IB Edexcel Science: Ecosystems Key Points | IB Edexcel 科学：生态系统考点精讲

📚 IB Edexcel Science: Ecosystems Key Points | IB Edexcel 科学：生态系统考点精讲

An ecosystem is a dynamic complex of plant, animal and micro-organism communities and their non-living environment interacting as a functional unit. Understanding ecosystems is fundamental in IB and Edexcel science courses, covering energy flow, nutrient cycling and interdependence.

生态系统是由植物、动物和微生物群落及其非生物环境相互作用形成的动态复合体，作为一个功能整体运作。在 IB 和 Edexcel 科学课程中，理解生态系统是基础，内容涵盖能量流动、营养物质循环和相互依存关系。

1. Ecosystem Structure and Components | 生态系统的结构与组成

An ecosystem consists of biotic (living) and abiotic (non-living) components. Biotic components include producers, consumers and decomposers, each playing a specific role in maintaining the system’s balance.

生态系统由生物（有生命的）和非生物（无生命的）成分组成。生物成分包括生产者、消费者和分解者，各自在维持系统平衡中发挥特定作用。

Abiotic factors such as sunlight, temperature, water, soil pH and mineral availability directly influence which organisms can survive and how energy and matter flow through the ecosystem. A change in one abiotic factor can have cascading effects on the entire community.

非生物因子，如阳光、温度、水分、土壤 pH 值和矿物质可用性，直接影响哪些生物能够生存以及能量和物质如何在生态系统中流动。一个非生物因子的变化可能对整个群落产生级联效应。

2. Producers, Consumers and Decomposers | 生产者、消费者与分解者

Producers, or autotrophs, are organisms that synthesise their own organic compounds using light or chemical energy. In most terrestrial ecosystems, green plants are the primary producers, converting sunlight into glucose through photosynthesis.

生产者，即自养生物，是利用光能或化学能合成自身有机化合物的生物。在大多数陆地生态系统中，绿色植物是初级生产者，通过光合作用将阳光转化为葡萄糖。

Consumers are heterotrophs that obtain energy by feeding on other organisms. Primary consumers (herbivores) eat producers; secondary consumers feed on primary consumers; tertiary consumers feed on secondary consumers, forming a trophic hierarchy.

消费者是异养生物，通过摄食其他生物获取能量。初级消费者（食草动物）以生产者为食；次级消费者捕食初级消费者；三级消费者捕食次级消费者，形成营养层级结构。

Decomposers, mainly bacteria and fungi, break down dead organic matter and waste products, releasing inorganic nutrients back into the environment for reuse by producers. This decomposition completes the nutrient cycle and is vital for ecosystem sustainability.

分解者，主要是细菌和真菌，分解死亡的有机质和废物，将无机养分释放回环境中，供生产者再利用。这一分解过程完善了营养循环，对生态系统的可持续性至关重要。

3. Food Chains and Food Webs | 食物链与食物网

A food chain is a linear sequence showing the transfer of energy and nutrients from one organism to another. A typical chain might start with a producer (grass), followed by a primary consumer (rabbit), then a secondary consumer (fox).

食物链是显示能量和营养物质从一个生物体传递到另一个生物体的线性序列。一条典型的链可能从生产者（草）开始，然后是初级消费者（兔子），再到次级消费者（狐狸）。

In reality, most organisms eat a variety of foods and are eaten by several different predators, creating a more complex food web. Food webs provide a more accurate representation of feeding relationships and energy flow within an ecosystem.

实际上，大多数生物食用多种食物，并且被多种不同的捕食者捕食，从而形成更复杂的食物网。食物网更准确地反映了生态系统内的摄食关系和能量流动。

Interconnected food chains in a web enhance ecosystem stability, as the loss of one species may be compensated for by alternative feeding pathways. However, keystone species have a disproportionately large effect on their environment relative to their abundance.

食物网中相互连接的食物链增强了生态系统的稳定性，因为一个物种的丧失可能由替代的摄食途径弥补。然而，关键物种对其环境的影响相对于其丰度而言异常巨大。

4. Trophic Levels and Energy Transfer | 营养级与能量传递

Each step in a food chain or web is called a trophic level. Producers occupy the first trophic level, primary consumers the second, secondary consumers the third, and so on. Decomposers process organic matter from all levels.

食物链或食物网中的每一步称为一个营养级。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，以此类推。分解者处理来自所有营养级的有机物质。

As energy is transferred from one trophic level to the next, a significant amount is lost as heat through respiration, movement and other metabolic activities. Only about 10% of the energy at one level is converted into new biomass at the next level.

当能量从一个营养级传递到下一个营养级时，大量的能量以热量形式通过呼吸作用、运动和其他代谢活动而损失。一个营养级的能量只有大约 10% 会在下一个营养级转化为新的生物量。

Energy transfer efficiency ≈ 10% (roughly 1/10th passes to the next trophic level).

能量传递效率 ≈ 10%（大约十分之一传递到下一个营养级）。

This low efficiency limits the number of trophic levels an ecosystem can support, usually no more than four or five. It also explains why biomass and population size generally decrease at higher trophic levels.

这种低效率限制了生态系统能够支持的食物链长度，通常不超过四到五个营养级。这也解释了为什么生物量和种群大小通常在较高的营养级会减小。

5. Ecological Pyramids: Numbers, Biomass and Energy | 生态金字塔：数量、生物量和能量

Ecological pyramids are graphical representations of the structure of trophic levels. The three main types are pyramids of numbers, pyramids of biomass, and pyramids of energy.

生态金字塔是营养级结构的图形化表示。主要三种类型是数量金字塔、生物量金字塔和能量金字塔。

A pyramid of numbers shows the count of individual organisms at each trophic level. It can sometimes be inverted, for example, when a single large tree supports many insect herbivores, but this does not violate ecological principles because energy transfer is still unidirectional.

数量金字塔显示每个营养级中生物个体的数量。它有时可能倒置，例如，一棵大树养活许多植食性昆虫，但这并不违反生态学原理，因为能量传递仍然是单向的。

A pyramid of biomass represents the total dry mass of living material at each level. It is usually upright for terrestrial ecosystems, but can be partly inverted in aquatic systems where phytoplankton biomass is low but reproduces rapidly.

生物量金字塔表示每个营养级中活体物质的总干重。对于陆地生态系统通常是正立的，但在浮游植物生物量低但繁殖迅速的水生系统中可能部分倒置。

A pyramid of energy is always upright because energy is lost at each transfer. It shows the rate of energy flow or productivity at successive trophic levels, measured in kJ m⁻² year⁻¹, and is the most accurate representation of ecosystem function.

能量金字塔始终是正立的，因为每次传递都会损失能量。它显示了连续营养级的能量流动速率或生产力，以 kJ m⁻² year⁻¹ 为单位，是生态系统功能最准确的表示。

6. Productivity: Gross and Net Primary Production | 生产力：总初级生产量与净初级生产量

Gross primary production (GPP) is the total amount of chemical energy fixed by photosynthesis in producers per unit area per unit time. Net primary production (NPP) is the energy remaining after subtracting the energy used by producers for respiration (R).

总初级生产量（GPP）是单位面积、单位时间内生产者通过光合作用固定的化学能总量。净初级生产量（NPP）是减去生产者用于呼吸作用（R）的能量后剩余的能量。

NPP = GPP − R

NPP represents the energy available to the next trophic level, the consumers. Ecosystems with high NPP, such as tropical rainforests and estuaries, support greater biodiversity and longer food chains.

NPP 代表可供下一营养级（消费者）利用的能量。具有高 NPP 的生态系统，如热带雨林和河口，支撑着更高的生物多样性和更长的食物链。

Human use of NPP through harvesting crops, timber and livestock requires careful management to avoid exceeding the sustainable yield. Understanding productivity helps in conservation and agriculture.

人类通过收割作物、采伐木材和饲养牲畜利用 NPP，需要谨慎管理以避免超过可持续产量。理解生产力有助于保护和农业。

7. Nutrient Cycles: The Carbon Cycle | 营养物质循环：碳循环

Carbon is a fundamental element in all organic molecules and cycles between the atmosphere, oceans, rocks, soil and living organisms. The carbon cycle maintains the balance of CO₂ in the atmosphere, crucial for regulating Earth’s temperature.

碳是所有有机分子的基本元素，在大气、海洋、岩石、土壤和生物体之间循环。碳循环维持着大气中 CO₂ 的平衡，对调节地球温度至关重要。

Key processes include photosynthesis (fixing CO₂ into organic carbon), respiration (releasing CO₂), decomposition (returning carbon to soil and air), combustion (burning fossil fuels releases CO₂), and ocean uptake and release.

关键过程包括光合作用（将 CO₂ 固定为有机碳）、呼吸作用（释放 CO₂）、分解作用（将碳返回土壤和空气）、燃烧（化石燃料燃烧释放 CO₂）以及海洋的吸收与释放。

Over the past century, human activities such as deforestation and the burning of fossil fuels have dramatically increased atmospheric CO₂ concentrations, enhancing the greenhouse effect and contributing to global climate change.

在过去一个世纪，森林砍伐和化石燃料燃烧等人类活动极大地增加了大气中 CO₂ 的浓度，加剧了温室效应，并促进了全球气候变化。

8. Nutrient Cycles: The Nitrogen Cycle | 营养物质循环：氮循环

Nitrogen is essential for proteins and nucleic acids, but most organisms cannot use atmospheric N₂ directly. The nitrogen cycle converts nitrogen into usable forms through several microbial processes.

氮对蛋白质和核酸至关重要，但大多数生物不能直接利用大气中的 N₂。氮循环通过几个微生物过程将氮转化为可用形式。

Nitrogen fixation: conversion of N₂ into ammonia (NH₃) or nitrate (NO₃⁻) by free-living bacteria (e.g., Azotobacter) or symbiotic bacteria (e.g., Rhizobium in legume root nodules).

固氮作用： 自由生活的细菌（如固氮菌）或共生细菌（如豆科植物根瘤中的根瘤菌）将 N₂ 转化为氨 (NH₃) 或硝酸盐 (NO₃⁻)。
Nitrification: the oxidation of ammonia to nitrite (NO₂⁻) and then to nitrate (NO₃⁻) by nitrifying bacteria, making nitrogen available to plants.

硝化作用： 硝化细菌将氨氧化为亚硝酸盐 (NO₂⁻)，再氧化为硝酸盐 (NO₃⁻)，使植物可利用氮。
Denitrification: conversion of nitrate back to N₂ gas by denitrifying bacteria in anaerobic conditions, returning it to the atmosphere.

反硝化作用： 在厌氧条件下，反硝化细菌将硝酸盐还原为 N₂ 气体，将其返回大气。

Agricultural fertilisers add excess nitrates to the soil, which can leach into water bodies causing eutrophication – a rapid growth of algae that depletes oxygen and harms aquatic life.

农业化肥向土壤添加过量硝酸盐，这些硝酸盐可能渗入水体，引起富营养化——藻类迅速生长，耗尽氧气，危害水生生物。

9. Species Interactions and Community Dynamics | 物种相互作用与群落动态

Species within a community interact in various ways: competition, predation, herbivory, symbiosis (mutualism, commensalism, parasitism). These interactions shape population sizes and community structure.

群落内的物种以各种方式相互作用：竞争、捕食、植食、共生（互利共生、偏利共生、寄生）。这些相互作用塑造了种群大小和群落结构。

Competition occurs when two species rely on the same limited resource. The competitive exclusion principle states that two species occupying exactly the same niche cannot coexist indefinitely; one will outcompete the other.

当两个物种依赖同一有限资源时，发生竞争。竞争排斥原理指出，占据完全相同生态位的两个物种无法无限期共存；一个物种会胜出竞争。

Predation can regulate prey populations and drive natural selection, leading to coevolution of defence mechanisms such as camouflage, warning coloration and mimicry. The predator–prey cycle often shows oscillating population numbers.

捕食可以调节猎物种群并驱动自然选择，导致防御机制的协同进化，如伪装、警戒色和拟态。捕食者-猎物周期常表现为种群数量的振荡。

Symbiotic relationships are close, long-term interactions. In mutualism both benefit (e.g., pollinators and flowers); in commensalism one benefits and the other is unaffected (e.g., barnacles on whales); in parasitism one benefits at the expense of the other (e.g., tapeworms in animals).

共生关系是密切的长期相互作用。在互利共生中双方受益（如传粉者和花朵）；在偏利共生中一方受益，另一方不受影响（如鲸鱼上的藤壶）；在寄生中一方受益而另一方受害（如动物体内的绦虫）。

10. Biodiversity, Stability and Succession | 生物多样性、稳定性与演替

Biodiversity, the variety of life at all levels, enhances ecosystem resilience. High species diversity often leads to greater stability because multiple species can perform similar ecological roles, buffering against disturbances.

生物多样性，即各个层面上生命的多样性，增强了生态系统的恢复力。高物种多样性通常带来更大的稳定性，因为多个物种可以执行相似的生态角色，缓冲干扰。

Ecological succession is the gradual, directional change in species composition over time. Primary succession occurs on newly exposed surfaces with no soil (e.g., lava flows, retreating glaciers); secondary succession occurs after disturbances where soil remains (e.g., after a fire or farming).

生态演替是物种组成随时间发生的逐渐的定向变化。初级演替发生在没有土壤的新暴露表面（如熔岩流、冰川退缩）；次级演替发生在土壤保留的干扰后（如火灾或农作后）。

Pioneer species such as lichens and mosses colonise bare rock, break it down and form thin soil. Over time, grasses, shrubs and finally trees establish, leading to a climax community. The process is accompanied by changes in abiotic conditions.

先锋物种，如地衣和苔藓，定植在裸露岩石上，分解岩石并形成薄土。随着时间的推移，草本植物、灌木最终树木定居，形成顶级群落。这一过程伴随着非生物条件的变化。

11. Human Impact on Ecosystems | 人类对生态系统的影响

Human activities significantly alter ecosystems through deforestation, urbanisation, pollution, overfishing and introduction of invasive species. These actions reduce biodiversity, disrupt food webs and degrade ecosystem services.

人类活动通过森林砍伐、城市化、污染、过度捕捞和引入入侵物种，显著改变生态系统。这些行为降低生物多样性，扰乱食物网，并降低生态系统服务功能。

Bioaccumulation is the build-up of persistent pollutants, such as heavy metals or pesticides (e.g., DDT), in an organism’s tissues over time. Biomagnification is the increasing concentration of these substances at higher trophic levels, severely affecting top predators.

生物累积是指持久性污染物，如重金属或杀虫剂（如滴滴涕），随时间在生物体组织中的积累。生物放大是这些物质在更高营养级中浓度增加的现象，严重影响顶级捕食者。

Climate change, driven by greenhouse gas emissions, shifts temperature and precipitation patterns, causing habitat loss, altered breeding cycles and species extinction. Ocean acidification from increased CO₂ affects marine calcifiers.

气候变化由温室气体排放驱动，改变温度和降水模式，导致栖息地丧失、繁殖周期改变和物种灭绝。CO₂ 增加引起的海洋酸化影响海洋钙化生物。

12. Conservation and Sustainable Management | 保护与可持续管理

Conservation strategies aim to protect species and habitats while allowing sustainable use of natural resources. Approaches include establishing protected areas, captive breeding programmes, habitat restoration and legislation against poaching.

保护战略旨在保护物种和栖息地，同时允许自然资源的可持续利用。方法包括建立保护区、圈养繁殖计划、栖息地恢复和反偷猎立法。

Sustainable management of fisheries, forests and agriculture ensures that resources are harvested at a rate that allows natural regeneration. Quotas, reforestation and integrated farming are practical applications of ecological principles.

渔业、森林和农业的可持续管理确保资源以允许自然再生的速度被收获。配额、重新造林和综合农业是生态学原理的实际应用。

The concept of ecosystem services highlights the benefits humans gain from ecosystems, including provisioning (food, water), regulating (climate, floods), supporting (nutrient cycles) and cultural services. Valuing these services strengthens the argument for conservation.

生态系统服务的概念强调了人类从生态系统获得的惠益，包括供给服务（食物、水）、调节服务（气候、洪水）、支持服务（营养循环）和文化服务。认识这些服务的价值加强了保护的理由。

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IB Edexcel Science: Ecosystems Key Points | IB Edexcel 科学：生态系统 考点精讲