📚 AQA A-Level Biology: Key Animal Topics Revision | AQA A-Level 生物：动物考点精讲
This comprehensive revision guide covers the essential animal biology topics examined in the AQA A-Level Biology specification. From eukaryotic cell ultrastructure to complex behaviours, each section pairs core explanations with exam-focused insights, helping you master concepts for Paper 1, Paper 2 and the synoptic essay.
这份综合复习指南涵盖了 AQA A-Level 生物考试大纲中的核心动物生物学主题。从真核细胞的超微结构到复杂的行为学，每个小节都将核心解释与应试要点配对，帮助你掌握用于试卷一、试卷二以及综合性论文的概念。
1. Animal Cell Structure | 动物细胞结构
Animal cells are eukaryotic and possess a true nucleus enclosed by a double membrane with nuclear pores, allowing controlled exchange of mRNA and proteins.
动物细胞是真核细胞，拥有真正的细胞核，由具有核孔的双层膜包裹，可控制 mRNA 和蛋白质的交换。
Key organelles include mitochondria with highly folded cristae for aerobic respiration, rough endoplasmic reticulum studded with ribosomes for protein synthesis, and the Golgi apparatus that modifies and packages proteins into vesicles.
关键的细胞器包括具有高度折叠嵴的线粒体（用于有氧呼吸）、附着核糖体的粗面内质网（用于蛋白质合成），以及修饰蛋白质并将其包装进囊泡的高尔基体。
Animal cells lack a cell wall and chloroplasts; instead they contain centrioles that organise the spindle fibres during mitosis, and lysosomes containing hydrolytic enzymes for intracellular digestion.
动物细胞没有细胞壁和叶绿体；它们含有中心粒，可在有丝分裂中组织纺锤丝，并含有含水解酶的溶酶体用于胞内消化。
2. Gas Exchange Systems | 气体交换系统
Gas exchange in animals relies on specialised surfaces that are thin, moist, and have a large surface area, such as the alveoli in mammalian lungs or the filamentous gills in fish.
动物的气体交换依赖于薄、湿润且表面积大的特化表面，例如哺乳动物肺中的肺泡或鱼类丝状的鳃。
In humans, air travels down the trachea, bronchi and bronchioles to reach alveolar sacs. Oxygen diffuses across the squamous epithelial cells and endothelial cells of capillaries down a concentration gradient.
在人体中，空气顺着气管、支气管和细支气管下行到达肺泡囊。氧气顺着浓度梯度通过鳞状上皮细胞和毛细血管内皮细胞扩散。
Countercurrent flow in fish gills maintains a steep oxygen concentration gradient along the entire length of the gill lamellae, maximising oxygen uptake even from water with low O₂ concentration.
鱼鳃中的逆流交换在整个鳃小片长度上维持了陡峭的氧浓度梯度，即使在 O₂ 浓度较低的水中也能最大限度地摄取氧气。
3. Circulatory Systems | 循环系统
Animals possess either an open circulatory system (e.g. insects) where haemolymph bathes organs directly, or a closed system (e.g. mammals) where blood is confined to vessels, allowing higher pressure and faster flow.
动物要么拥有开放的循环系统（如昆虫），血淋巴直接浸润器官；要么拥有封闭的系统（如哺乳动物），血液限制在血管内，能产生更高的压力和更快的流速。
| Feature | Open System | Closed System |
|---|---|---|
| Blood fluid | Haemolymph | Blood |
| Vessels | Few, open-ended | Arteries, veins, capillaries |
| Pressure | Low | High |
| Efficiency | Suitable for low metabolic rates | Supports high metabolic demands |
The mammalian heart is a double pump; the right side forces blood to the lungs (pulmonary circuit) and the left side delivers oxygenated blood to the body (systemic circuit). Atrioventricular and semilunar valves prevent backflow.
哺乳动物的心脏是一个双泵；右侧将血液压送至肺部（肺循环），左侧将含氧血液输送到全身（体循环）。房室瓣和半月瓣防止血液倒流。
4. Digestion and Absorption | 消化与吸收
Digestion breaks down large, insoluble polymers into small, soluble monomers. Carbohydrases (e.g. amylase, maltase) hydrolyse starch into glucose; proteases break proteins into amino acids; lipases with bile salts emulsify lipids into fatty acids and monoglycerides.
消化将大的不溶性聚合物分解为小的可溶性单体。糖酶（如淀粉酶、麦芽糖酶）将淀粉水解为葡萄糖；蛋白酶将蛋白质分解为氨基酸；脂肪酶与胆汁盐一起将脂质乳化为脂肪酸和单甘油酯。
The small intestine has finger-like villi and microvilli on enterocytes, massively increasing surface area. Sodium-dependent co-transport proteins actively absorb glucose and amino acids, while fatty acids diffuse and are reformed into chylomicrons in the lacteal.
小肠具有指状绒毛和肠上皮细胞上的微绒毛，极大地增加了表面积。钠依赖的协同转运蛋白主动吸收葡萄糖和氨基酸，而脂肪酸经扩散进入并被重新合成为乳腺管中的乳糜微粒。
5. Nervous Coordination | 神经协调
Neurones generate and transmit electrical impulses. A resting potential of around −70 mV is maintained by the Na⁺/K⁺ pump, which exports 3 Na⁺ for every 2 K⁺ imported, and by the greater permeability of the membrane to K⁺.
神经元产生并传导电冲动。静息电位约为 −70 mV，由 Na⁺/K⁺ 泵（每泵出 3 个 Na⁺ 即泵入 2 个 K⁺）以及膜对 K⁺ 的通透性较高来维持。
When a stimulus causes depolarisation to threshold, voltage-gated Na⁺ channels open, Na⁺ rushes in, and the membrane potential spikes to about +40 mV. Repolarisation occurs as K⁺ channels open and Na⁺ channels inactivate.
当刺激使去极化达到阈值，电压门控 Na⁺ 通道打开，Na⁺ 涌入，膜电位飙升至约 +40 mV。随着 K⁺ 通道开放和 Na⁺ 通道失活，复极化发生。
The action potential propagates by local circuits, and in myelinated axons saltatory conduction occurs at nodes of Ranvier, speeding transmission.
动作电位通过局部电流传播；在有髓轴突中，跳跃传导在郎飞结处发生，加快了传递速度。
6. Muscle Contraction | 肌肉收缩
Skeletal muscle is composed of myofibrils containing repeating sarcomeres. The sliding filament theory states that contraction results from actin (thin) filaments sliding over myosin (thick) filaments, shortening the sarcomere.
骨骼肌由含有重复肌节的肌原纤维组成。滑丝学说认为收缩是由于肌动蛋白（细）丝在肌球蛋白（粗）丝上滑动，从而缩短肌节。
When Ca²⁺ binds to troponin, the tropomyosin complex moves away from the myosin-binding sites on actin. Myosin heads with bound ADP and Pi attach, perform a power stroke, release ADP + Pi, and detach when ATP binds.
当 Ca²⁺ 与肌钙蛋白结合，原肌球蛋白复合体从肌动蛋白上的肌球蛋白结合位点移开。带有 ADP 和 Pi 的肌球蛋白头附着，执行力冲程，释放 ADP+Pi，在 ATP 结合时脱离。
ATP is essential both for the power stroke and for detaching myosin heads; without ATP, rigor mortis occurs.
ATP 对于力冲程和肌球蛋白头的脱离都至关重要；缺乏 ATP 会导致尸僵。
7. Hormonal Control and Homeostasis | 激素调控与稳态
Hormones are chemical messengers secreted by endocrine glands into the bloodstream, targeting specific cells with complementary receptors. They coordinate slow, long-lasting responses such as blood glucose regulation.
激素是由内分泌腺分泌到血液中的化学信使，作用于具有互补受体的特定靶细胞。它们协调缓慢、持久的反应，例如血糖调节。
When blood glucose rises, pancreatic β-cells release insulin, which stimulates hepatocytes and muscle cells to take up glucose and convert it to glycogen (glycogenesis).
当血糖升高，胰岛 β 细胞释放胰岛素，刺激肝细胞和肌细胞摄取葡萄糖并将其转化为糖原（糖原生成）。
In hypoglycaemia, α-cells release glucagon promoting glycogenolysis and gluconeogenesis. Adrenaline and the second messenger model using cyclic AMP also amplify the cellular response.
在低血糖时，α 细胞释放胰高血糖素，促进糖原分解和糖异生。肾上腺素和利用环磷酸腺苷的第二信使模型也能放大细胞反应。
8. Osmoregulation and the Kidney | 渗透调节与肾脏
The nephron is the functional unit of the kidney. Ultrafiltration in the Bowman’s capsule separates small molecules (water, glucose, ions, urea) from blood cells and plasma proteins due to the high hydrostatic pressure in the glomerulus.
肾单位是肾脏的功能单位。由于肾小球中的高静水压，鲍曼氏囊中的超滤作用将小分子（水、葡萄糖、离子、尿素）与血细胞和血浆蛋白分离。
Selective reabsorption occurs mainly in the proximal convoluted tubule: Na⁺ is actively transported out, and glucose co-transported back, followed by osmotic reabsorption of water.
选择性重吸收主要发生在近曲小管：Na⁺ 被主动转运出去，葡萄糖被协同转运回来，随后水通过渗透作用被重吸收。
In the loop of Henle, a countercurrent multiplier system creates a high medullary osmotic pressure, enabling the collecting duct to reabsorb water under the control of antidiuretic hormone (ADH).
在髓袢中，逆流倍增系统建立了高的髓质渗透压，使集合管能够在抗利尿激素 (ADH) 的控制下重吸收水分。
9. The Immune System | 免疫系统
The non-specific immune response includes physical barriers, phagocytosis by neutrophils and macrophages, and inflammation. Macrophages present antigens on MHC Class II to activate specific immunity.
非特异性免疫反应包括物理屏障、中性粒细胞和巨噬细胞的吞噬作用以及炎症。巨噬细胞在 MHC II 类分子上呈递抗原以激活特异性免疫。
Cell-mediated immunity involves T-lymphocytes: helper T cells bind to presented antigens and release cytokines, activating cytotoxic T cells that kill infected cells, and stimulating B cells.
细胞免疫涉及 T 淋巴细胞：辅助 T 细胞结合呈递的抗原并释放细胞因子，激活能杀死感染细胞的细胞毒性 T 细胞，并刺激 B 细胞。
Humoral immunity involves B cells that differentiate into plasma cells secreting specific antibodies. Memory cells provide long-term immunity, forming the basis of vaccination.
体液免疫涉及 B 细胞，它们分化为分泌特异性抗体的浆细胞。记忆细胞提供长期免疫，构成了疫苗接种的基础。
10. Animal Reproduction | 动物生殖
Asexual reproduction via mitosis produces genetically identical offspring, common in simple animals, while sexual reproduction involves meiosis and fusion of gametes, increasing genetic variation.
通过有丝分裂进行的无性生殖产生遗传相同的后代，常见于简单动物中；而有性生殖涉及减数分裂和配子融合，增加了遗传变异。
In mammals, spermatogenesis produces four haploid sperm cells per meiosis; oogenesis produces one functional ovum and two or three polar bodies. Fertilisation restores the diploid number.
在哺乳动物中，精子发生每次减数分裂产生四个单倍体精子细胞；卵子发生产生一个功能性卵子和两到三个极体。受精使染色体数目恢复为二倍体。
Hormonal cycles (e.g. oestrogen, progesterone, FSH, LH) regulate ovulation and the uterine lining, and the placenta secretes hCG to maintain the corpus luteum during early pregnancy.
激素周期（如雌激素、孕激素、卵泡刺激素、黄体生成素）调控排卵和子宫内膜，胎盘分泌 hCG 在孕早期维持黄体。
11. Classification and Evolution | 分类与进化
Modern animal classification uses a hierarchical system (domain, kingdom, phylum, class, order, family, genus, species) based on molecular phylogenetics, DNA sequences and evolutionary relationships.
现代动物分类使用基于分子系统发育学、DNA 序列和进化关系的等级体系（域、界、门、纲、目、科、属、种）。
Natural selection acts on intraspecific variation: individuals with advantageous alleles are more likely to survive, reproduce and pass on these alleles, shifting the population’s gene pool over generations.
自然选择作用于种内变异：具有有利等位基因的个体更可能存活、繁殖并传递这些等位基因，从而在世代间改变种群的基因库。
Allopatric speciation occurs when a geographical barrier isolates populations, allowing independent mutation and selection to lead to reproductive isolation. Sympatric speciation may arise from polyploidy or behavioural shifts.
异域物种形成发生在地理屏障隔离种群后，允许独立的突变和选择导致生殖隔离。同域物种形成可能源于多倍体化或行为改变。
12. Animal Behaviour | 动物行为
Behaviour can be innate (genetically determined, e.g. reflexes, taxis, kinesis) or learned through experience. Taxes are directional movements towards or away from a stimulus, while kineses change rate of random movement.
行为可以是先天的（由基因决定，如反射、趋性、动性），也可以是通过经验习得的。趋性是朝向或背离刺激的定向运动，而动性则改变随机运动的速率。
Classical conditioning involves associating an unconditioned stimulus with a neutral stimulus to produce a conditioned response (Pavlov’s dogs). Operant conditioning uses reinforcement or punishment to shape voluntary behaviour.
经典条件反射涉及将无条件刺激与中性刺激关联，产生条件反应（巴甫洛夫的狗）。操作性条件反射利用强化或惩罚来塑造自愿行为。
Social behaviour, such as cooperative hunting or dominance hierarchies, can increase individual fitness, and imprinting in young animals ensures recognition of and attachment to a parent.
社会行为，如合作猎食或等级优势，能增加个体适合度；而幼年动物的印随行为确保了对亲代的识别和依附。
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