Topic 1: Cell Biology 细胞生物学
The cell is the fundamental unit of life. You must understand the cell theory (all living things are composed of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells), the differences between prokaryotic and eukaryotic cells, and the structure and function of key organelles: nucleus, mitochondrion, ribosome, endoplasmic reticulum, Golgi apparatus, lysosome, and chloroplast. 细胞是生命的基本单位。你必须掌握细胞学说、原核细胞与真核细胞的区别，以及关键细胞器的结构与功能：细胞核、线粒体、核糖体、内质网、高尔基体、溶酶体和叶绿体。
Membrane structure and transport is a high-frequency exam topic. Know the fluid mosaic model, the roles of phospholipids and proteins, and the differences between simple diffusion, facilitated diffusion, osmosis, and active transport (including sodium-potassium pumps and endocytosis/exocytosis). 膜结构与物质运输是高频考点。掌握流动镶嵌模型、磷脂和蛋白质的作用，以及简单扩散、协助扩散、渗透和主动运输的区别。
Cell division: Understand the stages of mitosis (prophase, metaphase, anaphase, telophase) and cytokinesis. Know how cancer results from uncontrolled cell division. 细胞分裂：掌握有丝分裂各阶段及胞质分裂，理解癌症如何由细胞分裂失控引起。
Topic 2: Molecular Biology 分子生物学
This is arguably the most important topic in IB Biology. You need to know the four major macromolecules: carbohydrates, lipids, proteins, and nucleic acids. For each, memorize the monomer, polymer, bond type, and key functions. 这可能是IB生物最重要的主题。你需要掌握四大生物大分子：碳水化合物、脂质、蛋白质和核酸。每种都要记住其单体、聚合物、键类型和关键功能。
DNA replication, transcription, and translation form the central dogma of molecular biology. Be able to draw and label: DNA helicase unwinding the double helix, DNA polymerase adding nucleotides in the 5 to 3 direction on the leading and lagging strands (Okazaki fragments), RNA polymerase transcribing mRNA from the template strand, and ribosomes translating mRNA into polypeptide chains using tRNA. DNA复制、转录和翻译构成分子生物学的中心法则。要能画出并标注完整过程。
Enzymes: Know the lock-and-key and induced-fit models, how temperature, pH, and substrate concentration affect enzyme activity, and the difference between competitive and non-competitive inhibition. 酶：掌握锁钥模型和诱导契合模型，温度、pH和底物浓度如何影响酶活性，以及竞争性抑制与非竞争性抑制的区别。
Topic 3: Genetics 遗传学
Genetics in IB Biology covers classical Mendelian inheritance and modern molecular genetics. Master monohybrid and dihybrid crosses using Punnett squares, understand the concepts of dominant and recessive alleles, homozygous and heterozygous genotypes, and phenotypes. Be ready for pedigree charts — trace inheritance patterns through family trees and determine whether a trait is autosomal dominant, autosomal recessive, X-linked dominant, or X-linked recessive. IB生物遗传学涵盖经典孟德尔遗传和现代分子遗传学。掌握单基因杂交和双基因杂交的旁氏方格，理解显性隐性等位基因、纯合杂合基因型和表型。系谱图分析是重点题型。
Meiosis: Understand how crossing over in prophase I and independent assortment in metaphase I create genetic variation. Compare meiosis with mitosis in a table format. 减数分裂：理解前期I的交叉互换和中期I的独立分配如何产生遗传变异。用表格对比减数分裂和有丝分裂。
Gene mutations and karyotyping: Know the types of mutations (substitution, insertion, deletion, frameshift) and common chromosomal abnormalities like Down syndrome (trisomy 21). 基因突变与核型分析：掌握突变类型和常见染色体异常。
Topic 4: Ecology 生态学
Ecology connects all biological concepts in real-world contexts. Key areas include food chains and food webs (producers, primary/secondary/tertiary consumers, decomposers), energy flow through trophic levels (only ~10% of energy transfers between levels, which is why food chains rarely exceed 4-5 levels), and nutrient cycling — especially the carbon cycle and nitrogen cycle. 生态学将所有生物学概念与现实世界联系起来。重点包括食物链和食物网、能量在营养级之间的流动，以及碳循环和氮循环。
Population ecology: Understand exponential vs logistic growth curves, carrying capacity, and factors that limit population growth (density-dependent and density-independent). Greenhouse effect and climate change: Know how CO2, methane, and water vapor trap heat, and the consequences of rising global temperatures on ecosystems and biodiversity. 种群生态学：理解指数增长与逻辑斯蒂增长曲线、环境容纳量。温室效应与气候变化：掌握CO2、甲烷和水蒸气如何捕获热量。
Conservation: Know the difference between in situ conservation (protecting species in their natural habitat, e.g. nature reserves) and ex situ conservation (protecting species outside their habitat, e.g. zoos, seed banks). 保护生物学：区分就地保护和迁地保护。
Topic 5: Evolution and Biodiversity 进化与生物多样性
Natural selection is the driving force of evolution. Be able to explain the five key conditions for natural selection: overproduction of offspring, variation within a population, competition for limited resources, survival of the fittest, and inheritance of advantageous traits. Use real examples like antibiotic resistance in bacteria or Darwin's finches. 自然选择是进化的驱动力。能解释自然选择的五个关键条件，用抗生素耐药性细菌或达尔文雀等真实案例。
Evidence for evolution: Fossil records, homologous structures (same structure, different function — e.g. human arm, whale flipper, bat wing), analogous structures (different structure, same function — e.g. bird wing, insect wing), embryology, and DNA sequence comparisons. Speciation: Know allopatric speciation (geographic isolation) and sympatric speciation (reproductive isolation without geographic separation). 进化证据和物种形成是必考内容。
Classification and cladistics: Understand the hierarchical classification system (domain, kingdom, phylum, class, order, family, genus, species) and how to construct and interpret cladograms (phylogenetic trees) based on shared derived characteristics. 分类与分支系统学：理解分类等级和如何构建解读进化树。
Topic 6: Human Physiology 人体生理学
This is the largest single topic in IB Biology, covering six major body systems. Digestion: Know the path of food from mouth to anus, the enzymes involved at each stage (amylase in the mouth, pepsin in the stomach, pancreatic enzymes in the small intestine), and the role of villi and microvilli in absorption. 人体生理学是IB生物最大的单一主题，涵盖六大系统。消化系统：掌握食物从口腔到肛门的路径及每个阶段的酶。
The circulatory system: Understand the structure of the heart (four chambers, valves, SA node as pacemaker), the composition of blood (plasma, red blood cells, white blood cells, platelets), and the double circulation (pulmonary and systemic). The respiratory system: Know how ventilation works (diaphragm and intercostal muscles), gas exchange in alveoli, and how hemoglobin transports oxygen. 循环系统和呼吸系统：心脏结构、血液组成、双循环、肺泡气体交换。
The nervous system: Resting potential and action potential, synaptic transmission (neurotransmitters), and the difference between the central nervous system (CNS) and peripheral nervous system (PNS). The immune system: Non-specific defenses (skin, mucous membranes, phagocytes) and specific defenses (B lymphocytes producing antibodies, T lymphocytes). Know the difference between active and passive immunity. 神经系统与免疫系统同样重要。
SL vs HL: What You Need to Know
SL students cover Topics 1 through 6 above, plus one optional topic (commonly Neurobiology or Biotechnology). The SL exam includes Paper 1 (multiple choice, 45 min), Paper 2 (data-based + short answer + extended response, 1h 15min), and Paper 3 (Section A: data analysis based on a core practical, Section B: optional topic questions, 1h). SL学生涵盖以上Topic 1到6以及一个选修主题。考试包括Paper 1选择题、Paper 2数据分析与简答题、Paper 3实验题与选修题。
HL students study all SL topics PLUS five additional topics: Nucleic Acids (Topic 7), Metabolism and Cell Respiration/Photosynthesis (Topic 8), Plant Biology (Topic 9), Genetics and Evolution (Topic 10), and Animal Physiology (Topic 11). HL Paper 1 is 1 hour (40 questions), Paper 2 is 2h 15min (data-based + extended response), and Paper 3 is 1h 15min. HL学生还需学习额外的五大主题，考试时间更长、题目更深。
Internal Assessment (IA): Both SL and HL students must complete an individual investigation (10 hours, 6-12 pages). This is worth 20% of your final grade. Choose a feasible research question, collect sufficient data (at least 5x5 for statistical tests like chi-squared or t-test), and demonstrate personal engagement and evaluation. 无论是SL还是HL，内部评估IA占最终成绩的20%，选择一个可行的研究问题至关重要。
Exam Tips: How to Score a 7 考试技巧
1. Command terms are everything. IB uses precise command terms: "State" means give a specific name or value without explanation. "Describe" means give a detailed account. "Explain" means give a detailed account with reasons or causes. "Discuss" means give a balanced review with arguments for and against. "Evaluate" means make an appraisal by weighing strengths and limitations. Misreading a command term is the easiest way to lose marks. 指令词决定一切。State只需命名，Explain需解释原因，Evaluate需做评估。读错指令词最容易丢分。
2. Use precise scientific vocabulary. Never write "energy is made" — write "ATP is produced through oxidative phosphorylation." Never write "food is broken down" — write "macromolecules are hydrolyzed by specific enzymes in the alimentary canal." Exact terminology signals to the examiner that you understand the content at the 7 level. 使用精确的科学词汇。不要写能量被制造，要写ATP通过氧化磷酸化产生。
3. Draw, label, and annotate diagrams. IB loves diagrams: DNA structure, action potential graph, heart anatomy, nephron structure, food web, carbon cycle. Practice drawing these from memory. A well-drawn diagram with labels often earns full marks even when the accompanying text is minimal. 多练习画图标注：DNA结构、动作电位、心脏解剖、肾单位等。
4. Master data-based questions. Papers 2 and 3 always include graphs and tables. Calculate percentages, identify trends, state whether data supports a hypothesis, and evaluate the reliability of data (sample size, control variables, systematic vs random errors). 数据分析题是Paper 2和3的固定题型，学会计算百分比、识别趋势、评估数据可靠性。
5. Time management. For Paper 2, allocate roughly 1 minute per mark. For extended response questions (worth 7-9 marks), spend 2-3 minutes planning your answer structure before writing. A clear, well-organized answer with logical flow scores higher than a dense wall of text. 时间管理是关键，Paper 2约1分钟1分，大题先花2到3分钟规划结构再作答。
Recommended Study Resources 推荐学习资源
Textbooks: The Oxford IB Biology Course Companion (Allott and Mindorff) is the gold standard. The Pearson IB Biology textbook is excellent for HL students. Online: BioNinja (free, covers every syllabus point with concise notes), Save My Exams (paid, but excellent revision notes and topic questions), and Khan Academy Biology (free, great for foundational concepts). 推荐教材：Oxford IB Biology Course Companion是黄金标准，BioNinja免费覆盖所有大纲要点。
Past papers: Complete at least 5 years of past papers under timed conditions. The IB question bank (available through your school) is invaluable for topic-specific practice. Focus especially on data-based questions and extended response questions, which carry the most marks. 至少完成5年真题，重点练习数据分析题和长篇论述题。
A simple study schedule that works: Monday — review one topic, Tuesday — answer 15 multiple choice questions on that topic, Wednesday — review a second topic, Thursday — answer data-based questions, Friday — write one extended response under timed conditions, Saturday — review mistakes and revise weak areas, Sunday — rest. Consistency beats cramming every time. 一份有效的学习计划：每天固定时间复习一个主题并做对应练习题，坚持比突击有效得多。
IB Biology rewards deep understanding over rote memorization. When you can explain the why behind each biological process — why the sodium-potassium pump is essential for neuron function, why enzymes denature at high temperatures, why food chains are limited to 4-5 trophic levels — you are ready for the 7. Keep your notes organized by syllabus statement, use active recall instead of passive reading, and never skip the data analysis practice. The exam tests your ability to think like a biologist, not your ability to recite the textbook. IB生物奖励深度理解而非死记硬背。当你能解释每个生物过程背后的为什么时，你就准备好拿7分了。用大纲知识点组织笔记，用主动回忆代替被动阅读，别跳过数据分析练习。
Common Mistakes to Avoid 常见误区避雷
Mistake 1: Confusing "correlation" with "causation." Just because two variables change together does not mean one causes the other. Always consider confounding variables. In data-based questions, the IB frequently tests your ability to distinguish correlation from causation — this is one of the most common pitfalls that separates a 6 from a 7. 误区一：混淆相关性与因果性。两个变量一起变化不代表一个导致另一个，IB常考这个区分。
Mistake 2: Skipping the "compare and contrast" structure. When asked to compare X and Y, use a table or systematically address similarities first, then differences. Randomly listing facts without a clear organizational structure loses marks even if all the science is correct. 误区二：比较类题目缺乏结构。先用表格或系统性地列出相同点再列出不同点。
Mistake 3: Forgetting units and significant figures. In calculations for magnification, actual size, chi-squared tests, or Simpson's diversity index, always include the correct units and round to the appropriate number of significant figures. Every year, exam reports note that students lose easy marks on unit errors. 误区三：忘记单位和有效数字。放大倍数计算、卡方检验、辛普森多样性指数等，永远带上正确单位和有效位数。
Mistake 4: Memorizing without understanding processes. You can memorize that "DNA replication is semi-conservative," but if you cannot explain what semi-conservative means (each new DNA molecule contains one original strand and one newly synthesized strand) and how Meselson and Stahl proved it using nitrogen isotopes, you will not earn full marks. 误区四：只记忆不理解。你背下了DNA是半保留复制，但如果不能解释Meselson和Stahl如何用氮同位素证明，就拿不全分数。
Mistake 5: Neglecting the IA. Many students pour all their energy into exam preparation and leave the IA as an afterthought. But the IA is worth 20% of your final grade — the same weight as an entire exam paper. A strong IA (20+/24) provides a crucial safety net that can absorb a weaker Paper 2 performance. 误区五：忽视IA。IA占最终成绩20%，一份优秀的IA是你考砸某一卷时的安全网。
Practical Work and Required Labs 实验技能与必做实验
IB Biology includes at least 40 hours of practical work at SL and 60 hours at HL, covering seven required practicals. You must be able to: (1) Use a light microscope to investigate cells and measure size using an eyepiece graticule and stage micrometer. (2) Determine the osmolarity of plant tissue by measuring mass change in solutions of different solute concentrations. (3) Investigate factors affecting enzyme activity, such as temperature or pH, using catalase or amylase. (4) Separate photosynthetic pigments using paper chromatography and measure Rf values. (5) Set up an aquatic mesocosm to study ecosystem function over time. (6) Monitor ventilation rate or heart rate in humans in response to exercise. (7) Use databases and computer modeling to investigate the relationship between biodiversity and environmental factors. IB生物实验至少40小时SL和60小时HL，涵盖七项必做实验，从显微镜使用到酶活性探究，每个实验都可能出现在Paper 3的数据分析题中。
For each practical, know the independent variable (what you change), dependent variable (what you measure), and at least three controlled variables (what you keep constant). Be prepared to evaluate the methodology: was the sample size sufficient? Were there enough repeats? What were the sources of systematic error? How could the experiment be improved? 每个实验都要知道自变量、因变量和至少三个控制变量，并能评估实验方法是否完善。
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