Cell Division, Cell Diversity and Cellular Organisation: Experimental Design | 细胞分裂、细胞多样性与细胞组织：实验设计

📚 Cell Division, Cell Diversity and Cellular Organisation: Experimental Design | 细胞分裂、细胞多样性与细胞组织：实验设计

Understanding cell division, diversity, and organisation forms the backbone of biology. Designing robust experiments to investigate mitosis, compare cell types, and examine tissue structure allows you to uncover the fundamental principles governing life at the microscopic level. This article walks you through key experimental techniques, from preparing root tip squashes to calculating mitotic indices, while emphasising careful planning, variables, and safety considerations.

理解细胞分裂、细胞多样性与细胞组织是生物学的基石。设计严谨的实验来探究有丝分裂、比较细胞类型并观察组织结构，能让你揭示微观层面操控生命的根本原理。本文带你走过关键实验技术，从制备根尖压片到计算有丝分裂指数，同时强调周密的计划、变量的控制和安全考量。

1. Introduction to Cell Division and Diversity Experiments | 细胞分裂与多样性实验简介

Experimental design in cell biology revolves around observing dynamic processes and static structures. The most iconic A‑level investigation involves visualising mitosis in garlic or onion root tips, but you can also explore cell diversity by preparing wet mounts of plant epidermis and animal cheek cells. Cellular organisation is typically studied through prepared slides of tissues such as muscle, xylem, and phloem, linking structure to function.

细胞生物学的实验设计围绕着观察动态过程和静态结构。最具代表性的A Level探究是使用大蒜或洋葱根尖观察有丝分裂，但你也可以通过制备植物表皮和动物口腔细胞的临时装片来探索细胞多样性。细胞组织通常通过肌肉、木质部和韧皮部等组织的预制切片来研究，将结构与功能联系起来。

2. Preparing a Root Tip Squash for Mitosis Observation | 制备根尖压片观察有丝分裂

To capture cells actively undergoing division, you must select the meristematic region just behind the root cap. Cut the terminal 2–3 mm of a garlic or onion root tip and place it in a watch glass. Add a few drops of 1 M hydrochloric acid and warm gently using a water bath at 60 °C for 5 minutes to soften the middle lamella and separate cells. This hydrolysis step is critical—too short and cells won’t separate, too long and DNA may degrade.

要捕捉正在活跃分裂的细胞，必须选取根冠后方仅数毫米的分生组织区。切取大蒜或洋葱根尖末端2–3 mm，放入表面皿中。加入几滴1 mol/dm³盐酸，在60 °C水浴中温和加热5分钟，以软化胞间层并分离细胞。这一水解步骤至关重要——时间太短细胞无法分开，太长则DNA可能降解。

After hydrolysis, rinse the root tips with cold distilled water to remove excess acid and then blot dry. Transfer the tip to a clean microscope slide, add a drop of acetic orcein or toluidine blue stain, and allow it to act for 2–3 minutes. Gently tap the tissue with a mounted needle to break up the root, then apply a coverslip. Place the slide between folds of filter paper and press firmly, taking care not to twist the coverslip, to produce a thin monolayer of squashed cells.

水解后，用冷蒸馏水冲洗根尖以去除多余酸液，然后吸干。将根尖转移到洁净载玻片上，滴加一滴醋酸地衣红或甲苯胺蓝染液，作用2–3分钟。用拨针轻轻敲散组织，然后盖上盖玻片。把玻片夹在滤纸折层之间，用力按压，注意不要扭转盖玻片，以获得单层压扁的细胞。

3. Staining Techniques for Chromosome Visibility | 使染色体可见的染色技术

Chromosomes are not visible under standard bright‑field microscopy without staining. Acetic orcein binds to DNA, turning chromosomes dark purple‑red and making prophase, metaphase, anaphase, and telophase stages distinguishable. Toluidine blue is a metachromatic stain that gives a slightly different contrast—nuclei appear blue, and cytoplasm faintly blue‑green. Feulgen stain, though more complex, is specific for DNA and can be used for quantitative analysis.

在标准明场显微镜下，不经过染色无法看清染色体。醋酸地衣红与DNA结合，使染色体呈深紫红色，从而可区分前期、中期、后期和末期。甲苯胺蓝是一种异染性染料，呈现出不同的对比度——细胞核呈蓝色，细胞质呈浅蓝绿色。福尔根染色法虽然更复杂，但特异性地标记DNA，可用于定量分析。

The choice of stain depends on the purpose of your investigation. For routine observation of mitotic figures, acetic orcein is preferred because it is quick, cheap, and does not require destaining. Always follow the recommended staining time; overstaining can obscure nuclear details and reduce the contrast between chromosomes and cytoplasm.

染色剂的选择取决于调查目的。对于常规观察有丝分裂相，醋酸地衣红是首选，因为它快速、廉价且无需脱色。务必遵循推荐的染色时长；过度染色会掩盖细胞核细节并降低染色体与细胞质之间的反差。

4. Calculating the Mitotic Index | 计算有丝分裂指数

The mitotic index is a quantitative measure of proliferative activity in a tissue. It is defined as:

有丝分裂指数是组织中增殖活性的一个量化指标，其定义为：

Mitotic Index = (Number of cells in mitosis ÷ Total number of cells counted) × 100%

To calculate it, systematically scan the field of view using a mechanical stage, identifying every cell in any stage of mitosis (prophase, metaphase, anaphase, telophase) and the total number of cells. A tally counter is helpful. Count at least 500 cells to ensure statistical reliability. Record individual counts from several different fields of view and calculate the mean mitotic index.

计算时，使用移动尺系统地扫描视野，找出处于有丝分裂任何阶段（前期、中期、后期、末期）的每一个细胞以及细胞总数。使用计数器会很有帮助。至少计数500个细胞以确保统计可靠性。记录数个不同视野的单独计数，计算平均有丝分裂指数。

In a well‑prepared garlic root tip squash, a mitotic index of 5–15 % is typical. This value varies with root age, temperature, and species. If your index is abnormally low, consider whether you sampled older, non‑dividing tissue beyond the meristem. High mitotic index is characteristic of cancerous tissues and is used in pathology to grade tumour aggressiveness—linking your school experiment to real‑world diagnostic science.

在一个制备良好的大蒜根尖压片中，典型的有丝分裂指数为5–15 %。该数值因根龄、温度和物种而异。如果你的指数异常偏低，考虑是否采集了分生区之外较老、不再分裂的组织。高有丝分裂指数是癌性组织的特征，在病理学中用于对肿瘤的侵袭性进行分级——这样就将你的校内实验与真实世界的诊断科学联系了起来。

5. Observing Cell Diversity: Plant vs Animal Cells | 观察细胞多样性：植物细胞与动物细胞对比

Cell diversity can be explored by preparing simple temporary mounts. To view plant cells, peel a thin layer of epidermis from an onion scale leaf, place it flat in a drop of water on a slide, add a coverslip, and examine under low and high power. Iodine solution can be used to stain the nucleus and starch grains. Typical features you will identify include a rigid cell wall, a large central vacuole, and chloroplasts if using Elodea leaves.

通过制备简单的临时装片可以探索细胞多样性。观察植物细胞时，从洋葱鳞叶上撕下一薄层表皮，平铺在载玻片的水滴中，盖上盖玻片，用低倍和高倍镜检视。可用碘液染色细胞核和淀粉粒。你将能够识别的典型特征包括刚性细胞壁、大的中央液泡，以及若使用伊乐藻叶片时出现的叶绿体。

For animal cells, gently scrape the inside of your cheek with a clean cotton swab, smear onto a slide, and add a drop of methylene blue. Rinse with a gentle stream of water to remove excess stain, then cover. Animal cells lack a cell wall and are usually smaller and more irregular in shape; their nucleus stains intensely blue. By comparing these two preparations, you can compile a table of structural differences, emphasising the link between ultrastructure and organism classification.

观察动物细胞时，用洁净棉签轻刮口腔内壁，涂抹在载玻片上，滴加一滴亚甲蓝溶液。用缓和水流冲洗去除多余染液，然后盖上盖玻片。动物细胞缺乏细胞壁，通常更小且形状更不规则；其细胞核被染成深蓝色。通过比较这两种制片，你可以编制一张结构差异表，从而强调超微结构与生物分类之间的联系。

6. Measuring Cell Size Using an Eyepiece Graticule | 使用目镜测微尺测量细胞大小

An eyepiece graticule is a glass disc with a scale inscribed, fitted into the microscope eyepiece. Because the graticule scale is arbitrary, you must calibrate it for each objective lens using a stage micrometer—a slide with a precise 1 mm scale divided into 100 equal 10 µm divisions. Line up the two scales and determine how many graticule units correspond to a known micrometer length.

目镜测微尺是一片刻有标尺的玻璃圆片，安装在显微镜目镜内。由于测微尺的刻度是任意的，你必须使用镜台测微尺对其在每个物镜倍率下进行校准——后者是一片刻有精确1 mm标尺、分为100格每格10 µm的载玻片。将两把尺线对齐，确定多少个测微尺单位对应已知的测微尺长度。

Once calibrated, you can measure cell diameter, nuclear width, or chloroplast length directly under the microscope without removing the slide. Record measurements in appropriate SI units—micrometres (µm) for most organelles. For example, a typical human cheek cell is about 50–60 µm in diameter, whereas an onion epidermal cell can be over 200 µm long. Consistent conversion from graticule units to real length is essential for accurate data.

一旦校准完毕，你就能直接在显微镜下测量细胞直径、细胞核宽度或叶绿体长度，而无需移走玻片。以合适的国际单位记录测量值——大多数细胞器用微米（µm）。例如，典型的人口腔细胞直径约为50–60 µm，而洋葱表皮细胞可超过200 µm长。将测微尺单位一致地转换为实际长度对获得准确数据至关重要。

7. Tissue Preparation and Sectioning | 组织制备与切片

Studying cellular organisation often requires thin sections of biological material. Fresh specimens such as stems or leaves must first be fixed to prevent decay, then embedded in wax or resin. A microtome is used to cut sections 5–20 µm thick, which are mounted on slides and stained. In school laboratories, you may use prepared permanent slides of transverse sections through a dicotyledonous stem, showing epidermis, cortex, vascular bundles, and pith.

研究细胞组织常常需要生物材料的薄切片。新鲜标本如茎或叶必须首先固定以防腐败，然后包埋在石蜡或树脂中。用切片机切取5–20 µm厚的薄片，将其贴在载玻片上并染色。在学校实验室，你可以使用现成的永久玻片，观察双子叶植物茎的横切面，显示出表皮、皮层、维管束和髓。

Alternatively, you can study animal tissue slides, such as ciliated epithelium from a trachea, striated muscle fibres, and blood smears. Each illustrates a level of organisation—from cells aggregated into tissues to organs built from multiple tissues. Drawing low‑power plan diagrams that only outline tissue layers, without any individual cell detail, hones your observation skills as required by many A‑level specifications.

你也可以研究动物组织玻片，例如气管的纤毛上皮、横纹肌纤维和血液涂片。每一个例子都展示了一个组织层次——从细胞聚集成组织，到由多种组织构建成器官。绘制只勾勒组织层次而不描绘任何个别细胞细节的低倍平面图，可以磨练你的观察能力，这也是许多A Level大纲所要求的。

8. Using Differential Staining to Identify Cellular Organelles | 使用差异染色识别细胞器

Differential staining employs more than one dye to distinguish different structures within a cell. For instance, a common protocol combines haematoxylin (which stains nuclei blue‑black) and eosin (which stains cytoplasm pink). In plant histology, safranin and fast green differentiate lignified tissues (red) from cellulose-rich tissues (blue‑green). This approach enables you to relate the distribution of cell types, such as xylem vessels and sclerenchyma fibres, to their mechanical and transport roles.

差异染色使用不止一种染料来区分细胞内的不同结构。例如，一种常用方案结合了苏木精（将细胞核染成蓝黑色）和伊红（将细胞质染成粉红色）。在植物组织学中，番红和固绿可以将木质化的组织（红色）与富含纤维素的组织（蓝绿色）区分开来。这一方法能让你将细胞类型的分布，如木质部导管和厚壁纤维，与其机械和运输作用联系起来。

When performing differential staining, following the exact sequence of dyes, washing, and dehydration steps is vital. Even minor deviations can lead to poor contrast or misleading colours. Always keep a control slide treated with one stain only, so you can confirm which colour corresponds to which cellular component.

在进行差异染色时，严格遵循染料、漂洗和脱水步骤的顺序至关重要。即使是微小的偏差都可能导致对比度差或误导性的颜色。务必保留一片仅用单一染料的对照玻片，这样你就能确认哪种颜色对应哪种细胞组分。

9. Experimental Variables and Controls | 实验变量与对照

A well‑designed cell biology experiment identifies independent, dependent, and controlled variables. In a mitotic index investigation, the independent variable could be temperature or exposure to a root growth promoter, while the dependent variable is the mitotic index itself. Controlled variables include root age, species, light intensity, pH of the growing medium, and staining procedure. Only by keeping these constant can you attribute any change in the index to your treatment.

一项设计良好的细胞生物学实验要明确自变量、因变量和控制变量。在有丝分裂指数探究中，自变量可以是温度或暴露于根部生长促进剂，而因变量则是有丝分裂指数本身。控制变量包括根龄、物种、光照强度、生长介质pH值和染色程序。只有让这些保持不变，你才能将指数的任何变化归因于你所施加的处理。

For cell diversity comparisons, the independent variable might be the source organism (plant vs animal), and the presence of a cell wall, chloroplasts, or central vacuole becomes a categorical dependent observation. Including a positive control, such as a known meristematic tissue slide, confirms that your staining and microscopy setup is working correctly. A negative control, perhaps omitting the primary stain, helps verify that observed signals are not artefacts.

对于细胞多样性比较，自变量可以是来源生物（植物与动物），而细胞壁、叶绿体或中央液泡的有无则成为分类因变量观察指标。纳入一个阳性对照，例如一张已知的分生组织玻片，可以确认你的染色和显微镜设置正常工作。阴性对照，比如省略主染剂，有助于验证所观察到的信号不是假象。

10. Safety and Ethical Considerations | 安全与伦理考量

Biological stains like acetic orcein and toluidine blue can be irritants; wear gloves, goggles, and a lab coat. Hydrochloric acid is corrosive—always warm it in a water bath, never over a naked flame, and wash any spills immediately with plenty of water. Cutting instruments such as scalpels must be used with care; a cutting board and proper technique minimise the risk of injury.

醋酸地衣红和甲苯胺蓝等生物染色剂可能具有刺激性；应佩戴手套、护目镜和实验服。盐酸具有腐蚀性——务必在水浴中温热，绝不可明火加热，任何溅出物都要立即用大量水冲洗。手术刀等切割器具须谨慎使用；使用切割垫板和规范的操作手法可最大程度降低受伤风险。

When collecting plant material, ensure you have permission if using specimens from communal gardens or farms, and avoid damaging rare species. For cheek cell sampling, use sterile cotton swabs and dispose of biological waste in the appropriate biohazard container. Ethical treatment of living organisms extends to plants: if growing roots hydroponically, maintain nutrient solution and dispose of spent material responsibly.

采集植物材料时，如果使用公共花园或农场的标本，需先获得许可，并避免损害稀有物种。口腔细胞取样时，使用无菌棉签，并将生物废弃物弃置于适当的生物危害品容器中。对活生物的伦理考量也适用于植物：若采用水培方式生根，应维持营养液浓度并负责任地处理废弃材料。

11. Data Recording and Analysis | 数据记录与分析

Meticulous recording underpins reliable experimental conclusions. Draw a results table with clear headings, units, and columns for repeat readings. When calculating the mitotic index, record both the raw counts of mitotic and total cells for each field of view. Then compute percentage and average across fields. Examples of a well‑structured table include:

一丝不苟的记录是可靠实验结论的基础。绘制一张结果表格，标题、单位和重复读数的列目要清晰。计算有丝分裂指数时，记录每个视野的有丝分裂细胞数和总细胞数的原始计数。然后计算百分比和跨视野的平均值。一个结构良好的表格示例如下：

Field of view	Cells in mitosis	Total cells	Mitotic index (%)
1	12	284	4.23
2	18	312	5.77

Calculate the mean mitotic index and comment on variability. If you observe a wide spread, use standard deviation or range bars in a column chart. For cell size measurements, compute the mean and the uncertainty, typically taken as half the smallest division you can read. Recognise that biological variation is inherent; an outlier might actually be a multicellular cluster counted as one, so always include raw data notes.

计算平均有丝分裂指数并对变异性加以评述。如果观察到较大的离散度，在柱状图中使用标准差或范围条。对于细胞大小的测量值，计算平均值和不确定度，通常取你能读取的最小分度值的一半。要认识到生物变异是固有存在的；一个异常值可能实际上是被当作一个细胞计数的一团多细胞簇，因此务必附上原始数据注释。

12. Common Errors and Troubleshooting | 常见错误与故障排除

One frequent mistake is applying too much pressure when squashing the root tip, which can shatter the coverslip or displace cells. Practice applying even, firm pressure using thumbs on filter paper. If cells appear clumped and opaque, insufficient hydrolysis is likely the cause; increase acid treatment time slightly, but never exceed 10 minutes. Bubbles under the coverslip can be minimised by lowering it at a 45° angle using a mounting needle.

一个常见错误是在压片时施加过大压力，这可能导致盖玻片破碎或细胞移位。应练习隔着滤纸用拇指施加均匀且稳固的压力。如果细胞成团且不透明，很可能是水解不足所致；可略微延长酸处理时间，但切勿超过10分钟。用拨针以45°角缓慢放下盖玻片可最大限度地减少气泡。

During staining, a pale preparation may mean the stain was too diluted or insufficient time was allowed. Conversely, intensely dark nuclei suggest overstaining; you can rinse the slide and re‑examine. When using a graticule, a common error is forgetting to recalibrate after switching objectives—this yields false measurements. Always confirm the calibration factor at the start of each microscopy session. Finally, if you struggle to locate mitotic cells, focus your search within approximately 1 mm behind the root tip; cells in the elongation and differentiation zones rarely divide.

染色时，制片颜色过淡可能意味着染液过稀或染色时间不足。反之，细胞核过深则提示过度染色；你可冲洗玻片后重新观察。使用测微尺时，一个常见错误是切换物镜后忘记重新校准——这会导致错误的测量结果。每次镜检伊始务必确认校准系数。最后，如果你难以找到有丝分裂细胞，将搜索范围集中在根尖后方约1 mm的区域；伸长区和分化区的细胞极少分裂。

Published by TutorHao | Biology Revision Series | aleveler.com

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