OCR生物 生物多样性 Classification 采样 Simpson
📌 Exam Board: OCR A-Level Biology A (H420) | Module 4.2.1 & 4.2.2 | 本文涵盖生物多样性、分类系统、采样技术和Simpson多样性指数的完整备考攻略，帮助你在OCR考试中冲击A*。文中穿插中英对照核心术语和真题思路，建议保存收藏。
1. What is Biodiversity? 什么是生物多样性？
Biodiversity, or biological diversity, refers to the variety of life on Earth at all levels, from genes to ecosystems. In the OCR specification, you need to understand biodiversity at three distinct levels, and critically, you must be able to explain how each level contributes to overall ecosystem stability. 生物多样性指地球上生命的多样性，涵盖从基因到生态系统的各个层面。OCR考纲要求你理解三个不同层次的生物多样性，并能解释每个层次如何影响生态系统的稳定性。
The three levels of biodiversity are: genetic diversity (the variety of alleles within a species' gene pool), species diversity (the number of different species and their relative abundance in a given area), and ecosystem diversity (the range of different habitats and ecological niches within a region). A common exam pitfall is confusing these three — remember that genetic diversity operates within a single species, while species and ecosystem diversity involve multiple species and habitats. 三个层次分别是遗传多样性（一个物种种群内的等位基因变异）、物种多样性（给定区域内不同物种的数量及其相对丰度）、以及生态系统多样性（一个地区内不同栖息地和生态位的范围）。常见错误是把这三个层次混淆——记住，遗传多样性作用于单一物种内部，而物种多样性和生态系统多样性涉及多个物种及栖息地。
🧬 Genetic Diversity 遗传多样性
Variety of alleles in a gene pool. Higher genetic diversity means greater adaptive potential. Measured by proportion of polymorphic gene loci. 等位基因多样性越高，适应环境变化的能力越强。
🐾 Species Diversity 物种多样性
Species richness (number of species) + species evenness (relative abundance). Simpson's Index quantifies this. 物种丰富度和均匀度的综合指标，用Simpson指数量化。
🌍 Ecosystem Diversity 生态系统多样性
Range of habitats, communities, and ecological processes. Includes both terrestrial and aquatic ecosystems. 不同栖息地、生物群落和生态过程的总和，包括陆地和水生生态系统。
2. Classification and Taxonomy 分类与分类学
Classification is the process of organising living organisms into groups based on shared characteristics. In OCR Biology, you need to know the Linnaean hierarchical system and understand how modern phylogenetic classification — based on evolutionary relationships derived from DNA sequencing and molecular evidence — has refined traditional taxonomy. 分类学是将生物体按照共同特征进行归类的科学。OCR生物要求你掌握林奈分类层级系统，并理解基于DNA测序和分子证据的现代系统发育分类如何修正传统分类。
The Linnaean hierarchy, from largest to smallest, follows this order: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species. A useful mnemonic many students use is "Dear King Philip Come Over For Good Soup" — but make sure you can write them in the correct order in the exam without relying on mnemonics. At the species level, organisms are named using the binomial system (Genus species), e.g., Homo sapiens. The binomial name is always italicised or underlined, with the genus capitalised and the species in lowercase. 林奈分类层级从大到小依次是：域、界、门、纲、目、科、属、种。物种级别采用双名法命名（属名+种名），属名首字母大写，种名全小写，用斜体或下划线标注。
🔑 Three Domains 三域系统
Archaea — ancient prokaryotes, extreme environments
Bacteria — true bacteria, peptidoglycan cell walls
Eukarya — membrane-bound organelles, includes Protista, Fungi, Plantae, Animalia
🧬 Phylogeny 系统发育
Phylogenetic trees show evolutionary relationships. Branch points represent common ancestors. Cladistics uses shared derived characters (synapomorphies). DNA and protein sequencing provide the most reliable phylogenetic evidence.
Phylogenetic classification uses evidence from DNA sequencing, RNA analysis, and protein comparisons to determine evolutionary relationships. The more similar the base sequences of DNA or the amino acid sequences of proteins between two species, the more closely related they are. This molecular approach has led to major reclassifications — for example, the three-domain system (Archaea, Bacteria, Eukarya) proposed by Carl Woese replaced the older five-kingdom model. 系统发育分类利用DNA测序、RNA分析和蛋白质比较来确定进化关系。两个物种的DNA碱基序列或蛋白质氨基酸序列越相似，亲缘关系越近。这一分子方法导致了重大重新分类——例如Carl Woese提出的三域系统取代了旧的五界模型。
3. Sampling Techniques 采样技术 (Required Practical)
To measure biodiversity, ecologists use sampling techniques to estimate population sizes and community composition without counting every individual. OCR requires you to understand and evaluate three main sampling strategies: random sampling, systematic sampling, and stratified sampling. You must also be able to describe methods for sampling different types of organisms — plants (using quadrats and transects), mobile animals (using mark-release-recapture), and aquatic organisms (using kick sampling and nets). 为了测量生物多样性，生态学家使用采样技术来估算种群大小和群落组成。OCR要求你理解和评估三种主要采样策略：随机采样、系统采样和分层采样。你还必须能够描述不同类型生物的采样方法。
🎲 Random 随机
Select coordinates using a random number generator. Removes observer bias. Best for uniform habitats. Use frame quadrats or point quadrats.
📏 Systematic 系统
Samples taken at regular intervals along a transect. Line transect (record what touches the line) or belt transect (quadrats placed at intervals).
🗂️ Stratified 分层
Divide the area into strata (zones), then sample randomly within each stratum. Ensures all zones are represented proportionally.
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