📚 Mock Exam Analysis: Cell Biology and Transport | 单元测试模拟卷解析：细胞生物学与物质运输
This article provides a detailed walkthrough of a Year 10 CIE Biology unit test covering cell structure, magnification, specialised cells, diffusion, osmosis, and active transport. Each question is broken down with model answers, explanations, and common pitfalls to help you consolidate key concepts and exam technique.
本文详细解析一份 Year 10 CIE 生物单元测试模拟卷，内容涵盖细胞结构、放大倍数、特化细胞、扩散、渗透和主动运输。每道题均提供答案范本、解析以及常见错误提示，帮助你巩固核心概念和应试技巧。
1. Calculating Total Magnification | 计算总放大倍数
ctive lens marked ×40 to observe onion epidermis cells. Calculate the total magnification.
问题：学生用一架目镜标有×10、物镜标有×40的光学显微镜观察洋葱表皮细胞。计算总放大倍数。
Answer: Total magnification = eyepiece magnification × objective magnification = 10 × 40 = ×400.
答案：总放大倍数 = 目镜放大倍数 × 物镜放大倍数 = 10 × 40 = ×400。
Explanation: In a compound light microscope, the image is magnified twice – addition; remember it is multiplication. Also, ensure you write the final answer with the multiplication sign (×) and no units, because magnification is a ratio.
解析：在复合光学显微镜中，图像经过两次放大——先由物镜放大，再由目镜放大。总放大倍数是两者放大倍数的乘积。考生常误用加法；务必记住是乘法。此外，答案要带乘号（×）但不写单位，因为放大倍数是比值。
2. Identifying Organelles from a Diagram | 从示意图中识别细胞器
Question: The diagram shows a typical animal cell. Identify the organelles labelled A, B, and C. (Diagram: A – nucleus, B – mitochondrion, C – ribosome.)
问题：示意图显示一个典型的动物细胞。识别标有A、B和C的细胞器。（图：A – 细胞核，B – 线粒体，C – 核糖体。）
- Organelle A is the nucleus, which contains genetic material (DNA) and controls cell activities.
- Organelle B is a mitochondrion, the site of aerobic respiration where energy is released.
- Organelle C is a ribosome, which carries out protein synthesis.
- 细胞器A是细胞核，含有遗传物质（DNA），控制细胞活动。
- 细胞器B是线粒体，有氧呼吸的场所，释放能量。
- 细胞器C是核糖体，进行蛋白质合成。
Common mistake: Mixing up mitochondria with chloroplasts – remember animal cells never have chloroplasts or a cell wall. Also, ribosomes are tiny dots, often on rough endoplasmic reticulum but sometimes free in the cytoplasm; students may miss them if not drawn clearly.
常见错误：将线粒体与叶绿体混淆——牢记动物细胞没有叶绿体和细胞壁。另外，核糖体是极小的小点，常附着在粗糙内质网上，也可游离在细胞质中；若图示不清，学生可能漏看。
3. Comparing Plant and Animal Cells | 比较植物细胞与动物细胞
Question: State two structures present in a palisade mesophyll cell that are absent from a human cheek cell.
问题：说出栅栏叶肉细胞中存在而人口腔上皮细胞中不存在的两种结构。
| Structure (English) | 结构（中文） | Function |
|---|---|---|
| Cell wall | 细胞壁 | Provides support and shape |
| Chloroplast | 叶绿体 | Site of photosynthesis |
| Large permanent vacuole | 大液泡 | Maintains turgor pressure, stores cell sap |
Answer: Any two from the table above, e.g. cellulose cell wall and chloroplasts. The large central vacuole is also acceptable. Animal cells lack all three.
答案：从上表中任选两项，例如纤维素细胞壁和叶绿体。中央大液泡也可。动物细胞均不具备这三种结构。
Explanation: Plant cells share many organelles with animal cells (nucleus, mitochondria, ribosomes, cell membrane), but they have some unique features. Always mention 'cell wall' rather than just 'wall' to be precise. Chloroplasts and permanent vacuole are key distinguishing features. Note that not all plant cells have chloroplasts – root cells, for example, lack them.
解析：植物细胞与动物细胞共享许多细胞器（细胞核、线粒体、核糖体、细胞膜），但植物细胞有一些独有特征。务必使用“细胞壁”而非简单“壁”以求精确。叶绿体和中央大液泡是主要的区分特征。注意并非所有植物细胞都含叶绿体——例如根细胞就没有。
4. Bacterial Cell Structure | 细菌细胞结构
Question: Explain how the structure of a bacterial cell differs from that of a typical plant cell. Give one similarity.
问题：解释细菌细胞的结构与典型植物细胞有何不同。举出一个相似点。
Differences: Bacterial cells are much smaller (1–5 µm), have no nucleus – instead they contain a circular loop of DNA free in the cytoplasm; they lack membrane-bound organelles like mitochondria and chloroplasts; some possess a slime capsule and flagella for movement. Similarity: Both bacterial and plant cells have a cell wall, but the bacterial cell wall is made of peptidoglycan (not cellulose) and they both have cytoplasm and cell membrane.
不同点：细菌细胞小得多（1–5 µm），无细胞核——遗传物质是游离在细胞质中的环状DNA；缺乏膜包裹的细胞器如线粒体、叶绿体；有些细菌具荚膜和鞭毛用于运动。相似点：细菌和植物细胞都有细胞壁，但细菌细胞壁由肽聚糖构成（而非纤维素）；两者均有细胞质、细胞膜。
Exam tip: When asked for differences, always compare the same feature in both cell types. Saying 'bacteria have no nucleus, plant cells have a nucleus' is clearer than just 'bacteria have no nucleus'. The similarity can be: both have cell membrane, cytoplasm, ribosomes (though smaller 70S in bacteria). Avoid writing 'both are unicellular' as a similarity because a plant cell can be part of a multicellular organism; this comparison is at cellular level.
考试技巧：回答差异时，务必对同一特征在两种细胞间进行比较。如说“细菌无细胞核，植物细胞有细胞核”比仅说“细菌无细胞核”更清晰。相似点可以是：两者均有细胞膜、细胞质、核糖体（尽管细菌为70S小核糖体）。避免将“均为单细胞”作为相似点，因为植物细胞可来自多细胞生物，此处比较的是细胞层次。
5. Specialised Cells and Adaptation | 特化细胞及其适应
Question: The root hair cell is adapted for absorbing water and mineral ions. Describe two adaptations visible in a diagram and explain how each helps its function.
问题：根毛细胞适于吸收水分和矿质离子。描述示意图中可见的两种适应特征，并解释各自如何帮助其功能。
- Adaptation 1: The root hair cell has a long, thin extension (root hair) that dramatically increases surface area for efficient uptake of water by osmosis and mineral ions by active transport.
- Adaptation 2: It contains many mitochondria in the cytoplasm near the cell membrane to provide energy (ATP) for active transport of mineral ions against their concentration gradient.
- Adaptation 1: 根毛细胞具有细长的突起（根毛），极大地增加了表面积，有利于通过渗透高效吸收水分，通过主动运输吸收矿质离子。
- Adaptation 2: 其细胞质中靠近细胞膜处含有大量线粒体，为矿质离子逆浓度梯度的主动运输提供能量（ATP）。
Note: Other adaptations may include a thin cell wall (not lignified) to reduce diffusion distance, but the question specifies visible in a diagram, so the long projection and numerous mitochondria are most obvious. Always link the adaptation to the process (osmosis or active transport).
注意：其他适应特征可能包括薄且未木质化的细胞壁以缩短扩散距离，但题目要求示意图可见，因此长突起和大量线粒体最为明显。一定要将适应特征与生理过程（渗透或主动运输）联系起来。
6. Diffusion – Definition and Examples | 扩散——定义与实例
Question: Define diffusion and give one biological example of where it occurs in the human body.
问题：定义扩散，并给出人体内发生扩散的一个生物学实例。
Definition: Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient, as a result of their random motion. It is a passive process that does not require energy from respiration.
定义：扩散是粒子由于随机运动从高浓度区域向低浓度区域沿浓度梯度的净移动。它是被动过程，不需要呼吸作用提供的能量。
Example: Oxygen diffuses from the alveoli (high oxygen concentration) into the blood in the pulmonary capillaries (low oxygen concentration). Carbon dioxide diffuses in the opposite direction, from the blood into the alveoli, to be exhaled.
例子：氧气从肺泡（高氧气浓度）扩散进入肺毛细血管的血液中（低氧气浓度）。二氧化碳反向扩散，从血液进入肺泡，被呼出体外。
Common error: Students often write 'movement' instead of 'net movement', forgetting that particles move randomly in both directions. Also, stating 'diffusion requires energy' is incorrect – it is passive. Other valid examples: movement of glucose in the small intestine, or oxygen into respiring cells.
常见错误：学生常写“移动”而非“净移动”，忘记了粒子会随机双向运动。另外，声称“扩散需要能量”是错误的——它是被动过程。其他有效实例：葡萄糖在小肠中的移动，或氧气进入呼吸细胞。
7. Osmosis – Potato Strip Experiment | 渗透——土豆条实验
Question: A student placed identical strips of potato in pure water and in a concentrated sugar solution for 30 minutes. Predict and explain the changes in length and turgidity of the strips.
问题：学生将相同的土豆条分别放入纯水和浓蔗糖溶液中浸泡30分钟。预测并解释土豆条长度和膨胀度的变化。
In pure water: The potato strip will increase in length and become turgid (firm). Water molecules move into the potato cells by osmosis because the water potential inside the cells is lower (more negative) than pure water (0 kPa). The cells gain water, swell, and the cytoplasm pushes against the cell wall, making the tissue crisp.
在纯水中：土豆条长度增加，变得硬挺。水分子通过渗透进入土豆细胞，因为细胞内的水势比纯水（0 kPa）低（更负）。细胞吸水膨胀，细胞质推挤细胞壁，使组织变脆。
In concentrated sugar solution: The potato strip will decrease in length and become flaccid (limp). The water potential of the sugar solution is lower (more negative) than that of the cell cytoplasm, so water moves out of the cells by osmosis. The cells lose water, the cytoplasm shrinks and pulls away from the cell wall (incipient plasmolysis), causing the tissue to become soft and shrink.
在浓蔗糖溶液中：土豆条长度缩短，变得萎软。蔗糖溶液的水势比细胞质更低（更负），水通过渗透从细胞中移出。细胞失水，细胞质收缩并与细胞壁分离（初始质壁分离），导致组织变软、皱缩。
Examiners often credit the use of 'water potential' rather than 'water concentration'. Remember: water moves from a region of higher water potential (less negative) to a region of lower water potential (more negative). Using the term 'turgid' for plant cells and 'flaccid' for limp tissue gains marks.
评分者通常认可使用“水势”而非“水浓度”。记住：水从水势较高（较不负）的区域移向水势较低（较负）的区域。使用“硬挺”描述植物细胞的膨胀状态，“萎软”描述失水松弛的组织，可得高分。
8. Active Transport – Uptake of Ions | 主动运输——离子吸收
Question: Explain why root hair cells can absorb nitrate ions from soil water even when the nitrate concentration inside the cell is much higher.
问题：解释为什么根毛细胞能从土壤溶液中吸收硝酸根离子，即使细胞内硝酸根离子浓度已远高于外部。
Explanation: Nitrate ions are absorbed by active transport. Active transport is the movement of molecules or ions from a region of lower concentration to a region of higher concentration against the concentration gradient, using energy from respiration (ATP). Carrier proteins in the cell membrane bind to nitrate ions, change shape, and pump them into the cell. This process does not happen by diffusion because diffusion would only move ions down the gradient.
解释：硝酸根离子通过主动运输被吸收。主动运输是分子或离子逆浓度梯度从低浓度区域向高浓度区域的移动，需要呼吸作用提供的能量（ATP）。细胞膜上的载体蛋白与硝酸根离子结合，改变形状，将其泵入细胞内。扩散无法完成此过程，因为扩散只能使离子沿浓度梯度移动。
Key points to include: against concentration gradient, carrier protein, energy from respiration. Temperature and oxygen availability affect active transport because they influence the rate of respiration. If roots are waterlogged, lack of oxygen reduces respiration, so active transport slows and fewer nitrate ions are taken up, leading to poor growth.
答题要点：逆浓度梯度、载体蛋白、呼吸供能。温度与氧气供应影响主动运输，因其影响呼吸速率。若根部淹水缺氧，呼吸减弱，主动运输变慢，硝酸根离子吸收减少，导致植株生长不良。
9. Comparing Diffusion, Osmosis, and Active Transport | 比较扩散、渗透和主动运输
Question: Complete the table to compare the three transport processes.
问题：完成表格比较这三种运输过程。
| Feature | Diffusion | Osmosis | Active Transport |
|---|---|---|---|
| Particles moved | Any molecules or ions (e.g. O₂, CO₂) | Water molecules only | Specific ions or molecules (e.g. nitrate, glucose) |
| Direction of net movement | Down concentration gradient | Down water potential gradient | Against concentration gradient |
| Requires membrane? | No | Yes (partially permeable) | Yes (carrier proteins) |
| Energy needed? | No (passive) | No (passive) | Yes (ATP from respiration) |
Answer: See completed table above. Students must recognise that osmosis is a special case of diffusion involving water molecules across a partially permeable membrane. Active transport is fundamentally different because it requires metabolic energy and can move substances against their gradients.
答案：见上表。学生须认识到渗透是扩散的一种特殊情况，涉及水分子穿过半透膜。主动运输根本不同，因为需代谢能量并可逆浓度梯度运输物质。
Memory aid: “Diffusion is free, osmosis is water-specific and membrane-dependent but still free, active transport is the paid pump.” Always use scientific terms precisely: 'water potential' for osmosis, 'concentration gradient' for diffusion, and 'carrier proteins' for active transport.
记忆口诀：“扩散免费，渗透专运水且靠膜仍是免费，主动运输是付费泵。”务必准确使用科学术语：渗透用“水势”，扩散用“浓度梯度”，主动运输用“载体蛋白”。
10. Surface Area to Volume Ratio and Transport | 表面积与体积之比与运输
Question: Using the examples of a large Amoeba and a small Amoeba, explain why unicellular organisms do not require a circulatory system, whereas large multicellular organisms do.
问题：以大变形虫和小变形虫为例，解释为何单细胞生物不需循环系统，而大型多细胞生物需要。
Small unicellular organisms like Amoeba have a large surface area to volume ratio (SA:V). Substances such as oxygen and waste products can diffuse directly across the cell membrane fast enough to meet the cell's needs, because the diffusion distance is very short. Thus, no specialised transport system is required.
像变形虫这样的小型单细胞生物具有较大的表面积与体积之比（SA:V）。氧气和废物等物质可直接跨细胞膜扩散，速度足以满足细胞需求，因为扩散距离极短。因此无需专门的运输系统。
In contrast, as organisms get larger, their SA:V decreases. In a large Amoeba, the volume increases more rapidly than the surface area, so the relative surface area available for exchange is smaller and the diffusion distance to the centre is longer. Simple diffusion becomes too slow to supply all cells with oxygen and remove waste. Multicellular organisms evolved systems like the circulatory system to transport substances rapidly over long distances, with exchange surfaces like lungs and intestines to maximise absorption.
相反，当生物体增大时，其SA:V降低。在大型变形虫中，体积增加比表面积快得多，因此可用于交换的相对表面积变小，且到中心的扩散距离变长。简单扩散太慢，无法为所有细胞提供氧气并排除废物。多细胞生物进化出循环系统等，以长距离快速运输物质，并具备肺、肠等交换表面以最大化吸收。
ide. As side increases, the ratio falls. Always link this concept to diffusion efficiency.
数学支持：对立方体，表面积 = 6 × 边长²，体积 = 边长³；SA:V = 6/边长。边长越大，比值越小。一定要将此概念与扩散效率挂钩。
Published by TutorHao | Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图