📚 Case Study Practical Exercises | 案例分析实战演练
Welcome to the Year 8 AQA Science case study workout. You will encounter eight mini investigations covering biology, chemistry and physics. Each case presents a scenario, a data table and a series of analysis tasks that mirror real exam-style questions. Work through them to sharpen your skills in identifying variables, choosing graphs, drawing conclusions and evaluating methods.
欢迎来到 Year 8 AQA 科学案例实战训练。你将遇到八个涵盖生物、化学和物理的小型调查。每个案例都提供一个情境、一个数据表和一系列分析任务，它们模仿真实的考试题型。逐一完成它们，以强化你识别变量、选择图表、得出结论和评估方法的技能。
1. Case Study 1: Plant Growth and Light | 案例一：植物生长与光照
Sarah placed five bean seedlings at different distances from a lamp: 10 cm, 20 cm, 30 cm, 40 cm and 50 cm. She kept the amount of water, soil type and room temperature the same. After two weeks she recorded the height of each plant.
莎拉将五株豆苗放在离灯不同距离的地方：10 厘米、20 厘米、30 厘米、40 厘米和 50 厘米。她保持浇水量、土壤类型和室内温度相同。两周后她记录了每株植物的高度。
| Distance from lamp (cm) | 10 | 20 | 30 | 40 | 50 |
| Plant height (cm) | 15 | 12 | 9 | 7 | 5 |
Independent variable: distance from lamp (which changes light intensity). Dependent variable: height of the bean plant. Control variables: volume of water, soil type, temperature, type of seed, pot size.
独立变量：与灯的距离（它改变光照强度）。因变量：豆株的高度。控制变量：水量、土壤类型、温度、种子类型、花盆大小。
A line graph would be the best choice here because both distance and height are continuous measurements. Plot distance on the x‑axis and height on the y‑axis.
这里折线图是最佳选择，因为距离和高度都是连续测量值。将距离标在 x 轴，高度标在 y 轴。
The pattern shows that as distance from the lamp increases, the plant height decreases. This makes sense because plants need light for photosynthesis to produce food and grow.
模式表明，随着与灯距离的增加，植物高度降低。这很合理，因为植物需要光进行光合作用以制造有机物并生长。
To improve the investigation, Sarah could repeat the experiment three times for each distance and calculate a mean height. This would make the results more reliable and reduce the effect of anomalous results.
为了改进探究，莎拉可以对每个距离重复三次实验，并计算平均高度。这将使结果更可靠，并减少异常值的影响。
2. Case Study 2: Dissolving Sugar | 案例二：溶解糖
Jamal investigated how water temperature affects the time it takes for a sugar cube to dissolve completely. He used 200 ml of water in a beaker for each test and stirred gently. The temperatures tested were 20 °C, 40 °C, 60 °C and 80 °C. He timed how long it took for no solid sugar to be visible.
贾马尔研究了水温如何影响方糖完全溶解所需的时间。他在每次测试中使用一个烧杯装 200 毫升水，并轻轻搅拌。测试温度分别为 20 °C、40 °C、60 °C 和 80 °C。他记录了直到看不见固体糖为止所用的时间。
| Water temperature (°C) | 20 | 40 | 60 | 80 |
| Time to dissolve (s) | 125 | 62 | 30 | 14 |
Independent variable: water temperature. Dependent variable: time taken for the sugar cube to dissolve. Control variables: volume of water, mass of sugar cube, stirring speed (gentle and consistent), type of sugar.
独立变量：水温。因变量：方糖溶解所用的时间。控制变量：水的体积、方糖质量、搅拌速度（轻柔且一致）、糖的种类。
A line graph is suitable. The x‑axis would show water temperature and the y‑axis the time to dissolve. The points would show a downward curve.
折线图是合适的。x 轴表示水温，y 轴表示溶解时间。数据点将呈现一条下降的曲线。
As temperature rises, the dissolving time becomes shorter. This happens because particles move faster at higher temperatures, so water molecules collide with the sugar more often and with more energy, breaking the sugar apart quickly.
随着温度升高，溶解时间变短。这是因为温度越高粒子运动越快，因此水分子与糖的碰撞更频繁、能量更大，能迅速将糖瓦解。
One improvement would be to use a temperature sensor and stopwatch with split‑second accuracy. The point at which the last sugar grain disappears is hard to judge by eye, so repeating each test three times and averaging would improve reliability.
一项改进是使用温度传感器和秒表，达到瞬间精度。最后糖粒消失的时刻肉眼难以判断，因此每个温度重复三次并取平均值会提高可靠性。
3. Case Study 3: Simple Circuits and Current | 案例三：简单电路与电流
Mia built a series circuit with a bulb, an ammeter and different numbers of identical cells. She recorded the current for 1 cell, 2 cells and 3 cells. She used the same bulb and wires each time.
米娅用灯泡、电流表和不同数量的相同电池搭建了一个串联电路。她分别记录了使用 1 节、2 节和 3 节电池时的电流。每次她使用相同的灯泡和导线。
| Number of cells | 1 | 2 | 3 |
| Current (A) | 0.25 | 0.52 | 0.76 |
Independent variable: number of cells (which changes the voltage). Dependent variable: electric current. Control variables: bulb type, wire material and length, ammeter setting, temperature (assumed constant).
独立变量：电池数量（它改变电压）。因变量：电流。控制变量：灯泡类型、导线材料和长度、电流表设置、温度（假设恒定）。
Because the number of cells is a discrete category, a bar chart is usually the best choice. The height of each bar represents the current.
因为电池数量是一个离散的类别，条形图通常是最佳选择。每条的高度代表电流的大小。
The results show that more cells produce a larger current. This happens because adding cells increases the total voltage 'push', allowing more charge to flow per second through the same bulb.
结果表明，电池越多电流越大。这是因为增加电池会增大总电压的‘推动力’，使每秒流过相同灯泡的电荷更多。
To extend the investigation, Mia could measure the current with four cells and check if the trend continues. She should also repeat each reading twice to spot any anomalies caused by loose connections.
为了延伸探究，米娅可以测量 4 节电池时的电流，检查趋势是否延续。她还应该对每个读数重复两次，以发现因接触不良造成的任何异常。
4. Case Study 4: Insulation and Cooling | 案例四：保温与冷却
A group tested four different materials as insulators for a hot‑water cup: cotton wool, aluminium foil, newspaper and no wrapping. They poured 200 ml of hot water at 80 °C into identical beakers, wrapped them securely and recorded the temperature after 20 minutes.
一组同学测试了四种不同材料作为热水杯的绝热体：棉花、铝箔、报纸和无包裹。他们将 200 毫升 80 °C 的热水倒入相同的烧杯，严密包裹，并记录 20 分钟后的温度。
| Insulator material | Cotton wool | Aluminium foil | Newspaper | No wrapping |
| Temperature drop (°C) | 11 | 24 | 19 | 32 |
Independent variable: type of wrapping material. Dependent variable: temperature drop after 20 minutes. Control variables: initial water temperature (80 °C), volume of water, beaker size, room temperature, wrapping thickness (kept as similar as possible).
独立变量：包裹材料的种类。因变量：20 分钟后的温度下降值。控制变量：初始水温（80 °C）、水的体积、烧杯大小、室温、包裹厚度（尽可能保持一致）。
A bar chart is appropriate. The bars would be labelled with the material names, and the height shows how much heat was lost.
条形图是合适的。条形用材料名称标记，高度表示散失了多少热量。
Cotton wool allowed the smallest temperature drop, so it is the best insulator among those tested. Aluminium foil was the poorest insulator because metal is a good conductor; it helped heat escape quickly. The no‑wrapping beaker lost the most heat as expected.
棉花造成的温度下降最小，因此在测试材料中是最好的绝热体。铝箔是最差的绝热体，因为金属是良导体；它帮助热量迅速散失。无包裹的烧杯如预期那样散失了最多热量。
A possible improvement is to measure the temperature every two minutes for 20 minutes and plot cooling curves. The group could also test a vacuum flask as a comparison.
可能的改进是每两分钟测量一次温度，持续 20 分钟，并绘制冷却曲线。还可以测试一个保温瓶作为对比。
5. Case Study 5: Enzyme Action on Starch | 案例五：酶对淀粉的作用
Amylase is an enzyme that breaks down starch into sugar. Lee placed a mixture of starch solution and amylase in test tubes at five different temperatures: 20 °C, 30 °C, 40 °C, 50 °C and 60 °C. Every 30 seconds he tested a drop with iodine solution. He recorded the time until the iodine no longer turned blue‑black, showing the starch had been digested.
淀粉酶是一种将淀粉分解成糖的酶。李将淀粉溶液和淀粉酶的混合物置于五个不同温度的试管中：20 °C、30 °C、40 °C、50 °C 和 60 °C。每隔 30 秒他用碘液测试一滴样品。他记录直到碘液不再变蓝黑色所需的时间，表明淀粉已被消化。
| Temperature (°C) | 20 | 30 | 40 | 50 | 60 |
| Time for starch to disappear (s) | 180 | 75 | 35 | 50 | No change after 300 s |
Independent variable: temperature. Dependent variable: time taken for starch to be fully digested (iodine test negative). Control variables: concentration and volume of starch solution, volume and concentration of amylase, pH (kept at neutral).
独立变量：温度。因变量：淀粉完全被消化所需的时间（碘测试呈阴性）。控制变量：淀粉溶液的浓度和体积、淀粉酶体积和浓度、pH 值（保持中性）。
A line graph would clearly show the relationship. Temperature goes on the x‑axis, time on the y‑axis.
折线图能清晰地展示关系。温度放在 x 轴，时间放在 y 轴。
The fastest digestion happened at 40 °C. At 50 °C the enzyme started to work more slowly, and at 60 °C it was denatured – the active site changed shape so it could no longer bind starch. The optimum temperature for this amylase is around 40 °C.
最快的消化发生在 40 °C。在 50 °C 酶开始工作变慢，在 60 °C 酶已变性——活性位点形状改变，无法再与淀粉结合。这种淀粉酶的最适温度约为 40 °C。
To gain more precise information, Lee could test additional temperatures between 35 °C and 45 °C. The test should be repeated at least twice at each temperature to ensure the pattern is reliable.
为了获得更精确的信息，李可以测试 35 °C 至 45 °C 之间的更多温度。每个温度下的测试应至少重复两次，以确保模式可靠。
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