📚 IB CCEA Biology: Last-Minute Revision Notes | IB CCEA 生物：考前冲刺笔记
These revision notes distil the most frequently examined topics from the IB and CCEA Biology specifications into concise, exam-ready explanations. Use them to reinforce key concepts, review essential terminology, and build confidence before your assessment.
本冲刺笔记凝练了 IB 与 CCEA 生物课程中最高频的考点，以简明易记的方式呈现核心概念、术语和原理解释，帮助你在考前快速巩固知识、查漏补缺。
1. Cell Structure | 细胞结构
Prokaryotic vs Eukaryotic cells: Prokaryotes lack a membrane-bound nucleus and organelles; their DNA is circular and free in the cytoplasm. Eukaryotes have a true nucleus, linear DNA, and compartmentalised organelles such as mitochondria and the endoplasmic reticulum.
原核与真核细胞：原核细胞没有膜包围的细胞核和细胞器，其DNA呈环状，游离在细胞质中。真核细胞拥有真正的细胞核、线性DNA以及线粒体、内质网等区室化的细胞器。
Key organelles and their functions: Nucleus (stores genetic material), mitochondria (site of aerobic respiration, produces ATP), rough endoplasmic reticulum (protein synthesis and transport), smooth ER (lipid synthesis), Golgi apparatus (modifies and packages proteins), ribosomes (translation), lysosomes (digestion), chloroplasts (photosynthesis in plants), vacuole (storage and turgor support), cell wall (structural support in plants, fungi and bacteria).
关键细胞器与功能：细胞核（储存遗传物质）、线粒体（有氧呼吸场所，产生ATP）、粗面内质网（蛋白质合成与运输）、滑面内质网（脂质合成）、高尔基体（蛋白质修饰与包装）、核糖体（翻译）、溶酶体（消化）、叶绿体（植物光合作用）、液泡（储存与维持膨压）、细胞壁（植物、真菌和细菌的结构支持）。
Endosymbiotic theory: Mitochondria and chloroplasts evolved from engulfed prokaryotes. Evidence includes their own circular DNA, 70S ribosomes, and double membranes.
内共生学说：线粒体和叶绿体起源于被吞噬的原核生物。证据包括它们拥有自己的环状DNA、70S核糖体以及双层膜结构。
2. Biological Molecules | 生物大分子
Carbohydrates: Monosaccharides (glucose, fructose) are simple sugars. Disaccharides (maltose, sucrose, lactose) form via condensation reactions. Polysaccharides like starch (plant energy storage, composed of amylose and amylopectin), glycogen (animal energy storage, highly branched), and cellulose (plant cell wall structural polysaccharide, beta-glucose units) differ in structure and function.
碳水化合物：单糖（葡萄糖、果糖）为简单糖类。二糖（麦芽糖、蔗糖、乳糖）通过缩合反应形成。多糖如淀粉（植物储能，由直链淀粉和支链淀粉组成）、糖原（动物储能，高度分支）和纤维素（植物细胞壁结构多糖，由β-葡萄糖构成）在结构与功能上各不相同。
Lipids: Triglycerides consist of glycerol and three fatty acids joined by ester bonds. They are energy stores, thermal insulation, and protection. Phospholipids have a hydrophilic phosphate head and two hydrophobic fatty acid tails, forming the basis of cell membranes.
脂质：甘油三酯由甘油和三个脂肪酸通过酯键连接而成，用于能量储存、隔热和保护。磷脂具有亲水的磷酸头端和两条疏水脂肪酸尾端，是构成细胞膜的基本结构。
Proteins: Made of amino acids linked by peptide bonds. Protein structure has four levels: primary (sequence), secondary (alpha-helix, beta-pleated sheet), tertiary (3D folding due to R-group interactions, including disulfide bridges, ionic bonds, hydrophobic interactions, hydrogen bonds), and quaternary (multiple polypeptide chains).
蛋白质：由氨基酸通过肽键连接而成。蛋白质结构分为四级：一级（序列）、二级（α-螺旋、β-折叠片）、三级（因R基团相互作用形成的三维折叠，包括二硫键、离子键、疏水作用、氢键）和四级（多条多肽链组装）。
3. Enzymes | 酶
Enzyme action: Enzymes are biological catalysts that lower activation energy. They bind substrates at the active site. The induced-fit model explains that the active site changes shape slightly to accommodate the substrate, forming enzyme-substrate complex.
酶的作用：酶是降低活化能的生物催化剂。它们通过活性位点与底物结合。诱导契合模型指出，活性位点会略微改变形状以贴合底物，形成酶-底物复合物。
Factors affecting enzyme activity: Temperature (increase to optimum then denaturation), pH (optimum pH, extremes disrupt ionic and hydrogen bonds), substrate concentration (rate increases up to saturation point), and competitive inhibitors (bind active site) vs non-competitive inhibitors (bind allosteric site, change active site shape).
影响酶活性的因素：温度（升到最适温度后变性）、pH（最适pH，极端值破坏离子键和氢键）、底物浓度（速率增加直至饱和）、竞争性抑制剂（结合活性位点）与非竞争性抑制剂（结合变构位点，改变活性位点形状）。
Immobilised enzymes: Enzymes trapped in alginate beads allow continuous use, easier product separation, and increased stability. Used in industry, e.g., lactase in milk processing to produce lactose-free milk.
固定化酶：将酶包埋在海藻酸盐珠中可实现持续使用、易于产物分离并提高稳定性。工业应用如乳糖酶用于生产无乳糖牛奶。
4. Membrane Structure & Transport | 膜结构与运输
Fluid mosaic model: Phospholipid bilayer with embedded proteins, cholesterol (in animal cells) and glycoproteins. The membrane is fluid due to moving phospholipids and mosaic due to scattered proteins.
流动镶嵌模型：磷脂双分子层中镶嵌有蛋白质、胆固醇（动物细胞）和糖蛋白。膜因磷脂运动而具有流动性，因蛋白质散在分布而呈镶嵌状。
Passive transport: Diffusion (net movement from high to low concentration), facilitated diffusion (through channel or carrier proteins, no ATP), and osmosis (water movement across a partially permeable membrane from high water potential to low water potential).
被动运输：简单扩散（从高浓度向低浓度净移动）、协助扩散（通过通道蛋白或载体蛋白，不耗ATP）、渗透（水通过半透膜从高水势向低水势移动）。
Active transport: Uses ATP and carrier proteins to move substances against their concentration gradient, e.g., sodium-potassium pump. Endocytosis and exocytosis move large molecules via vesicles.
主动运输：消耗ATP，利用载体蛋白逆浓度梯度转运物质，如钠钾泵。胞吞作用和胞吐作用通过囊泡转运大分子。
5. DNA Replication & Protein Synthesis | DNA复制与蛋白质合成
DNA structure: Double helix of nucleotides (deoxyribose, phosphate, base). Complementary base pairing: A-T (2 hydrogen bonds) and C-G (3 hydrogen bonds). Strands are antiparallel (5′ to 3′ and 3′ to 5′).
DNA结构：由核苷酸（脱氧核糖、磷酸、碱基）构成的双螺旋。互补碱基配对：A-T（两个氢键），C-G（三个氢键）。两条链反向平行（5′到3′和3′到5′）。
Semi-conservative replication: DNA helicase unwinds and separates strands. DNA polymerase adds free nucleotides to the template strand in the 5′ to 3′ direction. Leading strand synthesised continuously, lagging strand in Okazaki fragments joined by DNA ligase.
半保留复制：DNA解旋酶解开双链并分离。DNA聚合酶沿模板链从5′到3′方向添加游离核苷酸。前导链连续合成，后随链以冈崎片段合成，由DNA连接酶连接。
Transcription & translation: RNA polymerase synthesises mRNA from the DNA template. mRNA is processed (in eukaryotes) and moves to ribosomes. tRNA anticodons bind to mRNA codons, bringing specific amino acids. Peptide bonds form between amino acids to build a polypeptide.
转录与翻译：RNA聚合酶以DNA为模板合成mRNA。mRNA经加工后（真核生物中）移至核糖体。tRNA反密码子与mRNA密码子结合，携带特定氨基酸。氨基酸间形成肽键，合成多肽链。
6. Cell Division (Mitosis & Meiosis) | 细胞分裂（有丝分裂与减数分裂）
Cell cycle: Interphase (G₁, S, G₂) – DNA replicates in S phase. M phase includes mitosis (nuclear division) and cytokinesis (cytoplasmic division). Checkpoints ensure accuracy.
细胞周期：间期（G₁期、S期、G₂期）——DNA在S期复制。M期包含有丝分裂（核分裂）和胞质分裂（细胞质分裂）。检查点确保精确性。
Mitosis stages: Prophase (chromosomes condense, spindle forms), metaphase (chromosomes align at equator), anaphase (sister chromatids separate), telophase (nuclear envelopes reform). Produces two genetically identical diploid cells, important for growth and repair.
有丝分裂阶段：前期（染色体凝集，纺锤体形成）、中期（染色体排列在赤道板）、后期（姐妹染色单体分离）、末期（核膜重新形成）。产生两个遗传相同的二倍体细胞，用于生长和修复。
Meiosis: Involves two divisions. Meiosis I separates homologous chromosomes, crossing over in prophase I creates genetic variation. Meiosis II separates sister chromatids. Result: four genetically varied haploid gametes.
减数分裂：包含两次分裂。减数第一次分裂分离同源染色体，前期I发生交叉互换，产生遗传变异。减数第二次分裂分离姐妹染色单体。结果：产生四个遗传组成不同的单倍体配子。
7. Genetics & Patterns of Inheritance | 遗传学与遗传模式
Key terms: Gene (DNA segment coding for a protein), allele (gene variant), genotype (genetic makeup), phenotype (observable trait), homozygous (identical alleles), heterozygous (different alleles), dominant/recessive, codominance.
关键术语：基因（编码蛋白质的DNA片段）、等位基因（基因变体）、基因型（遗传组成）、表现型（可观察的性状）、纯合（相同等位基因）、杂合（不同等位基因）、显性/隐性、共显性。
Monohybrid crosses: Use Punnett squares. F₂ phenotypic ratio for heterozygote cross is typically 3:1 for dominant-recessive traits. Codominance yields 1:2:1 ratio, e.g., ABO blood groups (alleles Iᴬ, Iᴮ, i).
单基因杂交：使用庞纳特方格。杂合子杂交的F₂代表现型比例通常为3:1（显性-隐性性状）。共显性产生1:2:1比例，例如ABO血型系统（等位基因Iᴬ、Iᴮ、i）。
Sex linkage: Genes on sex chromosomes (e.g., X-linked). Males are hemizygous for X-linked genes. Examples: haemophilia, red-green colour blindness. Inheritance patterns differ between sexes.
性连锁：位于性染色体上的基因（如X连锁）。男性对于X连锁基因是半合子。例子：血友病、红绿色盲。男女遗传模式存在差异。
8. Energy Transfer & Ecosystems | 能量传递与生态系统
Food chains & webs: Producers (autotrophs) capture light energy via photosynthesis. Consumers (heterotrophs) feed on other organisms. Trophic levels represent feeding positions. Energy is lost as heat, movement, and undigested material at each level.
食物链与食物网：生产者（自养生物）通过光合作用捕获光能。消费者（异养生物）以其他生物为食。营养级代表取食位置。每一级能量均以热、运动及未消化物质等形式散失。
Energy flow: Only about 10% of energy passes from one trophic level to the next. Pyramids of energy always remain upright. Net primary productivity (NPP) = gross primary productivity (GPP) − respiration (R).
能量流动：仅约10%的能量从某一营养级传递给下一级。能量金字塔始终保持正立。净初级生产力(NPP)=总初级生产力(GPP)−呼吸消耗(R)。
Nutrient cycling: Carbon cycle (photosynthesis, respiration, decomposition, combustion), nitrogen cycle (nitrogen fixation by Rhizobium, nitrification, denitrification, ammonification). Decomposers recycle nutrients.
养分循环：碳循环（光合作用、呼吸作用、分解作用、燃烧），氮循环（根瘤菌固氮作用、硝化作用、反硝化作用、氨化作用）。分解者使养分重新进入循环。
9. Human Physiology: Gas Exchange & Circulation | 人体生理：气体交换与循环
Ventilation: Inhalation – diaphragm contracts and flattens, external intercostal muscles contract, ribcage lifts, thoracic volume increases, pressure drops, air flows in. Exhalation is largely passive at rest.
通气：吸气 – 膈肌收缩并变平，外肋间肌收缩，肋骨上提，胸腔容积增大，压力下降，空气流入。呼气在静息时主要靠被动回弹。
Alveolar gas exchange: Oxygen diffuses from alveoli into blood down a concentration gradient; carbon dioxide diffuses from blood into alveoli. Alveoli have thin walls, large surface area, moist lining, and dense capillary network for efficient exchange.
肺泡气体交换：氧气沿浓度梯度从肺泡弥散入血液，二氧化碳从血液弥散入肺泡。肺泡壁薄、表面积大、湿润内膜、毛细血管网密集，有利于高效气体交换。
Cardiac cycle & blood: Heart has four chambers. SAN initiates heartbeat, causing atria to contract; AVN delays impulse; ventricles contract. Arteries carry blood away, veins return blood, capillaries where exchange occurs. Haemoglobin binds oxygen (oxyhaemoglobin).
心动周期与血液：心脏四腔。窦房结启动心跳，引起心房收缩；房室结延迟冲动；心室收缩。动脉输送血液离开心脏，静脉回血，毛细血管进行物质交换。血红蛋白结合氧气（氧合血红蛋白）。
10. Plant Biology: Photosynthesis & Transpiration | 植物生物学：光合作用与蒸腾作用
Photosynthesis overview: Light-dependent reactions in thylakoid membrane: photolysis of water (H₂O → 2H⁺ + 2e⁻ + ½O₂), electron transport, ATP and NADPH produced. Calvin cycle in stroma: CO₂ fixed by RuBisCO, using ATP and NADPH to produce glucose. Overall summary:
光合作用总览：光反应在类囊体膜上进行：水光解 (H₂O → 2H⁺ + 2e⁻ + ½O₂)、电子传递、产生ATP与NADPH。卡尔文循环在基质中进行：RuBisCO固定CO₂，利用ATP和NADPH合成葡萄糖。总方程式：
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Factors limiting photosynthesis: Light intensity, carbon dioxide concentration, and temperature. At low light, rate limited by light; beyond light saturation, CO₂ or temperature becomes limiting. Enzymes (e.g., RuBisCO) function optimally at moderate temperatures.
影响光合作用的限制因素：光照强度、二氧化碳浓度和温度。低光强下光成为限制因素；光饱和之后，CO₂或温度成为限制。酶（如RuBisCO）在适宜温度范围内发挥作用。
Transpiration stream: Water evaporated from mesophyll cells creates tension, pulling water up xylem (cohesion-tension theory). Adhesion of water to xylem walls aids movement. Stomata open and close via guard cell turgor to regulate water loss and gas exchange.
蒸腾流：叶肉细胞水分蒸发产生张力，拉动水在木质部中上升（内聚力-张力学说）。水与木质部壁的黏附有助于输送。气孔通过保卫细胞膨压变化开闭，调节水分散失和气体交换。
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