📚 Plant & Animal Responses | 植物与动物反应
Plants and animals both detect changes in their internal and external environments and produce coordinated responses that increase their chances of survival. However, the speed and mechanisms of these responses differ greatly. Plants rely mainly on chemical signals and growth movements, while animals often use rapid electrical impulses, muscles and glands. Both systems involve receptors, signalling pathways and effectors.
植物和动物都能检测内外环境的变化，并产生协调反应以提高生存概率。但两者的反应速度和机制差异很大。植物主要依靠化学信号和生长运动，动物则常使用快速的电冲动、肌肉和腺体。两个系统都涉及感受器、信号通路和效应器。
1. Plant Responses to Abiotic Stress | 植物对非生物胁迫的反应
Abiotic stresses include drought, temperature extremes, high light intensity and salinity. Plants reduce water loss by closing stomata, producing thick waxy cuticles, shedding leaves, or rolling leaves to trap humid air. Many temperate plants also respond to cold by producing antifreeze proteins or by making their cells more tolerant to ice crystal formation.
非生物胁迫包括干旱、极端温度、强光和盐害。植物通过关闭气孔、产生厚蜡质角质层、落叶或卷叶来减少水分损失。许多温带植物还通过产生抗冻蛋白或使细胞更能耐受冰晶形成来应对寒冷。
Abscisic acid (ABA) is a key hormone in drought stress. When soil water potential falls, root cells produce ABA, which is transported to the leaves. There it causes guard cells to lose potassium ions. Water then leaves the guard cells by osmosis, the cells become flaccid, and the stomata close, reducing transpiration.
脱落酸（ABA）是干旱胁迫中的关键激素。当土壤水势下降时，根细胞产生 ABA，并运输到叶片。在叶片中，ABA 使保卫细胞失去钾离子。水分随后通过渗透作用离开保卫细胞，保卫细胞变得松弛，气孔关闭，从而减少蒸腾作用。
2. Chemical Defences Against Herbivory | 植物对食草动物的化学防御
Plants produce many secondary metabolites that deter herbivores. Tannins are toxic to insects and bind to digestive enzymes in herbivore guts, making plant tissues harder to digest. Alkaloids such as nicotine and caffeine have bitter tastes and toxic or stimulant effects that reduce feeding by herbivores.
植物产生许多次生代谢物来抵御食草动物。单宁对昆虫有毒，并能与食草动物肠道中的消化酶结合，使植物组织难以消化。烟碱和咖啡因等生物碱具有苦味和毒性或刺激作用，从而减少食草动物的取食。
Some plants release pheromones when damaged. These volatile chemicals can attract predators or parasitoids of the herbivores, providing an indirect defence. For example, lima bean plants release volatiles that attract predatory mites, which then attack the herbivorous spider mites feeding on the plant.
有些植物在受损时释放信息素。这些挥发性化学物质可以吸引食草动物的天敌或寄生生物，提供间接防御。例如，利马豆释放的挥发物能吸引捕食性螨类，这些捕食性螨随后会攻击取食植物的植食性叶螨。
3. Plant Tropisms and Auxin | 植物向性与生长素
Tropisms are directional growth responses determined by the direction of an external stimulus. Phototropism is growth towards or away from light; gravitropism is growth in response to gravity. Shoots are positively phototropic and negatively gravitropic, while roots are positively gravitropic and usually negatively phototropic.
向性是生长反应，其方向取决于外部刺激的方向。向光性是朝向或背离光生长；向地性是响应重力生长。地上茎呈正向光性和负向地性，根呈正向地性，通常也呈负向光性。
Indole-3-acetic acid (IAA), an auxin, controls tropisms by uneven distribution. In a horizontally placed root, IAA accumulates on the lower side due to gravity. High IAA concentration inhibits root cell elongation, so upper side cells elongate more and the root bends downward. In shoots, IAA accumulates on the shaded side, promotes cell elongation there, and causes the shoot to bend towards light.
吲哚-3-乙酸（IAA）是一种生长素，通过不均匀分布控制向性。在水平放置的根中，IAA 因重力在下侧积累。高浓度 IAA 抑制根细胞伸长，因此上侧细胞伸长更多，根向下弯曲。在茎中，IAA 在背光侧积累，促进该侧细胞伸长，使茎向光弯曲。
4. Commercial Uses of Plant Hormones | 植物激素的商业应用
Auxins are used in rooting powders to stimulate adventitious root formation on cuttings. Synthetic auxins can also act as selective herbicides, making broad-leaved weeds grow abnormally and die while leaving narrow-leaved cereal crops relatively unaffected. This selective action is useful in agriculture.
生长素用于生根粉中，促进插条形成不定根。合成生长素也可作为选择性除草剂，使阔叶杂草生长异常死亡，而对窄叶谷类作物影响较小。这种选择性作用在农业中非常有用。
Gibberellins promote stem elongation and seed germination. In commercial fruit production, gibberellins can produce larger grapes, delay citrus fruit ageing, and break dormancy in seeds such as barley for malting. Ethene gas is used to ripen fruit and promote fruit drop for mechanical harvesting.
赤霉素促进茎伸长和种子萌发。在商业水果生产中，赤霉素可使葡萄增大、延缓柑橘衰老，并打破大麦等种子的休眠以用于麦芽生产。乙烯气体用于催熟果实并促进落果以便机械采收。
5. Animal Nervous Coordination: From Receptor to Effector | 动物神经协调：从感受器到效应器
Animals detect stimuli with receptors, which are specialised sensory cells or nerve endings. Receptor cells convert a stimulus into a generator potential; if threshold is reached, an action potential is produced in a sensory neurone. The central nervous system processes information and sends impulses along motor neurones to effectors, usually muscles or glands.
动物用感受器检测刺激，感受器是特化的感觉细胞或神经末梢。感受器细胞将刺激转换为发生器电位；若达到阈值，则在感觉神经元中产生动作电位。中枢神经系统处理信息并沿运动神经元将冲动发送至效应器，通常是肌肉或腺体。
r. Because the impulse crosses only a few synapses, the response is very fast and protects the body before conscious awareness.
简单的反射弧提供快速、不随意的反应以避免危险。其通路为：刺激 → 感受器 → 感觉神经元 → 脊髓中的中间神经元 → 运动神经元 → 效应器。由于冲动只经过少数突触，反应非常快，并在意识知觉之前保护身体。
6. Action Potentials and Synaptic Transmission | 动作电位与突触传递
An action potential is a rapid temporary change in membrane potential. When a neurone is stimulated and threshold is reached, voltage-gated Na⁺ channels open, Na⁺ enters, and the inside becomes positive. This is depolarisation. Then Na⁺ channels close, K⁺ channels open, K⁺ leaves, and the membrane repolarises. The resting potential is restored by the Na⁺/K⁺ pump.
动作电位是膜电位的快速暂时变化。当神经元受到刺激并达到阈值时，电压门控 Na⁺ 通道打开，Na⁺ 内流，膜内变为正电，这就是去极化。随后 Na⁺ 通道关闭，K⁺ 通道打开，K⁺ 外流，膜复极化。静息电位由 Na⁺/K⁺ 泵恢复。
At a synapse, an action potential causes voltage-gated Ca²⁺ channels to open. Calcium ions enter the presynaptic knob, causing vesicles to fuse with the membrane and release neurotransmitter into the synaptic cleft. The transmitter binds to receptors on the postsynaptic membrane, opening ligand-gated ion channels and triggering a new potential in the next neurone.
在突触处，动作电位使电压门控 Ca²⁺ 通道开放。钙离子进入突触前小体，使囊泡与膜融合，将神经递质释放到突触间隙。递质与突触后膜上的受体结合，打开配体门控离子通道，并在下一个神经元中触发新的电位。
7. Muscle Contraction: Sliding Filament Theory | 肌肉收缩：肌丝滑动学说
Skeletal muscle is made of myofibrils containing repeating sarcomeres. Thick filaments are made of myosin; thin filaments contain actin, tropomyosin and troponin. During contraction, myosin heads bind to actin forming cross-bridges, pivot to pull actin filaments towards the centre of the sarcomere, then detach using ATP. This shortens the sarcomere while filament lengths remain unchanged.
骨骼肌由肌原纤维组成，肌原纤维包含重复的肌节。粗肌丝由肌球蛋白组成；细肌丝包含肌动蛋白、原肌球蛋白和肌钙蛋白。收缩时，肌球蛋白头部与肌动蛋白结合形成横桥，转动将细肌丝拉向肌节中央，然后利用 ATP 解离。这使肌节缩短，而肌丝长度不变。
Contraction is initiated when an action potential arrives at the neuromuscular junction and releases acetylcholine. This depolarises the sarcolemma and travels down T-tubules, causing the sarcoplasmic reticulum to release Ca²⁺. Calcium ions bind to troponin, moving tropomyosin away from myosin-binding sites on actin, allowing cross-bridge cycling to begin.
收缩开始时，动作电位到达神经肌肉接头并释放乙酰胆碱。这使肌膜去极化并沿 T 小管传导，使肌浆网释放 Ca²⁺。钙离子与肌钙蛋白结合，使原肌球蛋白从肌动蛋白上的肌球蛋白结合位点移开，从而开始横桥循环。
8. Hormonal Coordination in Animals | 动物的激素协调
Hormones are chemical messengers secreted by endocrine glands into the blood. They travel to target cells with specific receptors and coordinate slower, longer-lasting responses than nerve impulses. Adrenaline is released from the adrenal medulla during stress or excitement; it binds to receptors on liver cells, activates glycogen phosphorylase, and increases blood glucose for increased respiration.
激素是由内分泌腺分泌到血液中的化学信使。它们运送到具有特异性受体的靶细胞，协调比神经冲动更慢但更持久的反应。肾上腺素在应激或兴奋时由肾上腺髓质释放；它与肝细胞受体结合，激活糖原磷酸化酶，提高血糖以增加呼吸作用。
Blood glucose concentration is regulated by insulin and glucagon. After a meal, beta cells in the pancreatic islets release insulin, causing liver and muscle cells to take up glucose and convert it to glycogen. When blood glucose falls, alpha cells release glucagon, which stimulates glycogenolysis and gluconeogenesis in the liver to raise blood glucose.
血糖浓度由胰岛素和胰高血糖素调节。进食后，胰岛中的 β 细胞释放胰岛素，使肝细胞和肌细胞摄取葡萄糖并将其转化为糖原。当血糖降低时，α 细胞释放胰高血糖素，刺激肝脏中的糖原分解和糖异生，使血糖升高。
9. Controlling Heart Rate | 心率的控制
Heart rate is controlled by the cardiovascular centre in the medulla oblongata. Sympathetic nerves release noradrenaline, which increases heart rate; parasympathetic vagus nerves release acetylcholine, which decreases heart rate. Baroreceptors in the carotid sinuses and aortic arch detect blood pressure changes, and chemoreceptors detect CO₂ concentration and pH.
心率由延髓中的心血管中枢控制。交感神经释放去甲肾上腺素，使心率加快；副交感迷走神经释放乙酰胆碱，使心率减慢。颈动脉窦和主动脉弓中的压力感受器检测血压变化，化学感受器检测 CO₂ 浓度和 pH。
During exercise, increased CO₂ and decreased pH in the blood stimulate chemoreceptors. They send more impulses to the cardiovascular centre, which increases sympathetic output and reduces parasympathetic output. Heart rate rises, increasing oxygen delivery to muscles. After exercise, the reverse occurs and heart rate returns to resting level.
运动期间，血液中 CO₂ 升高和 pH 降低刺激化学感受器。它们向心血管中枢发送更多冲动，中枢增加交感输出并减少副交感输出。心率升高，增加向肌肉输送氧气。运动后发生相反过程，心率恢复至静息水平。
10. Comparing Plant and Animal Responses | 植物与动物反应的比较
Both plants and animals use chemical signalling, but animals also use rapid electrical signalling along neurones. Plant responses are usually slower, involve changes in gene expression and cell elongation, and are often irreversible growth movements. Animal responses can be rapid and reversible, involving muscle contraction or secretion. Both systems are adaptive and regulated by feedback mechanisms.
植物和动物都使用化学信号，但动物还利用沿神经元的快速电信号。植物反应通常较慢，涉及基因表达和细胞伸长的变化，且往往是不可逆的生长运动。动物反应可以快速且可逆，涉及肌肉收缩或分泌。两个系统都是适应性的，并受反馈机制调节。
In plants, hormones such as auxin, gibberellins, ABA and ethene coordinate growth and stress responses over hours or days. In animals, the nervous system produces millisecond responses, while the endocrine system produces longer-lasting changes in metabolism and development. Despite these differences, both kingdoms achieve the same goal: maintaining favourable internal conditions and responding effectively to environmental challenges.
在植物中，生长素、赤霉素、ABA 和乙烯等激素在数小时或数天内协调生长和胁迫反应。在动物中，神经系统产生毫秒级反应，而内分泌系统产生更持久的代谢和发育变化。尽管存在这些差异，两个生物界都实现了相同的目标：维持有利的内部条件并有效应对环境挑战。
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