📚 Year 10 CIE Science: Case Study Practical Drill | CIE 10年级科学：案例分析实战演练
In the CIE IGCSE Science examinations, case study questions test your ability to apply biological, chemical and physical concepts to real‑world scenarios. This article takes you through a complete practical drill, modelling the thinking and skills needed to excel.
在剑桥 IGCSE 科学考试中，案例分析题考察你将生物、化学和物理概念应用于真实情境的能力。本文带领你完成一次完整的实战演练，模拟解题思维与必备技能。
1. The Scenario: Green Lake Investigation | 案例情境：绿湖调查
Green Lake is a freshwater lake surrounded by farmland. In recent years, local residents have noticed excessive algal growth, a foul smell, and dead fish washing ashore. A team of scientists was asked to investigate the causes and assess the health of the lake ecosystem. They collected water samples, measured physical factors, and surveyed organisms at different depths. The data are summarised in the table below.
绿湖是一个被农田环绕的淡水湖。近年来，当地居民注意到藻类过度繁殖、散发恶臭并有死鱼冲上岸边。一组科学家受邀调查原因并评估湖泊生态系统的健康状况。他们采集了水样，测量了物理因子，并调查了不同水深处的生物。所得数据总结于下表中。
| Depth / 深度 (m) | Light intensity / 光强 (% of surface) | Temperature / 温度 (°C) | Dissolved oxygen / 溶解氧 (mg/L) | Nitrate concentration / 硝酸盐浓度 (mg/L) | Algal cells / 藻类细胞 (cells/mL) |
|---|---|---|---|---|---|
| 0 | 100 | 22 | 8.2 | 4.5 | 12 000 |
| 1.5 | 52 | 21 | 7.6 | 5.0 | 8 500 |
| 3.0 | 14 | 18 | 3.1 | 9.8 | 2 100 |
| 5.0 (bottom / 底部) | 0 | 12 | 0.4 | 15.2 | 300 |
The food chain observed was: algae → zooplankton → small fish → large fish → herons. Using this scenario, we can practise the full case‑study approach.
观察到的食物链为：藻类 → 浮游动物 → 小鱼 → 大鱼 → 苍鹭。利用这一情境，我们可以演练完整的案例分析流程。
2. Identifying Biological Concepts | 识别生物学概念
First, we link observations to syllabus topics. The rapid growth of algae suggests eutrophication. Fertilisers (containing nitrates and phosphates) from farmland wash into the lake, providing nutrients that boost algal blooms. This is an example of human impact on ecosystems.
首先，我们将观察现象与考纲知识联系起来。藻类快速繁殖暗示了富营养化。来自农田的肥料（含硝酸盐和磷酸盐）被冲刷入湖，提供营养盐从而促进藻类爆发。这是人类对生态系统影响的一个实例。
The algal bloom blocks sunlight, causing submerged plants to die. Decomposers (bacteria and fungi) break down dead organic matter, consuming a large amount of dissolved oxygen. The sharp drop in oxygen from 8.2 mg/L at the surface to 0.4 mg/L at the bottom supports this. This process explains the death of fish due to suffocation.
藻华遮挡阳光，导致沉水植物死亡。分解者（细菌和真菌）分解死去的有机物，消耗大量溶解氧。溶解氧从表层的 8.2 mg/L 骤降至底层的 0.4 mg/L 印证了这一点。该过程解释了鱼类因缺氧而死亡的现象。
The food chain gives us a classic trophic level structure. Energy transfer between each level is only about 10%, which can be linked to the limited number of herons in the area.
食物链提供了一个典型的营养级结构。每个营养级之间能量传递效率仅约 10%，这与该区域苍鹭数量有限的现象相关联。
3. Biology: Decomposition and Oxygen Depletion | 生物学：分解作用与氧耗尽
The role of decomposers is crucial. When algae die, they sink and are decomposed by aerobic bacteria. The equation representing aerobic respiration is:
分解者的角色至关重要。当藻类死亡后，它们沉到湖底并被好氧细菌分解。表示有氧呼吸的方程式为：
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
This shows that glucose (from dead cells) reacts with oxygen, releasing carbon dioxide and water. The large biochemical oxygen demand (BOD) lowers the oxygen concentration, creating anoxic conditions that kill aerobic organisms.
这表明葡萄糖（来自死细胞）与氧气反应，释放出二氧化碳和水。巨大的生化需氧量 (BOD) 降低了氧气浓度，形成缺氧环境，杀死需氧生物。
Students often need to explain why nitrate levels increase at greater depths. As bacteria decompose proteins from dead algae and fish, ammonium compounds are excreted and then converted to nitrates by nitrifying bacteria. This is part of the nitrogen cycle, another key CIE topic.
学生通常需要解释为何深层水中的硝酸盐浓度升高。当细菌分解死藻和死鱼的蛋白质时，会释放出铵化合物，随后由硝化细菌转化为硝酸盐。这属于氮循环的一部分，也是 CIE 考试的另一个重点话题。
4. Chemistry: Water Quality and Ion Tests | 化学：水质与离子检测
In the lab, scientists can test for nitrate ions. The standard CIE test involves adding sodium hydroxide and aluminium foil, then warming gently. If ammonia gas is produced (detected by damp red litmus turning blue), nitrates are present. The relevant half‑equation can be simplified as:
在实验室中，科学家可以检测硝酸根离子。CIE 标准检测方法是加入氢氧化钠和铝箔，然后微热。若产生氨气（使湿润的红色石蕊试纸变蓝），则表明存在硝酸盐。相关的半方程式可简化为：
NO₃⁻ + 4Zn + 7OH⁻ → NH₃ + 4ZnO₂²⁻ + 2H₂O (simplified redox)
Phosphate ions, which also contribute to eutrophication, can be tested using ammonium molybdate solution and nitric acid; a yellow precipitate confirms phosphate.
同样导致富营养化的磷酸根离子可通过钼酸铵溶液和硝酸来检测；产生黄色沉淀即确认磷酸盐。
The pH of the lake water might be slightly acidic (if tested at the bottom) due to the production of carbon dioxide during decomposition, forming carbonic acid. This connects to the acid‑base topic: CO₂ dissolves to form a weak acid.
由于分解过程产生二氧化碳，溶于水形成碳酸，湖底水体的 pH 可能呈弱酸性。这与酸碱主题相关联：CO₂ 溶解后形成弱酸。
CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻
5. Physics: Light Intensity and Limiting Factors | 物理：光强与限制因子
Light intensity is a key limiting factor for photosynthesis in aquatic producers. The data show that light decreases dramatically with depth. Using the inverse square law is not necessary at IGCSE, but the trend can be described qualitatively. At 3.0 m, light is only 14% of the surface value, significantly reducing the photosynthetic rate of algae and plants.
光强是水生生产者光合作用的关键限制因子。数据显示光强随深度急剧下降。在 IGCSE 阶段无需使用平方反比定律，但可定性描述趋势。在 3.0 m 深处，光强仅为表层的 14%，这显著降低了藻类和植物的光合作用速率。
Temperature also drops with depth. Since enzyme activity is temperature‑dependent, the cooler water at the bottom (12°C) will slow down metabolic rates of all organisms, including decomposers. However, the decomposition process still consumes oxygen because of the large amount of organic matter.
温度也随深度下降而降低。由于酶活性依赖温度，底层较冷的水 (12°C) 会减慢所有生物（包括分解者）的代谢速率。然而，由于有机物数量庞大，分解过程仍然消耗大量氧气。
Photosynthesis efficiency can be calculated by comparing the energy captured by producers to the incident light energy. This links directly to the energy topic.
光合作用效率可以通过比较生产者捕获的能量与入射光能来计算。这直接与能量主题挂钩。
6. Energy Efficiency Calculation | 能量效率计算
Suppose the solar energy reaching the lake surface is 2.0 × 10⁶ J per m² per day, and the algae fix 2.4 × 10⁴ J of that energy per m² per day. The percentage efficiency is:
假设到达湖面的太阳能为每天每平方米 2.0 × 10⁶ J，而藻类每天每平方米固定了 2.4 × 10⁴ J 的能量。百分比效率为：
Efficiency = (useful output ÷ total input) × 100% = (2.4×10⁴ ÷ 2.0×10⁶) × 100% = 1.2%
This is a typical value for photosynthetic efficiency. When analysing food chains, a known rule of thumb is that only about 10% of the energy at one trophic level is passed on to the next. Therefore, from algae to zooplankton, energy would drop from 2.4 × 10⁴ J to approximately 2.4 × 10³ J.
这是光合效率的典型数值。在分析食物链时，一条常用的经验法则是：一个营养级的能量仅有约 10% 传递到下一营养级。因此，从藻类传递到浮游动物，能量将从 2.4 × 10⁴ J 降至大约 2.4 × 10³ J。
Visualising energy flow in a pyramid of energy helps to explain why top predators require a large base of producers and why their numbers are small.
在能量锥中可视化能量流动，有助于解释为何顶级捕食者需要庞大的生产者基础以及为何其数量稀少。
7. Data Analysis: Spotting Trends | 数据分析：发现趋势
When presented with a table like the one above, examiners expect you to describe patterns and use data to support conclusions. For example: “As depth increases, dissolved oxygen decreases from 8.2 mg/L at the surface to 0.4 mg/L at 5 m, a drop of 95%.” Always quote figures.
面对类似上表的数据时，考官期望你描述规律并使用数据支持结论。例如：“随着深度增加，溶解氧从表层的 8.2 mg/L 下降到 5 m 处的 0.4 mg/L，降幅达 95%。”一定要引用数值。
Another trend is the negative correlation between nitrate concentration and dissolved oxygen. At the surface, nitrate is 4.5 mg/L and oxygen is high; at the bottom, nitrate rises to 15.2 mg/L while oxygen is almost zero. This indicates that anaerobic or low‑oxygen conditions favour the accumulation of nitrates.
另一个趋势是硝酸盐浓度与溶解氧呈负相关。表层硝酸盐为 4.5 mg/L 且氧气丰富；底层硝酸盐升至 15.2 mg/L 而氧气几乎为零。这表明缺氧或低氧条件有利于硝酸盐的累积。
Algal cell numbers are highest at the surface due to light availability, but this can crash as light becomes limiting and cells die off, sinking to the bottom.
由于光照充足，表层的藻类细胞数量最高，但随着光照成为限制因子，藻类会大量死亡并沉入水底，导致细胞数量锐减。
8. Experimental Design: Limiting Factors Investigation | 实验设计：限制因子探究
To model the effect of nitrate concentration on algal growth, a student might design a lab investigation. The independent variable is nitrate concentration (e.g., 0, 2, 4, 8, 16 mg/L). The dependent variable is the number of algal cells after a fixed time. Control variables include light intensity, temperature (incubator at 20°C), and the initial number of algal cells.
为模拟硝酸盐浓度对藻类生长的影响，学生可以设计一个实验。自变量为硝酸盐浓度（例如 0、2、4、8、16 mg/L）。因变量为固定时间后的藻类细胞数。控制变量包括光强、温度（培养箱保持 20°C）以及藻类初始细胞数。
The expected result is that algal numbers increase with nitrate up to a certain point, after which another factor (e.g., light or carbon dioxide) becomes limiting. This illustrates the concept of limiting factors, central to photosynthesis and population studies.
预期结果是藻类数量随硝酸盐升高而增加，直至某一点后另一因子（如光或二氧化碳）成为限制因子。这阐明了限制因子的概念，是光合作用和种群研究中的核心内容。
9. Evaluating the Evidence: Reliability and Validity | 证据评估：可靠性与有效性
Case study questions often ask you to evaluate the data. Is the evidence reliable? The scientists took readings only once at each depth; to improve reliability, they should repeat measurements and calculate a mean. They should also sample at multiple locations to ensure results are representative.
案例分析题常要求你评估数据。证据是否可靠？科学家在每个水深只测量了一次；为提高可靠性，他们应重复测量并计算平均值。同时应在多个地点取样以确保结果具代表性。
Were other variables controlled? For example, weather conditions on the sampling day (cloud cover affecting light), time of day (O₂ concentration fluctuates with photosynthesis), and possible point sources of pollution might have skewed the data. A fair test would require all these to be standardised.
其他变量是否得到控制？例如，采样当天的天气（云量影响光照）、一天中的时间（O₂ 浓度随光合作用波动）以及可能的点源污染都可能使数据产生偏差。公平测试要求所有这些条件标准化。
Considering the source of the investigation is also important. The scientists might have been sponsored by a fertiliser company; bias could exist, so independent verification is needed.
考虑调查的来源也很重要。科学家可能由肥料公司赞助；可能存在偏见，因此需要独立验证。
10. Common Mistakes in Case Studies | 案例分析中的常见错误
A typical error is failing to link the data back to biological processes. Instead of just stating “oxygen decreased”, you should say “oxygen decreased because decomposers aerobically respired, using up dissolved oxygen as they broke down dead algae”. Always give the scientific reason.
一个典型错误是未能将数据与生物过程联系起来。不应仅仅陈述“氧气减少了”，而应解释：“氧气减少是因为分解者进行有氧呼吸，在分解死藻的过程中消耗了溶解氧”。始终给出科学依据。
Another pitfall is misreading units or scales. In the table, nitrate is in mg/L, but if a graph has different scales, students may misinterpret. Always check the axes. Also, do not confuse correlation with causation: high nitrate and low oxygen happen together, but the underlying cause is eutrophication, not a direct chemical reaction between nitrate and oxygen.
另一个陷阱是误读单位或尺度。表格中硝酸盐以 mg/L 为单位，若图表使用了不同刻度，学生可能误判。始终检查坐标轴。此外，切勿将相关性与因果关系混淆：高硝酸盐和低氧气同时出现，但其根本原因是富营养化，并非硝酸盐与氧气之间的直接化学反应。
Finally, in extended responses, structure answers logically: identify the problem, explain the process step by step, then state the consequences. Use keywords such as ‘nutrients’, ‘algal bloom’, ‘BOD’, ‘anoxic’ to secure marks.
最后，在展开式作答中，要逻辑清晰地组织答案：识别问题，一步步解释过程，再阐述后果。使用“营养物质”、“藻华”、“生化需氧量”、“缺氧”等关键词以获取分数。
11. Your Turn: Apply the Skills | 实战练习：技能运用
Now imagine a nearby lake, Clear Lake, has low nitrate levels (2 mg/L) and high biodiversity. The farmers want to convert a grassland buffer zone into crop fields. Predict the likely changes in the lake’s abiotic and biotic factors over two years. Suggest a plan to monitor the impact, naming the variables you would measure and the sampling strategy. Use the frameworks above to construct a full answer.
现在想象附近的清水湖，硝酸盐浓度低（2 mg/L），生物多样性高。农民希望将一片草缓冲带转变为农田。预测两年内湖泊的非生物因子和生物因子可能发生的变化。提出一个监测影响的计划，列出你要测量的变量和采样策略。利用上述框架构建一份完整答案。
An excellent response would include: the input of fertilisers raising nitrate and phosphate concentrations; a resulting algal bloom blocking light; declining dissolved oxygen due to decomposition; death of sensitive fish species; and possibly a shift in the food web. The monitoring plan should detail depth profiles, seasonal sampling, and replicates.
一份优秀答案应包括：肥料输入导致硝酸盐和磷酸盐浓度升高；随之而来的藻华遮挡光线；因分解作用导致溶解氧下降；敏感鱼类死亡；以及食物网可能的变化。监测计划应详述深度剖面、季节性采样和重复实验。
12. Conclusion and Exam Tips | 总结与备考建议
Case study questions reward those who can apply knowledge across Biology, Chemistry and Physics. Practice identifying the relevant science behind a scenario, extracting data, performing simple calculations, and critiquing experimental design. Always support your points with numerical evidence from the case.
案例分析题奖励那些能够跨生物学、化学和物理学运用知识的学生。练习识别情境背后的相关科学原理，提取数据，进行简单计算，并评论实验设计。始终用案例中的数字证据支持你的论点。
For CIE IGCSE Science, time management is essential: allocate one mark per minute. Start by reading the whole case, then answer the parts you find easiest, leaving the evaluation for last. Use clear scientific terminology and write in a logical sequence. With this practical drill, you are well prepared to tackle any case study.
对于 CIE IGCSE 科学，时间管理至关重要：每分值分配一分钟。先通读整个案例，然后从你认为最简单的部分答起，最后再处理评估性问题。使用清晰的科学术语并按逻辑顺序书写。经过这次实战演练，你已经做好了应对任何案例分析的充分准备。
Published by TutorHao | Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
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Cancel reply