📚 Key Concepts in SQA Higher Biology for Year 12 | Year 12 SQA 生物：核心知识点梳理
The SQA Higher Biology course is designed to deepen your understanding of the molecular processes that govern life, from the structure of DNA to the intricate interactions within ecosystems. This article provides a comprehensive review of the core concepts, structured to support Year 12 students in consolidating key knowledge and preparing for assessments. Each section pairs a concise English explanation with a Chinese translation, ensuring clarity for bilingual learners.
SQA Higher 生物课程旨在加深你对支配生命的分子过程的理解，从DNA的结构到生态系统中错综复杂的相互作用。本文对核心概念进行全面梳理，旨在帮助 Year 12 学生巩固关键知识并为评估做好准备。每个部分都将简明的英文解释与中文翻译配对，确保双语学习者能够清晰理解。
1. Structure of DNA and RNA | DNA 与 RNA 的结构
DNA is a double helix composed of nucleotides, each containing deoxyribose sugar, a phosphate group, and a nitrogenous base (adenine, thymine, guanine, or cytosine). The two strands run antiparallel and are held together by hydrogen bonds between complementary base pairs: A–T (2 bonds) and G–C (3 bonds). RNA is typically single-stranded, contains ribose sugar, and uses uracil in place of thymine.
DNA 是一个双螺旋结构，由核苷酸组成，每个核苷酸含有脱氧核糖、磷酸基团和含氮碱基（腺嘌呤、胸腺嘧啶、鸟嘌呤或胞嘧啶）。两条链呈反向平行排列，并通过互补碱基对之间的氢键维持：A–T（2个氢键）和 G–C（3个氢键）。RNA 通常为单链，含有核糖，并用尿嘧啶代替胸腺嘧啶。
The sequence of bases along a DNA strand forms the genetic code, which is organised into genes. Each gene codes for a specific polypeptide. The DNA in eukaryotic cells is tightly packaged around histone proteins to form chromatin, which condenses into chromosomes during cell division. Prokaryotic DNA is circular and not associated with histones.
DNA 链上碱基的排列顺序构成了遗传密码，这些密码被组织成基因。每个基因编码一种特定的多肽。真核细胞中的 DNA 紧密缠绕在组蛋白周围形成染色质，在细胞分裂时浓缩为染色体。原核生物的 DNA 是环状的，且不与组蛋白结合。
2. DNA Replication and PCR | DNA 复制与聚合酶链式反应
DNA replication is a semi-conservative process. The enzyme DNA helicase unwinds the double helix and breaks hydrogen bonds between bases, creating a replication fork. DNA polymerase then adds complementary free nucleotides to the template strands in a 5' to 3' direction. The leading strand is synthesised continuously, while the lagging strand is formed in short fragments (Okazaki fragments), later joined by DNA ligase.
DNA 复制是一个半保留过程。DNA 解旋酶解开双螺旋并断裂碱基间的氢键，形成复制叉。然后 DNA 聚合酶沿 5' 到 3' 方向将互补的游离核苷酸添加到模板链上。前导链是连续合成的，而后随链则以短片段（冈崎片段）的形式形成，随后由 DNA 连接酶连接。
The Polymerase Chain Reaction (PCR) is an in vitro technique used to amplify specific DNA sequences. It involves repeated cycles of heating to denature the DNA (94–96 °C), cooling to allow primers to anneal (50–65 °C), and warming to enable Taq polymerase to extend the new strand (72 °C). PCR is essential in forensics, genetic testing, and disease diagnosis.
聚合酶链式反应（PCR）是一种体外扩增特定 DNA 序列的技术。它包含重复的循环：高温使 DNA 变性（94–96 °C），降温使引物退火（50–65 °C），再升温使 Taq 聚合酶延伸新链（72 °C）。PCR 在法医学、基因检测和疾病诊断中至关重要。
3. Gene Expression: Transcription and Translation | 基因表达：转录与翻译
Gene expression involves two main stages. During transcription, RNA polymerase binds to a promoter region of DNA and synthesises a complementary mRNA strand using the template DNA strand. The mRNA is then processed in eukaryotes: a 5' cap and a poly-A tail are added, and introns are removed by splicing. The mature mRNA exits the nucleus.
基因表达包括两个主要阶段。在转录过程中，RNA 聚合酶与 DNA 的启动子区域结合，以模板 DNA 链为模版合成一条互补的 mRNA 链。随后，真核生物中的 mRNA 经过加工：添加 5' 帽和 poly-A 尾，并通过剪接去除内含子。成熟的 mRNA 离开细胞核。
Translation occurs on ribosomes. The mRNA codon is read, and transfer RNA (tRNA) molecules bring specific amino acids. The tRNA anticodon pairs with the mRNA codon, and amino acids are joined by peptide bonds to form a polypeptide chain. The process includes initiation, elongation, and termination. One gene can give rise to multiple proteins through alternative splicing.
翻译在核糖体上进行。读取 mRNA 的密码子，转运 RNA（tRNA）分子携带特定的氨基酸。tRNA 的反密码子与 mRNA 密码子配对，氨基酸通过肽键连接形成多肽链。该过程包括起始、延伸和终止。一个基因可通过可变剪接产生多种蛋白质。
4. Cellular Respiration | 细胞呼吸
Cellular respiration is the metabolic pathway that releases energy from glucose. Glycolysis occurs in the cytoplasm, splitting glucose (6C) into two pyruvate (3C) molecules, producing a net gain of 2 ATP and 2 NADH. In the presence of oxygen, pyruvate enters the matrix of the mitochondrion, where it is converted to acetyl CoA, releasing CO₂ and NADH.
细胞呼吸是从葡萄糖中释放能量的代谢途径。糖酵解发生在细胞质中，将葡萄糖（6碳）分解为两个丙酮酸（3碳）分子，净生成 2 ATP 和 2 NADH。在有氧条件下，丙酮酸进入线粒体基质，转化为乙酰辅酶 A，并释放 CO₂ 和 NADH。
The acetyl CoA then enters the citric acid cycle (Krebs cycle), which generates ATP, NADH, FADH₂, and CO₂. The electron transport chain, located on the inner mitochondrial membrane, uses NADH and FADH₂ to create a proton gradient, driving ATP synthase to produce a large amount of ATP through oxidative phosphorylation. Oxygen acts as the final electron acceptor, forming water.
乙酰辅酶 A 随后进入柠檬酸循环（克雷布斯循环），产生 ATP、NADH、FADH₂ 和 CO₂。位于线粒体内膜的电子传递链利用 NADH 和 FADH₂ 建立质子梯度，驱动 ATP 合酶通过氧化磷酸化产生大量 ATP。氧气作为最终电子受体，生成水。
5. Photosynthesis | 光合作用
Photosynthesis converts light energy into chemical energy stored in glucose. The light-dependent reactions take place in the thylakoid membranes of chloroplasts. Chlorophyll and other pigments absorb light, exciting electrons that move through an electron transport chain, generating ATP and reduced NADP. Water is split (photolysis), releasing O₂ and protons.
光合作用将光能转化为储存在葡萄糖中的化学能。光依赖反应发生在叶绿体的类囊体膜上。叶绿素和其他色素吸收光，激发电子通过电子传递链，产生 ATP 和还原型 NADP。水被分解（光解），释放出 O₂ 和质子。
The light-independent reactions (Calvin cycle) occur in the stroma. RuBisCO catalyses the fixation of CO₂ to ribulose bisphosphate (RuBP), forming an unstable 6C compound that splits into two 3C glycerate-3-phosphate (GP) molecules. ATP and reduced NADP from the light reactions are used to convert GP into triose phosphate (TP), some of which regenerates RuBP and some is used to synthesise glucose and other carbohydrates.
光不依赖反应（卡尔文循环）发生在基质中。RuBisCO 催化 CO₂ 与核酮糖二磷酸（RuBP）的固定，形成一个不稳定的 6 碳化合物，并分解为两个 3 碳的甘油酸-3-磷酸（GP）分子。光反应提供的 ATP 和还原型 NADP 将 GP 转化为磷酸丙糖（TP），其中一部分用于再生 RuBP，另一部分用于合成葡萄糖和其他碳水化合物。
6. Microbiology and Growth Kinetics | 微生物学与生长动力学
Microorganisms, including bacteria, archaea, and some fungi, can be grown in culture. Growth can be measured by cell counts (viable and total) or by turbidity. The growth of a bacterial population in a closed system follows a predictable curve: lag phase, exponential (log) phase, stationary phase, and death phase.
微生物，包括细菌、古菌和部分真菌，可以在培养基中生长。生长可通过细胞计数（活菌数和总数）或浊度来测量。封闭系统中细菌种群的生长遵循可预测的曲线：延滞期、指数（对数）期、稳定期和衰亡期。
During the exponential phase, the population doubles at regular intervals; the specific growth rate can be calculated. Limiting factors such as nutrient depletion, waste accumulation, and oxygen availability cause the culture to enter stationary phase. Sterile technique and aseptic conditions are essential to prevent contamination.
在指数期，种群数量每隔一定时间翻倍增长；可以计算出比生长速率。营养耗尽、废物累积和氧气供应等限制因素导致培养进入稳定期。无菌技术和无菌条件是防止污染的关键。
7. Nervous System and Neural Communication | 神经系统与神经通讯
Neurons transmit electrical impulses. The resting membrane potential (around –70 mV) is maintained by the sodium-potassium pump and differential permeability. An action potential is triggered when the membrane depolarises past the threshold, causing voltage-gated sodium channels to open. This is followed by repolarisation as potassium channels open and sodium channels inactivate.
神经元传递电冲动。静息膜电位（约 –70 mV）由钠钾泵和差异通透性维持。当膜去极化超过阈值时，触发动作电位，电压门控钠通道开放。随后钾通道开放、钠通道失活，膜发生复极化。
Myelination, provided by Schwann cells in the peripheral nervous system, allows saltatory conduction, greatly increasing the speed of impulse transmission. Neurotransmitters are released from the presynaptic knob into the synaptic cleft and bind to receptors on the postsynaptic membrane, initiating either excitatory or inhibitory potentials.
外周神经系统中施万细胞提供的髓鞘化使得跳跃传导成为可能，大大加快了冲动传递的速度。神经递质从突触前膨大释放到突触间隙，与突触后膜上的受体结合，启动兴奋性或抑制性电位。
8. Immune System and Defence | 免疫系统与防御
The immune system defends against pathogens through non-specific and specific responses. Physical barriers (skin, mucus) and chemical defences (lysozyme, stomach acid) form the first line. The non-specific inflammatory response involves histamine release, vasodilation, and phagocytosis by neutrophils and macrophages.
免疫系统通过非特异性和特异性反应防御病原体。物理屏障（皮肤、黏液）和化学防御（溶菌酶、胃酸）构成第一道防线。非特异性炎症反应涉及组胺释放、血管扩张以及中性粒细胞和巨噬细胞的吞噬作用。
Specific immunity involves lymphocytes. B cells produce antibodies that bind to specific antigens, neutralising toxins and marking pathogens for destruction. T helper cells activate B cells and cytotoxic T cells, which destroy infected host cells. Memory cells provide long-term immunity, the basis of vaccination.
特异性免疫涉及淋巴细胞。B 细胞产生抗体，与特定抗原结合，中和毒素并标记病原体以进行破坏。辅助性 T 细胞激活 B 细胞和细胞毒性 T 细胞，后者破坏受感染的宿主细胞。记忆细胞提供长期免疫力，这是疫苗接种的基础。
9. Mutations and Evolution | 突变与进化
Mutations are changes in the DNA sequence. Point mutations include substitution (silent, missense, nonsense) and frameshift mutations (insertions or deletions). Mutations can be caused by mutagens or errors in replication. They are the ultimate source of genetic variation, providing the raw material for evolution.
突变是 DNA 序列的改变。点突变包括替换（沉默、错义、无义）和移码突变（插入或缺失）。突变可由诱变剂或复制错误引起。它们是遗传变异的最终来源，为进化提供了原材料。
Natural selection acts on heritable variation. Individuals with advantageous alleles are more likely to survive and reproduce, passing these alleles to the next generation. Speciation occurs when populations become reproductively isolated, often by geographic, behavioural, or temporal barriers. Allopatric speciation involves geographic separation; sympatric speciation occurs without geographic isolation.
自然选择作用于可遗传的变异。具有优势等位基因的个体更可能存活和繁殖，将这些等位基因传递给下一代。当种群出现生殖隔离时便形成物种，隔离通常由地理、行为或时间障碍造成。异域物种形成涉及地理分离；同域物种形成则没有地理隔离。
10. Sustainability and Interdependence | 可持续性与相互依存
Ecosystems are dynamic communities of organisms interacting with their abiotic environment. Energy flows through food chains and webs, with significant losses at each trophic level due to respiration, heat, and uneaten materials. Biomass pyramids illustrate the decrease in available energy.
生态系统是由生物体与其非生物环境相互作用的动态群落。能量通过食物链和食物网流动，在每个营养层级因呼吸、散热和未食用的物质而大量损失。生物量金字塔显示了可用能量的逐级递减。
Human activities, such as habitat destruction, pollution, and overexploitation, threaten biodiversity. Conservation strategies include the establishment of protected areas, habitat restoration, and sustainable resource management. The maintenance of genetic diversity is crucial for species' adaptive potential and overall ecosystem resilience.
人类活动，如栖息地破坏、污染和过度开发，威胁着生物多样性。保护策略包括建立保护区、栖息地恢复和可持续资源管理。维持遗传多样性对于物种的适应潜力和整个生态系统的恢复力至关重要。
11. Cellular Transport and the Cell Membrane | 细胞运输与细胞膜
The cell membrane is described by the fluid mosaic model, consisting of a phospholipid bilayer with embedded proteins, cholesterol, and glycolipids. It is selectively permeable, allowing small non-polar molecules to diffuse freely. Membrane proteins serve as channels, carriers, or pumps for facilitated diffusion and active transport.
细胞膜用流动镶嵌模型描述，由磷脂双分子层及镶嵌的蛋白质、胆固醇和糖脂组成。它是选择性通透的，允许小的非极性分子自由扩散。膜蛋白作为通道、载体或泵，介导协助扩散和主动运输。
Active transport uses energy (ATP) to move substances against their concentration gradient, for example the sodium-potassium pump. Endocytosis and exocytosis are bulk transport mechanisms for large molecules. Water moves by osmosis from a region of higher water potential to one of lower water potential; animal cells can burst (lyse) in hypotonic solutions, while plant cells become turgid.
主动运输利用能量（ATP）将物质逆浓度梯度移动，例如钠钾泵。内吞作用和胞吐作用是大分子的大量运输机制。水通过渗透作用从水势较高的区域向水势较低的区域移动；动物细胞在低渗溶液中会胀破（裂解），而植物细胞则变为坚挺。
12. Experimental Design and Scientific Literacy | 实验设计与科学素养
Higher Biology assessments require understanding key scientific skills: identifying variables (independent, dependent, and controlled), formulating null hypotheses, and selecting appropriate statistical tests such as the t-test or chi-squared test. Data presentation, including graphs and error bars, must be accurate and clearly labelled.
Higher 生物评估要求掌握关键的科学技能：识别变量（自变量、因变量和受控变量），提出零假设，并选择合适的统计检验方法，如 t 检验或卡方检验。数据展示，包括图表和误差线，必须准确并清楚标注。
Critical evaluation involves discussing reliability, validity, and sources of error. Ethical considerations are paramount when working with living organisms. Informed consent, minimising harm, and respecting environmental integrity are fundamental principles guiding biological research.
批判性评估包括讨论可靠性、有效性和误差来源。在使用活体生物时，伦理考量至关重要。知情同意、尽量减少伤害以及尊重环境完整性是指导生物研究的基本原则。
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