Plant Hormones for GCSE AQA Biology | GCSE AQA 生物：植物激素考点精讲

📚 Plant Hormones for GCSE AQA Biology | GCSE AQA 生物：植物激素考点精讲

Plants may not have a nervous system or muscles, but they constantly respond to their environment using chemical messengers called plant hormones. This revision guide covers the key hormones – auxins, gibberellins, and ethene – their roles in tropisms, germination, ripening, and agriculture, exactly as required by the AQA GCSE Biology specification. Master how they coordinate growth and development to maximise your exam performance.

植物没有神经系统和肌肉，但它们通过被称为植物激素的化学信使不断对环境作出反应。本考点精讲按照 AQA GCSE 生物学大纲要求，系统梳理生长素、赤霉素和乙烯等关键激素，全面解析它们在向性运动、种子萌发、果实成熟以及农业应用中的作用。掌握植物如何协调生长发育，助你高效备考。

1. Introduction to Plant Hormones | 植物激素简介

Plant hormones are chemical substances produced in one part of a plant that travel to and exert effects in another part, often at very low concentrations. Unlike animal hormones, they are not produced in specialised glands and can act in the tissues where they are made. They control a wide range of processes including cell elongation, flowering, fruit ripening, leaf fall, and germination.

植物激素是植物某一部位产生的化学物质，在极低浓度下即可运输到其他部位发挥作用。不同于动物激素，它们并非由特化的腺体产生，常能在合成部位直接起效。这些激素调控细胞伸长、开花、果实成熟、落叶和种子萌发等多种生命活动。

For GCSE AQA Biology, you need to know about three main plant hormones: auxins, gibberellins, and ethene (formerly called ethylene). The specification also expects you to understand tropisms – phototropism and gravitropism (geotropism) – and explain them using unequal distribution of auxin.

在 AQA GCSE 生物学中，你需要掌握三种主要的植物激素：生长素、赤霉素和乙烯（旧称乙烯）。大纲还要求你理解向光性和向地性（向重力性），并能用生长素的不均匀分布加以解释。

2. Auxins: The Growth Regulators | 生长素：生长的调控者

Auxins are a family of plant hormones that primarily promote cell elongation in shoots. The most common natural auxin is indole-3-acetic acid (IAA). Auxins are synthesised in the tips of shoots and roots and then diffuse or are transported to zones of elongation behind the tip.

生长素是一类主要促进地上部分细胞伸长的植物激素。最常见的天然生长素是吲哚-3-乙酸 (IAA)。它在茎尖和根尖合成，随后通过扩散或主动运输到达尖端的伸长区。

In shoots, auxin stimulates cell elongation, leading to growth.
在茎中，生长素促进细胞伸长，引起生长。
In roots, auxin inhibits cell elongation at higher concentrations, so only very low levels promote growth. This difference in sensitivity is crucial for tropisms.
在根中，较高浓度的生长素反而抑制细胞伸长，只有极低浓度才促进生长。这种敏感性差异是向性运动的关键。

3. Phototropism: How Plants Bend Toward Light | 向光性：植物如何向光弯曲

Phototropism is the directional growth of a plant in response to light. Shoots are positively phototropic (grow toward light), which ensures leaves receive maximum light for photosynthesis. Roots are generally negatively phototropic or unaffected.

向光性是植物对光作出的定向生长反应。地上部分正向光性（朝向光源生长），以确保叶片获得最大光照进行光合作用。根通常负向光性或无反应。

When light shines on one side of a shoot tip, auxin produced in the tip is redistributed to the shaded side. The higher auxin concentration on the shaded side causes cells there to elongate more rapidly than cells on the illuminated side. This unequal elongation causes the shoot to bend towards the light.

当单侧光照射茎尖时，顶端产生的生长素重新分布到背光侧。背光侧较高的生长素浓度使该侧细胞比向光侧伸长更快，这种不均等伸长导致茎朝向光源弯曲。

This can be demonstrated by removing the tip or covering it with an opaque cap – no phototropic response occurs. If a thin block of agar is used between tip and stump, the signal (auxin) still passes through, confirming it is a chemical signal.

这可以通过切除尖端或戴上不透光帽来验证——向光反应消失。若用薄琼脂块连接尖端和残端，化学信号（生长素）仍能通过，证明这是一种化学信号。

4. Gravitropism (Geotropism): Roots and Shoots | 向地性：根与茎的垂直生长

Gravitropism refers to growth in response to gravity. Shoots are negatively gravitropic (grow upwards, away from the pull of gravity), while roots are positively gravitropic (grow downwards, in the direction of gravity). This ensures shoots grow into the light and roots into the soil for anchorage and water uptake.

向地性是对重力的生长反应。地上部分负向地性（向上生长，背离重力方向），根正向地性（向下生长，顺着重力方向）。这保证了茎伸向光照，根钻入土壤以固定和吸收水分。

In a root placed horizontally, auxin accumulates on the lower side due to gravity. Because roots are more sensitive to auxin, the high concentration on the lower side inhibits cell elongation. Meanwhile, the upper side has a lower, growth-promoting concentration of auxin, so cells elongate faster there. The root therefore curves downwards.

在水平放置的根中，生长素因重力在下侧积累。由于根对生长素更敏感，高浓度抑制了下侧细胞的伸长。而上侧生长素浓度较低，促进细胞伸长，因此根向下弯曲。

In a shoot placed horizontally, more auxin likewise accumulates on the lower side, but here the higher concentration stimulates cell elongation, so the lower side grows faster and the shoot bends upwards.

水平放置的茎同样下侧积累较多生长素，但此处高浓度促进细胞伸长，下侧长得更快，茎向上弯曲。

5. Auxin in Rooting Powders | 生长素与生根粉

Gardeners and horticulturists use synthetic auxins as rooting agents to encourage cuttings to develop roots. A cutting is a small piece of plant stem or leaf without roots. Dipping the base into rooting powder containing auxin such as NAA (naphthalene acetic acid) stimulates rapid root development, enabling the cutting to grow into a new plant.

园艺工作者使用人工合成的生长素作为生根剂，促使插穗生根。插穗是没有根的小段植物茎或叶。将基部蘸取含有萘乙酸 (NAA) 等生长素的生根粉，可快速刺激根的生长，使插穗发育成新植株。

At very low concentrations, auxin promotes root cell elongation; at slightly higher concentrations it can also induce undifferentiated cells in the stem to differentiate into root cells. This is an important commercial application – it allows mass propagation of desirable plants with identical genetic characteristics (clones).

在极低浓度下，生长素促进根细胞伸长；稍高浓度下还能诱导茎中的未分化细胞分化为根细胞。这是一项重要的商业应用，可大量繁殖具有相同遗传特性的优良植株（克隆）。

6. Auxin as Weedkillers | 生长素类除草剂

Synthetic auxins are also used as selective weedkillers (herbicides). They are designed to act only on broad-leaved weeds (dicots) without harming narrow-leaved crop plants like grasses and cereals (monocots). A common example is 2,4-D (2,4-dichlorophenoxyacetic acid).

人工合成生长素也用作选择性除草剂。它们仅作用于阔叶杂草（双子叶植物），却不伤害禾本科和谷类作物（单子叶植物）。常见的例子是 2,4-D（2,4-二氯苯氧乙酸）。

When sprayed onto weeds, the synthetic auxin is absorbed and causes uncontrolled, abnormally rapid cell elongation and growth. This leads to distortion and eventually death of the weed. Crop plants have a different metabolism that breaks down the chemical or the auxin is not transported into their vascular system efficiently, making them resistant.

喷洒到杂草上后，人工合成生长素被吸收，引起失控的异常快速细胞伸长和生长，最终导致杂草畸形并死亡。作物新陈代谢不同，能分解该物质，或者生长素不能有效地运输到其维管系统，因此作物具有抗性。

7. Gibberellins: Seed Germination and Stem Growth | 赤霉素：种子萌发与茎伸长

Gibberellins are another group of plant hormones that are especially important in controlling seed germination and stem elongation. Commercially, they are used to break dormancy, promote flowering, and increase fruit size.

赤霉素是另一类植物激素，对控制种子萌发和茎的伸长尤为重要。商业上用于打破休眠、促进开花和增大果实。

In seed germination, gibberellins trigger the production of enzymes such as amylase in the seed. These enzymes break down starch stored in the endosperm into sugars, which provide the energy and building blocks for the embryo to begin growing. Without gibberellins, many seeds remain dormant even under favourable conditions.

在种子萌发过程中，赤霉素启动种子中淀粉酶等酶类的合成。这些酶将胚乳中储存的淀粉分解成糖，为胚的萌动提供能量和原料。没有赤霉素，许多种子即使条件适宜也保持休眠。

In stem elongation, gibberellins promote cell elongation and division in internodes (the regions between leaves). This is why gibberellin application can produce taller plants, and mutant varieties lacking gibberellins are dwarf.

在茎伸长方面，赤霉素促进节间（叶着生点之间的区域）的细胞伸长和分裂。因此施加赤霉素能培育出较高的植株，而缺乏赤霉素的突变体则呈现矮化。

8. Gibberellins in Fruit Development and Dormancy | 赤霉素与果实发育及休眠

In certain seedless varieties of fruit (e.g., some grapes), gibberellins are sprayed to increase fruit size without the need for fertilisation. This results in larger, marketable seedless grapes and other fruits.

某些无籽果实（例如部分葡萄品种）通过喷洒赤霉素，无需受精即可增大果实。这样生产出来的无籽葡萄等果实更大，更受市场欢迎。

Gibberellins can also be used to break the dormancy of buds and seeds that require a cold period (vernalisation) or light exposure. This is very useful for producing uniform germination in malting barley for beer production – the hormone ensures all grains germinate simultaneously.

赤霉素还可用于打破那些需要低温春化或光照才能解除休眠的芽和种子。这项特性特别适合啤酒生产中的大麦发芽：激素可确保所有麦粒同步萌发，便于均匀制麦。

9. Ethene (Ethylene): Fruit Ripening | 乙烯：果实催熟

Ethene is a gaseous plant hormone that plays a central role in fruit ripening and leaf fall (abscission). It is produced by fruits as they mature and accelerates the ripening process by promoting enzyme activities that soften cell walls, convert starches to sugars, and change colour.

乙烯是一种气态植物激素，在果实成熟和落叶（离层）中起核心作用。果实成熟时自身会释放乙烯，通过促进细胞壁软化酶、淀粉转糖和颜色变化等加速成熟过程。

Commercially, fruit like bananas and tomatoes are often transported unripe while green and hard, which reduces damage during shipping. At their destination, they are exposed to a controlled amount of ethene gas to trigger ripening just before they reach the shops. This ensures fruit reaches consumers in prime condition.

商业上，香蕉、番茄等水果通常在未成熟、绿色坚硬的阶段运输，以减少损耗。到达目的地后，再进行一定浓度的乙烯气体处理，在上市前启动成熟。这保证了消费者获得最佳状态的水果。

Ethene also promotes leaf abscission – the shedding of leaves in autumn or under stress. It weakens the cell walls at the base of the leaf stalk, causing it to separate from the stem.

乙烯还促进落叶——秋季或胁迫条件下叶片的脱落。它削弱叶柄基部细胞壁，使叶片与茎分离。

10. Interactions of Plant Hormones | 植物激素的相互作用

Plant hormones do not work in isolation; they often interact synergistically (working together) or antagonistically (opposing each other). For instance, auxin and gibberellins both promote stem elongation, so their effects can be additive. However, auxin in roots inhibits elongation at high concentrations, while gibberellins may have different tissue-specific effects.

植物激素并非单独作用，它们常表现出协同或拮抗效应。例如，生长素和赤霉素都能促进茎伸长，效果可以叠加。但在根中，高浓度生长素抑制伸长，而赤霉素可能因组织而异。

Abscisic acid (ABA) – though not a required detail for AQA – works antagonistically with gibberellins in seed dormancy: gibberellins break dormancy, ABA maintains it. Understanding these balances helps explain why a single hormone can have diverse roles depending on concentration, target tissue, and presence of other hormones.

脱落酸 (ABA)（尽管 AQA 不要求详细掌握）在种子休眠中与赤霉素相拮抗：赤霉素打破休眠，ABA 则维持休眠。理解这些平衡有助于说明为什么同一激素根据浓度、靶组织和其它激素的存在可有多种角色。

11. Commercial Uses Summary | 商业应用概览

Plant Hormone / 激素	Commercial Use / 商业用途
Auxins (生长素)	Rooting powders, selective weedkillers, promoting cell elongation in tissue culture
Gibberellins (赤霉素)	Breaking seed dormancy, promoting uniform flowering, increasing fruit size, malting barley
Ethene (乙烯)	Controlled fruit ripening, promoting leaf drop in cotton and cherry harvesting

These applications make plant hormones valuable in agriculture and horticulture. They help reduce waste, improve yields, and allow year-round production of many fruits and ornamental plants.

这些应用使植物激素在农业和园艺中极具价值：它们有助于减少损耗、提高产量，并实现多种水果和观赏植物全年生产。

12. Exam Tips and Common Mistakes | 应试技巧与常见错误

Exam questions on plant hormones often focus on explaining tropisms step by step. Be precise: always say ‘unequal distribution of auxin’ instead of just ‘auxin causes growth’. Remember to link the side with more auxin to the response – in shoots more auxin = more elongation, in roots more auxin = less elongation.

有关植物激素的考题往往要求逐步解释向性运动。务必精准：使用“生长素的不均等分布”而非简单说“生长素引起生长”。要记住把生长素较多的一侧和反应对应起来——茎中生长素多 = 伸长更快，根中生长素多 = 伸长受抑。

Common mistakes: confusing the response of shoots and roots to auxin; forgetting that auxin is produced in the tip and then moves; stating that ethene kills plants rather than ripens fruit; and not naming a specific commercial use for each hormone. Use clear terms like ‘positive phototropism’ and ‘negative gravitropism’.

常见错误包括：混淆茎和根对生长素的反应；忘记生长素在尖端生成然后运输；错误认为乙烯是杀植物而非催熟果实；未能为每种激素举出一个具体商业用途。请使用“正向光性”、“负向地性”等清晰术语。

When describing experiments, mention the removal of the tip or the use of mica sheets to block auxin movement, and always link back to the hormone concept. Be ready to interpret graphs showing plant response to hormone concentrations.

在描述实验时，提及切除尖端或使用云母片阻断生长素运输，并始终关联到激素这一概念。还要能解读显示植物对激素浓度反应的图表。

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Plant Hormones for GCSE AQA Biology | GCSE AQA 生物：植物激素 考点精讲