IB生物 Core 细胞 分子 遗传 生态 备考
IB Biology Core covers all six mandatory topics tested in Papers 1 and 2, accounting for 80% of your final grade. IB生物Core阶段 涵盖全部六个必考模块，占Paper 1和Paper 2总分的80%. Whether you are aiming for a 6 or a 7, mastering the Core syllabus is your single highest-leverage move. 无论目标是6分还是7分，吃透Core考纲是最有效率的提分策略.
Topic 1: Cell Biology 细胞生物学
Start with ultrastructure: prokaryotes (no nucleus, 70S ribosomes, naked DNA, binary fission) vs eukaryotes (nucleus, 80S ribosomes, membrane-bound organelles). For organelles, know the electron micrograph appearance of rough ER (ribosome-studded), Golgi (cisternae stack), mitochondria (double membrane, cristae), and chloroplasts (thylakoids in grana). 先搞定细胞超微结构：原核生物 vs 真核生物的结构差异是Paper 1选择题的高频考点，务必能识别电子显微镜下的细胞器特征.
Membrane transport is where IB shifts from recall to application. Master the fluid mosaic model (phospholipid bilayer, cholesterol in animal cells, integral vs peripheral proteins) and then practice distinguishing simple diffusion, facilitated diffusion (channel vs carrier proteins), osmosis, active transport (Na+/K+ pump using ATP), and endocytosis/exocytosis (vesicle formation requiring ATP). IB loves data-based questions that present an experimental setup with different solute concentrations and ask you to predict net water movement. Always calculate osmolarity first, then determine direction of osmosis. 膜运输是IB从记忆到应用的转折点，数据题会给出实验装置和浓度梯度，要求你预测水的净移动方向：先算渗透压，再定方向.
Cell division: interphase (G1, S, G2), mitosis phases (prophase-metaphase-anaphase-telophase) with chromosome behavior, and cytokinesis (cleavage furrow in animals, cell plate in plants). The key concept is that mitosis produces two genetically identical diploid daughter cells. Be able to calculate the mitotic index from microscope images. 有丝分裂阶段和染色体行为必须能画图标注，mitotic index计算是Paper 2数据题的常客.
Topic 2: Molecular Biology 分子生物学
IB Topic 2 is the heaviest Core topic. Start with biomolecules: carbohydrates (monosaccharides, disaccharides via condensation, polysaccharides ： cellulose vs starch vs glycogen), lipids (triglycerides: glycerol + 3 fatty acids, ester bonds; phospholipids; steroid structure of cholesterol), and proteins (amino acid general structure, peptide bond formation, four structural levels with specific bond types ： primary = peptide bonds, secondary = hydrogen bonds in alpha-helix/beta-pleated sheet, tertiary = hydrophobic interactions/disulfide bridges/ionic bonds/hydrogen bonds, quaternary = multiple polypeptide subunits like hemoglobin). 蛋白质四级结构必须写清楚每一级对应的化学键类型，这是Paper 2 SAQ部分的送分题.
Enzymes: induced fit model (not lock-and-key), activation energy reduction, and factors affecting enzyme activity (temperature, pH, substrate concentration). The IB expects you to describe competitive inhibition (binds active site, same Vmax, raised Km) vs non-competitive inhibition (binds allosteric site, lowered Vmax, same Km). Draw these curves ： visual recall outperforms rote memorization. 酶的竞争性vs非竞争性抑制，Vmax和Km的变化方向是两条相反的规律，用曲线图辅助记忆.
DNA replication, transcription, and translation form the central dogma. Replication: helicase unzips, DNA polymerase III adds nucleotides in 5' to 3' direction, leading strand (continuous) vs lagging strand (Okazaki fragments), DNA polymerase I replaces RNA primers, ligase seals gaps. Transcription: RNA polymerase, sense vs antisense strand, mRNA with uracil replacing thymine. Translation: ribosome (A, P, E sites), tRNA anticodon pairing with mRNA codon, peptide bond formation. The genetic code is degenerate (64 codons, 20 amino acids) and universal across species. 中心法则三步必须能依次描述，Paper 2经常要求用带标注的流程图表示整个过程.
Topic 3: Genetics 遗传学
Genes and chromosomes: a gene is a heritable factor controlling a specific characteristic, occupying a specific locus on a chromosome. Alleles are alternative forms of a gene. Diploid organisms have two alleles per gene ： homozygous (same) or heterozygous (different), dominant or recessive. Know how to read a karyogram and identify chromosomal abnormalities (Down syndrome = trisomy 21). 基因、等位基因、基因座的定义需要准确区分，核型图的异常染色体识别经常出现在Paper 1选择题中.
Meiosis produces four genetically distinct haploid gametes. Crossing over in prophase I (chiasmata formation, recombinant chromatids) and independent assortment in metaphase I generate genetic variation. Compare this to mitosis side-by-side: purpose (gamete production vs growth/repair), outcome (4 haploid vs 2 diploid), and key distinguishing features (homologous pairing, crossing over). Mendelian genetics: monohybrid crosses (3:1 F2 ratio), test crosses to determine genotype of dominant-phenotype individuals, and pedigree analysis for autosomal dominant (appears every generation), autosomal recessive (skips generations), and sex-linked traits (more males affected, no male-to-male transmission). 减数分裂与有丝分裂的对比表是必做笔记，孟德尔遗传的系谱分析要学会从家族树中推断遗传模式.
Topic 4: Ecology 生态学
IB Ecology is concept-heavy but formula-light. Core ideas: species (interbreeding, fertile offspring), population (same species, same area, same time), community (interacting populations), ecosystem (community + abiotic environment). Energy flow through food chains is ~10% efficient at each trophic level ： the rest is lost as heat through respiration. Draw a pyramid of energy (always upright) vs pyramid of numbers (can be inverted, e.g., one oak tree supporting thousands of insects). 食物链能量传递效率仅约10%，能量金字塔永远正立，数量金字塔可以倒置，这是Paper 1的经典陷阱题.
Carbon cycling: photosynthesis fixes atmospheric CO2 into organic compounds, respiration and combustion release it back. Methane is produced by methanogenic archaea in anaerobic conditions (peat bogs, landfill, cattle rumen) and oxidized to CO2 in the atmosphere. Climate change: greenhouse gases (CO2, methane, water vapor, nitrous oxides) trap long-wave infrared radiation. Know the correlation between rising atmospheric CO2 and global temperature since the industrial revolution. IB expects you to discuss both the enhanced greenhouse effect and precautionary measures (reducing emissions, carbon sequestration). 碳循环要能画出完整的流程图，温室效应的增强与工业革命后CO2浓度上升的关联是数据分析题的常见素材.
Topic 5: Evolution and Biodiversity 进化与生物多样性
Evidence for evolution: fossil record (transitional forms like Archaeopteryx), homologous structures (pentadactyl limb across mammals), selective breeding (domestic dogs from wolves), and DNA sequence comparison (more similar sequences = more recent common ancestor). Natural selection requires heritable variation, overproduction of offspring, and differential survival/reproduction. Antibiotic resistance in bacteria is the IB's favorite example: overuse selects for resistant strains, explaining why incomplete antibiotic courses are dangerous. 自然选择的四个条件缺一不可，抗生素耐药性进化是Paper 2 Section B论述题的热门材料.
Classification: the three domains (Archaea, Bacteria, Eukarya) and hierarchical taxa (Kingdom-Phylum-Class-Order-Family-Genus-Species). Binomial nomenclature uses Genus species format, italicized. Cladistics builds phylogenetic trees from shared derived characteristics. Be able to read a cladogram and identify the most recent common ancestor of any two clades. 三域分类系统和支序分类图的解读是近年IB新增的考点，要学会从cladogram中推断进化关系.
Topic 6: Human Physiology 人体生理学
The largest Core topic by volume. Digestion: peristalsis, stomach (pepsin + HCl for protein digestion), small intestine (villi/microvilli for absorption, pancreatic enzymes ： amylase, lipase, trypsin), large intestine (water reabsorption). Circulatory system: heart structure (atria, ventricles, atrioventricular and semilunar valves), cardiac cycle (systole/diastole), SA node as pacemaker, arteries (thick muscular wall) vs veins (valves, thin wall) vs capillaries (one cell thick for diffusion). 消化酶的最适pH需要记住：胃蛋白酶pH 2，胰蛋白酶pH 7-8，这是Paper 1经典考点.
Immune defense: skin and mucous membranes (first line), phagocytic leukocytes (non-specific second line), and lymphocytes producing antibodies (specific third line). Antibiotics block prokaryotic pathways (cell wall synthesis) and are ineffective against viruses ： IB loves this distinction. Gas exchange: ventilation (inspiration: diaphragm contracts, external intercostals contract, volume increases, pressure decreases; expiration is passive at rest), alveoli features (large surface area, one cell thick, moist, rich capillary network). 免疫系统的三道防线和抗生素对病毒无效的原理，Paper 2 SAQ几乎必出一题.
Neurons and synapses: resting potential (-70mV, Na+/K+ pump, more Na+ outside), action potential (depolarization at -50mV threshold, Na+ channels open; repolarization via K+ efflux; hyperpolarization), propagation along axon, saltatory conduction in myelinated neurons. Synaptic transmission: Ca2+ influx triggers vesicle fusion, neurotransmitter (e.g., acetylcholine) diffuses across cleft, binds postsynaptic receptors, then acetylcholinesterase breaks it down. Hormones: insulin (beta cells, lowers blood glucose) vs glucagon (alpha cells, raises blood glucose), negative feedback in thermoregulation and blood glucose control. 动作电位的过程和突触传递的每一个步骤都需要按顺序描述：Ca2+内流→囊泡融合→神经递质释放→受体结合→酶解清除.
HL Extension Preview: Topics 7-11
If you are taking HL Biology, the Core topics above are your SL foundation plus HL material: Topic 7 (Nucleic Acids: DNA structure detail, Hershey-Chase experiment, nucleosomes), Topic 8 (Metabolism: enzyme kinetics with Vmax/Km calculations, cell respiration with electron transport chain ATP yield, photosynthesis with Calvin cycle intermediates), Topic 9 (Plant Biology: xylem transport, transpiration, phloem translocation, plant reproduction), Topic 10 (Genetics: dihybrid crosses, linked genes, polygenic inheritance), Topic 11 (Animal Physiology: antibody production, vaccination, muscle contraction sliding filament model, kidney osmoregulation). HL adds approximately 60 more teaching hours ： the Core mastery you build now directly supports HL understanding later. HL学生注意：Core阶段的基础打好后，HL扩展内容其实是在同样的概念框架上深化：酶动力学从定性描述变为定量计算，细胞呼吸从ATP产量概述变为电子传递链的详细机制.
Six-Week Study Plan 六周备考计划
Wk 1: Cell + Molecular BioWeek 1 focuses on Topic 1 (Cell Biology) and Topic 2 (Molecular Biology). These two topics form the conceptual backbone ： if you thoroughly understand organelles, membrane transport, and the central dogma, the remaining topics build cleanly on this base. Complete all Paper 1 MCQ banks for Topics 1 and 2. 第一周攻克Topic 1细胞生物学和Topic 2分子生物学：这两章是整个生物学的概念地基.
Wk 2: Genetics + EvolutionWeek 2 covers Topic 3 (Genetics) and Topic 5 (Evolution). Pairing genetics with evolution is intentional: meiosis generates variation, and natural selection acts on it. Practice pedigree analysis, Punnett squares for monohybrid crosses, and cladogram interpretation. 第二周将遗传学和进化搭配学习：减数分裂制造变异，自然选择作用于变异，两条线相辅相成.
Wk 3: Ecology + EnvironmentWeek 3 focuses on Topic 4 (Ecology) ： the most prose-driven Core topic. Master carbon cycling diagrams, energy pyramids, greenhouse gas mechanisms, and the precautionary principle. This topic is conceptually lighter, giving you a breather before Human Physiology. 第三周相对轻松：生态学以理解概念和绘制流程图为主，可以适当调整节奏.
Wk 4: Human Physiology 1Week 4 begins Topic 6 ： the largest Core topic. Focus on digestion, circulatory system, and defense against disease. Draw the heart with labeled chambers and valves, trace blood flow through systemic and pulmonary circuits. 第四周进入人体生理学：消化系统、循环系统和免疫防御，心脏结构图必须能默画.
Wk 5: Human Physiology 2Week 5 completes Topic 6 with gas exchange, neurons/synapses, and hormones/homeostasis. The action potential sequence and synaptic transmission steps must be committed to numbered-step memorization. Compare insulin vs glucagon effects side-by-side. 第五周完成生理学收尾：气体交换、神经突触和激素稳态，动作电位和突触传递步骤需要逐条背诵.
Wk 6: Full Review + Past PapersFinal week: complete at least 2 full Paper 1 sets (30 MCQs each) and 1 full Paper 2 (data-based + SAQs + one extended response). Identify weak topics from your error pattern, re-read those sections, then attempt a third Paper 1. Time management drill: Paper 1 = 45 minutes for 30 questions. 第六周至少完成2套完整真题，根据错题模式精准回补，最后再做一套热身.
Exam Tips and Common Mistakes 考试技巧与常见错误
Paper 1 Strategy 选择题策略30 multiple-choice in 45 minutes (SL) or 40 in 60 minutes (HL). No calculators. Watch for "except" and "not" keywords. Diagrams are frequently used as distractors: always read the question before analyzing the diagram. If stuck, eliminate two obviously wrong answers, then compare the remaining pair. 警惕except/not等否定词，图表常作干扰项，先读题再看图.
Paper 2 Data-Based 数据分析题Section A data-based question is compulsory. Read the x-axis and y-axis labels first, note units, and check if any data series use different scales. Answer "describe" questions with trend + data values, and "explain" questions with biological mechanism. Even if you cannot explain the phenomenon, describe the data precisely for partial marks. Data-based题先读坐标轴单位和量程，describe题要用数据点支撑趋势描述，explain题要落到具体的生物机制上.
Top 5 Common Mistakes 五大常见错误1. 混淆有丝分裂和减数分裂的染色体数目变化(mitosis vs meiosis chromosome count). 2. 将竞争性抑制的Vmax变化方向写反(competitive inhibition: same Vmax, raised Km). 3. 系谱分析错误判断显隐性遗传模式(pedigree: autosomal dominant vs recessive identification). 4. 动作电位过程中Na+/K+通道的开关时序记混(action potential ion channel sequence). 5. 碳循环流程图中遗漏甲烷氧化步骤(methane oxidation in the carbon cycle).
Internal Assessment Quick Guide IA实验快速指南
The Internal Assessment accounts for 20% of your final IB Biology grade. A strong IA begins with a well-focused research question that includes both independent and dependent variables. Your experimental design must control at least 5 key variables and collect sufficient data for statistical analysis (minimum 5 increments of the independent variable, 5 repeats each). The four assessment criteria are Personal Engagement (2 marks), Exploration (6 marks), Analysis (6 marks), and Evaluation (6 marks). The most common IA pitfall is weak evaluation: a genuine evaluation identifies specific limitations in your own method and proposes concrete, testable improvements ： not generic statements like "do more trials." IA实验占IB生物总分的20%. 好的IA从一个聚焦明确的研究问题开始，实验设计需要控制至少5个关键变量，收集足够数据供统计分析（自变量至少5个梯度，每个梯度5次重复）. 评估标准四项：Personal Engagement个人投入(2分)、Exploration探索(6分)、Analysis分析(6分)、Evaluation评估(6分). 最常见失分点是评估部分写得空泛：真正的评估要指出自己实验方法的具体局限，并提出可操作的改进方案，而不是笼统地说"多做几次实验".
Key Bilingual Terms 关键双语术语
Ultrastructure 超微结构 | Fluid Mosaic Model 流动镶嵌模型 | Osmosis 渗透作用 | Active Transport 主动运输 | Mitosis 有丝分裂 | Meiosis 减数分裂 | Peptide Bond 肽键 | Induced Fit Model 诱导契合模型 | Okazaki Fragments 冈崎片段 | Anticodon 反密码子 | Allele 等位基因 | Crossing Over 交叉互换 | Trophic Level 营养级 | Greenhouse Effect 温室效应 | Natural Selection 自然选择 | Cladistics 支序分类学 | Peristalsis 蠕动 | SA Node 窦房结 | Action Potential 动作电位 | Synaptic Transmission 突触传递 | Homeostasis 稳态 | Insulin 胰岛素 | Glucagon 胰高血糖素
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