📚 IB & AQA Science: Plant Biology Key Concepts | IB 与 AQA 科学：植物生物学考点精讲
Plants are fundamental to life on Earth, providing oxygen, food, and habitats. In both IB and AQA science courses, plant biology is a core topic that combines cell biology, physiology, and ecology. This guide covers essential concepts, from photosynthesis to plant transport, hormones, and reproduction, helping you master exam-style questions with confidence.
植物是地球生命的基础，提供氧气、食物和栖息地。在 IB 和 AQA 科学课程中，植物生物学是一个融合了细胞生物学、生理学和生态学的核心主题。本指南涵盖从光合作用到植物运输、激素和繁殖的关键概念，帮助你自信应对考试题型。
1. Plant Cells and Tissues | 植物细胞与组织
Plant cells are eukaryotic and have several distinctive features: a cellulose cell wall, a large permanent vacuole, and chloroplasts for photosynthesis.
植物细胞是真核细胞，具有几个独特特征：纤维素细胞壁、一个永久性大液泡和进行光合作用的叶绿体。
Palisade mesophyll cells are located beneath the upper epidermis and are packed with chloroplasts to capture light energy efficiently.
栅栏叶肉细胞位于上表皮下方，富含叶绿体以高效捕获光能。
Spongy mesophyll cells have irregular shapes and air spaces, facilitating gas exchange of CO₂ and O₂.
海绵叶肉细胞形状不规则且有气室，便于二氧化碳和氧气的气体交换。
Guard cells surround stomata and change shape to regulate water loss and gas entry. They swell when turgid, opening the stoma.
保卫细胞围绕气孔，通过改变形状来调节水分流失和气体进入。当它们吸水膨胀时，气孔张开。
2. Photosynthesis: Light and Dark Reactions | 光合作用：光反应与暗反应
Photosynthesis converts light energy into chemical energy stored in glucose. The overall word equation is:
光合作用将光能转化为储存在葡萄糖中的化学能。总文字方程为：
carbon dioxide + water → glucose + oxygen
二氧化碳 + 水 → 葡萄糖 + 氧气
The balanced symbol equation is:
平衡的化学方程式为：
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
In IB Biology, the process is divided into light-dependent reactions occurring in the thylakoid membranes, producing ATP and NADPH, and light-independent reactions (Calvin cycle) in the stroma, which fix CO₂ into glucose.
在 IB 生物中，该过程分为在类囊体膜上进行的光反应，产生 ATP 和 NADPH，以及在基质中进行的暗反应（卡尔文循环），将二氧化碳固定为葡萄糖。
For AQA, students must know that photosynthesis requires chlorophyll and takes place in chloroplasts; it is an endothermic reaction that uses energy from light.
对于 AQA，学生必须知道光合作用需要叶绿素并在叶绿体中进行；这是一个利用光能的吸热反应。
3. Factors Affecting Photosynthesis | 影响光合作用的因素
Light intensity, carbon dioxide concentration, and temperature are the three main limiting factors of photosynthesis.
光照强度、二氧化碳浓度和温度是光合作用的三个主要限制因素。
At low light intensities, the rate of photosynthesis is limited by light; as intensity increases, the rate rises until another factor becomes limiting.
在低光照强度下，光合作用速率受光照限制；随着强度增加，速率上升，直到另一个因素成为限制。
Temperature affects enzyme activity in the Calvin cycle. Too high a temperature denatures enzymes, causing a sharp decline in photosynthesis rate.
温度影响卡尔文循环中的酶活性。温度过高会使酶变性，导致光合作用速率急剧下降。
AQA practicals often involve using pondweed to measure oxygen bubble production under varied light or CO₂ levels, while IB may require designing an experiment to investigate a limiting factor.
AQA 实验常用水蕴草在不同的光照或二氧化碳水平下测量氧气气泡的产生，而 IB 可能要求设计实验来探究某一限制因素。
4. Transpiration and Water Transport | 蒸腾作用与水分运输
Transpiration is the loss of water vapour from plant leaves through stomata. It creates a tension that draws water up the xylem from the roots.
蒸腾作用是植物叶片通过气孔散失水蒸气的过程。它产生拉力，将水分从根部通过木质部向上牵引。
The transpiration stream relies on cohesion and adhesion of water molecules, enabling continuous water flow in narrow xylem vessels.
蒸腾流依赖于水分子之间的内聚力和附着力，使得水在狭窄的木质部导管中连续流动。
Factors increasing transpiration rate include higher temperature, lower humidity, increased air movement, and higher light intensity.
提高蒸腾速率的因素包括较高的温度、较低的湿度、增加空气流动和较强的光照强度。
Root hair cells absorb water by osmosis and mineral ions by active transport, contributing to the water potential gradient that drives uptake.
根毛细胞通过渗透作用吸收水分，通过主动运输吸收矿质离子，形成驱动吸水的水势梯度。
5. Translocation in the Phloem | 韧皮部中的转运
Translocation is the movement of sugars and other organic solutes through the phloem from sources (leaves) to sinks (roots, fruits, meristems).
转运是指糖类和其他有机溶质通过韧皮部从源（叶片）运到库（根、果实、分生组织）的过程。
The pressure-flow hypothesis explains that sugars are actively loaded into the sieve tubes at the source, lowering water potential and drawing water in by osmosis, generating pressure to push sap towards the sink.
压力流动假说解释，糖类在源处被主动装载到筛管中，降低水势，水分通过渗透进入，产生压力将液流推向库。
Companion cells provide energy for active transport, as sieve tube elements lack nuclei and many organelles.
伴胞为主动运输提供能量，因为筛管分子缺少细胞核和许多细胞器。
AQA requires knowledge of phloem structure and function, while IB exams may ask you to analyse data on aphid stylet experiments tracing translocation.
AQA 要求掌握韧皮部的结构和功能，而 IB 考试可能要求分析利用蚜虫口针追踪转运的实验数据。
6. Plant Hormones: Auxins and Tropisms | 植物激素：生长素与向性
Auxins are plant hormones that control cell elongation and are central to phototropism and gravitropism (geotropism).
生长素是控制细胞伸长的植物激素，在向光性和向地性中起核心作用。
In shoot phototropism, auxin accumulates on the shaded side, causing cells there to elongate more, bending the shoot toward light.
在茎的向光性中，生长素在背光侧积累，使该侧细胞伸长更多，导致茎向光弯曲。
In root gravitropism, auxin accumulates on the lower side, but high auxin concentration inhibits root cell growth, so the root bends downward.
在根的向地性中，生长素在下方积累，但高浓度的生长素抑制根细胞生长，因此根向下弯曲。
AQA practicals often use seedlings in a clinostat to remove gravitational stimulus, while IB requires understanding of auxin transport proteins.
AQA 实验常用转器培养幼苗以消除重力刺激，而 IB 要求理解生长素转运蛋白。
7. Reproduction in Flowering Plants | 开花植物的繁殖
Flowers are the reproductive structures, containing male stamens (anther and filament) and female carpels (stigma, style, ovary).
花是繁殖结构，含有雄性雄蕊（花药和花丝）和雌性心皮（柱头、花柱、子房）。
Pollination is the transfer of pollen from anther to stigma; it can be self-pollination or cross-pollination, often aided by wind, insects, or other vectors.
传粉是花粉从花药转移到柱头的过程；可以是自花传粉或异花传粉，常借助风、昆虫或其他媒介。
Fertilisation involves a pollen tube growing down the style, delivering male gametes to the ovule for double fertilisation, forming a zygote and endosperm.
受精涉及花粉管沿着花柱向下生长，将雄配子送至胚珠完成双受精，形成合子和胚乳。
After fertilisation, the ovary develops into a fruit, and ovules become seeds, enabling dispersal and dormancy.
受精后，子房发育成果实，胚珠发育成种子，有助于传播和休眠。
8. Seed Germination and Dormancy | 种子萌发与休眠
Germination is the resumption of metabolic activity and growth of the embryo after a period of dormancy, requiring water, oxygen, and a suitable temperature.
萌发是休眠后胚的代谢活动和生长的重新开始，需要水、氧气和适宜的温度。
Water activates enzymes that break down stored food reserves in the cotyledons or endosperm into soluble sugars, amino acids, and other nutrients for the growing seedling.
水激活酶，将子叶或胚乳中储存的营养物质分解为可溶性糖、氨基酸等，供生长的幼苗使用。
Gibberellins are plant hormones that trigger the production of amylase, initiating starch breakdown in cereal grains during germination.
赤霉素是植物激素，在谷物种子萌发时触发淀粉酶的产生，开始分解淀粉。
AQA may ask about factors necessary for germination; IB may require experimental design to investigate the effect of gibberellin on seed germination.
AQA 可能考查萌发的必需条件；IB 可能要求设计实验探究赤霉素对种子萌发的影响。
9. Plant Adaptations to Environments | 植物对环境的适应
Xerophytes are plants adapted to arid conditions, with adaptations like thick waxy cuticles, sunken stomata, rolled leaves, and extensive roots to reduce water loss.
旱生植物适应干旱条件，具有厚蜡质角质层、内陷气孔、卷曲叶片和发达的根系等减少水分流失的适应特征。
Hydrophytes live in water or saturated soils; they have thin cuticles, large air spaces for buoyancy and gas exchange, and stomata on the upper leaf surface.
水生植物生活在水中或水饱和土壤中；它们具有薄的角质层、大的气室提供浮力和气体交换，气孔位于叶片上表面。
Halophytes tolerate high salt concentrations by excreting salt or accumulating solutes to maintain water potential.
盐生植物通过泌盐或积累溶质来维持水势，耐受高盐浓度。
In IB, you may need to compare adaptations of C3, C4, and CAM plants, while AQA focuses more on structural adaptations and their link to water loss.
在 IB 中，你可能需要比较 C3、C4 和 CAM 植物的适应机制，而 AQA 更侧重于结构适应及其与水分流失的关系。
10. Experimental Techniques in Plant Biology | 植物生物学实验技术
Potometers are used to measure water uptake by a stem, giving an indirect measurement of transpiration rate under different conditions.
蒸腾计用于测量茎的水分吸收量，间接测定不同条件下的蒸腾速率。
Chromatography can separate photosynthetic pigments like chlorophyll a, chlorophyll b, carotenes, and xanthophylls, helping calculate Rf values.
色谱法可以分离叶绿素 a、叶绿素 b、胡萝卜素和叶黄素等光合色素，并计算 Rf 值。
Using hydrogencarbonate indicator, we can measure CO₂ concentration changes due to photosynthesis and respiration in aquatic plants, a common AQA practical.
使用碳酸氢盐指示剂，可以测量水生植物光合作用和呼吸作用引起的二氧化碳浓度变化，这是 AQA 常见实验。
IB internal assessments may involve designing investigations on factors affecting seed germination, chlorophyll extraction, or using data loggers to monitor environmental variables on photosynthesis.
IB 内部评估可能包括设计探究影响种子萌发因素的实验、提取叶绿素，或使用数据记录仪监测环境变量对光合作用的影响。
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