Core Knowledge Review for Pre-U Cambridge Biology | 剑桥 Pre-U 生物核心知识点梳理

📚 Core Knowledge Review for Pre-U Cambridge Biology | 剑桥 Pre-U 生物核心知识点梳理

A strong foundation in biology is essential for success in the Cambridge Pre-U examination. This article provides a streamlined overview of the most crucial topics, from cellular structures to whole-organism physiology and ecological interactions. Each section pairs key concepts with explanations to reinforce understanding and highlight common areas of assessment.

扎实的生物学基础是剑桥 Pre-U 考试成功的关键。本文对最关键的主题进行了精简概述，从细胞结构到整个生物体的生理学和生态相互作用。每个部分将关键概念与解释配对，以加深理解并突出常见的评估领域。

1. Cell Structure and Function | 细胞结构与功能

All living organisms are composed of cells, which can be prokaryotic or eukaryotic. Eukaryotic cells contain membrane-bound organelles including the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes. Prokaryotic cells lack a true nucleus and most organelles but possess a cell wall, plasma membrane, ribosomes, and a circular DNA molecule.

所有生物体都由细胞组成，细胞可以是原核细胞或真核细胞。真核细胞含有膜包围的细胞器，包括细胞核、线粒体、内质网、高尔基体和溶酶体。原核细胞没有真正的细胞核和大多数细胞器，但具有细胞壁、质膜、核糖体和环状DNA分子。

Microscopy techniques, such as light microscopy and electron microscopy (TEM and SEM), have enabled scientists to distinguish these structures. The magnification and resolution of an electron microscope far exceed those of a light microscope, allowing visualisation of ultrastructure.

显微镜技术，如光学显微镜和电子显微镜（透射电镜和扫描电镜），使科学家能够区分这些结构。电子显微镜的放大倍数和分辨率远超光学显微镜，使得超微结构的可视化成为可能。

Key organelles and their functions: the nucleus stores genetic material and coordinates cell activities; mitochondria are the site of aerobic respiration, producing ATP; ribosomes synthesise proteins; the rough ER modifies and transports proteins; the Golgi apparatus packages and distributes proteins; lysosomes digest macromolecules; chloroplasts (in plants) carry out photosynthesis; and the large central vacuole in plant cells maintains turgor pressure.

关键细胞器及其功能：细胞核储存遗传物质并协调细胞活动；线粒体是有氧呼吸的场所，产生ATP；核糖体合成蛋白质；粗面内质网修饰和运输蛋白质；高尔基体包装和分发蛋白质；溶酶体消化大分子；叶绿体（植物中）进行光合作用；植物细胞中的大液泡维持膨压。

Organelle / 细胞器	Function / 功能
Nucleus / 细胞核	Houses DNA; transcription / 储存DNA；转录
Mitochondrion / 线粒体	Aerobic respiration; ATP synthesis / 有氧呼吸；ATP合成
Ribosome / 核糖体	Translation; protein synthesis / 翻译；蛋白质合成
Chloroplast / 叶绿体	Photosynthesis / 光合作用
Golgi apparatus / 高尔基体	Modify, sort, package proteins / 修饰、分类、包装蛋白质

2. Biological Molecules | 生物分子

Biological systems are built from four major classes of macromolecules: carbohydrates, lipids, proteins, and nucleic acids. Each is composed of smaller monomeric subunits. Carbohydrates are made of monosaccharides (e.g., glucose, galactose); lipids are composed of glycerol and fatty acids; proteins are polymers of amino acids; and nucleic acids (DNA and RNA) are polymers of nucleotides.

生物系统由四类主要的大分子构建而成：碳水化合物、脂质、蛋白质和核酸。每种都由较小的单体亚基组成。碳水化合物由单糖组成（如葡萄糖、半乳糖）；脂质由甘油和脂肪酸组成；蛋白质是氨基酸的聚合物；核酸（DNA和RNA）是核苷酸的聚合物。

Water is a universal solvent and participates in many metabolic reactions. Its high specific heat capacity, cohesion, and polarity make it essential for life. The properties of water arise from hydrogen bonding between molecules.

水是一种万能溶剂，参与许多代谢反应。水的高比热容、内聚力和极性使其对生命至关重要。水的性质源于分子间的氢键。

Proteins have four levels of structure: primary (amino acid sequence), secondary (α-helices and β-pleated sheets), tertiary (3D folding due to R-group interactions), and quaternary (assembly of multiple polypeptide chains). Haemoglobin is a classic example of a quaternary structure with two α and two β chains.

蛋白质有四个结构层次：一级结构（氨基酸序列）、二级结构（α-螺旋和β-折叠）、三级结构（由于R基相互作用而形成的三维折叠）和四级结构（多个多肽链的组装）。血红蛋白是具有两个α链和两个β链的四级结构的典型例子。

Tests for biological molecules include Benedict’s test for reducing sugars, biuret test for proteins, iodine test for starch, and the emulsion test for lipids.

生物分子的检测包括：本尼迪克特试剂检测还原糖、双缩脲试剂检测蛋白质、碘液检测淀粉、乳液试验检测脂质。

3. Enzymes | 酶

Enzymes are globular proteins that act as biological catalysts, lowering activation energy without being consumed. They display specificity for substrates due to the unique shape of their active site. The induced-fit model describes how the active site slightly changes shape upon substrate binding to achieve an optimal fit.

酶是球状蛋白质，作为生物催化剂，降低活化能而不被消耗。由于其活性位点的独特形状，它们对底物表现出特异性。诱导契合模型描述了活性位点在底物结合时如何稍微改变形状以实现最佳契合。

Factors affecting enzyme activity include temperature, pH, enzyme concentration, and substrate concentration. Each enzyme has an optimal temperature and pH; deviations can cause denaturation, where the three-dimensional structure is disrupted. Competitive inhibitors bind to the active site, while non-competitive inhibitors bind elsewhere, altering the enzyme’s shape.

影响酶活性的因素包括温度、pH、酶浓度和底物浓度。每种酶都有最适温度和pH；偏离这些值可能导致变性，三维结构被破坏。竞争性抑制剂与活性位点结合，而非竞争性抑制剂结合在其他部位，改变酶的形状。

Immobilised enzymes are useful in biotechnology because they can be recovered and reused. They are employed in the production of lactose-free milk and in biosensors. The initial rate of reaction is measured to determine enzyme kinetics and can be analysed using Michaelis–Menten plots.

固定化酶在生物技术中很有用，因为它们可以回收和重复使用。它们用于生产无乳糖牛奶和生物传感器。测量反应的初始速率以确定酶动力学，并可使用米氏图进行分析。

4. Cell Membranes and Transport | 细胞膜与运输

The plasma membrane is described by the fluid mosaic model: a phospholipid bilayer with embedded proteins and cholesterol. The phospholipids are amphipathic, with hydrophilic phosphate heads facing outwards and hydrophobic fatty acid tails facing inwards. This arrangement allows selective permeability.

质膜由流动镶嵌模型描述：磷脂双分子层，其中嵌有蛋白质和胆固醇。磷脂是两亲性的，亲水性磷酸头朝外，疏水性脂肪酸尾朝内。这种排列允许选择透过性。

Passive transport processes include simple diffusion, facilitated diffusion (via channel or carrier proteins), and osmosis. Active transport requires metabolic energy (ATP) to move substances against their concentration gradient. Bulk transport occurs via endocytosis and exocytosis.

被动运输过程包括简单扩散、易化扩散（通过通道蛋白或载体蛋白）和渗透。主动运输需要代谢能量（ATP）将物质逆浓度梯度移动。批量运输通过胞吞和胞吐作用进行。

Water potential is the tendency of water to move; it is affected by solute potential and pressure potential. In plant cells, the cell wall exerts a pressure potential that results in turgor when the cell is in a hypotonic environment. Animal cells lack a cell wall and may burst (lysis) in hypotonic solutions or crenate in hypertonic solutions.

水势是水移动的趋势；受溶质势和压力势的影响。在植物细胞中，细胞壁施加压力势，当细胞处于低渗环境时会导致膨压。动物细胞缺乏细胞壁，在低渗溶液中可能破裂（溶解），或在高渗溶液中皱缩。

5. The Cell Cycle and Mitosis | 细胞周期与有丝分裂

The cell cycle consists of interphase (G₁, S, G₂) and the mitotic phase (mitosis and cytokinesis). During interphase, the cell grows, carries out its normal functions, and replicates DNA in the S phase. After DNA replication, each chromosome consists of two sister chromatids held together at the centromere.

细胞周期包括间期（G₁期、S期、G₂期）和有丝分裂期（有丝分裂和胞质分裂）。在间期，细胞生长、执行正常功能，并在S期复制DNA。DNA复制后，每条染色体由两条由着丝粒连接在一起的姐妹染色单体组成。

Mitosis is divided into prophase, metaphase, anaphase, and telophase. In prophase, chromosomes condense, the nuclear envelope breaks down, and the spindle apparatus forms. During metaphase, chromosomes align at the metaphase plate. Anaphase separates sister chromatids to opposite poles, and telophase sees the re-formation of nuclear envelopes around the two sets of chromosomes. Cytokinesis divides the cytoplasm.

有丝分裂分为前期、中期、后期和末期。在前期，染色体凝集，核膜破裂，纺锤体形成。在中期，染色体排列在赤道板上。后期将姐妹染色单体分离到两极，末期在两组染色体周围重新形成核膜。胞质分裂将细胞质分开。

Mitosis produces two genetically identical daughter cells and is essential for growth, repair, and asexual reproduction. Cancer arises from uncontrolled cell division due to mutations in genes that regulate the cell cycle.

有丝分裂产生两个遗传上相同的子细胞，对生长、修复和无性繁殖至关重要。癌症是由于调节细胞周期的基因突变导致细胞分裂失控而产生的。

6. DNA and Protein Synthesis | DNA与蛋白质合成

Deoxyribonucleic acid (DNA) is a double helix composed of nucleotides. Each nucleotide contains deoxyribose sugar, a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, or guanine). A pairs with T (two hydrogen bonds), and C pairs with G (three hydrogen bonds). The two strands run antiparallel.

脱氧核糖核酸（DNA）是由核苷酸组成的双螺旋结构。每个核苷酸含有一个脱氧核糖、一个磷酸基团和一个含氮碱基（腺嘌呤、胸腺嘧啶、胞嘧啶或鸟嘌呤）。A与T配对（两个氢键），C与G配对（三个氢键）。两条链反向平行。

DNA replication is semi-conservative, as demonstrated by Meselson and Stahl. The enzyme helicase unwinds the double helix, and DNA polymerase adds complementary nucleotides to each template strand in the 5′ to 3′ direction. The leading strand is synthesised continuously; the lagging strand is synthesised in short Okazaki fragments.

DNA复制是半保留的，Meselson和Stahl的实验证明了这一点。解旋酶解开双螺旋，DNA聚合酶从5’到3’方向向每条模板链添加互补核苷酸。前导链是连续合成的；后随链以短的冈崎片段合成。

Protein synthesis involves transcription and translation. During transcription, RNA polymerase synthesises a complementary mRNA strand from a DNA template. In eukaryotes, mRNA is processed (splicing, capping, and addition of a poly-A tail) before leaving the nucleus. Translation occurs on ribosomes, where tRNA molecules bring specific amino acids according to the mRNA codon sequence. The genetic code is degenerate, universal, and non-overlapping.

蛋白质合成包括转录和翻译。在转录过程中，RNA聚合酶从DNA模板合成一条互补的mRNA链。在真核生物中，mRNA在离开细胞核前经过加工（剪接、加帽和添加poly-A尾）。翻译在核糖体上进行，tRNA分子根据mRNA的密码子序列带来特定的氨基酸。遗传密码是简并的、通用的和不重叠的。

7. Genetics and Inheritance | 遗传学与遗传规律

Mendelian genetics describes the inheritance of characteristics determined by single genes with dominant and recessive alleles. The phenotypic ratio for a monohybrid cross of two heterozygotes is typically 3:1, while a dihybrid cross yields a 9:3:3:1 ratio when genes assort independently.

孟德尔遗传学描述了由具有显性和隐性等位基因的单个基因决定的性状的遗传。两个杂合子的单基因杂交通常产生3:1的表型比，而双基因杂交在基因独立分配时产生9:3:3:1的比率。

Linkage, sex-linkage, codominance, and multiple alleles produce variations in expected ratios. X-linked recessive traits, such as red-green colour blindness and haemophilia, appear more frequently in males because they have only one X chromosome. Codominance results in both alleles being expressed, as in AB blood type.

连锁、性连锁、共显性和复等位基因产生预期比例的变异。X连锁隐性性状，如红绿色盲和血友病，在男性中更常见，因为他们只有一条X染色体。共显性导致两个等位基因都表达，如AB血型。

Chi-squared (χ²) test is used to determine whether observed results deviate significantly from expected Mendelian ratios. The formula is χ² = Σ (O − E)² / E. A low χ² value indicates that differences are likely due to chance, while a high value suggests a significant difference.

卡方（χ²）检验用于确定观察结果是否与预期的孟德尔比率显著偏离。公式为 χ² = Σ (O − E)² / E。较低的χ²值表明差异很可能由偶然因素造成，而较高的值则表明存在显著差异。

8. Evolution and Natural Selection | 进化和自然选择

Darwin’s theory of evolution by natural selection requires heritable variation, overproduction of offspring, and differential survival and reproduction. Organisms with traits better suited to their environment are more likely to survive and pass on those advantageous alleles.

达尔文的自然选择进化理论需要可遗传的变异、后代过剩以及差异性的生存和繁殖。具有更适合其环境的性状的生物更有可能存活并将这些有利等位基因传递给后代。

Speciation occurs when populations become reproductively isolated. Allopatric speciation results from geographical barriers, while sympatric speciation occurs without physical separation, often through changes in behaviour, polyploidy, or habitat differentiation. Reproductive isolation mechanisms can be prezygotic or postzygotic.

当种群达到生殖隔离时就会发生物种形成。异域物种形成由地理屏障引起，而同域物种形成则在没有物理隔离的情况下发生，通常通过行为改变、多倍体或栖息地分化实现。生殖隔离机制可以是合子前的或合子后的。

Evidence for evolution comes from palaeontology (fossils), comparative anatomy (homologous and analogous structures), comparative biochemistry (DNA and protein sequences), and biogeography. The pentadactyl limb is a classic example of a homologous structure across diverse mammals.

进化的证据来自古生物学（化石）、比较解剖学（同源和同功结构）、比较生物化学（DNA和蛋白质序列）以及生物地理学。五指肢是多种哺乳动物同源结构的典型例子。

9. Ecology and Ecosystems | 生态学与生态系统

Ecosystems consist of communities of organisms interacting with their abiotic environment. Energy flows through ecosystems via food chains and food webs, entering through photosynthesis and ultimately being lost as heat through respiration. Approximately only 10% of energy is transferred between trophic levels, which limits the length of food chains.

生态系统由生物群落及其与非生物环境的相互作用组成。能量通过食物链和食物网流经生态系统，通过光合作用进入，并最终通过呼吸以热的形式散失。大约只有10%的能量在营养级之间传递，这限制了食物链的长度。

Nutrients, such as carbon and nitrogen, are recycled through biogeochemical cycles. The carbon cycle involves photosynthesis, respiration, decomposition, combustion, and fossilisation. The nitrogen cycle includes nitrogen fixation, nitrification, assimilation, ammonification, and denitrification – all driven largely by microorganisms.

营养物质，如碳和氮，通过生物地球化学循环得到再循环。碳循环涉及光合作用、呼吸作用、分解作用、燃烧和化石化。氮循环包括固氮作用、硝化作用、同化作用、氨化作用和反硝化作用——所有这些主要由微生物驱动。

Population growth is influenced by birth rate, death rate, immigration, and emigration. Exponential growth is described by dN/dt = rN, while logistic growth incorporates carrying capacity (K): dN/dt = rN ( (K − N) / K ).

人口增长受出生率、死亡率、迁入率和迁出率的影响。指数增长由 dN/dt = rN 描述，而逻辑斯蒂增长包含了环境容纳量（K）：dN/dt = rN ( (K − N) / K )。

10. Animal Physiology: Gas Exchange and Circulation | 动物生理学：气体交换与循环

Gas exchange surfaces require a large surface area, thin walls, and a steep concentration gradient. In mammals, the alveoli in the lungs provide an enormous surface area and are well supplied with capillaries. Ventilation maintains concentration gradients of O₂ and CO₂. The diaphragm and intercostal muscles coordinate to change thoracic volume, causing inspiration and expiration.

气体交换表面需要较大的表面积、薄壁和陡峭的浓度梯度。在哺乳动物中，肺部的肺泡提供了巨大的表面积并富有毛细血管。通气维持O₂和CO₂的浓度梯度。膈肌和肋间肌协调改变胸腔容积，引起吸气和呼气。

Fish gills use a counter-current exchange system where blood flows in the opposite direction to water, maintaining a concentration gradient for oxygen uptake. The efficiency of this system allows fish to extract a high percentage of dissolved oxygen from water.

鱼鳃采用逆流交换系统，血液与水流方向相反，维持氧气摄取的浓度梯度。该系统的效率使鱼能够从水中提取高比例的溶解氧。

The mammalian circulatory system is a closed, double circulation. The heart is a muscular pump with four chambers; the right side pumps deoxygenated blood to the lungs, and the left side pumps oxygenated blood to the rest of the body. The cardiac cycle is initiated by the sinoatrial node (SAN) and regulated by the autonomic nervous system. Haemoglobin in red blood cells transports oxygen, and its binding affinity is influenced by partial pressure of oxygen, CO₂, and pH (Bohr effect).

哺乳动物的循环系统是封闭式的双循环。心脏是一个具有四个腔室的肌肉泵；右侧将脱氧血泵送到肺部，左侧将含氧血泵送到身体其他部位。心动周期由窦房结（SAN）发起，受自主神经系统调节。红细胞中的血红蛋白运输氧气，其结合亲和力受氧分压、CO₂和pH值的影响（玻尔效应）。

11. Plant Physiology: Photosynthesis and Transpiration | 植物生理学：光合作用与蒸腾作用

Photosynthesis converts light energy into chemical energy. The overall equation is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. The light-dependent reactions occur in the thylakoid membranes and involve photolysis of water, production of ATP, and reduction of NADP to NADPH. The light-independent reactions (Calvin cycle) occur in the stroma, using ATP and NADPH to fix CO₂ and produce triose phosphate.

光合作用将光能转化为化学能。总方程式为：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。光反应发生在类囊体膜上，涉及水的光解、ATP的产生以及NADP还原为NADPH。暗反应（卡尔文循环）发生在基质中，利用ATP和NADPH固定CO₂并产生磷酸丙糖。

Limiting factors for photosynthesis include light intensity, carbon dioxide concentration, and temperature. At low light intensities, the rate is limited by light; at high CO₂, temperature or other factors become limiting.

光合作用的限制因素包括光照强度、二氧化碳浓度和温度。在低光照强度下，速率受光限制；在高CO₂下，温度或其他因素成为限制因素。

Transpiration is the loss of water vapour from leaves through stomata. It is driven by the water potential gradient and cohesion-tension mechanism. The opening and closing of stomata are regulated by guard cells according to light, CO₂ concentration, and water availability. Xerophytes have adaptations such as thick cuticles, sunken stomata, and reduced leaves to minimise water loss.

蒸腾作用是水蒸气通过气孔从叶片散失的过程。它由水势梯度和内聚力-张力机制驱动。气孔的开闭由保卫细胞根据光照、CO₂浓度和水分供应进行调节。旱生植物具有加厚的角质层、内陷气孔和缩小叶片等适应性特征，以最大限度地减少水分损失。

12. Homeostasis and Excretion | 稳态与排泄

Homeostasis is the maintenance of a relatively constant internal environment. Key homeostatic variables include blood glucose concentration, core body temperature, and water potential of the blood. Negative feedback mechanisms are fundamental, where a change triggers a response that counteracts the change.

稳态是维持相对恒定的内环境。关键的稳态变量包括血糖浓度、核心体温和血液的水势。负反馈机制是基础，其中一个变化引发一个抵消该变化的反应。

The mammalian kidney plays a central role in osmoregulation and nitrogenous waste excretion. The nephron is the functional unit: ultrafiltration occurs at the glomerulus, producing filtrate that is then selectively reabsorbed in the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct. Antidiuretic hormone (ADH) increases the permeability of the collecting duct to water, regulating water reabsorption.

哺乳动物的肾脏在渗透调节和含氮废物排泄中起核心作用。肾单位是功能单位：超滤发生在肾小球，产生的滤液随后在近曲小管、亨利氏袢、远曲小管和集合管中被选择性重吸收。抗利尿激素（ADH）增加集合管对水的通透性，调节水的重吸收。

Blood glucose regulation involves insulin and glucagon secreted by the pancreas. Insulin lowers blood glucose by promoting uptake and conversion to glycogen (glycogenesis); glucagon raises blood glucose by stimulating glycogenolysis and gluconeogenesis. Diabetes mellitus results from inadequate insulin production (Type 1) or resistance to insulin (Type 2).

血糖调节涉及胰腺分泌的胰岛素和胰高血糖素。胰岛素通过促进葡萄糖摄取和转化为糖原（糖生成）来降低血糖；胰高血糖素通过刺激糖原分解和糖异生来升高血糖。糖尿病是由胰岛素分泌不足（1型）或胰岛素抵抗（2型）引起的。

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Core Knowledge Review for Pre-U Cambridge Biology | 剑桥 Pre-U 生物核心知识点梳理