📚 Cell Division, Cell Diversity and Cellular Organisation Exam Practice | 细胞分裂、细胞多样性与细胞组织真题精练
This article is designed to strengthen your exam skills on the topic of cell division, cell diversity and cellular organisation. You will encounter typical question types, model thinking steps and common pitfalls. Each section reinforces key concepts through the lens of what examiners actually look for.
本文旨在强化你在细胞分裂、细胞多样性与细胞组织这一主题下的应试能力。你将遇到典型题型、模范解题思路以及常见误区。每个小节都从考官真正的关注点出发，巩固核心概念。
1. Mastering Mitosis Terminology | 掌握有丝分裂术语
Examiners often begin with direct recall of the names and order of mitotic phases: prophase, metaphase, anaphase and telophase. A single mark may depend on using ‘chromatid’ rather than ‘chromosome’ at the correct stage.
考官常从直接回忆有丝分裂各阶段的名称和顺序开始：前期、中期、后期和末期。在正确阶段使用‘染色单体’而非‘染色体’可能就决定了一分的得失。
During prophase, chromosomes condense and become visible as two sister chromatids joined at the centromere. The nuclear envelope breaks down and the spindle apparatus begins to form.
在前期，染色体凝缩，以着丝粒相连的两条姐妹染色单体形态可见。核膜解体，纺锤体开始形成。
A common mistake is describing metaphase as ‘chromosomes line up at the equator’ without mentioning attachment of spindle fibres to centromeres. Always state that spindle fibres attach to the centromeres and align the chromosomes at the metaphase plate.
常见错误是描述中期时只说‘染色体排列在赤道面’，未提及纺锤丝与着丝粒的连接。务必说明纺锤丝连接到着丝粒并将染色体排列在中期板上。
2. Distinguishing Mitosis from Meiosis in Exam Responses | 在答题中区分有丝分裂与减数分裂
Questions frequently require you to compare the two types of nuclear division. Mitosis produces two genetically identical diploid daughter cells, whereas meiosis produces four genetically varied haploid cells.
题目经常要求比较这两种核分裂方式。有丝分裂产生两个遗传上相同的二倍体子细胞，而减数分裂产生四个遗传上不同的单倍体细胞。
You must also link the reduction in chromosome number in meiosis I to the separation of homologous chromosomes, not sister chromatids. Meiosis II resembles mitosis, but the starting cell is haploid.
你还必须将减数第一次分裂中染色体数目的减半与同源染色体的分离联系起来，而不是姐妹染色单体的分离。减数第二次分裂类似有丝分裂，但起始细胞是单倍体。
When describing genetic variation, explicitly name crossing over in prophase I and independent assortment in metaphase I. Avoid vague phrases such as ‘genes get mixed’.
在描述遗传变异时，要明确指出前期I的交叉互换和中期I的独立分配。避免使用‘基因混合’等模糊表述。
3. Interpreting Diagrams of Cell Division | 解读细胞分裂图谱
Exam diagrams often show cells in different stages. You must identify the stage by looking at chromosome position, presence of a nuclear envelope, and whether chromosomes are in homologous pairs or as single chromatids.
考题图示常展现不同阶段的细胞。你必须通过观察染色体位置、核膜是否存在以及染色体是以同源对还是单一染色单体形态存在来判断阶段。
If a diagram shows four chromosomes lined up in two rows at the cell’s equator, it is metaphase I of meiosis. If chromosomes are in a single file, it is metaphase of mitosis or metaphase II.
如果图示显示四条染色体在细胞赤道面排成两行，这是减数分裂中期I。如果染色体排成单列，则是有丝分裂中期或减数第二次分裂中期。
Count the centromeres to determine chromosome number. A common error is counting chromatids as chromosomes, especially in anaphase when they separate.
通过计数着丝粒来确定染色体数目。常见错误是将染色单体误计为染色体，特别在后期它们分离时。
4. Tackling Data-Based Questions on the Cell Cycle | 攻克细胞周期数据题
You may be given a graph showing the relative DNA content of a population of cells. The first peak represents G₁ phase (2C DNA), the second peak G₂ and M phases (4C DNA), and the area in between represents S phase.
你可能会遇到显示细胞群体相对DNA含量的图表。第一个峰代表G₁期（2C DNA），第二个峰代表G₂和M期（4C DNA），中间区域代表S期。
To estimate the duration of a phase, multiply the total cycle time by the percentage of cells in that phase. For example, if 30% of cells are in S phase and the cycle lasts 20 hours, S phase lasts about 6 hours.
要估算某一阶段的时长，将总周期时间乘以该阶段细胞所占百分比。例如，如果30%的细胞处于S期而周期持续20小时，S期大约持续6小时。
Pay attention to units: DNA content can be measured in arbitrary units or picograms. Always quote the unit in your answer and show your working clearly.
注意单位：DNA含量可以用任意单位或皮克衡量。答题时始终写明单位，并清晰展示计算过程。
5. Stem Cells and Their Potency | 干细胞及其潜能
Mark schemes reward precise descriptions of cell potency. Totipotent stem cells can give rise to any cell type, including extra-embryonic tissues. Pluripotent cells can form any fetal cell type but not whole organisms. Multipotent cells are limited to a specific lineage.
评分方案对细胞潜能的确切描述给予加分。全能干细胞能产生任何细胞类型，包括胚胎外组织。多能干细胞能形成任何胎儿细胞类型，但不能形成完整生物体。专能干细胞限于特定谱系。
A typical question asks why embryonic stem cells are more useful than adult stem cells in therapy. You must mention pluripotency and the ability to differentiate into a wider range of cell types, plus the practical issue of supply.
典型问题会问为什么胚胎干细胞在治疗中比成体干细胞更有用。你必须提及多能性以及分化成更广泛细胞类型的能力，还有供应的实际问题。
Ethical considerations appear regularly. You might need to discuss the destruction of embryos versus the potential to cure diseases. Present a balanced argument if the question asks for discussion.
伦理考量频繁出现。你可能需要讨论破坏胚胎与治愈疾病潜力之间的权衡。如果题目要求讨论，要给出均衡的观点。
6. Cell Differentiation and Gene Expression | 细胞分化与基因表达
Differentiation is the process by which a cell becomes specialised. At the molecular level, some genes are switched on while others are switched off. Only the activated genes are transcribed and translated to produce specific proteins.
分化是细胞变得专门化的过程。在分子水平上，一些基因被开启而另一些被关闭。只有活化的基因被转录翻译，产生特定蛋白质。
Exam questions often ask how the structure of a differentiated cell is adapted to its function. For example, erythrocytes have no nucleus for more haemoglobin space, and are biconcave for large surface area.
考题常问分化细胞的结构如何适应功能。例如，红细胞无核以腾出更多空间容纳血红蛋白，呈双凹形以增大表面积。
Relate the adaptation to a measurable advantage, such as faster diffusion of oxygen. Use quantitative terms where possible: ‘short diffusion distance’ rather than just ‘small’.
要将适应性与可测量的优势联系起来，比如氧气扩散更快。尽可能使用量化术语：‘扩散距离短’而不仅仅是‘小’。
7. Levels of Organisation: From Cell to System | 组织层次：从细胞到系统
Cells of the same type form a tissue, different tissues form an organ, and organs work together in an organ system. A clear hierarchy must be presented when answering organisation questions.
同类细胞构成组织，不同组织构成器官，器官协同工作构成器官系统。在回答组织层次问题时，必须清晰呈现这一层级关系。
When describing the trachea, do not just list tissues; explain how each contributes to function: ciliated epithelium moves mucus, cartilage holds the airway open, smooth muscle constricts.
描述气管时，不要只列举组织；要解释每种组织如何贡献功能：纤毛上皮移动黏液，软骨保持气道开放，平滑肌收缩。
Comparison questions might ask you to relate X-ray images or microscope sections to tissue damage, such as emphysema destroying alveolar walls. Refer to the loss of elastic tissue and reduced surface area.
比较题可能要求你将X光图像或显微镜切片与组织损伤联系起来，比如肺气肿破坏肺泡壁。要提及弹性组织丧失和表面积减少。
8. Cancer and Uncontrolled Cell Division | 癌症与细胞分裂失控
Cancer results from uncontrolled mitosis due to mutations in genes that regulate the cell cycle, such as proto-oncogenes and tumour suppressor genes. Proto-oncogenes become oncogenes when mutated, leading to constant activation of cell division.
癌症源于调节细胞周期的基因突变导致的有丝分裂失控，如原癌基因和肿瘤抑制基因。原癌基因突变成为癌基因，导致细胞分裂持续激活。
A typical data question provides a survival graph for patients with different treatments. You must interpret the median survival time and comment on the significance of the difference, often using a statistical test.
典型的数据题会给出接受不同治疗的患者的生存曲线。你必须解读中位生存期，并对差异的显著性进行评论，常需使用统计检验。
Be prepared to explain how chemotherapy drugs target rapidly dividing cells by disrupting spindle formation or DNA replication. This links directly to your knowledge of the cell cycle.
准备好解释化疗药物如何通过干扰纺锤体形成或DNA复制来靶向快速分裂的细胞。这直接关联到你关于细胞周期的知识。
9. Common Mistakes in Exam Technique | 答题技巧常见错误
Misinterpreting the command word is a frequent error. ‘Describe’ requires an account of what happens; ‘explain’ demands reasons and mechanisms. A description of meiosis stages will not score full marks on an ‘explain’ question about genetic variation.
误解指令词是常见错误。“描述”要求叙述发生的过程；“解释”则需要原因和机制。在关于遗传变异的“解释”题中，仅描述减数分裂阶段不会得满分。
Another mistake is not using the data provided. If a question gives a table of mitotic index values for different tissues, you must quote the numbers and compare them, not just state that cancer tissue has a higher mitotic index.
另一个错误是不使用所给数据。如果题目给出了不同组织有丝分裂指数的表格，你必须引用数字并比较，而不仅仅是陈述癌组织有丝分裂指数更高。
Diagrams drawn by candidates often lack labels or are too small. Spend time drawing clear, large diagrams with ruled label lines. In mitotic diagrams, show the correct number of chromosomes as given.
考生画的图常缺乏标注或过小。花时间绘制清晰、大尺寸的图并用直尺引线标注。在有丝分裂图中，要显示题目给出的正确染色体数目。
10. Exam-Style Summary Question and Model Answer | 考试风格总结题与示范解答
Question: A scientist treats cultured human cells with a drug that inhibits DNA polymerase. She records the percentage of cells in each phase of the cell cycle over 24 hours. The results show an accumulation of cells in G₁ phase. Explain these results. (4 marks)
问题：科学家用抑制DNA聚合酶的药物处理培养的人类细胞。她记录了24小时内细胞周期各阶段的细胞百分比。结果显示G₁期细胞累积。解释这些结果。（4分）
Model answer: DNA polymerase is needed to replicate DNA during S phase. Without functional DNA polymerase, cells cannot progress through S phase. Consequently, cells complete mitosis but are unable to enter S phase, so they accumulate in G₁. The percentage of cells in G₁ therefore increases over the 24‑hour period as cycling cells become arrested before DNA replication.
示范解答：DNA聚合酶是在S期复制DNA所必需的。没有功能性DNA聚合酶，细胞无法通过S期。因此，细胞完成有丝分裂后不能进入S期，因而累积在G₁期。于是，随着周期细胞在DNA复制前被阻滞，G₁期细胞百分比在24小时内上升。
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