📚 Year 12 CCEA Biology: Core Concepts Revision | Year 12 CCEA 生物：核心知识点梳理
This comprehensive revision guide covers the essential topics for Year 12 CCEA Biology, including biological molecules, cell structure, genetics and physiology. Each section is presented in a concise point-form style with paired English and Chinese explanations to reinforce understanding and aid retention.
这份全面的复习指南涵盖了Year 12 CCEA生物的核心主题，包括生物分子、细胞结构、遗传学和生理学。每个部分都以简洁的要点形式呈现，并配有中英对照解释，以加深理解并巩固记忆。
1. Biological Molecules: Carbohydrates & Lipids | 生物分子：碳水化合物与脂质
Monosaccharides are the simplest carbohydrates, with the general formula (CH₂O)ₙ. Key triose (3C), pentose (5C, e.g. ribose) and hexose (6C, e.g. glucose) sugars serve as energy sources and building blocks. Glucose exists as alpha- and beta-isomers that differ in the orientation of the –OH group on carbon 1.
单糖是最简单的碳水化合物，通式为 (CH₂O)ₙ。重要的丙糖 (3C)、戊糖 (5C，如核糖) 和己糖 (6C，如葡萄糖) 是能量来源和结构单元。葡萄糖有 α- 和 β- 异构体，其区别在于碳1上 –OH 基团的取向。
Disaccharides form when two monosaccharides join by a condensation reaction, creating a glycosidic bond. Examples include maltose (glucose + glucose), sucrose (glucose + fructose) and lactose (glucose + galactose).
两个单糖通过缩合反应连接形成二糖，同时产生糖苷键。例如麦芽糖（葡萄糖+葡萄糖）、蔗糖（葡萄糖+果糖）和乳糖（葡萄糖+半乳糖）。
Polysaccharides are long chains of monosaccharides. Starch (a mixture of amylose and amylopectin) is the main storage carbohydrate in plants, while glycogen is the animal storage equivalent. Cellulose is a structural polysaccharide composed of beta-glucose chains that form strong microfibrils in plant cell walls.
多糖是由许多单糖组成的长链。淀粉（直链淀粉和支链淀粉的混合物）是植物中主要的储存碳水化合物，而糖原是动物中的储存形式。纤维素是一种结构多糖，由 β-葡萄糖链组成，在植物细胞壁中形成坚固的微纤维。
Lipids include triglycerides, which consist of one glycerol molecule bonded to three fatty acids via ester bonds. Fatty acids may be saturated (no double bonds) or unsaturated (one or more double bonds). Phospholipids have a hydrophilic phosphate head and two hydrophobic fatty acid tails, making them essential components of cell membranes.
脂质包括甘油三酯，由一个甘油分子与三个脂肪酸通过酯键结合而成。脂肪酸可以是饱和的（无双键）或不饱和的（一个或多个双键）。磷脂具有一个亲水的磷酸头部和两条疏水的脂肪酸尾部，是细胞膜的重要组分。
Biochemical tests: Benedict's solution is used to detect reducing sugars (blue to brick‑red upon heating), while non-reducing sugars require acid hydrolysis first. Iodine solution turns blue‑black with starch, and the ethanol emulsion test gives a cloudy white layer with lipids.
生化检验：本尼迪克特试剂用于检测还原糖（加热后由蓝色变为砖红色），非还原糖需先经酸水解。碘液遇淀粉呈蓝黑色，乙醇乳化试验遇脂质产生白色浑浊层。
2. Proteins | 蛋白质
Proteins are polymers of amino acids. Each amino acid has a central carbon atom bonded to an amino group (NH₂), a carboxyl group (COOH), a hydrogen atom and a variable R group. Amino acids join via peptide bonds formed by condensation reactions.
蛋白质是氨基酸的聚合物。每个氨基酸都有一个中央碳原子，连接着一个氨基（NH₂）、一个羧基（COOH）、一个氢原子和一个可变的R基。氨基酸通过缩合反应形成肽键连接在一起。
The primary structure is the linear sequence of amino acids. Secondary structure arises from hydrogen bonding within the polypeptide backbone, producing alpha‑helices or beta‑pleated sheets. Tertiary structure is the overall 3D folding held by hydrogen bonds, ionic bonds, disulfide bridges and hydrophobic interactions. Quaternary structure involves the assembly of multiple polypeptide subunits (e.g. haemoglobin).
一级结构是氨基酸的线性序列。二级结构由多肽主链内的氢键形成，产生 α-螺旋或 β-折叠片。三级结构是由氢键、离子键、二硫桥和疏水相互作用维持的整体三维折叠。四级结构涉及多个多肽亚基的组装（如血红蛋白）。
Fibrous proteins (e.g. collagen, keratin) have long, insoluble polypeptide chains with structural roles. Globular proteins (e.g. enzymes, haemoglobin) are compact, soluble and metabolic in function.
纤维蛋白（如胶原蛋白、角蛋白）具有长而不溶的多肽链，起结构作用。球状蛋白（如酶、血红蛋白）结构紧凑、可溶，具有代谢功能。
3. Enzymes | 酶
Enzymes are globular proteins that act as biological catalysts by lowering activation energy. The active site has a specific shape complementary to the substrate; the induced‑fit model suggests the active site moulds around the substrate upon binding.
酶是球状蛋白质，通过降低活化能起生物催化剂作用。活性位点具有与底物互补的特定形状；诱导契合模型认为，活性位点在底物结合时会围绕底物发生构形变化。
Factors affecting enzyme activity include temperature (increases kinetic energy up to an optimum before denaturation), pH (alters ionic charges at the active site), substrate concentration (rate plateaus at saturation) and enzyme concentration. Competitive inhibitors bind to the active site, while non‑competitive inhibitors bind elsewhere, altering the active site shape.
影响酶活性的因素包括温度（在变性前增加动能，达到最适温度）、pH（改变活性位点处的离子电荷）、底物浓度（饱和时速率趋于平稳）和酶浓度。竞争性抑制剂结合于活性位点，而非竞争性抑制剂结合于别处，改变活性位点形状。
4. Nucleic Acids, DNA Replication & Protein Synthesis | 核酸、DNA 复制与蛋白质合成
Nucleotides are the monomers of nucleic acids and consist of a pentose sugar, a phosphate group and a nitrogenous base. In DNA the sugar is deoxyribose and the bases are A, T, C, G; in RNA the sugar is ribose and uracil (U) replaces thymine. DNA forms a double helix with complementary base pairing (A–T, C–G) and antiparallel strands.
核苷酸是核酸的单体，由一个戊糖、一个磷酸基团和一个含氮碱基组成。DNA 中的糖是脱氧核糖，碱基为 A、T、C、G；RNA 中的糖是核糖，尿嘧啶 (U) 代替胸腺嘧啶。DNA 形成双螺旋结构，具有互补碱基配对（A–T，C–G）和反向平行的链。
DNA replication is semi‑conservative. Helicase unwinds the double helix, and DNA polymerase adds nucleotides to the exposed template strands in a 5' to 3' direction. The leading strand is synthesised continuously, while the lagging strand is formed in short Okazaki fragments joined by DNA ligase.
DNA 复制是半保留式的。解旋酶解开双螺旋，DNA 聚合酶沿 5' 到 3' 方向将核苷酸添加到暴露的模板链上。前导链连续合成，而后随链以短小的冈崎片段形式合成，再由 DNA 连接酶连接。
Protein synthesis involves transcription and translation. During transcription, RNA polymerase binds to DNA and synthesises a complementary mRNA strand. In translation, ribosomes read the mRNA codons, and tRNA molecules with anticodons bring specific amino acids, forming a polypeptide chain. The genetic code is degenerate and universal.
蛋白质合成包括转录和翻译。转录时，RNA 聚合酶与 DNA 结合，合成互补的 mRNA 链。翻译时，核糖体读取 mRNA 密码子，携带反密码子的 tRNA 将特定氨基酸搬运到位，形成多肽链。遗传密码是简并且通用的。
5. Cell Structure | 细胞结构
Eukaryotic cells contain membrane‑bound organelles, including a nucleus (stores genetic material), mitochondria (aerobic respiration), ribosomes (protein synthesis), rough and smooth endoplasmic reticulum (protein processing and lipid synthesis), Golgi apparatus (modifies and packages proteins), lysosomes (digestion), chloroplasts (photosynthesis in plants) and a large permanent vacuole in plant cells. Plant cells also have a cellulose cell wall.
真核细胞含有具膜细胞器，包括细胞核（储存遗传物质）、线粒体（有氧呼吸）、核糖体（蛋白质合成）、粗面与滑面内质网（蛋白质加工与脂质合成）、高尔基体（修饰与包装蛋白质）、溶酶体（消化）、植物中的叶绿体（光合作用）以及植物细胞中的大液泡。植物细胞还具有纤维素细胞壁。
Prokaryotic cells lack a true nucleus; their DNA is circular and free in the cytoplasm. They have 70S ribosomes, a cell wall containing peptidoglycan, and may possess plasmids, a capsule and flagella.
原核细胞没有真正的细胞核；其 DNA 是环状的，游离在细胞质中。它们含有 70S 核糖体、由肽聚糖组成的细胞壁，并可能具有质粒、荚膜和鞭毛。
. An eyepiece graticule calibrated with a stage micrometer is used to measure cells under a light microscope.
放大率的计算为图像大小除以实际大小（M = I/A）。使用目镜测微尺经镜台测微尺校准后，可在光学显微镜下测量细胞。
6. Cell Membranes & Transport | 细胞膜与运输
The fluid mosaic model describes the cell membrane as a phospholipid bilayer with embedded proteins. Cholesterol maintains fluidity, and glycoproteins/glycolipids act as receptors and recognition sites. Intrinsic proteins span the bilayer, while extrinsic proteins are on the surface.
流动镶嵌模型将细胞膜描述为磷脂双分子层，其中嵌有蛋白质。胆固醇维持膜的流动性，糖蛋白/糖脂充当受体和识别位点。内在蛋白贯穿双分子层，而外在蛋白位于表面。
Passive transport does not require energy. Simple diffusion is the movement of small, non‑polar molecules down a concentration gradient. Facilitated diffusion uses channel or carrier proteins for larger or charged molecules. Osmosis is the net movement of water from a region of higher water potential to lower water potential through a partially permeable membrane.
被动运输不需要能量。简单扩散是小分子、非极性分子顺浓度梯度的运动。易化扩散利用通道蛋白或载体蛋白运输较大或带电分子。渗透是水通过半透膜从较高水势区域向较低水势区域的净移动。
Active transport uses ATP to move substances against their concentration gradient via carrier proteins. Bulk transport includes endocytosis (into the cell) and exocytosis (out of the cell), which use membrane vesicles.
主动运输利用 ATP 通过载体蛋白逆浓度梯度运输物质。批量运输包括内吞（进入细胞）和外排（排出细胞），均涉及膜泡。
7. The Cell Cycle & Mitosis | 细胞周期与有丝分裂
The cell cycle consists of interphase (G₁, S, G₂) and the mitotic phase. During interphase the cell grows, synthesises proteins and replicates its DNA. Mitosis is nuclear division producing two genetically identical daughter nuclei.
细胞周期由间期（G₁ 期、S 期、G₂ 期）和分裂期组成。在间期，细胞生长、合成蛋白质并复制 DNA。有丝分裂是细胞核分裂，产生两个遗传物质完全相同的子细胞核。
Stages of mitosis: prophase (chromosomes condense, spindle forms), metaphase (chromosomes align at the equator), anaphase (sister chromatids separate to poles) and telophase (nuclear envelopes reform). Cytokinesis divides the cytoplasm. Mitosis is essential for growth, repair and asexual reproduction.
有丝分裂各阶段：前期（染色体凝缩，纺锤体形成）、中期（染色体排列在赤道板）、后期（姐妹染色单体分开移向两极）和末期（核膜重新形成）。胞质分裂将细胞质分开。有丝分裂对生长、修复和无性生殖至关重要。
Uncontrolled cell division can lead to cancer. Oncogenes and tumour‑suppressor genes regulate the cell cycle; mutations can cause the formation of tumours.
细胞分裂失控可导致癌症。原癌基因和肿瘤抑制基因调控细胞周期；突变可能导致肿瘤形成。
8. Genetics & Inheritance | 遗传学与遗传
A gene is a segment of DNA that codes for a polypeptide. Alleles are different versions of a gene. The genotype is the genetic constitution, while the phenotype is the observable characteristic. A dominant allele is expressed in the heterozygous condition; a recessive allele is only expressed when homozygous.
基因是编码一条多肽的 DNA 片段。等位基因是同一基因的不同形式。基因型是遗传组成，表型是可观察的特征。显性等位基因在杂合状态下表达；隐性等位基因仅在纯合时表达。
Monohybrid crosses can be predicted using Punnett squares. Co‑dominance occurs when both alleles are expressed equally in the heterozygote (e.g. AB blood type). Sex‑linked traits are carried on the X chromosome and affect males more often (e.g. haemophilia, red‑green colour blindness). Pedigree charts help track inheritance patterns.
单基因杂交可用庞纳特方格预测。共显性指的是杂合子中两个等位基因均等表达（如 AB 血型）。伴性遗传性状由 X 染色体携带，男性发病率更高（如血友病、红绿色盲）。系谱图有助于追踪遗传模式。
9. Gas Exchange in Mammals | 哺乳动物的气体交换
The human respiratory system includes the trachea, bronchi, bronchioles and alveoli. Alveoli provide a large surface area, are thin‑walled and moist, and are surrounded by dense capillary networks for efficient gas exchange. Oxygen diffuses into the blood, and carbon dioxide diffuses out.
人体呼吸系统包括气管、支气管、细支气管和肺泡。肺泡提供了巨大的表面积，壁薄且湿润，并被密集的毛细血管网包围，以实现高效的气体交换。氧气扩散进入血液，二氧化碳扩散排出。
Ventilation is achieved by changes in thoracic volume. During inspiration the diaphragm contracts and flattens, and the external intercostal muscles contract, raising the ribcage; this increases volume and lowers pressure (Boyles law), drawing air in. Expiration at rest is
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