📚 A-Level AQA Biology: End-of-Term Revision Guide | A-Level AQA 生物：期末复习提纲
This revision guide provides a comprehensive summary of the key topics covered in the AQA A-level Biology specification. It is designed to support your end-of-term review by highlighting essential concepts, processes, and terminology. Each section pairs a concise English explanation with a Chinese translation to reinforce bilingual understanding.
本复习提纲全面概括了 AQA A-level 生物学大纲的核心主题，旨在通过突出基本概念、关键过程和重要术语来支持你的期末复习。每个部分均以简洁的英文解释与中文译文配对呈现，以巩固双语理解。
1. Biological Molecules | 生物分子
Carbohydrates are composed of monosaccharides such as glucose (C₆H₁₂O₆). Disaccharides (e.g. sucrose) and polysaccharides (e.g. starch, glycogen, cellulose) are formed by glycosidic bonds through condensation reactions.
碳水化合物由单糖如葡萄糖 (C₆H₁₂O₆) 组成。双糖（例如蔗糖）与多糖（例如淀粉、糖原、纤维素）通过缩合反应形成的糖苷键连接。
Lipids include triglycerides, which consist of one glycerol molecule bonded to three fatty acids via ester bonds. Phospholipids have a hydrophilic phosphate head and two hydrophobic fatty acid tails, making them essential for membrane structure.
脂质包括甘油三酯，由一个甘油分子与三个脂肪酸通过酯键连接而成。磷脂具有亲水的磷酸头部和两个疏水的脂肪酸尾部，这对膜结构至关重要。
Proteins are polymers of amino acids joined by peptide bonds. Their primary structure is the sequence of amino acids; secondary structures include α-helices and β-pleated sheets; tertiary structure is the 3D folding determined by hydrogen, ionic, and disulfide bonds; quaternary structure involves multiple polypeptide chains.
蛋白质是由氨基酸通过肽键连接而成的聚合物。一级结构是氨基酸序列；二级结构包括 α-螺旋和 β-折叠；三级结构由氢键、离子键和二硫键决定的三维折叠；四级结构涉及多条多肽链。
Nucleic acids DNA and RNA are polynucleotides. DNA stores genetic information using the bases adenine (A), thymine (T), cytosine (C), and guanine (G), paired via A–T and C–G hydrogen bonds. RNA contains uracil (U) instead of thymine and is involved in protein synthesis.
核酸 DNA 和 RNA 是多核苷酸。DNA 利用碱基腺嘌呤 (A)、胸腺嘧啶 (T)、胞嘧啶 (C) 和鸟嘌呤 (G) 储存遗传信息，通过 A–T 和 C–G 氢键配对。RNA 含尿嘧啶 (U) 替代胸腺嘧啶，参与蛋白质合成。
2. Cell Structure and Function | 细胞结构与功能
Prokaryotic cells (e.g. bacteria) lack a membrane-bound nucleus and organelles such as mitochondria, whereas eukaryotic cells (animal, plant, fungal) have a distinct nucleus and membrane-bound organelles.
原核细胞（如细菌）缺乏膜包被的细胞核和线粒体等细胞器，而真核细胞（动物、植物、真菌）具有明显的细胞核和膜包被的细胞器。
Key organelles: mitochondria (site of aerobic respiration), chloroplasts (site of photosynthesis), endoplasmic reticulum (rough ER for protein synthesis, smooth ER for lipid synthesis), Golgi apparatus (modifies and packages proteins), lysosomes (digestion), ribosomes (protein synthesis).
关键细胞器：线粒体（有氧呼吸场所）、叶绿体（光合作用场所）、内质网（粗面内质网参与蛋白质合成，滑面内质网参与脂质合成）、高尔基体（修饰和包装蛋白质）、溶酶体（消化）、核糖体（蛋白质合成）。
Viruses are acellular and contain genetic material (DNA or RNA) enclosed in a protein coat. They replicate only inside host cells. Electron microscopes reveal ultrastructure and distinguish organelles.
病毒是非细胞结构，含有包裹在蛋白质外壳内的遗传物质（DNA 或 RNA）。它们只能在宿主细胞内复制。电子显微镜揭示超微结构并分辨细胞器。
3. Cell Membranes and Transport | 细胞膜与运输
The fluid mosaic model describes the membrane as a phospholipid bilayer with embedded proteins, cholesterol, and glycoproteins. Phospholipids can move laterally, and the membrane is selectively permeable.
流动镶嵌模型将膜描述为具有嵌入蛋白质、胆固醇和糖蛋白的磷脂双分子层。磷脂可横向移动，膜具有选择透过性。
Diffusion is the passive movement of molecules from high to low concentration. Facilitated diffusion uses channel or carrier proteins. Osmosis is the movement of water across a partially permeable membrane from a region of higher water potential to lower water potential.
扩散是分子从高浓度到低浓度的被动运动。易化扩散利用通道蛋白或载体蛋白。渗透是水通过部分通透膜从高水势区域向低水势区域的运动。
Active transport moves substances against their concentration gradient using energy from ATP, via carrier proteins. Co-transport couples the movement of one substance (e.g. glucose) with the movement of Na⁺ down its electrochemical gradient.
主动运输利用载体蛋白和 ATP 提供的能量，逆浓度梯度移动物质。协同运输将一种物质（如葡萄糖）的运动与 Na⁺ 沿其电化学梯度的运动相耦联。
4. Enzymes | 酶
Enzymes are biological catalysts that lower activation energy by forming an enzyme–substrate complex. The active site has a specific shape complementary to the substrate, explained by the lock-and-key model and the induced-fit model.
酶是生物催化剂，通过形成酶-底物复合物降低活化能。活性位点具有与底物互补的特定形状，可由锁钥模型和诱导契合模型解释。
Factors affecting enzyme activity include temperature (increase up to optimum, then denaturation), pH (optimum pH, extreme pH denatures), enzyme concentration, and substrate concentration (which can reach Vmax).
影响酶活性的因素包括温度（升高至最适温度后变性）、pH（最适 pH，极端 pH 导致变性）、酶浓度和底物浓度（可达到 Vmax）。
Competitive inhibitors have a similar shape to the substrate and compete for the active site; their effect can be overcome by increasing substrate concentration. Non-competitive inhibitors bind to an allosteric site, altering the active site shape and cannot be overcome by excess substrate.
竞争性抑制剂形状与底物相似，竞争活性位点；增加底物浓度可克服其效应。非竞争性抑制剂与别构位点结合，改变活性位点形状，过量底物无法克服。
5. The Immune System | 免疫系统
Non-specific defences include physical barriers (skin, mucus) and phagocytosis. Phagocytes engulf pathogens into a phagosome, which fuses with lysosomes where enzymes digest the pathogen.
非特异性防御包括物理屏障（皮肤、黏液）和吞噬作用。吞噬细胞将病原体吞入吞噬体，吞噬体与溶酶体融合，酶消化病原体。
Specific immunity involves T lymphocytes (cell-mediated) and B lymphocytes (humoral). Helper T cells release cytokines that activate cytotoxic T cells and B cells. B cells differentiate into plasma cells that produce antibodies and memory cells for long-term immunity.
特异性免疫涉及 T 淋巴细胞（细胞免疫）和 B 淋巴细胞（体液免疫）。辅助 T 细胞释放细胞因子，激活细胞毒性 T 细胞和 B 细胞。B 细胞分化为产生抗体的浆细胞和提供长期免疫的记忆细胞。
Antibodies are Y-shaped proteins with variable regions that bind specific antigens, forming an antigen–antibody complex, leading to agglutination and neutralisation. Vaccination introduces antigens to stimulate the production of memory cells without causing disease. Monoclonal antibodies are used in targeting cancer cells and pregnancy testing. HIV infects and destroys helper T cells, weakening the immune system.
抗体是具有可变区的 Y 形蛋白质，可变区与特定抗原结合形成抗原-抗体复合物，导致凝集和中和。疫苗接种引入抗原，在不致病的情况下刺激记忆细胞的产生。单克隆抗体用于靶向癌细胞和妊娠检测。HIV 感染并破坏辅助 T 细胞，削弱免疫系统。
6. Gas Exchange and Mass Transport | 气体交换与物质运输
In humans, gas exchange occurs in alveoli, which have a large surface area, thin walls (one cell thick), and a steep concentration gradient maintained by ventilation and blood flow. Oxygen binds haemoglobin in red blood cells; the oxygen–haemoglobin dissociation curve shows the Bohr effect (shifted right by increased CO₂ or temperature).
人体的气体交换发生在肺泡中，肺泡具有大面积、薄壁（单细胞厚），并通过通气和血流维持陡峭的浓度梯度。氧气与红细胞中的血红蛋白结合；氧解离曲线显示波尔效应（CO₂ 升高或温度升高使曲线右移）。
The heart is a double pump: the right ventricle pumps deoxygenated blood to the lungs; the left ventricle pumps oxygenated blood to the body. Key vessels: aorta, vena cava, pulmonary artery, pulmonary vein. Cardiac cycle includes atrial systole, ventricular systole, and diastole. The SAN, AVN, and Purkinje fibres coordinate contraction.
心脏是双泵：右心室将缺氧血泵送至肺部；左心室将氧合血泵送至全身。主要血管：主动脉、腔静脉、肺动脉、肺静脉。心动周期包括心房收缩、心室收缩和舒张。SAN、AVN 和浦肯野纤维协调收缩。
In plants, xylem transports water and minerals via transpiration pull, cohesion, and adhesion. Phloem transports sucrose by mass flow from sources to sinks (translocation), explained by the pressure-flow hypothesis.
在植物中，木质部通过蒸腾拉力、内聚力和附着力运输水和矿物质。韧皮部通过集流从源到汇运输蔗糖（运输），可由压力流动假说解释。
7. DNA, Genes and Protein Synthesis | DNA、基因与蛋白质合成
helicase (unwinding strands) and DNA polymerase (adding complementary nucleotides in the 5'→3' and Stahl’s experiment confirmed semi-conservative replication using N¹⁵ and N¹⁴ isotopes.
DNA 复制是半保留的，由 DNA 解旋酶（解开链）和 DNA 聚合酶（沿 5'→3' 方向添加互补核苷酸）催化。Meselson 和 Stahl 的实验利用 N¹⁵ 和 N¹⁴ 同位素证实了半保留复制。
Transcription produces mRNA using RNA polymerase, which reads the template strand of DNA. In eukaryotes, pre-mRNA is spliced to remove introns. Translation occurs on ribosomes: tRNA molecules carry specific amino acids, and anticodons bind to mRNA codons, forming a polypeptide chain.
转录利用 RNA 聚合酶读取 DNA 模板链产生 mRNA。在真核生物中，前体 mRNA 被剪接以去除内含子。翻译在核糖体上进行：tRNA 分子携带特定的氨基酸，反密码子与 mRNA 密码子结合，形成多肽链。
Gene mutations include substitution (may cause silent, missense, or nonsense mutations) and insertion/deletion, which can cause frameshifts. Mutagenic agents increase mutation rate.
基因突变包括置换（可能导致沉默、错义或无义突变）和插入/缺失，后者可引起移码。诱变剂增加突变率。
8. Genetic Diversity and Adaptation | 遗传多样性与适应
Meiosis produces haploid gametes through two divisions. Crossing over in prophase I and independent assortment in metaphase I generate genetic variation. Random fertilisation further increases diversity.
减数分裂通过两次分裂产生单倍体配子。前期 I 的交叉和中期 I 的独立分配产生遗传变异。随机受精进一步增加多样性。
Variation arises from mutation and sexual reproduction. Natural selection acts on phenotypic variation; individuals with advantageous alleles are more likely to survive and reproduce, increasing allele frequency in the gene pool (directional, stabilising, or disruptive selection).
变异源于突变和有性生殖。自然选择作用于表型变异；具有有利等位基因的个体更易存活和繁殖，增加其等位基因在基因库中的频率（定向、稳定化或分裂选择）。
Allopatric speciation occurs when populations are geographically isolated, preventing gene flow. Over time, different selection pressures lead to reproductive isolation and the formation of new species. Sympatric speciation can occur through mechanisms like polyploidy.
异域物种形成发生在种群地理隔离、阻止基因流动时。随着时间的推移，不同的选择压导致生殖隔离和新物种形成。同域物种形成可通过多倍体等机制发生。
9. Photosynthesis and Respiration | 光合作用与呼吸作用
Photosynthesis consists of the light-dependent reactions (thylakoid membranes) and the light-independent reactions (Calvin cycle in the stroma). Light energy splits water (photolysis), producing O₂, ATP, and reduced NADP. The Calvin cycle fixes CO₂ into glycerate 3-phosphate (GP) which is reduced to triose phosphate (TP) using ATP and reduced NADP; some TP regenerates ribulose bisphosphate (RuBP).
光合作用包括光依赖反应（类囊体膜）和光不依赖反应（基质中的卡尔文循环）。光能分解水（光解），产生 O₂、ATP 和还原性 NADP。卡尔文循环将 CO₂ 固定为甘油酸-3-磷酸 (GP)，GP 利用 ATP 和还原性 NADP 还原为磷酸丙糖 (TP)；部分 TP 再生成核酮糖二磷酸 (RuBP)。
ner mitochondrial membrane). Overall equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP).
有氧呼吸分为四个阶段：糖酵解（细胞质）、链接反应（基质）、克氏循环（基质）和氧化磷酸化（线粒体内膜）。总方程式：C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 能量 (ATP)。
Anaerobic respiration in animals produces lactate (lactic acid) and in plants/fungi produces ethanol and CO₂. Both regenerate NAD⁺ from reduced NAD, allowing glycolysis to continue producing a small yield of ATP.
动物无氧呼吸产生乳酸，植物/真菌产生乙醇和 CO₂。两种方式均从还原性 NAD 再生 NAD⁺，使糖酵解得以继续产生少量 ATP。
10. Energy and Ecosystems | 能量与生态系统
ry consumers → tertiary consumers. Energy is transferred between levels, but only about 10% ed on; the rest is lost as heat through respiration, inedible parts, or undigested matter.
食物链显示营养级：生产者 → 初级消费者 → 次级消费者 → 三级消费者。能量在营养级间传递，但仅约 10% 被传递；其余通过呼吸以热的形式散失、不可食部分或未消化物质而损失。
primary production (GPP) − plant respiration (R). NPP represents the energy available to the next trophic level. Pyramids of energy, biomass, and numbers can represent ecological relationships.
净初级生产力 (NPP) = 总初级生产力 (GPP) − 植物呼吸 (R)。NPP 代表可供下一个营养级利用的能量。能量锥、生物量锥和数量锥可表示生态关系。
The carbon cycle involves photosynthesis, respiration, decomposition, combustion, and feeding. The nitrogen cycle includes nitrogen fixation (by Rhizobium, Azotobacter), ammonification, nitrification (Nitrosomonas, Nitrobacter), and denitrification.
碳循环涉及光合作用、呼吸作用、分解、燃烧和摄食。氮循环包括固氮作用（根瘤菌、自生固氮菌）、氨化作用、硝化作用（亚硝化单胞菌、硝化杆菌）和反硝化作用。
11. Response to Stimuli and Nervous Coordination | 刺激反应与神经协调
Receptors detect stimuli and generate generator potentials. The Pacinian corpuscle detects pressure changes via stretch-mediated sodium channels. Photoreceptors in the eye include rods (sensitive in dim light, detect black/white) and cones (colour vision, high acuity).
感受器检测刺激并产生发生器电位。环层小体通过牵张介导的钠通道检测压力变化。眼内的光感受器包括视杆细胞（在弱光下敏感，检测黑白）和视锥细胞（色觉，高敏锐度）。
Resting potential (−70 mV) is maintained by the Na⁺/K⁺ pump and differential permeability. An action potential is triggered by depolarisation past threshold; Na⁺ channels open (depolarisation), then K⁺ channels open (repolarisation). The refractory period ensures unidirectional propagation. Myelination (Schwann cells) speeds up impulses via saltatory conduction.
静息电位 (−70 mV) 由 Na⁺/K⁺ 泵和差异通透性维持。动作电位由去极化超过阈值引发；Na⁺ 通道开放（去极化），随后 K⁺ 通道开放（复极化）。不应期确保单向传导。髓鞘化（施万细胞）通过跳跃传导加快冲动。
Synaptic transmission involves Ca²⁺ entry into the presynaptic knob, fusion of vesicles, release of neurotransmitter (e.g. acetylcholine), binding to receptors on the postsynaptic membrane, and generation of EPSPs or IPSPs. Acetylcholinesterase breaks down acetylcholine in the cleft.
突触传递涉及 Ca²⁺ 进入突触小体、囊泡融合、神经递质（如乙酰胆碱）释放、与突触后膜受体结合，并产生 EPSP 或 IPSP。乙酰胆碱酯酶在间隙中分解乙酰胆碱。
Skeletal muscle contraction follows the sliding filament theory: myosin heads bind actin, pull, and release, powered by ATP. The sarcoplasmic reticulum releases Ca²⁺ which exposes binding sites on actin.
骨骼肌收缩遵循滑丝理论：肌球蛋白头与肌动蛋白结合、牵拉并释放，由 ATP 供能。肌浆网释放 Ca²⁺，暴露肌动蛋白上的结合位点。
12. Homeostasis and Gene Expression | 稳态与基因表达
Homeostasis involves negative feedback mechanisms. Blood glucose regulation: insulin (β-cells of islets of Langerhans) lowers glucose by increasing uptake and glycogenesis; glucagon (α-cells) raises glucose by glycogenolysis and gluconeogenesis. Insulin secretion involves K⁺ and Ca²⁺ channels.
稳态涉及负反馈机制。血糖调节：胰岛素（胰岛 β 细胞）通过增加摄取和糖原生成降低血糖；胰高血糖素（α 细胞）通过糖原分解和糖异生升高血糖。胰岛素分泌涉及 K⁺ 和 Ca²⁺ 通道。
Thermoregulation: hypothalamus detects blood temperature and coordinates responses. In heat, vasodilation and sweating; in cold, vasoconstriction, shivering, and increased metabolic rate (thyroxine).
体温调节：下丘脑检测血液温度并协调反应。热时血管扩张和出汗；冷时血管收缩、战栗和代谢率增加（甲状腺素）。
Gene expression is regulated at the transcriptional level by transcription factors that bind to promoter regions. Oestrogen can diffuse into cells and bind to a receptor, forming a complex that acts as a transcription factor, illustrating hormonal gene regulation.
基因表达在转录水平受转录因子调控，转录因子与启动子区域结合。雌激素可扩散入细胞并与受体结合，形成充当转录因子的复合物，这体现了激素基因调控。
Epigenetic modifications (methylation, acetylation) alter gene expression without changing the DNA sequence. RNA interference (siRNA) can degrade mRNA or inhibit translation. These mechanisms are important in development and disease.
表观遗传修饰（甲基化、乙酰化）在不改变 DNA 序列的情况下改变基因表达。RNA 干扰 (siRNA) 可降解 mRNA 或抑制翻译。这些机制在发育和疾病中至关重要。
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