📚 5.5 Plant and Animal Responses Exam Practice | 5.5 植物与动物反应真题精练
Welcome to this focused revision session on plant and animal responses. This topic is a core component of A-Level Biology, encompassing plant tropisms, hormonal control, the mammalian nervous system, muscle contraction, and homeostasis. Mastering these concepts through exam-style practice questions is essential for achieving top grades.
欢迎参加本次植物与动物反应专题复习。该主题是A-Level生物学的核心内容，涵盖植物向性、激素调控、哺乳动物神经系统、肌肉收缩和稳态。通过考试真题式练习掌握这些概念，对取得高分至关重要。
1. Overview of Plant and Animal Responses | 植物与动物反应概述
Organisms must detect and respond to changes in their internal and external environments to survive. Plants rely on chemical coordination through hormones, while animals have evolved complex nervous and endocrine systems.
生物必须探测并响应内外部环境的变化才能生存。植物依赖激素进行化学协调，而动物则进化出复杂的神经系统和内分泌系统。
Exam questions often ask you to compare plant and animal responses, analyse experimental data, and explain physiological mechanisms in detail. A solid grasp of feedback loops, cell signalling, and muscle contraction is required.
考题经常要求你比较植物和动物的反应，分析实验数据，并详细解释生理机制。扎实掌握反馈回路、细胞信号传导和肌肉收缩是必需的。
2. Plant Tropisms and Hormones | 植物向性与激素
Phototropism is the directional growth of a plant in response to light. In shoots, auxin (IAA) accumulates on the shaded side, causing cells there to elongate more than on the illuminated side, bending the shoot towards light.
向光性是植物朝向光的方向生长。在茎中，生长素（IAA）在背光侧积累，导致该侧细胞比向光侧伸长更多，使茎向光弯曲。
Gravitropism in roots: auxin accumulates on the lower side, inhibiting cell elongation in root cells, causing the root to curve downwards. This differential sensitivity to auxin concentration is key.
根的向地性：生长素在根的下侧积累，抑制根细胞的伸长，导致根向下弯曲。这种对生长素浓度的差异性敏感是关键。
Other plant hormones include gibberellins (stem elongation, seed germination), ethene (fruit ripening), and ABA (stomatal closure under water stress). Remember to associate each hormone with its specific responses for the exam.
其他植物激素包括赤霉素（茎伸长、种子萌发）、乙烯（果实成熟）和ABA（水分胁迫下气孔关闭）。考试中要对每种激素的特异性反应进行匹配。
3. Experimental Analysis of Phototropism | 向光性实验分析
The classic experiments by Darwin, Boysen-Jensen, and Went demonstrated that a diffusible chemical (auxin) produced in the tip of the coleoptile is responsible for phototropic curvature. Agar blocks were used to collect and redistribute the chemical.
达尔文、博伊森-詹森和温特的经典实验证明，胚芽鞘尖端产生的可扩散化学物质（生长素）是引起向光性弯曲的原因。琼脂块被用来收集和重新分配这种化学物质。
In data-analysis questions, you may be given diagrams of coleoptiles with cut tips, or with agar blocks placed asymmetrically. Predict the direction of curvature: auxin promotes growth in shoots, so the side with higher auxin elongates more.
在数据分析题中，可能会给出尖端被切除或带有不对称放置琼脂块的胚芽鞘图解。预测弯曲方向：生长素促进茎生长，因此生长素浓度高的一侧伸长更多。
4. The Nervous System: Reflex Arc | 神经系统：反射弧
ensory neurone → relay neurone (spinal cord) → motor neurone → effector (muscle or gland).
反射弧提供对刺激的快速、非自主性反应。途径：刺激 → 感受器 → 感觉神经元 → 中间神经元（脊髓）→ 运动神经元 → 效应器（肌肉或腺体）。
The knee-jerk reflex is a monosynaptic reflex, while the withdrawal reflex involves multiple synapses. Synaptic transmission ensures that impulses travel in one direction only.
膝跳反射是单突触反射，而缩手反射涉及多个突触。突触传递确保冲动只能单向传递。
Myelinated axons conduct impulses faster due to saltatory conduction. The myelin sheath insulates the axon, and depolarisation only occurs at nodes of Ranvier.
有髓轴突因跳跃传导而更快地传播冲动。髓鞘使轴突绝缘，去极化仅发生在郎飞氏结。
5. Action Potential and Synaptic Transmission | 动作电位与突触传递
At resting potential, the inside of a neurone is negative (-70 mV). Depolarisation occurs when voltage-gated Na⁺ channels open, allowing Na⁺ influx. Repolarisation is due to K⁺ efflux. The Na⁺/K⁺ pump restores resting potential.
静息电位时，神经元内部为负（-70 mV）。去极化时电压门控Na⁺通道开放，Na⁺内流。复极化由K⁺外流引起。Na⁺/K⁺泵恢复静息电位。
An action potential is all-or-nothing. At the synapse, depolarisation triggers Ca²⁺ entry, causing vesicles to release neurotransmitter (e.g., acetylcholine) into the synaptic cleft. The neurotransmitter binds to receptors on the postsynaptic membrane, generating an EPSP or IPSP.
动作电位是全或无的。在突触处，去极化触发Ca²⁺进入，导致囊泡释放神经递质（如乙酰胆碱）到突触间隙。递质与突触后膜受体结合，产生兴奋性或抑制性突触后电位。
Acetylcholine is broken down by acetylcholinesterase to prevent continuous stimulation. Many drugs and toxins affect synaptic function, a common context for application questions.
乙酰胆碱被乙酰胆碱酯酶分解，防止持续刺激。许多药物和毒素影响突触功能，是应用题常见背景。
6. Muscle Contraction: Sliding Filament Model | 肌肉收缩：滑丝模型
Skeletal muscle is composed of myofibrils containing sarcomeres. The sliding filament model explains that actin filaments slide over myosin filaments, shortening the sarcomere without the filaments themselves changing length.
骨骼肌由含有肌节的肌原纤维组成。滑丝模型解释肌动蛋白丝在肌球蛋白丝上滑动，缩短肌节，而细丝本身长度不变。
stroke using energy from ATP hydrolysis (ATP → ADP + Pᵢ), and detach when a new ATP binds.
收缩需要Ca²⁺和ATP。Ca²⁺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。肌球蛋白头结合，利用ATP水解的能量（ATP → ADP + 无机磷酸）执行强力冲刺，并在新ATP结合时脱离。
When stimulation ceases, Ca²⁺ is actively pumped back into the sarcoplasmic reticulum, and the muscle relaxes. Phosphocreatine regenerates ATP rapidly during intense exercise.
刺激停止时，Ca²⁺被主动泵回肌质网，肌肉舒张。剧烈运动时磷酸肌酸快速再生ATP。
7. Endocrine System and Blood Glucose Regulation | 内分泌系统与血糖调节
The endocrine system uses hormones secreted into the blood. Blood glucose regulation is a classic example of negative feedback. Insulin (from beta cells of islets of Langerhans) lowers blood glucose by increasing cellular uptake and glycogenesis; glucagon (from alpha cells) raises it by glycogenolysis and gluconeogenesis.
内分泌系统通过激素分泌到血液中。血糖调节是负反馈的经典例子。胰岛素（由胰岛β细胞分泌）通过增加细胞摄取和糖原合成降低血糖；胰高血糖素（由α细胞分泌）通过糖原分解和糖
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