Year 10 CAIE Biology: Case Study Practice Drill | Year 10 CAIE 生物：案例分析实战演练

📚 Year 10 CAIE Biology: Case Study Practice Drill | Year 10 CAIE 生物：案例分析实战演练

Case study questions are a key component of the CAIE IGCSE Biology exam. They test your ability to apply biological principles to real-world scenarios, interpret experimental data and draw evidence-based conclusions. This practice drill presents ten carefully selected case studies covering enzymes, photosynthesis, human physiology, plant transport, food tests, immunity, genetics and ecology. Each case provides data or a scenario, followed by a guided analysis. Work through them to sharpen your problem-solving skills and deepen your understanding of core syllabus topics.

案例分析题是CAIE IGCSE生物学考试的关键组成部分。这类题目考查你在真实情境中运用生物学原理、解读实验数据并得出基于证据的结论的能力。本实战练习精选了十个案例，涵盖酶、光合作用、人体生理、植物运输、食物测试、免疫、遗传和生态等内容。每个案例都提供了数据或情境以及引导式分析。通过逐一练习，你可以提高解题能力，深化对核心大纲主题的理解。

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1. Temperature and Enzyme Activity | 温度与酶活性案例分析

A student investigated the effect of temperature on the activity of salivary amylase. A starch solution and amylase were mixed at various temperatures, and the time taken for the starch to disappear (tested with iodine solution) was recorded. The results are shown in the table below.

一名学生研究了温度对唾液淀粉酶活性的影响。在不同温度下将淀粉溶液与淀粉酶混合，记录淀粉消失（用碘液检测）所需的时间。结果见下表。

Temperature/°C	Time for starch to disappear/s
10	150
20	80
30	45
40	30
50	65
60	No change after 300 s

The shortest time (30 s) occurred at 40 °C, indicating the highest rate of enzyme activity. At 40 °C, the amylase worked fastest because the temperature provided the optimum kinetic energy for effective collisions between the enzyme and starch. Below this temperature, the activity was slower because the molecules had less kinetic energy. Above 40 °C, the time increased sharply, and at 60 °C the starch was not digested at all. This suggests the enzyme had been denatured: the high temperature broke the hydrogen bonds maintaining the enzyme's three-dimensional shape, so the active site was no longer complementary to the starch substrate. The permanent loss of activity is a key distinction between denaturation and the reversible slowing at low temperatures.

最短的时间（30秒）出现在40°C，表明酶活性最高。在40°C时，淀粉酶分解速度最快，因为该温度提供了最佳动能，使酶与淀粉之间发生有效碰撞。低于此温度时，活性减慢，因为分子动能较低。超过40°C后，时间急剧增加；在60°C时淀粉完全没有被消化。这说明酶已变性：高温破坏了维持酶三维结构的氢键，因此活性位点不再与淀粉底物互补。永久丧失活性是变性与低温下可逆减缓之间的关键区别。

Key takeaway: Enzymes have an optimum temperature; excessive heat causes irreversible denaturation. In designing this experiment, a water bath should be used to maintain each temperature accurately, and the pH must be kept constant to ensure a fair test.

关键要点：酶具有最适温度；过热会导致不可逆的变性。在设计此实验时，应使用水浴来精确维持每个温度，并且必须保持pH恒定以确保公平测试。

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2. Light Intensity and Photosynthesis | 光照强度与光合作用案例分析

An aquatic plant (Elodea) was placed in a beaker of water with a lamp at different distances to vary light intensity. The rate of photosynthesis was measured by counting the number of oxygen bubbles released per minute. The data are given below.

将一株水生植物（伊乐藻）放入盛水的烧杯中，用不同距离的灯泡来改变光照强度。通过计数每分钟释放的氧气气泡数量来测量光合作用速率。数据如下。

Distance of lamp/cm	Bubbles per minute
100	5
80	8
60	14
40	22
20	24
10	25

As the lamp distance decreased (higher light intensity), the bubble rate increased up to 25 bubbles per minute at 10 cm. However, the increase was not linear: from 20 cm to 10 cm the rate barely changed. This indicates that light intensity was no longer the limiting factor. At high light intensities, carbon dioxide concentration or temperature may have become the limiting factor. In this experiment, the concentration of CO₂ in the water was fixed (no extra sodium hydrogencarbonate was added, or the plant may have been using the limited dissolved CO₂). To test this, one could add a fixed mass of sodium hydrogencarbonate to provide more CO₂ and observe whether the bubble rate increases further. The data clearly illustrate the concept of limiting factors in photosynthesis.

随着灯泡距离减小（光照强度增加），气泡速率不断提高，在10厘米处达到每分钟25个气泡。然而，这种增长并不是线性的：从20厘米到10厘米，速率几乎不变。这表明光照强度已经不再是限制因素。在高光照强度下，二氧化碳浓度或温度可能成为限制因素。在本实验中，水中的CO₂浓度是固定的（没有额外添加碳酸氢钠，或者植物可能在使用有限的溶解CO₂）。为了验证这一点，可以加入一定量的碳酸氢钠来提供更多的CO₂，观察气泡速率是否进一步提高。这些数据清楚地说明了光合作用中限制因素的概念。

Students should also consider control variables: temperature should be maintained using a water bath, and the same piece of Elodea should be used. The oxygen bubbles could be captured and identified by the glowing splint test.

学生们还需考虑控制变量：使用水浴维持温度，并使用同一株伊乐藻。可以通过带火星的木条复燃来验证收集到的气体是氧气。

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3. Digestion and Absorption in the Small Intestine | 小肠消化与吸收案例分析

A patient has a condition in which the pancreatic duct is blocked, preventing pancreatic juice from reaching the small intestine. A doctor monitors the patient's blood glucose concentration after a starch meal. The data for the patient and a healthy person are shown below.

一名患者因胰管堵塞，导致胰液无法进入小肠。医生监查了该患者在进食淀粉餐后的血糖浓度。患者与健康人的数据如下所示。

Time after meal/min	Healthy person blood glucose/mmol L⁻¹	Patient's blood glucose/mmol L⁻¹
0	5.0	5.0
30	8.0	5.8
60	7.5	6.2
120	5.5	5.9

The healthy person shows a sharp rise in blood glucose 30 minutes after the meal because starch is efficiently digested into glucose. The pancreas produces pancreatic amylase, which, along with salivary amylase, breaks starch into maltose; maltase on the intestinal wall then completes the digestion to glucose. In the patient, the pancreatic amylase cannot reach the small intestine, so starch digestion is much slower. Although some starch is broken down in the mouth, the majority remains undigested, and glucose absorption is limited. Consequently, the patient's blood glucose rises only slightly. The case highlights the role of the pancreas as a gland that secretes digestive enzymes and also demonstrates how absorption of soluble products occurs mainly in the ileum. Without pancreatic juice, the body would also suffer from inadequate fat and protein digestion, leading to malnutrition.

健康人在餐后30分钟血糖急剧升高，因为淀粉被高效消化为葡萄糖。胰腺产生胰淀粉酶，与唾液淀粉酶一起将淀粉分解为麦芽糖；肠壁上的麦芽糖酶随后将麦芽糖进一步消化为葡萄糖。患者的胰淀粉酶无法到达小肠，因此淀粉消化速度慢得多。虽然部分淀粉在口腔中被分解，但大部分仍未被消化，葡萄糖吸收有限。因此，患者的血糖只轻微升高。该案例突出了胰腺作为分泌消化酶的腺体的作用，也说明了可溶性产物的吸收主要发生在回肠。如果没有胰液，身体还会面临脂肪和蛋白质消化不良，导致营养不良。

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4. Heart Rate and Exercise | 心率与运动案例分析

A trained athlete and an untrained individual performed the same step-up exercise for 5 minutes. Their heart rates were measured before, immediately after, and during recovery. The results are summarised in the table.

一名训练有素的运动员和一名未受训练的个体进行了相同的5分钟台阶运动。在运动前、运动后即刻以及恢复期间测量其心率。结果总结于下表中。

Condition	Athlete heart rate/bpm	Untrained heart rate/bpm
Resting	55	72
Immediately after exercise	130	155
2 minutes after exercise	70	115
5 minutes after exercise	60	85

Both individuals experienced an increase in heart rate during exercise because working muscles required more oxygen and glucose for aerobic respiration, and produced more carbon dioxide that needed to be removed. The athlete showed a lower resting heart rate, a smaller increase during exercise and a much faster return towards resting values. These differences indicate a higher cardiac efficiency: the athlete's heart has a larger stroke volume, so it can pump more blood per beat, and the cardiovascular system is better adapted at delivering oxygen and removing wastes. The untrained person's heart had to beat faster to compensate for lower stroke volume and less efficient gas exchange. The rapid recovery of the athlete also reflects a greater proportion of slow-twitch muscle fibres and a more effective removal of lactic acid.

两人在运动中心率均升高，因为工作的肌肉需要更多的氧气和葡萄糖进行有氧呼吸，同时产生更多需要清除的二氧化碳。运动员表现出较低的静息心率、运动时增加幅度较小以及更快恢复至静息值。这些差异表明运动员具有更高的心脏效率：其心脏每搏输出量更大，因此每次搏动能泵出更多血液，心血管系统在输送氧气和清除废物方面更适应。未受训练者需要加快心率来弥补较低的每搏输出量和较低效的气体交换。运动员的快速恢复也反映了慢肌纤维比例较高及乳酸清除更有效。

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5. Smoking and Lung Function | 吸烟与肺功能案例分析

A lung function test measured the forced expiratory volume in one second (FEV₁) and the forced vital capacity (FVC) for a non-smoker and a long-term smoker. The data are shown below.

一项肺功能测试测量了一名非吸烟者和一名长期吸烟者的一秒用力呼气容积（FEV₁）和用力肺活量（FVC）。数据如下。

	Non-smoker	Smoker
FVC/L	4.8	3.4
FEV₁/L	3.9	1.8
FEV₁/FVC ratio	0.81	0.53

Both FVC and FEV₁ are significantly lower in the smoker. The reduced FVC indicates a loss of lung volume, partly due to the destruction of alveolar walls (emphysema), which reduces the surface area for gas exchange. The much lower FEV₁ and FEV₁/FVC ratio point to airway obstruction. Tar and other chemicals in cigarette smoke damage the cilia, leading to a build-up of mucus and coughing (chronic bronchitis). Damaged cilia cannot effectively clear pathogens, making the smoker more susceptible to infections. Less oxygen is absorbed into the blood, causing shortness of breath and reduced stamina. This case study illustrates how lifestyle factors can directly impair the structure and function of the respiratory system.

吸烟者的FVC和FEV₁都显著降低。FVC降低表明肺活量减少，部分原因是肺泡壁被破坏（肺气肿），从而减少了气体交换的表面积。FEV₁和FEV₁/FVC比值大幅降低则指向气道阻塞。香烟烟雾中的焦油和其他化学物质损伤纤毛，导致黏液积聚和咳嗽（慢性支气管炎）。受损的纤毛无法有效清除病原体，使吸烟者更容易感染。血液中吸收的氧气减少，导致呼吸急促和耐力下降。该案例说明了生活方式因素如何直接损害呼吸系统的结构和功能。

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6. Transpiration and Wind Speed | 蒸腾作用与风速案例分析

A potometer was used to measure the rate of water uptake by a leafy shoot under different wind conditions produced by an electric fan. The student recorded the movement of an air bubble along the capillary tube over 5 minutes. The results are shown below.

使用蒸腾计测量了一株带叶枝条在不同电扇风速条件下的吸水速率。学生记录了5分钟内气泡沿毛细管移动的距离。结果如下。

Wind condition	Distance moved by bubble per 5 min/mm
No wind (still air)	8
Low fan speed	24
High fan speed	38

The water uptake (a proxy for transpiration rate) increased with wind speed. Transpiration is the loss of water vapour from the leaves through stomata. Wind removes the layer of humid air that accumulates near the leaf surface, maintaining a steeper water

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