📚 Plant Biology Key Points for IB OCR Science | IB OCR 科学：植物考点精讲
Plants are the foundation of almost every ecosystem and a core topic in IB and OCR science courses. From the intricate structure of a single leaf cell to the whole‑plant transport networks, a solid grasp of plant biology is vital for exam success. This revision guide covers the key concepts: cell specialisation, photosynthesis, transport, mineral nutrition, hormonal control, reproduction, and practical investigations, pairing every point in English and Chinese to help you learn actively.
植物是几乎所有生态系统的基础，也是 IB 与 OCR 科学课程的核心主题。从单个叶细胞的精细结构到整个植物的运输网络，扎实掌握植物生物学对考试成功至关重要。本复习指南涵盖关键概念：细胞特化、光合作用、运输、矿质营养、激素调控、生殖以及实验探究，每条要点均以中英双语对照，帮助你主动学习。
1. Plant Cells and Organelles | 植物细胞与细胞器
Plant cells share many organelles with animal cells, but three features set them apart: a cellulose cell wall, a large permanent vacuole, and chloroplasts. The cell wall, made of bundled cellulose microfibrils, gives the cell mechanical strength and prevents osmotic lysis. It is fully permeable to water and solutes.
植物细胞与动物细胞共有许多细胞器，但有三个特征使其截然不同：纤维素细胞壁、大液泡和叶绿体。由成束纤维素微纤丝构成的细胞壁赋予细胞机械强度，并防止渗透裂解，它对水和溶质都是全透性的。
The central vacuole is surrounded by a membrane called the tonoplast. It stores cell sap — a solution of sugars, salts, and sometimes pigments — and maintains turgor pressure against the cell wall. When the vacuole is full, the plant stands upright; if water is lost, the plant wilts.
中央液泡被一层称为液泡膜的膜包围。它储存细胞液——糖、盐、有时还有色素的溶液——并对细胞壁施加膨压。液泡充盈时，植物挺立；如果失水，植物就会萎蔫。
Chloroplasts are the site of photosynthesis. Each chloroplast is enclosed by a double membrane and contains stacks of thylakoids called grana, where the light‑dependent reactions occur. The fluid matrix, the stroma, is where the Calvin cycle uses ATP and reduced NADP to fix CO₂ into sugar. Chloroplasts also contain their own DNA and ribosomes, evidence for the endosymbiotic theory.
叶绿体是光合作用的场所。每个叶绿体被双层膜包裹，内含称为基粒的类囊体堆叠，光依赖反应即在此发生。流体基质——叶绿体基质——是卡尔文循环利用 ATP 和还原型 NADP 将 CO₂ 固定为糖的场所。叶绿体还含有自身的 DNA 和核糖体，这是内共生理论的证据。
2. Photosynthesis: Equation and Stages | 光合作用：方程与阶段
Photosynthesis is the process by which plants convert light energy into chemical energy stored in carbohydrates. The overall word equation is:
光合作用是植物将光能转化为储存在碳水化合物中的化学能的过程。总文字方程为：
carbon dioxide + water → glucose + oxygen
二氧化碳 + 水 → 葡萄糖 + 氧气
The balanced chemical equation, showing the stoichiometry, is:
展示化学计量配平的化学方程式为：
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
The process occurs in two main stages. The light‑dependent reactions take place in the thylakoid membranes. Water is split by photolysis (2H₂O → 4H⁺ + 4e⁻ + O₂), releasing oxygen as a by‑product. Light energy is absorbed by chlorophyll and used to generate ATP and reduced NADP. These products then pass to the stroma for the light‑independent reactions.
这一过程分为两个主要阶段。光依赖反应发生在类囊体膜上。水通过光解被分解（2H₂O → 4H⁺ + 4e⁻ + O₂），释放氧气作为副产物。光能被叶绿素吸收，用于产生 ATP 和还原型 NADP。这些产物随后进入基质，用于光不依赖反应。
The Calvin cycle is the light‑independent stage. It uses CO₂, ATP, and reduced NADP to synthesise triose phosphate, which can be converted into glucose, starch, or cellulose. The cycle regenerates RuBP so that carbon fixation can continue.
卡尔文循环即不依赖光阶段。它利用 CO₂、ATP 和还原型 NADP 合成磷酸丙糖，后者可转变为葡萄糖、淀粉或纤维素。该循环可再生 RuBP，使固碳持续进行。
3. Limiting Factors and Graphs | 限制因素与图表
The rate of photosynthesis is affected by light intensity, carbon dioxide concentration, and temperature. According to the law of limiting factors, the factor in shortest supply controls the rate. If light intensity increases while CO₂ remains constant, the rate rises until CO₂ becomes limiting.
光合作用速率受光照强度、二氧化碳浓度和温度的影响。根据限制因素定律，最缺乏的因素控制反应速率。如果在 CO₂ 保持不变时增加光照强度，速率会上升，直到 CO₂ 成为限制因素。
When interpreting graphs: a curve that levels off shows that a different factor is now limiting. For temperature, the rate increases to an optimum (usually 25–30 °C in temperate plants) and then declines sharply as enzymes denature. At very low CO₂ concentration, photosynthesis may be completely halted.
解读图表时：曲线趋于平稳表明此时另一因素成为限制。对于温度，速率上升到最适点（温带植物通常为 25–30 °C）后急剧下降，因为酶变性。在极低的 CO₂ 浓度下，光合作用可能完全停止。
Practical investigations often use an aquatic plant like Elodea placed in water with a solution of sodium hydrogencarbonate (source of CO₂). Counting oxygen bubbles produced per minute gives a measure of the rate, allowing students to explore how changing one factor alters photosynthesis.
实验探究常使用伊乐藻等水生植物，置于含碳酸氢钠溶液（提供 CO₂）的水中。数每分钟产生的氧气泡数目可衡量速率，让学生探索改变某一因素如何影响光合作用。
4. Leaf Structure and Gas Exchange | 叶片结构与气体交换
A dicotyledonous leaf is a masterpiece of adaptation for photosynthesis. The upper epidermis is transparent to allow light penetration and is covered by a waxy cuticle that minimises water loss. Just beneath, the palisade mesophyll layer is packed with elongated cells rich in chloroplasts, arranged vertically to maximise light capture.
双子叶植物的叶片是适应光合作用的杰作。上表皮透明，让光进入，并被蜡质角质层覆盖以减少水分流失。其下方，栅栏组织层密布富含叶绿体的细长细胞，且垂直排列以最大限度地捕获光能。
The spongy mesophyll layer below has irregular cells with large air spaces, facilitating rapid diffusion of CO₂ and O₂. The lower epidermis contains many stomata, each surrounded by a pair of guard cells. Guard cells regulate opening and closing; when turgid, the stoma opens allowing gas exchange, and when flaccid, it closes to conserve water.
下方的海绵组织层具有不规则细胞和发达的气隙，便于 CO₂ 和 O₂ 的快速扩散。下表皮含有许多气孔，每个气孔由一对保卫细胞环绕。保卫细胞调控气孔开闭；膨胀时气孔打开，允许气体交换；松弛时气孔关闭，以减少水分消耗。
Most photosynthesis occurs in the palisade layer, while the spongy layer and stomata ensure a short diffusion pathway. The vascular bundles (veins) contain xylem and phloem, delivering water and removing sugars.
光合作用大部分在栅栏组织中进行，海绵组织和气孔则确保了较短的扩散路径。维管束（叶脉）包含木质部和韧皮部，负责输送水分并运出糖分。
5. Xylem, Phloem and Vascular Bundles | 木质部、韧皮部与维管束
Water and dissolved minerals move upwards through xylem vessels, while sugars are transported both up and down through phloem sieve tubes. Xylem vessels are dead, hollow tubes with no end walls, strengthened by lignin in annular or spiral patterns. They carry water from roots to leaves via the transpiration stream.
水和溶解的矿物质通过木质部导管向上运输，而糖分则通过韧皮部筛管进行双向运输。木质部导管为死细胞、中空而两端无隔板，并因木质素环纹或螺旋加厚而加固。它们通过蒸腾流将水从根输送至叶。
Phloem consists of living sieve tube elements and companion cells. Sieve tubes lack most organelles but are connected by sieve plates; companion cells provide metabolic support and load sucrose through active transport. Translocation moves sucrose from sources (e.g. leaves) to sinks (e.g. roots, growing tips).
韧皮部由活筛管分子和伴胞构成。筛管缺乏多数细胞器，但通过筛板彼此相连；伴胞提供代谢支持，并通过主动运输装载蔗糖。运输作用将蔗糖从源（如叶）输送到库（如根、生长点）。
| Feature / 特征 | Xylem / 木质部 | Phloem / 韧皮部 |
|---|---|---|
| Cells / 细胞 | Dead, hollow / 死细胞，中空 | Living / 活细胞 |
| Material transported / 运输物质 | Water and minerals / 水和矿物质 | Sucrose and amino acids / 蔗糖与氨基酸 |
| Direction / 方向 | Upwards / 向上 | Both directions / 双向 |
| Wall / 壁 | Lignified / 木质化 | Cellulose, no lignin / 纤维素，无木质素 |
6. Transpiration: Factors and Measurement | 蒸腾作用：因素与测量
Transpiration is the evaporation of water from the aerial parts of a plant, mainly through stomata. It drives the transpiration stream, helping to transport minerals and cool the leaf. The rate is influenced by four main environmental factors: light intensity, temperature, humidity, and air movement.
蒸腾作用是水分从植物地上部分蒸发的过程，主要通过气孔。它驱动蒸腾流，有助于运输矿物质和冷却叶片。其速率受四个主要环境因素影响：光照强度、温度、湿度和空气流动。
- Light: in bright light stomata open widely; higher light → faster transpiration. / 光照：强光下气孔大开；光照越强，蒸腾越快。
- Temperature: higher temperature increases the kinetic energy of water molecules, speeding evaporation. / 温度：温度升高增加了水分子的动能，蒸发加快。
- Humidity: high humidity reduces the water vapour concentration gradient between leaf and air, slowing transpiration. / 湿度：高湿度减小了叶片与空气间的水汽浓度梯度，使蒸腾变慢。
- Wind: moving air removes humid air from around the leaf, maintaining a steep gradient. / 风：流动空气带走叶片周围的湿空气，保持较大的浓度梯度。
A potometer is used to estimate transpiration rate by measuring water uptake in a cut shoot. It works on the principle that the rate of water loss is proportional to water uptake. The distance moved by an air bubble in a capillary tube over time is recorded, and careful experimental control is needed to maintain a valid comparison.
蒸腾计用于通过测量切枝的吸水量来估算蒸腾速率。其原理是失水速率与吸水速率成正比。记录毛细管中气泡在一段时间内移动的距离，并需进行严格的实验控制以保持有效比较。
7. Mineral Ions and Deficiency Symptoms | 矿质离子与缺乏症
Plants require several inorganic ions to synthesise essential molecules. Nitrate ions (NO₃⁻) are needed for amino acid and protein production; magnesium ions (Mg²⁺) form the central atom of chlorophyll; phosphate ions (PO₄³⁻) are required for ATP and nucleic acids; potassium ions (K⁺) regulate stomatal opening and enzyme activation.
植物需要多种无机离子合成必要的分子。硝酸根离子（NO₃⁻）是制造氨基酸和蛋白质所需；镁离子（Mg²⁺）构成叶绿素中心原子；磷酸根离子（PO₄³⁻）是合成 ATP 和核酸所需；钾离子（K⁺）调控气孔开闭与酶激活。
| Ion / 离子 | Function / 功能 | Deficiency symptom / 缺乏症状 |
|---|---|---|
| NO₃⁻ | Protein, DNA, chlorophyll / 蛋白质、DNA、叶绿素 | Stunted growth, yellowing of older leaves / 生长矮小，老叶黄化 |
| Mg²⁺ | Chlorophyll synthesis / 叶绿素合成 | Interveinal chlorosis, yellow leaves / 脉间失绿，叶片黄化 |
| PO₄³⁻ | ATP, nucleic acids, membranes / ATP、核酸、膜 | Poor root growth, purple patches on leaves / 根系不良，叶片紫斑 |
| K⁺ | Stomatal regulation, enzyme activation / 气孔调节
Published by TutorHao | IB Science Revision Series | aleveler.com 更多咨询请联系16621398022（同微信） CommentsMore posts |
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导