📚 AS WJEC Biology: Core Knowledge Review | AS WJEC 生物：核心知识点梳理
This article provides a concise yet comprehensive review of the core topics covered in the WJEC AS Biology specification. Each section highlights key concepts that are essential for exam success, from biological molecules to transport systems.
本文对 WJEC AS 生物课程中的核心知识进行了简洁而全面的梳理。每个小节都提炼了考试必备的关键概念，涵盖从生物大分子到运输系统的全部重点内容。
1. Biological Molecules: Carbohydrates, Lipids, Proteins | 生物分子：糖类、脂质、蛋白质
Carbohydrates are organic compounds made of carbon, hydrogen and oxygen. Monosaccharides such as glucose (C₆H₁₂O₆) are the monomers, and they join via glycosidic bonds to form disaccharides (e.g. maltose, sucrose) and polysaccharides (starch, glycogen, cellulose).
碳水化合物是由碳、氢、氧组成的有机物。单糖（如葡萄糖 C₆H₁₂O₆）是单体，通过糖苷键连接形成二糖（如麦芽糖、蔗糖）和多糖（淀粉、糖原、纤维素）。
Starch is a mixture of amylose and amylopectin and serves as the main energy storage in plants. Glycogen, highly branched, is the animal storage equivalent. Cellulose provides structural support in plant cell walls because its β-glucose chains form microfibrils.
淀粉是直链淀粉与支链淀粉的混合物，是植物的主要储能物质。糖原分支多，是动物的储能多糖。纤维素由 β-葡萄糖链构成微纤维，为植物细胞壁提供结构支撑。
Lipids include triglycerides, formed by one glycerol molecule and three fatty acids linked by ester bonds. Phospholipids have a phosphate group instead of one fatty acid, making them amphipathic – key components of cell membranes.
脂类包括甘油三酯，由一分子甘油和三分子脂肪酸通过酯键连接而成。磷脂用磷酸基团取代一条脂肪酸，具有两亲性，是细胞膜的关键组分。
Proteins are polymers of amino acids joined by peptide bonds. The primary structure is the sequence of amino acids. Secondary structure includes α-helices and β-pleated sheets held by hydrogen bonds. Tertiary structure is the overall 3D folding, maintained by hydrogen bonds, ionic bonds, disulfide bridges and hydrophobic interactions. Quaternary structure arises when two or more polypeptide chains associate.
蛋白质是由氨基酸通过肽键连接而成的多聚体。一级结构是氨基酸序列；二级结构包括由氢键维持的 α-螺旋和 β-折叠；三级结构是肽链整体的三维折叠，由氢键、离子键、二硫键和疏水作用维持；两条及以上多肽链聚集则形成四级结构。
2. Water and Inorganic Ions | 水与无机盐
Water is a polar molecule, forming hydrogen bonds. Its properties – high specific heat capacity, high latent heat of vaporisation, cohesion, adhesion and excellent solvent ability – make it vital for life.
水是极性分子，能形成氢键。水的特性——高比热容、高汽化潜热、内聚力、附着力和强溶解能力——使其对生命至关重要。
Ice is less dense than liquid water because hydrogen bonds hold molecules in a fixed lattice, allowing organisms to survive beneath frozen surfaces. Water's cohesion enables transpiration pull in plants.
冰的密度小于液态水，因为氢键将水分子固定于晶格中，使生物能在冰层下存活。水的内聚力为植物的蒸腾拉力提供了基础。
Inorganic ions are essential: nitrate ions (NO₃⁻) are needed for amino acids and nucleotides; phosphate ions (PO₄³⁻) for ATP, nucleic acids and phospholipids; magnesium ions (Mg²⁺) for chlorophyll; iron ions (Fe²⁺) are a component of haemoglobin; calcium ions (Ca²⁺) are involved in muscle contraction and cell wall formation.
无机离子必不可少：硝酸根离子（NO₃⁻）用于合成氨基酸和核苷酸；磷酸根离子（PO₄³⁻）构成 ATP、核酸和磷脂；镁离子（Mg²⁺）是叶绿素的组分；亚铁离子（Fe²⁺）是血红蛋白的成分；钙离子（Ca²⁺）参与肌肉收缩和细胞壁形成。
3. Cell Structure and Organelles | 细胞结构与细胞器
Eukaryotic cells contain membrane-bound organelles. The nucleus stores genetic material and controls cell activities. Mitochondria are the sites of aerobic respiration, with a double membrane and cristae to increase surface area.
真核细胞含有膜包被的细胞器。细胞核储存遗传物质并调控细胞活动。线粒体是有氧呼吸的场所，具有双层膜和增加表面积的嵴。
Rough endoplasmic reticulum (RER) is studded with ribosomes and synthesises proteins for secretion. Smooth ER (SER) synthesises lipids. The Golgi apparatus modifies and packages proteins into vesicles. Lysosomes contain hydrolytic enzymes for digestion.
粗面内质网表面附着核糖体，合成分泌蛋白；滑面内质网合成脂类。高尔基体修饰蛋白质并将其包装成囊泡。溶酶体含有水解酶，负责胞内消化。
Plant cells additionally possess chloroplasts (site of photosynthesis), a large permanent vacuole containing cell sap, and a cellulose cell wall. Prokaryotic cells lack a nucleus and membrane-bound organelles; bacterial DNA is circular and may be accompanied by plasmids. Viruses are acellular, consisting of nucleic acid surrounded by a protein coat.
植物细胞还含有叶绿体（光合作用场所）、含细胞液的大液泡以及纤维素细胞壁。原核细胞没有细胞核和膜包被的细胞器；细菌 DNA 为环状，常伴有质粒。病毒是非细胞结构，由核酸和蛋白质外壳组成。
g an eyepiece graticule and stage micrometer, you can measure specimens and convert units.
Magnification = Image size ÷ Actual size
显微镜计算：放大倍数 = 图像尺寸 ÷ 实际尺寸。使用目镜测微尺和镜台测微尺可以测量标本并进行单位换算。
4. Cell Membranes and Transport | 细胞膜与物质运输
The fluid mosaic model describes the cell membrane as a phospholipid bilayer with embedded proteins, cholesterol (in animal cells) and glycoproteins. Phospholipids are fluid, allowing lateral movement, while proteins act as channels, carriers and receptors.
流动镶嵌模型将细胞膜描述为磷脂双分子层，其中镶嵌着蛋白质、胆固醇（动物细胞）和糖蛋白。磷脂可流动，允许侧向运动；蛋白质则充当通道、载体和受体。
Passive transport does not require ATP. Simple diffusion is the net movement of small, non-polar molecules down a concentration gradient. Facilitated diffusion uses channel or carrier proteins for polar or charged molecules. Osmosis is the diffusion of water through a selectively permeable membrane from a region of higher water potential to lower water potential.
被动运输不消耗 ATP。简单扩散是小分子非极性物质沿浓度梯度的净移动。易化扩散通过通道蛋白或载体蛋白运输极性或带电分子。渗透是水通过选择透过性膜从高水势区向低水势区的扩散。
Active transport requires energy from ATP to move substances against a concentration gradient, using specific carrier proteins. Endocytosis and exocytosis are bulk transport mechanisms where vesicles fuse with the membrane to import or export large materials.
主动运输需要 ATP 供能，利用特定载体蛋白逆浓度梯度运输物质。胞吞和胞吐是批量运输方式，囊泡与细胞膜融合以输入或输出大分子物质。
5. Enzymes and Factors Affecting Activity | 酶及其影响因素
Enzymes are globular proteins that act as biological catalysts, lowering activation energy. The lock-and-key and induced-fit models explain enzyme-substrate specificity. The active site is complementary to the substrate.
酶是球状蛋白质，作为生物催化剂降低活化能。锁钥模型和诱导契合模型解释了酶与底物之间的特异性。活性位点与底物互补。
Temperature affects enzyme activity: as temperature rises, kinetic energy increases the rate of reaction up to an optimum; beyond that, bonds break, the enzyme denatures and activity falls. pH changes alter ionic charges in the active site, also leading to denaturation if extreme.
温度影响酶活性：温度升高，动能增加，反应速率上升直至最适温度；超过该温度后氢键断裂，酶变性失活。pH 变化会改变活性位点的离子电荷，极端 pH 同样导致变性。
Substrate concentration increases rate until all active sites are saturated (Vmax is reached). Enzyme concentration is directly proportional to reaction rate when substrate is in excess. Competitive inhibitors resemble substrate and compete for the active site; non-competitive inhibitors bind elsewhere, altering active site shape.
底物浓度增加会提高反应速率，直至活性位点饱和（达到 Vmax）。酶浓度在底物过量的条件下与反应速率成正比。竞争性抑制剂与底物结构相似，争夺活性位点；非竞争性抑制剂在其他部位结合，改变活性位点构象。
6. Nucleic Acids: DNA and RNA | 核酸：DNA 与 RNA
DNA (deoxyribonucleic acid) is a polynucleotide made of nucleotide monomers. Each nucleotide consists of deoxyribose sugar, a phosphate group and a nitrogenous base (adenine, thymine, cytosine or guanine). Two polynucleotide strands form a double helix, with complementary base pairing: A pairs with T via two hydrogen bonds, C pairs with G via three hydrogen bonds.
DNA（脱氧核糖核酸）是由核苷酸单体组成的多聚核苷酸。每个核苷酸由脱氧核糖、磷酸基团和含氮碱基（腺嘌呤、胸腺嘧啶、胞嘧啶或鸟嘌呤）组成。两条多核苷酸链构成双螺旋结构，遵循互补碱基配对：A 与 T 通过两个氢键配对，C 与 G 通过三个氢键配对。
RNA (ribonucleic acid) differs from DNA: it contains ribose sugar, uracil (U) instead of thymine, and is usually single-stranded. Three types are involved in protein synthesis: mRNA (carries the genetic code), tRNA (transfers amino acids) and rRNA (forms ribosomes).
RNA（核糖核酸）与 DNA 的区别在于：含核糖而非脱氧核糖，以尿嘧啶（U）替代胸腺嘧啶，且通常为单链。参与蛋白质合成的 RNA 有三种：mRNA（携带遗传密码）、tRNA（转运氨基酸）和 rRNA（构成核糖体）。
7. DNA Replication and Protein Synthesis | DNA 复制与蛋白质合成
DNA replication is semi-conservative: each new DNA molecule contains one original strand and one newly synthesised strand. DNA helicase unwinds the double helix by breaking hydrogen bonds. DNA polymerase adds complementary nucleotides to the template strand in the 5' to 3' direction.
DNA 复制是半保留复制：每个新 DNA 分子含有一条原始链和一条新合成链。DNA 解旋酶通过断裂氢键解开双螺旋。DNA 聚合酶以模板链为模板，沿 5' 到 3' 方向添加互补核苷酸。
The leading strand is synthesised continuously; the lagging strand is synthesised in short Okazaki fragments, later joined by DNA ligase. Primers are needed for DNA polymerase to begin synthesis.
前导链连续合成；后随链以短冈崎片段的形式合成，随后由 DNA 连接酶连接。DNA 聚合酶起始合成需要引物。
Protein synthesis involves transcription and translation. In transcription, RNA polymerase binds to DNA and synthesises a complementary mRNA strand. The mRNA then moves to ribosomes. During translation, tRNA anticodons pair with mRNA codons, bringing specific amino acids that are joined by peptide bonds to form a polypeptide chain.
蛋白质合成包括转录和翻译。转录中，RNA 聚合酶与 DNA 结合并合成互补的 mRNA 链。mRNA 移至核糖体。翻译时，tRNA 的反密码子与 mRNA 的密码子配对，携带特定氨基酸，通过肽键连接形成多肽链。
8. Cell Cycle and Mitosis | 细胞周期与有丝分裂
The cell cycle consists of interphase (G1, S, G2) and mitotic phase (mitosis and cytokinesis). In G1, proteins and organelles are synthesised; S phase sees DNA replication; G2 involves further growth and preparation.
细胞周期包括间期（G1、S、G2）和分裂期（有丝分裂与胞质分裂）。G1 期合成蛋白质和细胞器；S 期进行 DNA 复制；G2 期继续生长并为分裂做准备。
Mitosis ensures genetically identical daughter cells. Prophase: chromosomes condense, spindle fibres form, nuclear envelope breaks down. Metaphase: chromosomes align at the equator. Anaphase: sister chromatids are pulled to opposite poles. Telophase: nuclear envelopes re-form, chromosomes decondense. Cytokinesis divides the cytoplasm, producing two daughter cells.
有丝分裂产生遗传相同的子细胞。前期：染色体凝聚，纺锤体形成，核膜解体。中期：染色体排列在赤道板。后期：姐妹染色单体被拉向两极。末期：核膜重新形成，染色体解旋。胞质分裂将细胞质分开，形成两个子细胞。
Uncontrolled cell division can lead to cancer. Cancer cells bypass normal checkpoints, forming tumours. Mitotic index (cells in mitosis ÷ total cells) is used to assess growth rate.
细胞分裂失控可导致癌症。癌细胞越过正常检查点，形成肿瘤。有丝分裂指数（分裂期细胞数 ÷ 总细胞数）可用于评估生长速率。
9. Classification, Adaptation and Biodiversity | 分类、适应性与生物多样性
Organisms are classified using a hierarchical system: domain, kingdom, phylum, class, order, family, genus, species. Binomial nomenclature gives each species a unique two-part Latin name (e.g. Homo sapiens).
生物通过等级系统分类：域、界、门、纲、目、科、属、种。双名法为每个物种提供唯一的双词拉丁学名（如 Homo sapiens）。
Originally, the five kingdoms were Animalia, Plantae, Fungi, Protoctista and Prokaryotae. The three-domain system divides life into Bacteria, Archaea and Eukarya, based on rRNA analysis. Phylogenetic trees show evolutionary relationships.
最初五界系统包括动物界、植物界、真菌界、原生生物界和原核生物界。三域系统基于 rRNA 分析将生命划分为细菌域、古菌域和真核域。系统发育树展示进化关系。
ures that improve survival and reproduction. Natural selection occurs when organisms with advantageous alleles survive and pass them on. Biodiversity can be measured using Simpson' ber of individuals of a species and N is total individuals. Sampling techniques include random quadrats and systematic transects.
适应性指能提高生存和繁殖能力的遗传特征。当具有有利等位基因的个体存活并传递该基因时，就发生了自然选择。生物多样性可用辛普森指数（D = 1 - Σ(n/N)²）衡量，其中 n 为某一物种个体数，N 为总个体数。取样方法包括随机样方和系统样带。
10. Gas Exchange Systems | 气体交换系统
In mammals, gas exchange occurs in alveoli within the lungs. Thin squamous epithelium, a dense capillary network and surfactant reduce diffusion distance. Ventilation is achieved by the diaphragm and intercostal muscles.
哺乳动物的气体交换在肺的肺泡中进行。单层扁平上皮、密集的毛细血管网与表面活性物质缩短了扩散距离。通气由膈肌和肋间肌完成。
Fish gills use a countercurrent exchange system: blood flows in the opposite direction to water, maintaining a concentration gradient along the entire gill lamella. This maximises oxygen uptake.
鱼鳃采用逆流交换系统：血液与水流方向相反，使整个鳃瓣上始终保持浓度梯度，极大提高了氧气吸收效率。
Insects have a tracheal system: air enters through spiracles and travels along tracheae and tracheoles, delivering oxygen directly to tissues. Ventilation can be aided by abdominal pumping. Plants exchange gases through stomata, which can open and close to balance CO₂ uptake and water loss. The spongy mesophyll provides a large surface for diffusion.
昆虫拥有气管系统：空气通过气门进入，沿气管和小气管直达组织。腹部泵动可辅助通气。植物通过气孔进行气体交换，气孔的开闭可平衡二氧化碳摄取与水分蒸腾。海绵组织为扩散提供了巨大表面积。
11. Transport in Animals | 动物体内的运输
Animals transport oxygen, nutrients and waste via circulatory systems. Open systems (e.g. insects) have blood bathing tissues directly. Closed systems (e.g. mammals) keep blood within vessels. Mammals have a double circulatory system (pulmonary and systemic circuits).
动物通过循环系统运输氧气、营养物质和废物。开放循环（如昆虫）的血液直接浸润组织；闭式循环（如哺乳动物）的血液始终在血管内流动。哺乳动物具有双循环系统（肺循环和体循环）。
The mammalian heart has
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