📚 Core Knowledge Review for AS CIE Biology | AS CIE 生物：核心知识点梳理
The AS CIE Biology syllabus covers a wide range of fundamental biological concepts, from the microscopic world of cells and molecules to the macroscopic systems of transport and gas exchange in organisms. Mastering these core topics is essential for success in the examination. This article provides a concise yet comprehensive review of the key knowledge areas.
AS CIE 生物教学大纲涵盖了广泛的生物学基础概念，从微观世界的细胞和分子到生物体内的运输和气体交换等宏观系统。掌握这些核心主题对于在考试中取得成功至关重要。本文对这些关键知识领域进行了简洁而全面的梳理。
1. Cell Structure | 细胞结构
All living organisms are composed of cells, the basic unit of life. Cells can be classified as eukaryotic (with a true nucleus and membrane-bound organelles) or prokaryotic (lacking a nucleus).
所有生物体都由细胞组成，细胞是生命的基本单位。细胞可分为真核细胞（具有真正的细胞核和膜包被的细胞器）和原核细胞（没有细胞核）。
Animal and plant cells are eukaryotic. They contain a nucleus that houses DNA organised into chromosomes, mitochondria for aerobic respiration, ribosomes for protein synthesis, and an extensive endomembrane system including the endoplasmic reticulum and Golgi apparatus.
动物和植物细胞是真核细胞。它们含有储存染色体DNA的细胞核、进行有氧呼吸的线粒体、合成蛋白质的核糖体以及包括内质网和高尔基体在内的复杂内膜系统。
Plant cells possess additional structures: a cellulose cell wall that provides support, a large permanent vacuole for storage and turgor pressure, and chloroplasts that carry out photosynthesis.
植物细胞具有额外的结构：提供支持作用的纤维素细胞壁、用于储存和产生膨压的中央大液泡，以及进行光合作用的叶绿体。
Prokaryotic cells, such as bacteria, are much smaller. They lack membrane-bound organelles; their DNA is a single circular molecule found in the cytoplasm. They have 70S ribosomes, a cell wall containing peptidoglycan, and may have a capsule or flagella.
原核细胞，如细菌，要小得多。它们没有膜包被的细胞器；其DNA是存在于细胞质中的单条环状分子。它们有70S核糖体、含有肽聚糖的细胞壁，并可能具有荚膜或鞭毛。
Viruses are acellular, consisting of genetic material (DNA or RNA) enclosed in a protein coat, and they can only reproduce inside host cells.
病毒是无细胞结构的，由遗传物质（DNA或RNA）包裹在蛋白质外壳中，它们只能在宿主细胞内繁殖。
2. Biological Molecules | 生物分子
Carbohydrates include monosaccharides like glucose (C₆H₁₂O₆) and fructose, which are used as energy sources. Disaccharides such as sucrose and lactose are formed by condensation reactions, linking two monosaccharides with a glycosidic bond.
碳水化合物包括单糖，如葡萄糖（C₆H₁₂O₆）和果糖，它们被用作能源物质。双糖（如蔗糖和乳糖）是由两分子单糖通过缩合反应以糖苷键连接而成的。
Polysaccharides are polymers of monosaccharides. Starch (amylose and amylopectin) is a plant storage carbohydrate; glycogen is the animal equivalent. Cellulose is a structural polysaccharide in plant cell walls, with β-glucose chains forming strong fibres.
多糖是单糖的聚合物。淀粉（直链淀粉和支链淀粉）是植物的储存性碳水化合物；糖原是动物体内的对应物。纤维素是植物细胞壁中的结构多糖，其β-葡萄糖链形成坚韧的纤维。
Lipids, mainly triglycerides, are composed of glycerol and three fatty acids joined by ester bonds. They serve as energy stores, thermal insulation, and protection. Phospholipids are key components of cell membranes, having a hydrophilic head and hydrophobic tails.
脂质主要是甘油三酯，由甘油和三个脂肪酸通过酯键连接而成。它们用于储存能量、隔热和保护。磷脂是细胞膜的关键成分，具有一个亲水头部和两条疏水尾部。
Proteins are polymers of amino acids. Each amino acid has an amino group (–NH₂), a carboxyl group (–COOH), and a variable R group. Amino acids are joined by peptide bonds to form polypeptide chains, which fold into specific primary, secondary, tertiary, and quaternary structures.
蛋白质是氨基酸的聚合物。每个氨基酸都有一个氨基（–NH₂）、一个羧基（–COOH）和一个可变的R基团。氨基酸通过肽键连接形成多肽链，并折叠成特定的一级、二级、三级和四级结构。
Water is a vital biological molecule due to its properties as a solvent, its high specific heat capacity, and its cohesive and adhesive forces, which are crucial for transport and temperature regulation.
水是至关重要的生物分子，因为它具有溶剂作用、高比热容以及内聚力和附着力，这些特性对运输和温度调节至关重要。
3. Enzymes | 酶
Enzymes are globular proteins that act as biological catalysts, lowering the activation energy of reactions without being consumed. The active site of an enzyme is complementary to its specific substrate, described by the lock-and-key model, and the more accurate induced-fit model.
酶是球状蛋白质，充当生物催化剂，降低反应的活化能而不被消耗。酶的活性部位与其特定底物互补，可用锁钥模型描述，而更精确的是诱导契合模型。
The rate of an enzyme-catalysed reaction is affected by temperature, pH, enzyme concentration, and substrate concentration. At low temperatures, kinetic energy is low; as temperature rises, activity increases until the enzyme begins to denature. Each enzyme has an optimum pH.
酶促反应的速率受温度、pH、酶浓度和底物浓度的影响。低温时动能较低；随着温度升高，活性增加，直到酶开始变性。每种酶都有其最适pH。
Competitive inhibitors have a shape similar to the substrate and bind to the active site, blocking it. Increasing substrate concentration can overcome this inhibition. Non-competitive inhibitors bind to a site other than the active site, altering the enzyme's shape and reducing its activity regardless of substrate concentration.
竞争性抑制剂的形状与底物相似，与活性部位结合从而阻断它。增加底物浓度可以克服这种抑制。非竞争性抑制剂与活性部位以外的位点结合，改变酶的形状，无论底物浓度高低都会降低其活性。
The activity of many enzymes is also regulated by end-product inhibition (feedback control), where the final product of a metabolic pathway inhibits an early step.
许多酶的活性还受到终产物抑制（反馈调控）的调节，即代谢途径的最终产物抑制早期的某个步骤。
4. Cell Membranes and Transport | 细胞膜与物质运输
Cell membranes are described by the fluid mosaic model: a phospholipid bilayer with embedded proteins, cholesterol (in animal cells), and glycoproteins. The phospholipids can move laterally, giving the membrane fluidity.
细胞膜可用流动镶嵌模型描述：一个嵌有蛋白质、胆固醇（动物细胞中）和糖蛋白的磷脂双层。磷脂可以在侧向移动，赋予膜的流动性。
Small, non-polar molecules and water can pass through the membrane by simple diffusion, moving down a concentration gradient. Facilitated diffusion uses channel proteins (e.g., for ions) and carrier proteins (e.g., for glucose) to transport polar or charged molecules down their concentration gradient, without energy expenditure.
小的非极性分子和水可以沿着浓度梯度通过简单扩散穿过细胞膜。易化扩散利用通道蛋白（如离子通道）和载体蛋白（如转运葡萄糖）来沿着浓度梯度运输极性或带电分子，不消耗能量。
Osmosis is the net movement of water molecules through a partially permeable membrane from a region of higher water potential to a region of lower water potential. Water potential is reduced by the presence of solutes.
渗透作用是水分子通过半透膜从水势较高的区域向水势较低的区域净移动。溶质的存在会降低水势。
Active transport requires energy in the form of ATP to move molecules or ions against their concentration gradient. An example is the sodium-potassium pump (Na⁺/K⁺ ATPase), which transports Na⁺ out of the cell and K⁺ into the cell.
主动运输需要以ATP形式存在的能量来逆浓度梯度移动分子或离子。一个例子是钠钾泵（Na⁺/K⁺ ATP酶），它将Na⁺泵出细胞，将K⁺泵入细胞。
Large particles can be moved across the membrane by endocytosis (into the cell) and exocytosis (out of the cell), involving vesicles formed from the membrane.
大的颗粒可以通过胞吞（进入细胞）和胞吐（排出细胞）的方式穿过细胞膜，这过程中涉及由膜形成的囊泡。
5. Cell Division (Mitosis) | 细胞分裂（有丝分裂）
The cell cycle consists of interphase (G1, S, G2 phases) and the mitotic phase. During interphase, the cell grows, carries out normal functions, and replicates its DNA in the S phase. The chromosomes are duplicated, each now consisting of two sister chromatids held together at the centromere.
细胞周期由间期（G1期、S期、G2期）和有丝分裂期组成。在间期，细胞生长、行使其正常功能并在S期复制DNA。染色体被复制，每条染色体现在由着丝粒连接的两条姐妹染色单体组成。
Mitosis ensures that two daughter cells receive identical sets of chromosomes. It is divided into prophase (chromosomes condense, nuclear envelope breaks down), metaphase (chromosomes align at the equator), anaphase (sister chromatids separate to opposite poles), and telophase (new nuclear envelopes form). Cytokinesis then divides the cytoplasm.
有丝分裂确保两个子细胞获得一套完全相同的染色体。它分为前期（染色体凝缩、核膜解体）、中期（染色体排列在赤道板上）、后期（姐妹染色单体分离移向两极）和末期（新的核膜形成）。随后胞质分裂将细胞质分开。
Mitosis is essential for growth, replacement of worn-out cells, and asexual reproduction. Uncontrolled cell division can lead to the formation of tumours, which may become cancerous.
有丝分裂对于生长、替换衰老细胞和无性繁殖至关重要。不受控制的细胞分裂可导致肿瘤的形成，并可能癌变。
6. Nucleic Acids and Protein Synthesis | 核酸与蛋白质合成
DNA is a double helix composed of two strands of nucleotides. Each nucleotide contains a deoxyribose sugar, a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, or guanine). The two strands are antiparallel and held together by hydrogen bonds between complementary base pairs (A-T and C-G).
DNA是一个双螺旋结构，由两条核苷酸链组成。每个核苷酸包含一分子脱氧核糖、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）。两条链反平行，通过互补碱基对（A-T和C-G）之间的氢键维系在一起。
DNA replication occurs during the S phase and is semi-conservative: each new DNA molecule consists of one original strand and one newly synthesised strand. The enzyme helicase unwinds the helix, and DNA polymerase adds complementary nucleotides in the 5' to 3' direction.
DNA复制发生在S期，并且是半保留的：每个新DNA分子包含一条原始链和一条新合成的链。解旋酶解开双螺旋，DNA聚合酶沿5'到3'方向添加互补的核苷酸。
Protein synthesis involves transcription and translation. During transcription in the nucleus, the enzyme RNA polymerase synthesises a messenger RNA (mRNA) molecule complementary to the template strand of DNA, replacing thymine with uracil. The mRNA then moves to the cytoplasm.
蛋白质合成包括转录和翻译。在细胞核内转录时，RNA聚合酶合成一条与DNA模板链互补的信使RNA（mRNA）分子，胸腺嘧啶被尿嘧啶取代。然后mRNA移动到细胞质中。
Translation occurs at ribosomes. Transfer RNA (tRNA) molecules with specific anticodons bring amino acids to the mRNA. The ribosome reads the mRNA codons, and tRNA anticodons pair with them, linking amino acids together via peptide bonds to form a polypeptide chain.
翻译在核糖体上进行。具有特定反密码子的转运RNA（tRNA）将氨基酸带到mRNA上。核糖体读取mRNA的密码子，tRNA的反密码子与之配对，通过肽键将氨基酸连接起来形成多肽链。
7. Transport in Plants | 植物运输
Xylem vessels transport water and dissolved mineral ions from the roots upwards through the stem to the leaves. The flow is driven by transpiration pull, created when water evaporates from leaf mesophyll cells into the air spaces and diffuses out through stomata.
木质部导管将水和溶解的矿物离子从根部向上运输经过茎到达叶片。流动由蒸腾拉力驱动，当水分从叶肉细胞蒸发到细胞间隙并通过气孔扩散出去时，就产生了蒸腾拉力。
Cohesion between water molecules (due to hydrogen bonding) and adhesion between water and the xylem walls help maintain an unbroken column of water under tension. The rate of transpiration is affected by temperature, humidity, light intensity, and air movement.
水分子间的内聚力（由氢键引起）以及水与木质部壁之间的附着力有助于维持张力下连续的水柱。蒸腾速率受温度、湿度、光照强度和空气流动的影响。
Phloem transports assimilates, mainly sucrose, from sources (where they are produced, e.g., leaves) to sinks (where they are used or stored, e.g., roots, fruits). This active process, called translocation, is explained by the pressure flow hypothesis.
韧皮部将同化物（主要是蔗糖）从源（产生部位，如叶片）运输到库（使用或储存部位，如根、果实）。这个主动过程称为易位，可用压力流动假说来解释。
At the source, sucrose is actively loaded into sieve tubes, lowering the water potential. Water enters by osmosis, creating high hydrostatic pressure. At the sink, sucrose is unloaded, water leaves, and pressure drops, generating a pressure gradient that drives mass flow.
在源端，蔗糖被主动装载到筛管中，降低了水势。水分通过渗透进入，产生高的静水压。在库端，蔗糖被卸载，水分流出，压力下降，由此产生的压力梯度驱动了集流。
8. Transport in Mammals | 哺乳动物运输
Mammals have a closed, double circulatory system. The heart pumps deoxygenated blood to the lungs (pulmonary circulation) and oxygenated blood to the rest of the body (systemic circulation). This allows high pressure and efficient delivery of oxygen and nutrients.
哺乳动物具有封闭的双循环系统。心脏将缺氧血泵送到肺部（肺循环），将富氧血泵送到身体其余部分（体循环）。这样能产生高压并有效地输送氧气和养料。
The heart has four chambers: right and left atria, and right and left ventricles. The sinoatrial node (SAN) initiates the heartbeat, and the atrioventricular node (AVN) delays the impulse to ensure ventricles fill before contracting. Valves prevent backflow of blood.
心脏有四个腔：左右心房和左右心室。窦房结（SAN）启动心跳，房室结（AVN）延缓冲动，以确保心室在收缩前充满血液。瓣膜防止血液倒流。
Arteries carry blood away from the heart; they have thick, elastic walls to withstand high pressure. Veins return blood to the heart and contain valves. Capillaries are one-cell thick to allow efficient exchange of substances with tissues.
动脉将血液带离心脏；它们有厚而有弹性的管壁以承受高压。静脉将血液送回心脏并含有瓣膜。毛细血管仅由一层细胞构成，便于与组织高效地进行物质交换。
Blood consists of plasma, red blood cells (erythrocytes), white blood cells (leucocytes), and platelets. Red blood cells contain haemoglobin, which binds oxygen in the lungs and releases it in tissues. The oxygen dissociation curve shows the relationship between oxygen partial pressure and haemoglobin saturation, and it shifts right in the presence of increased CO₂ (Bohr effect).
血液由血浆、红细胞（红血球）、白细胞（白血球）和血小板组成。红细胞含有血红蛋白，它在肺部结合氧气并在组织中释放。氧解离曲线显示了氧分压与血红蛋白饱和度之间的关系，当CO₂浓度升高时曲线右移（玻尔效应）。
Tissue fluid is formed when plasma is forced out of capillaries at the arterial end due to high blood pressure, delivering nutrients to cells. Most of it returns at the venous end by osmosis, aided by plasma proteins.
组织液是在动脉端因血压较高而使血浆滤出毛细血管
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