IB Biology: Last-Minute Revision Notes | IB 生物：考前冲刺笔记

📚 IB Biology: Last-Minute Revision Notes | IB 生物：考前冲刺笔记

These concise revision notes cover the core concepts tested in IB Biology, from cell ultrastructure to physiology and ecology. Each section pairs English explanations with Chinese translations, perfect for last-minute review and reinforcing both content and bilingual terminology.

这份考前冲刺笔记浓缩了 IB 生物的核心考点，涵盖从细胞超微结构到人体生理与生态的关键内容。每个小节先提供英文讲解，再给出对应中文，便于快速复习并同时巩固知识要点与双语术语。

1. Cell Theory and Ultrastructure | 细胞理论与超微结构

All living organisms are composed of cells, which are the basic unit of life. The cell theory states that cells arise from pre-existing cells, and that organisms can be unicellular or multicellular. Prokaryotic cells lack a true nucleus and membrane-bound organelles, while eukaryotic cells have compartmentalised structures such as the nucleus, mitochondria, endoplasmic reticulum and Golgi apparatus.

所有生物都由细胞构成，细胞是生命的基本单位。细胞学说指出细胞来自已有的细胞，生物可以是单细胞或多细胞。原核细胞没有真正的细胞核和膜包被的细胞器，而真核细胞则有高度区室化的结构，如细胞核、线粒体、内质网和高尔基体。

Key differences: prokaryotes have 70S ribosomes, a single circular DNA molecule, and may possess plasmids; eukaryotes have 80S ribosomes, linear DNA associated with histones, and organelles like chloroplasts (in plants) and lysosomes.

主要区别：原核生物含有 70S 核糖体、单个环状 DNA，可能带有质粒；真核生物含有 80S 核糖体、与组蛋白结合的线性 DNA，以及叶绿体（植物）和溶酶体等细胞器。

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2. Membrane Structure and Transport | 膜结构与运输

Cell membranes are composed of a phospholipid bilayer with embedded proteins. The fluid mosaic model describes the membrane as a dynamic structure where lipids and proteins can move laterally. Phospholipids are amphipathic, with hydrophilic phosphate heads facing outward and hydrophobic fatty acid tails inward.

细胞膜由磷脂双分子层和嵌入的蛋白质组成。流动镶嵌模型说明膜是动态结构，脂质和蛋白质能够侧向移动。磷脂是两亲性分子，亲水的磷酸头部朝向外部，疏水的脂肪酸尾部朝向内部。

Transport across membranes can be passive (diffusion, facilitated diffusion, osmosis) requiring no energy, or active requiring ATP. Endocytosis and exocytosis move bulk materials. Aquaporins facilitate rapid water transport. The sodium-potassium pump is a key example of active transport, exchanging 3 Na⁺ out for 2 K⁺ in per ATP.

跨膜运输可分为不耗能的被动运输（扩散、协助扩散、渗透）和消耗 ATP 的主动运输。内吞与外排用于大块物质转运。水通道蛋白实现水分快速运输。钠-钾泵是重要的主动运输实例，每消耗一分子 ATP 将 3 个 Na⁺ 泵出、2 个 K⁺ 泵入。

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3. Origin of Cells and Cell Division | 细胞起源与细胞分裂

The first cells arose from non-living chemical systems via abiotic synthesis of organic molecules. The endosymbiotic theory explains the origin of mitochondria and chloroplasts from engulfed prokaryotes. Evidence includes double membranes, their own 70S ribosomes and circular DNA.

最早的细胞通过有机分子的非生物合成，从非生命化学系统演化而来。内共生学说解释了线粒体和叶绿体由被吞噬的原核生物起源。证据包括双层膜、自身含有 70S 核糖体和环状 DNA。

Cell division in eukaryotes occurs via mitosis and meiosis. Mitosis produces two genetically identical daughter cells for growth and repair, with phases: prophase, metaphase, anaphase, telophase. Meiosis reduces chromosome number by half and generates genetic variation through crossing over and independent assortment.

真核细胞的分裂通过有丝分裂和减数分裂完成。有丝分裂产生两个遗传相同的子细胞，用于生长与修复，包含前期、中期、后期和末期。减数分裂将染色体数目减半，通过交叉和自由组合产生遗传变异。

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4. Molecular Biology: DNA, RNA and Protein Synthesis | 分子生物学：DNA、RNA 与蛋白质合成

DNA is a double helix composed of nucleotides with a sugar-phosphate backbone and nitrogenous bases (A, T, C, G). Complementary base pairing (A-T, C-G) ensures accurate replication. The two strands run antiparallel (5′ to 3′ and 3′ to 5′).

DNA 是双螺旋结构，由核苷酸构成，包含糖-磷酸骨架和含氮碱基（A、T、C、G）。互补碱基配对（A-T、C-G）保证复制的精确性。两条链反向平行（5′ → 3′ 和 3′ → 5’）。

Replication is semi-conservative and involves helicase, DNA polymerase, and ligase. Transcription produces mRNA from a DNA template; in eukaryotes, mRNA is processed (5′ cap, poly-A tail, splicing). Translation occurs on ribosomes, where tRNA anticodons match mRNA codons to assemble amino acids into a polypeptide.

复制为半保留复制，需要解旋酶、DNA 聚合酶和 DNA 连接酶。转录以 DNA 为模板合成 mRNA；真核生物的 mRNA 需加工（5′ 端加帽、多聚腺苷酸尾、剪接）。翻译在核糖体上进行，tRNA 反密码子与 mRNA 密码子配对，氨基酸依次连接成多肽链。

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5. Enzymes and Metabolism | 酶与代谢

Enzymes are globular proteins that act as biological catalysts, lowering activation energy. They have a specific active site that binds substrates. The lock-and-key and induced-fit models describe enzyme-substrate interaction. Factors affecting enzyme activity include temperature, pH, and substrate concentration.

酶是球状蛋白，作为生物催化剂降低活化能。它们具有特定的活性位点与底物结合。锁钥模型和诱导契合模型描述酶与底物的相互作用。影响酶活性的因素包括温度、pH 和底物浓度。

Denaturation is a permanent loss of structure and function due to extremes of temperature or pH. Competitive inhibitors resemble the substrate and block the active site; non-competitive inhibitors bind to an allosteric site, changing enzyme shape. End-product inhibition is a common feedback mechanism in metabolic pathways.

变性是由于极端温度或 pH 导致的酶结构与功能永久丧失。竞争性抑制剂结构与底物相似，占据活性位点；非竞争性抑制剂结合别构位点，改变酶的形状。终产物抑制是代谢途径中常见的反馈调节机制。

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6. Genetics: Inheritance and Genes | 遗传学：遗传与基因

Genes are segments of DNA that code for a specific polypeptide. Alleles are alternative forms of a gene. Genotype is the combination of alleles, while phenotype is the observable trait. Dominant alleles mask recessive ones in heterozygotes. Codominance and incomplete dominance show blending or joint expression.

基因是编码特定多肽的 DNA 片段。等位基因是基因的不同形式。基因型是等位基因的组合，表型是可观察的性状。显性等位基因在杂合子中掩盖隐性等位基因的作用。共显性和不完全显性则呈现混合或共同表达。

Mendelian crosses can be studied using Punnett grids. Dihybrid crosses reveal independent assortment if genes are on different chromosomes. Sex linkage occurs when genes are on X or Y chromosomes. Mutation and meiosis are sources of genetic variation. The Human Genome Project has mapped all human genes.

孟德尔遗传可通过庞纳特方格研究。若基因位于不同染色体上，双因子杂交体现自由组合。基因位于 X 或 Y 染色体上时表现为伴性遗传。突变和减数分裂是遗传变异的来源。人类基因组计划已绘制出全部人类基因图谱。

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7. Ecology and Energy Flow | 生态学与能量流动

Ecosystems consist of communities interacting with abiotic factors. Energy enters most ecosystems as sunlight and is captured by autotrophs through photosynthesis. Energy flows through trophic levels: producers → primary consumers → secondary consumers → tertiary consumers. Only about 10% of energy is transferred to the next level; the rest is lost as heat through respiration.

生态系统由生物群落与非生物因素相互作用构成。能量大多通过阳光进入生态系统，由自养生物通过光合作用固定。能量沿营养级流动：生产者 → 初级消费者 → 次级消费者 → 三级消费者。只有约 10% 的能量传递到下一营养级，其余以热的形式通过呼吸作用散失。

Carbon cycling involves photosynthesis, respiration, decomposition, and combustion. Nitrogen-fixing bacteria convert atmospheric N₂ into ammonia; nitrifying bacteria oxidise ammonia to nitrates; denitrifying bacteria return N₂ to the atmosphere. Food webs illustrate complex feeding relationships.

碳循环涉及光合作用、呼吸作用、分解作用和燃烧。固氮细菌将大气中的 N₂ 转变为氨；硝化细菌将氨氧化为硝酸盐；反硝化细菌将硝酸盐还原为 N₂ 返回大气。食物网呈现更复杂的捕食关系。

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8. Evolution and Natural Selection | 进化与自然选择

Evolution is the cumulative change in heritable characteristics of a population over generations. Natural selection acts on variation: individuals with advantageous traits are more likely to survive and reproduce, passing those traits to offspring. Antibiotic resistance in bacteria is a classic example.

进化是种群可遗传特征在世代间的累积变化。自然选择作用于变异：具有有利性状的个体更易存活并繁殖，将性状传递给后代。细菌的抗生素抗性是一个经典实例。

Evidence for evolution includes fossil records, homologous structures, selective breeding, and molecular comparisons. Speciation occurs when populations become reproductively isolated, often by geographical or behavioural barriers. Adaptive radiation, like Darwin’s finches, illustrates divergence from a common ancestor.

进化证据包括化石记录、同源结构、人工选择育种和分子比对。当种群出现生殖隔离时便会形成新物种，常见隔离机制有地理隔离和行为隔离。适应性辐射（如达尔文雀）展示了从共同祖先分化而来的过程。

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9. Human Physiology: Digestion and Absorption | 人体生理学：消化与吸收

The digestive system breaks down macromolecules into smaller absorbable units. Mechanical digestion begins in the mouth; chemical digestion involves enzymes like amylase (starch → maltose), pepsin (proteins → peptides), and lipase (lipids → fatty acids and glycerol). Bile emulsifies fats to increase surface area for lipase action.

消化系统将大分子分解为可吸收的小单位。机械消化始于口腔；化学消化依赖淀粉酶（淀粉 → 麦芽糖）、胃蛋白酶（蛋白质 → 多肽）和脂肪酶（脂肪 → 脂肪酸和甘油）等酶。胆汁乳化脂肪，增大脂肪酶的作用面积。

Absorption mainly occurs in the small intestine. Villi and microvilli increase surface area. Nutrients are absorbed into blood capillaries (monosaccharides, amino acids) or lacteals (fatty acids and monoglycerides reassembled into chylomicrons). The large intestine absorbs water and salts.

吸收主要在小肠进行。绒毛和微绒毛增大了表面积。营养成分被吸收入毛细血管（单糖、氨基酸）或乳糜管（脂肪酸和单酰甘油重新组装成乳糜微粒）。大肠吸收水分和无机盐。

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10. Human Physiology: Circulation and Gas Exchange | 人体生理学：循环与气体交换

The heart is a double pump: the right side pumps deoxygenated blood to the lungs, the left side pumps oxygenated blood to the body. Valves prevent backflow. The pacemaker (SA node) initiates contraction. Arteries carry blood away from the heart; veins return blood, with valves to aid flow.

心脏是一个双泵：右侧将缺氧血泵入肺，左侧将富氧血泵至全身。瓣膜防止血液倒流。起搏点（窦房结）引发心跳。动脉将血液带离心脏，静脉将血液送回，静脉中的瓣膜辅助回流。

Gas exchange occurs in alveoli, where oxygen diffuses into blood and carbon dioxide diffuses out. Ventilation is driven by the diaphragm and intercostal muscles. Type I pneumocytes form the alveolar wall; type II pneumocytes secrete surfactant to reduce surface tension. Haemoglobin binds oxygen cooperatively.

气体交换在肺泡进行，氧气扩散入血，二氧化碳扩散排出。呼吸运动由膈肌和肋间肌驱动。I 型肺泡细胞构成肺泡壁；II 型肺泡细胞分泌表面活性物质以降低表面张力。血红蛋白以协同方式结合氧气。

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11. Neurons and Synapses | 神经元与突触

Neurons transmit electrical impulses. Resting potential (-70 mV) is maintained by Na⁺/K⁺ pumps and leakage channels. An action potential is triggered when depolarisation reaches threshold, followed by repolarisation and hyperpolarisation. It follows the all-or-none principle.

神经元传导电脉冲。静息电位（-70 mV）由钠钾泵和漏通道维持。当去极化达到阈值时触发动作电位，随后复极化并出现超极化。动作电位遵循全或无原则。

Synaptic transmission occurs when Ca²⁺ influx causes vesicles to release neurotransmitter into the synaptic cleft. Neurotransmitters bind to receptors on the postsynaptic membrane, opening ion channels and generating excitatory or inhibitory postsynaptic potentials. Acetylcholine in cholinergic synapses is broken down by acetylcholinesterase.

突触传递时，Ca²⁺ 内流促使囊泡释放神经递质到突触间隙。神经递质与突触后膜受体结合，打开离子通道，产生兴奋性或抑制性突触后电位。胆碱能突触中的乙酰胆碱被乙酰胆碱酯酶分解。

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12. Data Analysis and Experimental Skills | 数据分析与实验技能

IB Biology assessments frequently require interpretation of graphs, error bars, and statistical tests such as the t-test or correlation coefficient. Understand standard deviation and standard error; overlapping error bars often suggest no significant difference. Always state a null hypothesis when discussing statistical analysis.

IB 生物考试常要求解读图表、误差线和统计检验（如 t 检验或相关系数）。理解标准差和标准误差；误差线重叠往往表示差异不显著。讨论统计分析时，务必写出零假设。

Key experimental techniques include microscopy (magnification calculations), chromatography (Rf value), colorimetry and spectrophotometry, osmolarity estimation, and using databases for molecular biology. When designing experiments, identify independent, dependent, and controlled variables and state the ethical considerations.

核心实验技术包括显微镜操作（放大倍数计算）、色谱法（Rf 值）、比色法与分光光度法、渗透浓度估算，以及使用分子生物学数据库。设计实验时，需明确自变量、因变量和控制变量，并说明伦理考量。

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