Core Knowledge Review for Year 13 CAIE Biology | A2 生物核心知识点梳理

📚 Core Knowledge Review for Year 13 CAIE Biology | A2 生物核心知识点梳理

Year 13 CAIE Biology, covering the A2 syllabus, builds on AS knowledge and deepens understanding of complex biological processes. This article provides a structured review of the core topics, highlighting key concepts, mechanisms, and practical applications essential for examination success. It covers energy transfers, homeostasis, coordination, genetics, evolution, and ecology.

A2 CAIE 生物课程在AS基础上进一步深化对复杂生物过程的理解。本文对核心主题进行结构化梳理，突出关键概念、机制及实际应用，帮助考生把握考试重点。内容涵盖能量传递、稳态、协调、遗传、进化与生态等方面。

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1. Energy and Respiration | 能量与呼吸

Respiration is the process by which living cells release energy from organic molecules, primarily glucose, to produce ATP. The process occurs in several stages: glycolysis in the cytoplasm, the link reaction, the Krebs cycle, and the electron transport chain within the mitochondria.

呼吸作用是活细胞从有机分子（主要是葡萄糖）中释放能量、产生ATP的过程。该过程分为几个阶段：细胞质中的糖酵解、线粒体内的连接反应、克雷布斯循环和电子传递链。

Glycolysis splits one glucose molecule (6C) into two molecules of pyruvate (3C), yielding a net gain of 2 ATP and reducing 2 NAD⁺ to 2 NADH. The link reaction then converts pyruvate into acetyl CoA, releasing CO₂ and further reducing NAD⁺.

糖酵解将一个葡萄糖分子（6碳）分解为两个丙酮酸分子（3碳），净产生2个ATP，并将2个NAD⁺还原为2个NADH。连接反应随后将丙酮酸转化为乙酰辅酶A，释放CO₂并进一步还原NAD⁺。

The Krebs cycle takes place in the mitochondrial matrix and oxidises acetyl groups entirely into CO₂. It generates 2 ATP (via GTP), 6 NADH, and 2 FADH₂ per glucose. The electron transport chain uses the energy from these reduced coenzymes to pump protons across the inner membrane, creating a proton gradient that drives ATP synthase.

克雷布斯循环发生在线粒体基质中，将乙酰基完全氧化为CO₂。每个葡萄糖分子可产生2个ATP（通过GTP）、6个NADH和2个FADH₂。电子传递链利用这些还原辅酶的能量，将质子泵过内膜，形成驱动ATP合酶的质子梯度。

When oxygen is absent, cells may undergo anaerobic respiration. In animals, pyruvate is reduced to lactate; in yeast, it is decarboxylated to ethanol. Both pathways regenerate NAD⁺, enabling glycolysis to continue. The respiratory quotient (RQ = CO₂ produced / O₂ consumed) indicates the substrate used: carbohydrates give an RQ of about 1.0, fats about 0.7, and proteins about 0.9.

缺氧时，细胞可进行无氧呼吸。在动物中，丙酮酸被还原为乳酸；在酵母中，则脱羧成乙醇。两种途径都能再生NAD⁺，保证糖酵解继续进行。呼吸商（RQ = CO₂产生量 / O₂消耗量）可指示底物类型：碳水化合物的RQ约1.0，脂肪约0.7，蛋白质约0.9。

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2. Photosynthesis | 光合作用

Photosynthesis converts light energy into chemical energy in glucose, occurring in chloroplasts. It consists of the light-dependent stage on the thylakoid membranes and the light-independent stage (Calvin cycle) in the stroma.

光合作用在叶绿体中将光能转化为葡萄糖中的化学能。它由类囊体膜上的光依赖阶段和基质中的卡尔文循环（光不依赖阶段）组成。

In the light-dependent stage, light energy splits water (photolysis), producing O₂, protons, and electrons. The electrons pass through carriers, generating ATP via chemiosmosis and reducing NADP⁺ to NADPH. The products ATP and NADPH are then used in the Calvin cycle.

在光依赖阶段，光能分解水（光解），产生O₂、质子和电子。电子通过一系列载体传递，通过化学渗透生成ATP，并将NADP⁺还原为NADPH。产物ATP和NADPH随后用于卡尔文循环。

The Calvin cycle fixes CO₂ using the enzyme RuBisCO, which combines CO₂ with ribulose bisphosphate (RuBP) to form two molecules of glycerate 3-phosphate (GP). GP is reduced to triose phosphate (TP) using ATP and NADPH. Some TP regenerates RuBP, while the rest is used to synthesise glucose, starch, and other carbohydrates.

卡尔文循环利用RuBisCO酶固定CO₂，该酶将CO₂与核酮糖二磷酸（RuBP）结合，生成两个甘油酸-3-磷酸（GP）。GP在ATP和NADPH作用下被还原为磷酸丙糖（TP）。部分TP用于再生RuBP，其余用于合成葡萄糖、淀粉及其他碳水化合物。

C₄ plants and CAM plants have adaptations to reduce photorespiration. C₄ plants spatially separate initial carbon fixation in mesophyll cells from the Calvin cycle in bundle sheath cells. CAM plants open stomata at night to store CO₂ as malate, then perform the Calvin cycle during the day with closed stomata.

C₄植物和CAM植物具有减少光呼吸的适应机制。C₄植物在空间上将叶肉细胞中的初始碳固定与维管束鞘细胞中的卡尔文循环分离。CAM植物夜间打开气孔将CO₂储存为苹果酸，白天在气孔关闭时进行卡尔文循环。

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3. Homeostasis | 稳态

Homeostasis is the maintenance of a stable internal environment through negative feedback mechanisms. These detect deviations from a set point and trigger corrective responses to return the system to normal.

稳态是通过负反馈机制维持稳定内部环境的过程。负反馈可检测偏离设定点的情况，并触发纠正反应，使系统恢复常态。

Blood glucose regulation involves the pancreatic hormones insulin and glucagon. When blood glucose rises, beta cells secrete insulin, promoting glucose uptake and glycogen synthesis in the liver and muscles. When glucose falls, alpha cells release glucagon, stimulating glycogenolysis and gluconeogenesis.

血糖调节涉及胰腺激素胰岛素和胰高血糖素。血糖升高时，β细胞分泌胰岛素，促进肝脏和肌肉摄取葡萄糖并合成糖原。血糖降低时，α细胞释放胰高血糖素，刺激糖原分解和糖异生。

Thermoregulation in mammals is coordinated by the hypothalamus. In cold, vasoconstriction reduces heat loss, shivering generates heat, and increased metabolic rate raises body temperature. In heat, vasodilation increases blood flow to the skin and sweating promotes evaporative cooling.

哺乳动物的体温调节由下丘脑协调。寒冷时，血管收缩减少散热，颤抖产热，代谢率升高使体温上升。炎热时，血管舒张增加皮肤血流，出汗促进蒸发冷却。

The kidneys regulate water balance and excrete nitrogenous waste. In the nephron, ultrafiltration in the Bowman’s capsule is followed by selective reabsorption of glucose, amino acids, and most water in the proximal convoluted tubule. The loop of Henle creates a countercurrent multiplier, establishing a high solute concentration in the medulla. ADH increases the permeability of the collecting duct to water, allowing formation of concentrated urine.

肾脏调节水分平衡并排泄含氮废物。在肾单位中，经过鲍曼囊的超滤作用后，近曲小管选择性地重吸收葡萄糖、氨基酸和大部分水。亨勒袢建立逆流倍增系统，在髓质形成高溶质浓度。抗利尿激素（ADH）增加集合管对水的通透性，使肾脏能产生浓缩尿液。

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4. Nervous Coordination | 神经协调

Nervous coordination uses rapid electrical signals along neurones. The resting potential (around -70 mV) is maintained by the Na⁺/K⁺ pump and differential membrane permeability to K⁺. An action potential is triggered when depolarisation reaches the threshold, causing voltage-gated Na⁺ channels to open; repolarisation follows as K⁺ channels open.

神经协调通过神经元传导快速电信号。静息电位（约-70 mV）由Na⁺/K⁺泵和膜对K⁺的选择性通透维持。当去极化达到阈电位时，电压门控Na⁺通道开放，引发动作电位；随后K⁺通道开放导致复极化。

Impulse propagation occurs via local circuits. In myelinated axons, the action potential ‘jumps’ between nodes of Ranvier (saltatory conduction), greatly increasing speed. At a synapse, the arrival of an action potential causes Ca²⁺ influx, triggering exocytosis of neurotransmitter. The transmitter diffuses across the cleft and binds to receptors on the postsynaptic membrane, generating an excitatory or inhibitory postsynaptic potential.

冲动通过局部电流传导。在有髓轴突中，动作电位在郎飞结之间“跳跃”（跳跃传导），大大加快速度。在突触处，动作电位到达引起Ca²⁺内流，触发神经递质的胞吐作用。递质扩散过间隙并与突触后膜受体结合，产生兴奋性或抑制性突触后电位。

Muscle contraction follows the sliding filament model. Calcium ions bind to troponin, shifting tropomyosin and exposing myosin-binding sites on actin. Myosin heads attach, perform a power stroke using ATP hydrolysis, and pull actin filaments towards the centre of the sarcomere. Repeated cycles shorten the muscle.

肌肉收缩遵循滑丝模型。钙离子与肌钙蛋白结合，使原肌球蛋白移动，暴露肌动蛋白上的肌球蛋白结合位点。肌球蛋白头附着，利用ATP水解进行动力冲程，拉动肌动蛋白丝向肌节中心滑行。重复循环使肌肉缩短。

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5. Hormonal Coordination | 激素协调

Hormones are chemical messengers transported in the blood to target cells with specific receptors, producing slow but prolonged responses. Adrenaline, for example, prepares the body for action by increasing heart rate, dilating bronchioles, and raising blood glucose.

激素是通过血液运输至具有特异性受体的靶细胞的化学信使，产生缓慢但持久的反应。例如，肾上腺素通过增加心率、扩张细支气管和升高血糖，使身体做好行动准备。

Plant coordination depends on plant growth substances. Auxin (IAA) is synthesised in shoot tips and promotes cell elongation. It accumulates on the shaded side of a stem, causing differential growth and phototropism. Auxin also maintains apical dominance by inhibiting lateral bud growth.

植物协调依赖生长物质。生长素（IAA）在茎尖合成，促进细胞伸长。它积累在茎的背阴侧，引起不均匀生长，导致向光性。生长素还通过抑制侧芽生长来维持顶端优势。

Gibberellins stimulate stem elongation and are crucial in seed germination. They promote the synthesis of amylase in the aleurone layer of cereal grains, which hydrolyses starch into sugars for the growing embryo.

赤霉素刺激茎的伸长，在种子萌发中起关键作用。它们促进谷物糊粉层中淀粉酶的合成，将淀粉水解为供胚生长的糖。

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6. Inherited Change | 遗传与变异

Genes are located on chromosomes and exist in different allelic forms. Dominant alleles mask the effect of recessive alleles in heterozygotes, while co-dominance shows both alleles fully expressed. Dihybrid crosses illustrate Mendel’s law of independent assortment, but linked genes on the same chromosome do not assort independently unless crossing over occurs.

基因位于染色体上，存在不同的等位基因形式。显性等位基因在杂合子中遮盖隐性等位基因的效应，共显性则使两个等位基因都完全表达。双因子杂交体现了孟德尔的自由组合定律，但同一条染色体上的连锁基因不发生独立分配，除非发生交叉互换。

Variation can be discontinuous (distinct categories, such as blood groups) or continuous (a range, such as height). The chi-squared (χ²) test is used to compare observed and expected ratios in genetic crosses, determining whether differences are due to chance.

变异可以是非连续的（如血型）或连续的（如身高）。卡方（χ²）检验用于比较遗传杂交中的观察值与期望值，判断差异是否由偶然因素造成。

The Hardy-Weinberg principle states that allele frequencies remain constant from generation to generation in large, randomly mating populations with no selection, mutation, migration, or drift. The equations p + q =

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