📚 Year 12 CCEA Biology: Core Revision Notes | CCEA 生物 Year 12 核心知识点梳理
This revision guide covers the essential content for Year 12 CCEA Biology, focusing on the AS units: Molecules and Cells (AS 1) and Organisms and Biodiversity (AS 2). Key concepts are explained in a clear, bilingual format to support exam preparation and deeper understanding.
本复习指南涵盖 Year 12 CCEA 生物的核心内容，聚焦 AS 单元：分子与细胞 (AS 1) 以及生物体与生物多样性 (AS 2)。关键概念以清晰的中英双语形式呈现，助力考试准备与深度学习。
1. Biological Molecules | 生物分子
Biological molecules include carbohydrates, lipids, proteins, and water. All are composed of smaller subunits and are vital for the structure and function of cells.
生物分子包括碳水化合物、脂质、蛋白质和水。它们都由更小的亚基组成，对细胞的结构和功能至关重要。
Monosaccharides such as glucose (C₆H₁₂O₆) are simple sugars that provide energy. They can form disaccharides (e.g., maltose) via condensation reactions, releasing water.
葡萄糖（C₆H₁₂O₆）等单糖是提供能量的简单糖类。它们可以通过缩合反应形成二糖（如麦芽糖），同时释放水。
Polysaccharides like starch and glycogen store glucose units. Starch in plants is a mixture of amylose (unbranched) and amylopectin (branched), while glycogen in animals is highly branched.
淀粉和糖原等多糖储存葡萄糖单位。植物中的淀粉是直链淀粉（无分支）和支链淀粉（有分支）的混合物，而动物中的糖原高度分支。
Lipids are composed of fatty acids and glycerol. Triglycerides store energy, and phospholipids form the basis of cell membranes with their hydrophilic heads and hydrophobic tails.
脂质由脂肪酸和甘油组成。甘油三酯储存能量，磷脂以其亲水头部和疏水尾部构成细胞膜的基础。
Proteins are polymers of amino acids joined by peptide bonds. The primary structure is the sequence of amino acids; secondary structures include α-helices and β-pleated sheets; tertiary structure is the 3D folding held by hydrogen bonds, ionic bonds, and disulfide bridges.
蛋白质是由肽键连接的氨基酸聚合物。一级结构是氨基酸序列；二级结构包括α-螺旋和β-折叠片；三级结构是由氢键、离子键和二硫键维持的三维折叠。
2. Cell Structure | 细胞结构
Cells are the basic units of life. Eukaryotic cells have membrane-bound organelles, while prokaryotic cells lack a nucleus and most organelles.
细胞是生命的基本单位。真核细胞具有膜包裹的细胞器，而原核细胞缺乏细胞核和大多数细胞器。
| Feature | Prokaryotic Cell | Eukaryotic Cell |
|---|---|---|
| Nucleus | Absent | Present |
| DNA | Circular, in cytoplasm | Linear, in nucleus |
| Organelles | No membrane-bound organelles | Mitochondria, ER, Golgi, etc. |
Key eukaryotic organelles include mitochondria (site of aerobic respiration), ribosomes (protein synthesis), rough endoplasmic reticulum (protein transport), and Golgi apparatus (modification and packaging).
真核细胞的关键细胞器包括线粒体（有氧呼吸场所）、核糖体（蛋白质合成）、粗面内质网（蛋白质运输）和高尔基体（修饰和包装）。
3. Cell Membranes and Transport | 细胞膜与运输
The cell membrane is described by the fluid mosaic model, consisting of a phospholipid bilayer with embedded proteins, cholesterol, and glycoproteins.
细胞膜由流动镶嵌模型描述，由磷脂双层组成，并嵌有蛋白质、胆固醇和糖蛋白。
Passive transport does not require ATP. Diffusion is the net movement of particles down a concentration gradient; facilitated diffusion uses channel or carrier proteins.
被动运输不需要 ATP。扩散是粒子顺浓度梯度的净移动；协助扩散利用通道蛋白或载体蛋白。
Osmosis is the diffusion of water through a selectively permeable membrane from a region of higher water potential to lower water potential.
渗透作用是水通过选择性渗透膜从较高水势区域向较低水势区域的扩散。
Active transport requires energy (ATP) to move substances against their concentration gradient, often using carrier proteins. Bulk transport occurs via endocytosis and exocytosis.
主动运输需要能量（ATP）逆浓度梯度移动物质，通常使用载体蛋白。批量运输通过胞吞和胞吐进行。
4. Enzymes | 酶
Enzymes are biological catalysts that lower activation energy. They are globular proteins with an active site specific to a substrate, explained by the lock-and-key and induced-fit models.
酶是降低活化能的生物催化剂。它们是球状蛋白质，具有与底物特异结合的活性位点，可由锁钥模型和诱导契合模型解释。
Factors affecting enzyme activity include temperature, pH, substrate concentration, and inhibitor presence. High temperature or extreme pH can denature the enzyme, altering the active site shape.
影响酶活性的因素包括温度、pH、底物浓度和抑制剂的存在。高温或极端 pH 会使酶变性，改变活性位点的形状。
Competitive inhibitors resemble the substrate and bind to the active site, while non-competitive inhibitors bind elsewhere and change the enzyme's shape.
竞争性抑制剂与底物相似，结合于活性位点；非竞争性抑制剂结合于别处，改变酶的形状。
5. Nucleic Acids and Protein Synthesis | 核酸与蛋白质合成
DNA is a double helix of nucleotides, each containing deoxyribose sugar, a phosphate group, and a nitrogenous base (A, T, C, G). RNA has ribose and uracil (U) instead of thymine.
DNA 是核苷酸的双螺旋，每个核苷酸包含脱氧核糖、磷酸基团和含氮碱基（A、T、C、G）。RNA 含有核糖和尿嘧啶（U）而非胸腺嘧啶。
DNA replication is semi-conservative. Helicase unwinds the double helix, and DNA polymerase adds complementary nucleotides to each original strand, forming two identical DNA molecules.
DNA 复制是半保留的。解旋酶解开双螺旋，DNA 聚合酶将互补核苷酸添加到每条原始链上，形成两个相同的 DNA 分子。
Transcription produces mRNA from a DNA template. RNA polymerase binds to the promoter, and the mRNA strand is complementary to the template strand.
转录以 DNA 为模板产生 mRNA。RNA 聚合酶结合到启动子，mRNA 链与模板链互补。
Translation occurs on ribosomes. tRNA molecules carry specific amino acids and match their anticodons to mRNA codons, assembling the polypeptide chain.
翻译在核糖体上进行。tRNA 分子携带特定氨基酸，将其反密码子与 mRNA 的密码子配对，组装多肽链。
6. Cell Division and Genetics | 细胞分裂与遗传学
Mitosis produces two genetically identical daughter cells for growth and repair. Stages include prophase, metaphase, anaphase, and telophase.
有丝分裂产生两个遗传上相同的子细胞，用于生长和修复。阶段包括前期、中期、后期和末期。
Meiosis reduces the chromosome number by half to form haploid gametes. It involves two divisions and generates genetic variation through crossing over and independent assortment.
减数分裂将染色体数目减半，形成单倍体配子。它涉及两次分裂，并通过交叉互换和独立分配产生遗传变异。
Monohybrid inheritance follows Mendel's laws. A homozygous dominant (AA) crossed with homozygous recessive (aa) produces heterozygous offspring (Aa) with the dominant phenotype.
单基因杂种遗传遵循孟德尔定律。纯合显性（AA）与纯合隐性（aa）杂交产生杂合子代（Aa），表现显性性状。
Codominance results in both alleles being expressed in the phenotype (e.g., blood group AB). Sex-linked traits are carried on the X chromosome, affecting males more frequently.
共显性导致两个等位基因都在表型中表达（如 AB 血型）。伴性性状位于 X 染色体上，男性受影响更频繁。
7. Exchange and Transport in Animals | 动物体内的交换与运输
Gas exchange surfaces are thin, moist, and have a large surface area. In mammals, alveoli in the lungs are surrounded by capillaries to maximise oxygen and carbon dioxide diffusion.
气体交换表面薄、湿润且具有大的表面积。在哺乳动物中，肺部的肺泡被毛细血管包围，以最大限度地促进氧气和二氧化碳的扩散。
The circulatory system is a closed, double system. The heart pumps deoxygenated blood to the lungs and oxygenated blood to the body. Arteries carry blood away, veins return it, and capillaries facilitate exchange.
循环系统是封闭的双循环系统。心脏将缺氧血泵送至肺部，将富氧血泵送至全身。动脉将血液带离，静脉将血液送回，毛细血管促进交换。
Haemoglobin in red blood cells binds oxygen reversibly. The oxygen dissociation curve shifts with changes in CO₂ concentration (Bohr effect), temperature, and pH.
红细胞中的血红蛋白可逆地结合氧气。氧解离曲线随 CO₂ 浓度（波尔效应）、温度和 pH 的变化而移动。
8. Exchange and Transport in Plants | 植物体内的交换与运输
Plants exchange gases through stomata in leaves. Carbon dioxide enters for photosynthesis, and oxygen and water vapour exit. Stomatal opening is regulated by guard cells.
植物通过叶片上的气孔交换气体。二氧化碳进入用于光合作用，氧气和水蒸气排出。气孔开闭由保卫细胞调节。
Water is transported in xylem vessels. Transpiration pulls water up from roots to leaves, driven by evaporation and the cohesive-tension theory. Mineral ions are also carried in xylem.
水分在水质部导管中运输。蒸腾作用拉动水分从根部上升到叶片，由蒸发和内聚力-张力理论驱动。矿质离子也在木质部中运输。
Phloem translocates dissolved sugars (mainly sucrose) from sources to sinks. The mass flow hypothesis explains movement via pressure gradients generated by active loading at the source.
韧皮部将溶解的糖（主要是蔗糖）从源运输到库。压力流动假说通过源端主动装载产生的压力梯度解释运输。
9. Biodiversity and Classification | 生物多样性及分类
Biodiversity refers to the variety of life, including genetic, species, and ecosystem diversity. It is measured using species richness and indices of diversity.
生物多样性指生命的多样性，包括遗传多样性、物种多样性和生态系统多样性。可通过物种丰富度和多样性指数进行衡量。
Classification organises organisms into hierarchical groups: domain, kingdom, phylum, class, order, family, genus, species. The five-kingdom system includes Prokaryotae, Protoctista, Fungi, Plantae, and Animalia.
分类将生物组织为等级群体：域、界、门、纲、目、科、属、种。五界系统包括原核生物界、原生生物界、真菌界、植物界和动物界。
The binomial system names each species with a genus and species epithet (e.g., Homo sapiens). Phylogenetic trees show evolutionary relationships based on similarities and molecular evidence.
双名法为每个物种赋予属名和种名（如 Homo sapiens）。系统发育树基于相似性和分子证据展示进化关系。
10. Evolution and Natural Selection | 进化与自然选择
Natural selection is the mechanism of evolution. Individuals with advantageous alleles are more likely to survive, reproduce, and pass on those alleles, increasing their frequency in the population.
自然选择是进化的机制。具有有利等位基因的个体更有可能存活、繁殖并将这些等位基因传递下去，从而增加其在种群中的频率。
Speciation occurs when populations become reproductively isolated. Allopatric speciation results from geographical barriers, while sympatric speciation occurs without physical separation.
当种群出现生殖隔离时，物种形成就会发生。异域物种形成由地理屏障导致，而同域物种形成则在无物理隔离的情况下发生。
Antibiotic resistance in bacteria is an example of evolution by natural selection. Mutations confer resistance, and the use of antibiotics selects for resistant strains, increasing their prevalence.
细菌的抗生素耐药性是自然选择进化的一个例子。突变赋予耐药性，抗生素的使用筛选出耐药菌株，从而增加其流行。
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