级

Energy enters most ecosystems as sunlight and is captured by producers through photosynthesis. Each feeding level is called a trophic level. As energy is transferred from one trophic level to the next, about 90% is lost, mainly through respiration (as heat), movement, egestion of undigested material, and uneaten parts. Therefore, only about 10% of the energy is passed on to the next trophic level. This limits the length of food chains.

能量通常以阳光形式进入生态系统，由生产者通过光合作用捕获。每一个摄食层级称为一个营养级。当能量从一个营养级传递到下一个时，约 90% 会损失，主要是通过呼吸作用（以热的形式）、运动、未消化物质的排泄以及不被食用的部分。因此，只有约 10% 的能量传递到下一个营养级。这限制了食物链的长度。

5. Pyramids of Number, Biomass, and Energy | 数量、生物量和能量金字塔

Ecological pyramids represent the structure of trophic levels. A pyramid of numbers shows the count of organisms at each level; it can be any shape (e.g. upright or inverted, such as one oak tree supporting many insects). A pyramid of biomass shows the dry mass of living material; it is usually upright, but can be inverted in aquatic ecosystems where phytoplankton have a lower biomass than zooplankton at any given time. The pyramid of energy is always upright because energy is lost at each transfer.

生态金字塔表示营养级结构。数量金字塔显示每个层级生物的数量；它可以是任何形状（例如正置或倒置，比如一棵橡树供养许多昆虫）。生物量金字塔显示生物材料的干质量；它通常是正置的，但在水生生态系统中，浮游植物的生物量可能暂时低于浮游动物。能量金字塔总是正置的，因为每次传递都会损失能量。

6. The Carbon Cycle | 碳循环

Carbon is cycled between the atmosphere (as CO₂), living organisms, the soil, and fossil fuels. Key processes:

碳在大气（以 CO₂ 形式）、生物体、土壤和化石燃料之间循环。

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