📚 Plant and Animal Responses: Visual Memory Guide | 植物与动物反应：图解记忆指南
Welcome to this visual memory guide on plant and animal responses, designed to help you master A-Level Biology topic 5.5. By linking key concepts to memorable diagrams, flowcharts, and comparison tables, you will retain the details of tropisms, auxin action, nerve impulses, muscle contraction, and hormonal control. Let’s visualise the pathways together.
欢迎阅读本图解记忆指南，内容涵盖 A-Level 生物学 5.5 植物与动物反应。通过将关键概念与难忘的图表、流程图和对比表联系起来，您将牢记向性、生长素作用、神经冲动、肌肉收缩和激素控制等细节。让我们一起将通路形象化。
1. Tropisms and the Role of Auxin | 向性及生长素的作用
A tropism is a directional growth response of a plant to an external stimulus. Phototropism is growth towards or away from light, while gravitropism (geotropism) is growth relative to gravity. In shoots, positive phototropism bends the shoot toward light; in roots, negative phototropism and positive gravitropism ensure downward growth.
向性是植物对外部刺激作出的定向生长反应。向光性是指朝向或背向光生长，而向地性是指相对于重力的生长。在茎中，正向光性使茎弯向光；在根中，负向光性和正向地性确保向下生长。
The plant hormone indole-3-acetic acid (IAA), a type of auxin, controls these responses. In phototropism, light causes IAA to move to the shaded side of the shoot tip. A higher concentration of IAA on the shaded side promotes cell elongation, causing the shoot to bend toward the light.
植物激素吲哚-3-乙酸（IAA），一种生长素，控制这些反应。在向光性中，光导致 IAA 移动到茎尖的背阴侧。背阴侧较高的 IAA 浓度促进细胞伸长，使茎弯向光。
In gravitropism, IAA is redistributed to the lower side of the root or shoot. In roots, a high concentration of IAA inhibits cell elongation, so the lower side grows more slowly, causing the root to bend downward. In shoots, IAA promotes elongation, so the lower side grows faster, curving the shoot upward.
在向地性中，IAA 被重新分配到根或茎的下侧。在根中，高浓度 IAA 抑制细胞伸长，因此下侧生长较慢，导致根向下弯曲。而在茎中，IAA 促进伸长，所以下侧生长更快，使茎向上弯曲。
Visual memory tip: Draw a shoot tip divided into illuminated and shaded sides, with arrows showing IAA movement and a table comparing root and shoot responses.
图解记忆提示：画一个茎尖分成光照侧和阴影侧，用箭头表示 IAA 移动，并制作表格比较根和茎的反应。
2. Apical Dominance and Leaf Abscission | 顶端优势与落叶
Apical dominance is the inhibition of lateral bud growth by the apical bud. Auxin produced in the apical bud travels downwards and suppresses the growth of lateral shoots. If the apical bud is removed, lateral buds grow, giving a bushier appearance.
顶端优势是指顶芽抑制侧芽生长的现象。顶芽产生的生长素向下运输，抑制侧枝生长。若去除顶芽，侧芽便会生长，使植株更茂密。
Leaf abscission (leaf fall) is regulated by auxin and ethene. In autumn, auxin production in the leaf decreases, making the abscission zone sensitive to ethene. Ethene stimulates the production of enzymes that break down the cell walls in the separation layer, causing the leaf to drop.
落叶受生长素和乙烯的调控。秋季，叶片中生长素的产生减少，使离层对乙烯变得敏感。乙烯刺激产生酶，分解离层中的细胞壁，导致叶片脱落。
Visual memory: Create a diagram of a stem with apical and lateral buds, with bold arrows for auxin flow. For leaf fall, sketch a leaf base with the abscission zone labelled.
图解记忆：绘制一个主茎，标注顶芽和侧芽，用粗箭头表示生长素流向。对于落叶，画出叶基部并标注离层。
3. Gibberellins and Commercial Uses of Plant Hormones | 赤霉素与植物激素的商业应用
Gibberellins are plant hormones that promote stem elongation and seed germination. They stimulate the production of enzymes that break down food reserves in seeds, providing energy for growth. Mutant plants lacking gibberellins have dwarf stems.
赤霉素是促进茎伸长和种子萌发的植物激素。它们刺激产生分解种子内贮藏养分的酶，为生长提供能量。缺乏赤霉素的突变植株茎秆矮小。
Plant hormones are used commercially: auxins as rooting powders, herbicides, and for fruit setting without fertilisation; gibberellins to delay senescence in citrus fruits, produce seedless grapes, and speed up malting in brewing; ethene to ripen fruits; and cytokinins to promote cell division in tissue culture.
植物激素在商业上应用广泛：生长素用作生根粉、除草剂，以及无需受精的坐果剂；赤霉素用于延缓柑橘类水果衰老、生产无籽葡萄，以及加速酿造中的发芽；乙烯用于催熟水果；细胞分裂素用于组织培养中促进细胞分裂。
Memory table: Make a 2-column table – Hormone and Commercial Use – with brief icons (e.g., a grape for gibberellin).
记忆表格：制作一个两栏表格——激素与商业用途——并配上简要图标（例如用葡萄表示赤霉素）。
4. Organisation of the Nervous System | 神经系统的组织
The mammalian nervous system is divided into the central nervous system (CNS: brain and spinal cord) and the peripheral nervous system (PNS: cranial and spinal nerves). The PNS further splits into the somatic (voluntary) and autonomic (involuntary) systems. The autonomic system consists of sympathetic and parasympathetic divisions, which generally have opposing effects.
哺乳动物的神经系统分为中枢神经系统（CNS：脑和脊髓）和外周神经系统（PNS：脑神经和脊神经）。外周神经系统又分为躯体（随意）和自主（不随意）系统。自主系统包括交感神经和副交感神经，它们通常具有相反的效应。
Visual: Draw a flowchart from CNS to PNS to somatic and autonomic, and further to sympathetic and parasympathetic. Include organs they target.
图解：绘制从 CNS 到 PNS 到躯体和自主，再到交感和副交感的流程图，并包括它们所作用的器官。
5. Structure and Function of Neurones | 神经元的结构与功能
A neurone consists of a cell body, dendrites (receiving signals), and an axon (transmitting impulses). The axon may be covered by a myelin sheath, formed by Schwann cells, with nodes of Ranvier between them. Sensory neurones carry impulses from receptors to the CNS; relay (intermediate) neurones connect neurones within the CNS; motor neurones transmit impulses from the CNS to effectors (muscles/glands).
神经元由细胞体、树突（接收信号）和轴突（传递冲动）组成。轴突可能被由施万细胞形成的髓鞘包裹，其间有郎飞氏结。感觉神经元将冲动从感受器传至中枢神经系统；中继神经元连接中枢神经系统内的神经元；运动神经元将冲动从中枢神经系统传至效应器（肌肉/腺体）。
Myelinated neurones conduct impulses much faster than unmyelinated ones because saltatory conduction occurs: the impulse jumps from node to node. The direction of transmission is always from dendrite to axon terminal.
有髓神经元传导冲动的速度远快于无髓神经元，因为发生跳跃传导：冲动从一结跳至下一结。传递方向总是从树突到轴突末梢。
6. Action Potential: Generation and Transmission | 动作电位的产生与传导
At rest, the inside of a neurone is negatively charged compared to the outside, creating the resting potential of about -70 mV. This is maintained by the sodium-potassium pump, which actively transports 3Na⁺ out and 2K⁺ in per ATP, and by greater membrane permeability to K⁺ than Na⁺.
静息时，神经元内部相对于外部带负电，产生约 -70 mV 的静息电位。这由钠钾泵（每分子 ATP 主动转运 3 个 Na⁺ 出和 2 个 K⁺ 进）以及膜对 K⁺ 的通透性大于 Na⁺ 来维持。
When a stimulus depolarises the membrane to the threshold (~-55 mV), voltage-gated Na⁺ channels open, Na⁺ rushes in, causing depolarisation to about +40 mV. Then Na⁺ channels close and voltage-gated K⁺ channels open, K⁺ rushes out, causing repolarisation. The membrane briefly hyperpolarises (more negative than resting) before returning to -70 mV.
当刺激使膜去极化达到阈电位（约 -55 mV）时，电压门控 Na⁺ 通道开放，Na⁺ 涌入，导致去极化至约 +40 mV。随后 Na⁺ 通道关闭，电压门控 K⁺ 通道开放，K⁺ 涌出，引起复极化。膜电位短暂超极化（比静息更负）后恢复至 -70 mV。
After an action potential, the refractory period ensures the impulse travels in one direction and limits frequency.
动作电位后，不应期确保冲动单向传导并限制频率。
Visual memory: Plot the action potential curve labelled with these phases. Use a mnemonic ‘Rise, Fall, Undershoot’ for depolarisation, repolarisation, hyperpolarisation.
图解记忆：标出动作电位曲线中的各阶段，并用记忆口诀“升、降、下冲”对应去极化、复极化、超极化。
7. Synaptic Transmission and Effects of Drugs | 突触传递与药物影响
A synapse is a junction between two neurones. An action potential arriving at the presynaptic knob opens voltage-gated Ca²⁺ channels; Ca²⁺ influx triggers vesicles containing neurotransmitter (e.g., acetylcholine, ACh) to fuse with the presynaptic membrane and release ACh into the synaptic cleft by exocytosis.
突触是两个神经元之间的连接。动作电位到达突触前末梢时，电压门控 Ca²⁺ 通道打开；Ca²⁺ 内流触发含有神经递质（如乙酰胆碱 ACh）的囊泡与突触前膜融合，并以胞吐方式将 ACh 释放到突触间隙。
ACh diffuses across the cleft and binds to receptors on the postsynaptic membrane, opening Na⁺ channels. If the resulting excitatory postsynaptic potential (EPSP) reaches threshold, an action potential is generated. Acetylcholinesterase breaks down ACh in the cleft to stop the signal.
ACh 扩散通过间隙，与突触后膜上的受体结合，打开 Na⁺ 通道。若产生的兴奋性突触后电位（EPSP）达到阈值，便会产生动作电位。乙酰胆碱酯酶在间隙中分解 ACh，终止信号。
Drugs affect synaptic transmission: e.g., nicotine mimics ACh, stimulating receptors; curare blocks ACh receptors, causing paralysis; organophosphates inhibit acetylcholinesterase, leading to overstimulation. Synapses can also be inhibitory, releasing neurotransmitters that open Cl⁻ channels, hyperpolarising the postsynaptic membrane.
药物影响突触传递：例如，尼古丁模拟 ACh，刺激受体；箭毒阻断 ACh 受体，导致麻痹；有机磷酸盐抑制乙酰胆碱酯酶，引起过度刺激。突触也可以是抑制性的，释放神经递质打开 Cl⁻ 通道，使突触后膜超极化。
Visual: Draw a synaptic cleft with vesicles, ACh, receptors, and acetylcholinesterase, labelling each step with numbers.
图解：画出突触间隙，包括囊泡、ACh、受体和乙酰胆碱酯酶，并用数字标注每一步骤。
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