📚 GCSE Biology: Plant Hormones – Key Exam Points | GCSE 生物：植物激素 考点精讲
Plant hormones are the chemical messengers that control growth, development and responses to the environment. In GCSE Biology, mastering the roles of auxin, gibberellins and ethene is essential for scoring highly on plant physiology questions. This article breaks down every key point, experimental evidence and real-world application you need to know, all presented in clear bilingual pairs.
植物激素是控制生长、发育以及对环境响应的化学信使。在GCSE生物中，掌握生长素、赤霉素和乙烯的作用，对于在植物生理学题目中取得高分至关重要。本文通过清晰的中英对照，为你解析每一个关键点、实验证据和实际应用。
1. What Are Plant Hormones? | 什么是植物激素？
Plant hormones, also called plant growth regulators, are signalling molecules produced in microscopic amounts. Unlike animal hormones, they usually act close to where they are made and control processes such as cell elongation, germination and fruit ripening. The three main hormones in the GCSE specification are auxin, gibberellins and ethene.
植物激素又称植物生长调节剂，是微量产生的信号分子。与动物激素不同，它们通常在靠近产生位点的地方起作用，并控制细胞伸长、萌发和果实成熟等过程。GCSE考纲中三种主要激素是生长素、赤霉素和乙烯。
Auxins are synthesised in the tips of shoots and roots, while gibberellins are produced in young leaves and seeds. Ethene is a simple gaseous hormone that diffuses through the plant tissue. Understanding their distribution and effects is the key to explaining tropisms and commercial uses.
生长素在茎尖和根尖合成，赤霉素则在幼叶和种子中产生。乙烯是一种简单气体激素，通过植物组织扩散。理解它们的分布和效应是解释向性和商业应用的关键。
2. Auxin and Phototropism | 生长素与向光性
Phototropism is the growth of a shoot towards light. When light shines from one side, auxin produced in the shoot tip redistributes to the shaded side. This higher auxin concentration on the shaded side stimulates cells to elongate more than on the illuminated side, causing the shoot to bend towards the light source.
向光性是指茎朝向光生长。当光线从一侧照射时，茎尖产生的生长素重新分布到背光侧。背光侧生长素浓度较高，刺激该侧细胞比向光侧伸长更多，导致茎向光源弯曲。
The mechanism relies on cell elongation, not cell division. Auxin loosens the cell wall by activating enzymes, allowing the cells to take up water and stretch. Crucially, the tip of the shoot detects the light direction; if the tip is removed, phototropism does not occur.
这一机制依赖于细胞伸长而非细胞分裂。生长素通过激活酶来松弛细胞壁，使细胞吸水拉伸。关键是，茎尖能够感知光的方向；如果切除茎尖，向光性就不会发生。
3. Auxin and Gravitropism (Geotropism) | 生长素与向地性
Gravitropism is a directional growth response to gravity. In a horizontally placed root, auxin accumulates on the lower side due to gravity. Unlike shoots, roots are highly sensitive to auxin. The high auxin concentration on the lower side inhibits cell elongation, so the upper side grows faster, bending the root downwards.
向地性是对重力的定向生长反应。将根水平放置时，重力使生长素积累在下侧。与茎不同，根对生长素高度敏感。下侧的高浓度生长素抑制细胞伸长，因此上侧生长更快，使根向下弯曲。
In a horizontal shoot, auxin also accumulates on the lower side, but here it promotes elongation. Consequently, the lower side grows faster and the shoot bends upwards, away from gravity. This explains why shoots grow up and roots grow down, even in the dark.
在水平放置的茎中，生长素同样在下侧积累，但此处它会促进伸长。因此下侧生长更快，茎向上弯曲，远离重力。这就解释了为何即使在黑暗中，茎向上长而根向下长。
4. Explaining Shoot and Root Responses to Auxin | 解释芽和根对生长素的反应
The opposite effects of auxin on shoots and roots are due to different optimal concentrations. Shoots are stimulated by auxin levels that are high enough to inhibit roots. The summary table below helps compare these responses, a favourite in GCSE analysis questions.
生长素对茎和根的相反效应源于不同的最适浓度。足以抑制根的生长素水平却会刺激茎。下面的总结表有助于比较这些反应，这是GCSE分析题中的常见内容。
| Organ | Response to high auxin | Response to low auxin |
| Shoot | Promotes elongation | Slower elongation |
| Root | Inhibits elongation | Promotes elongation |
In roots, even moderate auxin levels cause inhibition, which is why when auxin accumulates on the lower side of a root, growth slows there and the root bends down. Shoots require much higher auxin before inhibition occurs, so they bend up instead.
在根中，即使是中等的生长素水平也会造成抑制，这就是为什么当生长素在根的下侧积累时，那里生长变慢，根向下弯曲。茎则需要在更高生长素浓度下才会被抑制，因此它们向上弯曲。
5. Experimental Evidence for Phototropism | 向光性的实验证据
Classic experiments provide the evidence that auxin from the tip controls phototropism. If the shoot tip is cut off, no bending occurs. If the cut tip is placed back onto the stump with a permeable agar block, auxin diffuses through and the shoot bends towards light.
经典实验证明了来自尖端的生长素控制向光性。如果切掉茎尖，不会发生弯曲。如果将切下的尖端用可渗透琼脂块放回切面，生长素会扩散通过，茎就会向光弯曲。
If a thin sheet of mica (impermeable) is inserted on the shaded side between the tip and the stump, auxin movement is blocked, and the shoot does not bend. Inserting mica on the illuminated side does not prevent bending, confirming that auxin travels down the shaded side.
如果在背光侧于尖端和切面间插入一片薄云母（不可渗透），生长素的移动被阻断，茎便不弯曲。在向光侧插入云母则不会阻止弯曲，这证实了生长素沿背光侧向下运输。
6. Experimental Evidence for Gravitropism | 向地性的实验证据
A simple demonstration uses a germinating bean seedling placed horizontally in a dark, moist container. After 24 hours, the root curves downwards and the shoot curves upwards. The absence of light ensures the response is purely due to gravity.
一个简单演示是将正在萌发的豆苗水平放置在黑暗潮湿的容器中。24小时后，根向下弯曲，茎向上弯曲。没有光确保了这种反应纯粹由重力引起。
Using a clinostat, a slowly rotating wheel that cancels the directional pull of gravity, causes the seedling to grow straight in any orientation. This proves that gravity, rather than the seedling 'knowing' up from down, drives the redistribution of auxin.
使用回转器——一个缓慢旋转的轮子来抵消重力的定向拉力——会使幼苗在任何方向上都保持直立生长。这证明是重力，而非幼苗自身‘知道’上下，驱动了生长素的重新分配。
7. Uses of Auxin: Weedkillers and Rooting Powder | 生长素的应用：除草剂与生根粉
Synthetic auxins such as 2,4-D are widely used as selective herbicides. They cause broad-leaved weeds to grow rapidly and uncontrollably, distorting their tissues and eventually killing them. Cereal crops with narrow leaves are less affected, making these chemicals useful in farming.
合成生长素如2,4-D被广泛用作选择性除草剂。它们导致阔叶杂草快速失控生长，组织变形，最终死亡。窄叶的谷类作物受影响较小，这使得此类化学品在农业中非常有用。
Auxins are also the active ingredient in rooting powder. When a plant cutting is dipped into rooting powder and placed in soil, the auxin promotes the development of adventitious roots from the cut end. This technique is essential for commercial plant propagation.
生长素也是生根粉的活性成分。将插条蘸取生根粉后插入土壤，生长素会促进从切端发育出不定根。这一技术对商业植物繁殖至关重要。
8. Gibberellins: Seed Germination and Beyond | 赤霉素：种子萌发及其他
Gibberellins are key to ending seed dormancy. When water is absorbed, the embryo secretes gibberellins, which diffuse to the aleurone layer of the seed. There they activate genes that code for the enzyme α-amylase.
赤霉素是结束种子休眠的关键。吸水后，胚分泌赤霉素，扩散到种子的糊粉层。在那里它们激活编码α-淀粉酶的基因。
The newly synthesised α-amylase hydrolyses starch stored in the endosperm into maltose and glucose. These sugars are then transported to the growing embryo to fuel respiration and growth. This process is commercially exploited in malting barley for brewing.
新合成的α-淀粉酶将胚乳中的淀粉水解为麦芽糖和葡萄糖。这些糖随后被运输到正在生长的胚，为呼吸和生长提供燃料。这一过程在酿造中用于大麦制麦芽时被商业化利用。
Gibberellins are also sprayed on certain fruit crops to increase fruit size and on grape vines to elongate the stems, allowing grapes to grow larger and with more space, reducing fungal infections.
赤霉素还可喷洒在某些水果作物上以增大果实，或用于葡萄藤以延长枝梗，使葡萄颗粒更大且更分散，减少真菌感染。
9. Ethene and Fruit Ripening | 乙烯与果实成熟
Ethene is a gaseous hormone that accelerates fruit ripening, leaf fall and flower withering. It works by triggering the breakdown of chlorophyll, conversion of starch to sugar and softening of cell walls, turning a hard green fruit into a sweet, soft one.
乙烯是一种加速果实成熟、落叶和花凋谢的气体激素。它通过触发叶绿素分解、淀粉转化为糖以及细胞壁软化，将硬绿果实变为香甜柔软的状态。
In commercial supply chains, fruits such as bananas and tomatoes are picked unripe while still firm. They are transported, and just before reaching the supermarket, they are exposed to a controlled dose of ethene gas to ripen them uniformly and improve appearance.
在商业供应链中，香蕉和番茄等水果在还硬绿时采摘。运输后，在抵达超市之前，它们会被暴露于受控剂量的乙烯气体中，以实现均匀成熟并改善外观。
10. Exam Focus: Interpreting Data and Designing Experiments | 考试聚焦：数据解读与实验设计
GCSE questions frequently present line graphs showing how root and shoot growth vary with auxin concentration. The key pattern is that roots show maximum growth at very low auxin concentrations, while shoots require higher concentrations for optimal growth. The curves cross because high concentrations inhibit roots but stimulate shoots.
GCSE题目常给出折线图，展示根和茎的生长如何随生长素浓度变化。关键模式是根在极低浓度下生长最快，而茎需要较高浓度才达到最佳生长。曲线交叉是因为高浓度抑制根却刺激茎。
When asked to design an investigation, always identify the independent variable (e.g. light direction, presence of tip), dependent variable (angle of bending, length of curvature) and control variables (temperature, moisture, darkness). Use these to write a step-by-step method and predict results using auxin theory.
被要求设计探究实验时，一定要明确自变量（如光的方向、有无尖端）、因变量（弯曲角度、弯曲长度）和控制变量（温度、湿度、黑暗条件）。利用这些写出步骤方法，并运用生长素理论预测结果。
For six-mark questions, structure your answer by first describing the stimulus, then explaining auxin redistribution and finally linking to differential growth. Mentioning supporting experiments, such as the use of agar blocks or clinostats, strengthens your explanation.
对于六分大题，这样组织答案：先描述刺激，然后解释生长素重新分布，最后联系到差异性生长。提及琼脂块或回转器等支持性实验能进一步强化你的解释。
Published by TutorHao | Biology Revision Series | aleveler.com
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