📚 IB Biology: High-Frequency Exam Topics Summary | IB 生物：高频考点总结
This article distils the most frequently examined concepts in IB Biology, spanning the Core and AHL topics. Mastering these will help you to secure high marks in both Paper 1 and Paper 2, as well as in data‑response and essay questions. We cover essential cellular processes, molecular genetics, physiology, ecology, and evolution, always linking structure to function.
本文精炼了 IB 生物学中最常考查的概念，涵盖核心与附加高级主题。掌握这些内容有助于你在试卷一、试卷二以及数据分析题和论题中稳拿高分。我们涵盖必需的细胞过程、分子遗传学、生理学、生态学和进化，始终将结构与功能联系起来。
1. Cell Membrane Structure & Transport | 细胞膜结构与物质运输
The fluid mosaic model describes the cell membrane as a phospholipid bilayer with embedded proteins, cholesterol (in animal cells), and glycoproteins. Phospholipids have hydrophilic heads and hydrophobic tails, forming a selectively permeable barrier.
流动镶嵌模型将细胞膜描述为磷脂双分子层，其中嵌有蛋白质、胆固醇（动物细胞）和糖蛋白。磷脂具有亲水头部和疏水尾部，形成选择透过性屏障。
Passive transport includes simple diffusion, facilitated diffusion via channel or carrier proteins, and osmosis. Active transport uses ATP to move substances against their concentration gradient, e.g. the Na⁺/K⁺ pump. Endocytosis and exocytosis transport large molecules via vesicles.
被动运输包括简单扩散、通过通道蛋白或载体蛋白的协助扩散，以及渗透。主动运输利用 ATP 逆浓度梯度转运物质，例如钠钾泵。内吞和胞吐通过囊泡运输大分子。
Exam tip: be able to predict the effect of changes in solute concentration on animal and plant cells (crenation, lysis, plasmolysis, turgidity).
考试提示：要能预测溶质浓度变化对动物和植物细胞的影响（皱缩、胀破、质壁分离、饱满）。
2. Mitosis & Meiosis | 有丝分裂与减数分裂
Mitosis produces two genetically identical diploid daughter cells for growth, repair, and asexual reproduction. The four stages – prophase, metaphase, anaphase, telophase – are followed by cytokinesis. Chromosomes condense, align at the equator, sister chromatids separate, and nuclear envelopes reform.
有丝分裂产生两个遗传相同的二倍体子细胞，用于生长、修复和无性生殖。四个阶段——前期、中期、后期、末期——之后是胞质分裂。染色体浓缩，排列在赤道板上，姐妹染色单体分离，核膜重新形成。
Meiosis involves two divisions, reducing chromosome number by half to produce haploid gametes. In prophase I, homologous chromosomes pair up and crossing over occurs, generating genetic variation. Independent assortment in metaphase I further shuffles alleles.
减数分裂包含两次分裂，将染色体数目减半以产生单倍体配子。在前期 I，同源染色体配对并发生交叉，产生遗传变异。中期 I 的独立分配进一步重组等位基因。
Non‑disjunction in meiosis can lead to aneuploidy, e.g. trisomy 21 (Down syndrome).
减数分裂中的不分离可导致非整倍体，如 21 三体综合征（唐氏综合征）。
3. DNA Replication, Transcription & Translation | DNA 复制、转录与翻译
DNA replication is semi‑conservative. Helicase unwinds the double helix, and DNA polymerase adds complementary nucleotides in the 5′ to 3′ direction. The leading strand is synthesised continuously, while the lagging strand forms Okazaki fragments.
DNA 复制是半保留的。解旋酶解开双螺旋，DNA 聚合酶沿 5′ 到 3′ 方向添加互补核苷酸。前导链连续合成，而后随链形成冈崎片段。
Transcription produces mRNA from a DNA template. RNA polymerase binds to the promoter, unwinds the DNA, and adds RNA nucleotides complementary to the template strand. In eukaryotes, introns are removed by splicing to leave exons.
转录以 DNA 为模板产生 mRNA。RNA 聚合酶与启动子结合，解开 DNA，并按模板链添加互补的 RNA 核苷酸。在真核生物中，内含子通过剪接去除，保留外显子。
Translation occurs on ribosomes. tRNA molecules carry specific amino acids, their anticodons pairing with mRNA codons. The ribosome catalyses peptide bond formation, building a polypeptide chain.
翻译在核糖体上进行。tRNA 分子携带特定氨基酸，其反密码子与 mRNA 密码子配对。核糖体催化肽键形成，构建多肽链。
A gene mutation (substitution, insertion, deletion) may alter the amino acid sequence, with effects ranging from silent to frame‑shift.
基因突变（替换、插入、缺失）可能改变氨基酸序列，其影响从无义到移码不等。
4. Enzymes & Factors Affecting Activity | 酶及其活性影响因素
Enzymes are globular proteins that act as biological catalysts, lowering activation energy. The active site is specific to a substrate, explained by the lock‑and‑key or induced‑fit model. The enzyme‑substrate complex forms, reaction occurs, and products are released.
酶是球状蛋白质，作为生物催化剂降低活化能。活性部位对底物具有特异性，可用锁钥模型或诱导契合模型解释。形成酶‑底物复合物，发生反应，释放产物。
Temperature and pH affect enzyme activity. As temperature rises, kinetic energy increases the rate, but beyond an optimum, denaturation unfolds the enzyme irreversibly. pH alters the charges of the active site, also causing denaturation if too extreme.
温度和 pH 影响酶活性。温度升高时，动能增加反应速率，但超过最适温度后，变性使酶不可逆地伸展。pH 改变活性部位的电荷，若过极端也会导致变性。
Substrate concentration increases rate until saturation (Vmax). Competitive inhibitors resemble the substrate and bind to the active site; non‑competitive inhibitors bind elsewhere, changing the shape of the active site.
底物浓度增加速率直至饱和（Vmax）。竞争性抑制剂与底物相似，结合于活性部位；非竞争性抑制剂结合于别处，改变活性部位形状。
5. Mendelian Genetics & Pedigrees | 孟德尔遗传与家系图
Mendel’s law of segregation states that each individual has two alleles for a gene, which separate during gamete formation. The law of independent assortment applies to genes on different chromosomes.
孟德尔分离定律表明，每个个体的基因有两个等位基因，在配子形成时分离。自由组合定律适用于不同染色体上的基因。
Monohybrid crosses give genotypic ratios e.g. 1:2:1 and phenotypic ratios 3:1 for complete dominance. Codominance and incomplete dominance produce different phenotypes. Sex‑linkage involves genes on the X chromosome, affecting inheritance patterns (e.g. colour blindness).
单基因杂交产生基因型比例如 1:2:1，完全显性下表现型比例 3:1。共显性和不完全显性产生不同表现型。伴性遗传涉及 X 染色体上的基因，影响遗传模式（如色盲）。
Pedigree charts allow inference of inheritance patterns: dominant traits appear in every generation; recessive traits may skip generations; sex‑linked recessive traits occur more frequently in males.
家系图能推断遗传模式：显性性状每代出现；隐性性状可能隔代出现；伴X隐性性状在男性中更常见。
6. Natural Selection & Evolution | 自然选择与进化
Natural selection operates on heritable variation. Individuals with advantageous alleles are more likely to survive and reproduce, increasing the frequency of those alleles in the population. Examples include antibiotic resistance in bacteria and beak shape in Darwin’s finches.
自然选择作用于可遗传的变异。携带有利等位基因的个体更可能生存和繁殖，从而增加该等位基因在种群中的频率。例子包括细菌的抗生素抗性以及达尔文雀的喙形。
Selection can be stabilising, directional, or disruptive, affecting the distribution of phenotypes. Speciation occurs when populations become reproductively isolated – geographically (allopatric) or by behavioural/temporal barriers (sympatric).
选择可以是稳定化、定向或分裂型，影响表现型分布。当种群在地理上（异域）或由行为/时间障碍（同域）导致生殖隔离时，就发生物种形成。
Evidence for evolution includes the fossil record, homologous structures, DNA sequence comparisons, and observed evolution in real time (e.g. peppered moth).
进化证据包括化石记录、同源结构、DNA 序列比较以及实时观察到的进化（如桦尺蛾）。
7. Energy Flow & Nutrient Cycles | 能量流动与物质循环
In ecosystems, energy enters as sunlight, is converted to chemical energy by producers, and flows through food chains. Only about 10% of energy is transferred between trophic levels; the rest is lost through respiration, heat, and undigested material. Pyramids of energy are always upright.
在生态系统中，能量以阳光形式进入，被生产者转化为化学能，然后沿食物链流动。营养级之间仅有约10%的能量传递，其余通过呼吸、热量和未消化物质散失。能量金字塔总是正立的。
The carbon cycle involves photosynthesis, respiration, combustion, and decomposition. Carbon is exchanged between the atmosphere, organisms, oceans, and fossil fuels. Deforestation and burning fossil fuels increase atmospheric CO₂, contributing to climate change.
碳循环涉及光合作用、呼吸作用、燃烧和分解。碳在大气、生物、海洋和化石燃料之间交换。森林砍伐和化石燃料燃烧增加了大气 CO₂，导致气候变化。
The nitrogen cycle relies on nitrogen‑fixing bacteria, nitrifying bacteria, denitrifying bacteria, and decomposers to convert N₂ into usable forms (ammonium, nitrates) and back. Human activities such as fertiliser use disrupt these cycles.
氮循环依赖固氮菌、硝化菌、反硝化菌和分解者将 N₂ 转化为可用形式（铵盐、硝酸盐）并转化回去。化肥使用等人类活动干扰了这些循环。
8. Cardiac Cycle & Blood Vessels | 心动周期与血管
The heart is a double pump. The sinoatrial node (SA node) initiates the heartbeat; electrical impulses spread through the atria, then pass to the atrioventricular node (AV node) and along Purkinje fibres, causing coordinated contraction. The cardiac cycle comprises atrial systole, ventricular systole, and diastole.
心脏是一个双泵。窦房结（SA结）发动心跳；电信号传遍心房，然后传到房室结（AV结），再沿浦肯野纤维传导，引起协调收缩。心动周期包含心房收缩期、心室收缩期和舒张期。
Arteries have thick elastic and muscular walls to withstand high pressure; veins have valves to prevent backflow and thinner walls; capillaries are one cell thick to allow exchange. Blood pressure decreases from arteries to veins.
动脉壁厚且富有弹性和肌肉，以承受高压；静脉有瓣膜防止回流，壁较薄；毛细血管仅一层细胞厚以利于交换。血压从动脉到静脉递减。
Coronary heart disease is caused by atherosclerosis – plaque build‑up in coronary arteries, reducing oxygen supply to the heart muscle. Risk factors include high LDL cholesterol, smoking, and hypertension.
冠心病由动脉粥样硬化引起——冠状动脉内斑块积聚，减少心肌供氧。风险因素包括高LDL胆固醇、吸烟和高血压。
9. Immune Response & Antibodies | 免疫应答与抗体
The immune system distinguishes self from non‑self. Phagocytes (macrophages, neutrophils) carry out non‑specific internal defence by engulfing pathogens. Lymphocytes are responsible for specific immunity: B cells produce antibodies (humoral response), while T cells coordinate cell‑mediated responses and help B cells.
免疫系统分辨自身和非自身。吞噬细胞（巨噬细胞、中性粒细胞）通过吞噬病原体执行非特异性内防御。淋巴细胞负责特异性免疫：B细胞产生抗体（体液应答），T细胞协调细胞介导应答并辅助B细胞。
Antibodies are Y‑shaped proteins with variable regions that bind specific antigens. They neutralise pathogens, agglutinate them, or mark them for destruction. Memory cells remain after an infection, giving long‑term rapid response upon re‑exposure.
抗体是Y形蛋白质，具有与特定抗原结合的可变区。它们中和病原体、使之凝集或标记以被消灭。感染后记忆细胞存留，再接触时提供长期快速应答。
Vaccination triggers an immune response without causing disease, leading to active artificial immunity. Monoclonal antibodies are produced from a single B cell clone, used in diagnosis and therapy.
疫苗接种在不引起疾病的情况下触发免疫应答，产生人工主动免疫。单克隆抗体由单个B细胞克隆产生，用于诊断和治疗。
10. Neurons, Synapses & Action Potential | 神经元、突触与动作电位
Neurons transmit electrical impulses. The resting potential (–70 mV) is maintained by the Na⁺/K⁺ pump and differential membrane permeability. An action potential is generated when a stimulus depolarises the membrane to threshold, opening voltage‑gated Na⁺ channels; K⁺ channels open later, repolarising the membrane.
神经元传递电信号。静息电位（–70 mV）由钠钾泵和膜通透性差异维持。当刺激使膜去极化达到阈电位时，产生动作电位，打开电压门控Na⁺通道；稍后K⁺通道开放，复极化膜。
The impulse jumps between Nodes of Ranvier in myelinated axons (saltatory conduction), increasing speed. At the synapse, neurotransmitter is released from vesicles, diffuses across the cleft, and binds to receptors on the postsynaptic membrane, generating an excitatory or inhibitory postsynaptic potential.
在有髓轴突中，冲动在郎飞结间跳跃（跳跃传导），提高速度。在突触处，神经递质从囊泡释放，扩散跨越间隙，与突触后膜受体结合，产生兴奋性或抑制性突触后电位。
Exam application: explain how anaesthetics or psychoactive drugs affect synaptic transmission (e.g. by blocking receptors or inhibiting reuptake).
考试应用：解释麻醉剂或精神活性药物如何影响突触传递（例如阻断受体或抑制再摄取）。
11. Hormonal Control: Insulin, Glucagon & Thyroxin | 激素调控：胰岛素、胰高血糖素与甲状腺素
Blood glucose regulation is a classic negative feedback loop. After a meal, β‑cells in the islets of Langerhans secrete insulin, which promotes glucose uptake by cells and glycogen synthesis in the liver. When blood glucose falls, α‑cells secrete glucagon, stimulating glycogen breakdown and gluconeogenesis.
血糖调节是一个典型的负反馈回路。餐后，胰岛中的β细胞分泌胰岛素，促进细胞摄取葡萄糖和肝脏合成糖原。血糖下降时，α细胞分泌胰高血糖素，刺激糖原分解和糖异生。
Type I diabetes is due to autoimmune destruction of β‑cells, resulting in no insulin production. Type II diabetes involves insulin resistance. Both lead to hyperglycaemia if untreated.
I型糖尿病源于自身免疫破坏β细胞，不产生胰岛素。II型糖尿病涉及胰岛素抵抗。两者若不治疗都会导致高血糖。
Thyroxin regulates metabolic rate and body temperature. It is released by the thyroid gland in response to TSH from the anterior pituitary, which is in turn regulated by TRH from the hypothalamus. Deficiency causes lethargy, weight gain; excess leads to weight loss and heat intolerance.
甲状腺素调节代谢率和体温。它由甲状腺响应垂体前叶分泌的TSH而释放，TSH又受下丘脑TRH调控。缺乏引起嗜睡、体重增加；过量导致体重减轻和怕热。
12. Plant Biology (HL): Transport & Reproduction | 植物生物学（高级）：运输与繁殖
Xylem transports water and mineral ions from roots to leaves. Transpiration pull, cohesion‑tension, and adhesion facilitate this unidirectional flow. Phloem translocates organic solutes (sucrose) from sources to sinks via pressure flow, requiring active loading at the source.
木质部将水和矿物离子从根运输到叶。蒸腾拉力、内聚力‑张力和附着力促成这种单向流动。韧皮部通过压力流将有机溶质（蔗糖）从源运输到库，需要在源处主动装载。
Flowering plants exhibit a life cycle with alternation of generations. Pollination transfers pollen to the stigma; after fertilisation, the ovule develops into a seed and the ovary into a fruit. Seed germination requires water, oxygen, and suitable temperature; gibberellin triggers amylase production to mobilise stored starch.
有花植物表现出世代交替的生活史。传粉将花粉传到柱头；受精后，胚珠发育为种子，子房发育成果实。种子萌发需要水、氧气和适宜温度；赤霉素触发淀粉酶产生以动用储存的淀粉。
Photoperiodism and phytochrome control flowering according to day length. Phototropism and gravitropism are regulated by auxin (IAA), which promotes cell elongation on the shaded or lower side.
光周期现象和光敏色素根据日照长度控制开花。向光性和向地性由生长素（IAA）调控，生长素促进背光侧或下方侧的细胞伸长。
Published by TutorHao | Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图