📚 Year 9 CIE Science: Case Study Practical Exercises | 九年级CIE科学：案例分析实战演练
Case studies are an excellent way to develop scientific thinking and apply knowledge to real-world scenarios. In this revision article, we will explore ten practical examples across physics, chemistry and biology, each designed to reinforce key concepts from the Year 9 CIE Science syllabus. You will practise interpreting data, performing calculations, and drawing evidence-based conclusions.
案例研究是培养科学思维、将知识应用于真实情境的绝佳方式。在这篇复习文章中，我们将探讨十个涵盖物理、化学和生物的实践案例，每个案例旨在巩固九年级CIE科学课程中的核心概念。你将练习解读数据、进行计算并得出基于证据的结论。
1. Investigating Reaction Rate: Magnesium and Hydrochloric Acid | 探究反应速率：镁与盐酸
An experiment was carried out to measure the rate of reaction between magnesium ribbon and excess dilute hydrochloric acid. The reaction produces hydrogen gas and magnesium chloride: Mg + 2HCl → MgCl₂ + H₂↑. The mass of the reaction flask was recorded every 10 seconds, as the loss of mass indicates the escape of hydrogen.
进行了一项测量镁条与过量稀盐酸反应速率的实验。反应生成氢气和氯化镁：Mg + 2HCl → MgCl₂ + H₂↑。每10秒记录一次反应烧瓶的质量，质量的减少表明氢气的逸出。
Rate of loss of mass = (change in mass) / (change in time)
质量损失速率 = 质量变化 / 时间变化
| Time (s) | Total mass (g) |
|---|---|
| 0 | 120.0 |
| 10 | 118.5 |
| 20 | 117.4 |
| 30 | 116.6 |
| 40 | 116.0 |
| 50 | 115.7 |
The average reaction rate for the first 10 s is calculated as (120.0 – 118.5) g / 10 s = 0.15 g s⁻¹. Between 30 s and 40 s the rate drops to (116.6 – 116.0) g / 10 s = 0.06 g s⁻&# acid molecules falls as they are used up, reducing the frequency of successful collisions.
前10秒的平均反应速率计算为 (120.0 – 118.5) g / 10 s = 0.15 g s⁻¹。在30至40秒之间，速率降至 (116.6 – 116.0) g / 10 s = 0.06 g s⁻¹。速率下降的原因是酸分子随着反应消耗浓度降低，成功碰撞的频率减少。
2. Photosynthesis and Light Intensity | 光合作用和光照强度
An aquatic plant (Elodea) was placed in a beaker of water under a lamp. The number of oxygen bubbles released per minute was counted at different distances from the lamp. Light intensity follows the inverse-square law: intensity ∝ 1/d².
将水生植物伊乐藻放在烧杯的水中，置于灯下。计数不同距离下每分钟释放的氧气气泡数。光照强度遵循平方反比定律：光强 ∝ 1/d²。
| Distance (cm) | Bubbles per minute |
|---|---|
| 10 | 45 |
| 20 | 22 |
| 30 | 10 |
| 40 | 6 |
As the distance doubles from 10 cm to 20 cm, the bubble count falls from 45 to 22, roughly halving, but not exactly quartering because other factors such as CO₂ concentration or temperature may limit the rate. At very low light intensity, light becomes the limiting factor; when the plant reaches light saturation, further increases in intensity will not raise the photosynthesis rate.
当距离从10厘米加倍到20厘米时，气泡数从45降到22，大约减半，但并未严格减少到四分之一，因为二氧化碳浓度或温度等其他因素可能限制了速率。在光照极低时，光照成为限制因素；当植物达到光饱和点时，继续增加光强不会提高光合作用速率。
3. Ohm's Law in a Simple Circuit | 简单电路中的欧姆定律
s that V = IR, so the ratio V/I should be constant for a resistor at constant temperature.
学生将一个固定电阻器连接到可调电源上，并测量了几个电压下的电流。欧姆定律指出 V = IR，因此在恒温条件下，电阻器的 V/I 比值应该恒定。
| Voltage (V) | Current (A) |
|---|---|
| 0.0 | 0.00 |
| 2.0 | 0.20 |
| 4.0 | 0.40 |
| 6.0 | 0.60 |
| 8.0 | 0.80 |
Resistance R = V/I = 2.0 V / 0.20 A = 10 Ω
电阻 R = V/I = 2.0 V / 0.20 A = 10 Ω
All V/I pairs give 10 Ω, confirming the resistor is ohmic at these values. If the resistor became hot, its resistance could increase owing to increased vibrations of the metal ions, which scatter the drifting electrons more.
所有 V/I 组合都得10欧姆，证实该电阻在这些数值下是欧姆性的。如果电阻器变热，其电阻可能会因金属离子振动加剧而增大，从而更严重地散射漂移电子。
4. Determining Density of Solids | 测定固体密度
lock’s volume was found by ruler, and an irregular stone’s volume was found by displacement of water in a measuring cylinder.
密度 (ρ) 是单位体积的质量：ρ = m / V。规则铝块的体积用尺子测量，不规则石块的体积通过量筒排水法测得。
Al block: mass = 54.0 g, dimensions 2.0 cm × 3.0 cm × 4.0 cm → volume = 24.0 cm³. ρ = 54.0 / 24.0 = 2.25 g cm⁻³. Stone: mass = 35.0 g, water level rose from 50 cm³ to 64 cm³ → volume = 14.0 cm³. ρ = 35.0 / 14.0 = 2.5 g cm⁻³.
铝块：质量 54.0 g，尺寸 2.0 cm × 3.0 cm × 4.0 cm → 体积 = 24.0 cm³。ρ = 54.0 / 24.0 = 2.25 g cm⁻³。石块：质量 35.0 g，水面从 50 cm³ 升至 64 cm³ → 体积 = 14.0 cm³。ρ = 35.0 / 14.0 = 2.5 g cm⁻³。
The stone’s density suggests it may be a mineral like quartzite. Systematic errors such as air bubbles sticking to the stone would increase the apparent volume and lower the calculated density.
石块的密度提示它可能是石英岩之类的矿物。系统误差，例如石块上附着的气泡，会使表观体积增大，计算密度偏低。
5. Energy Flow in a Food Chain | 食物链中的能量流动
A simple food chain was studied: grass → grasshopper → frog → snake → eagle. Energy at each trophic level was estimated (kJ m⁻² yr⁻¹). Typically, only about 10% of energy is transferred to the next level.
研究了一条简单的食物链：草 → 蚱蜢 → 青蛙 → 蛇 → 鹰。估算了每个营养级的能量 (kJ m⁻² yr⁻¹)。通常只有大约10%的能量传递到下一级。
| Trophic level | Energy (kJ m⁻² yr⁻¹) |
|---|---|
| Grass (producer) | 50 000 |
| Grasshopper | 5 000 |
| Frog | 500 |
| Snake | 50 |
| Eagle | 5 |
The efficiency between grass and grasshopper is (5000 / 50000) × 100% = 10% and undigested material. This explains why food chains rarely exceed five trophic levels.
草与蚱蜢之间的效率为 (5000 / 50000) × 100% = 10%。大部分能量通过呼吸、运动、散热和未消化物质流失。这就解释了为什么食物链很少超过五个营养级。
6. Acid Rain Simulation: Seed Germination | 酸雨模拟：种子发芽
To model the effect of acid rain, cress seeds were watered with solutions of different pH (pH 4, 5, 6 and a distilled water control, pH 7). Each dish had 20 seeds. After 5 days the number of germinated seeds was recorded.
为模拟酸雨的影响，用不同pH值（pH 4、5、6以及蒸馏水对照 pH 7）的溶液浇灌水芹种子。每个培养皿放20粒种子。5天后记录发芽种子数。
| pH of water | Number germinated |
|---|---|
| 7 (control) | 19 |
| 6 | 18 |
| 5 | 15 |
| 4 | 9 |
The results show a clear trend: lower pH (more acidic) reduces germination success. Acidic conditions can damage seed coats and inhibit enzyme activity. To improve validity, the experiment should be repeated and standardised variables (light, temperature, water volume) kept constant.
结果显示清晰趋势：pH越低（酸性越强），发芽率越低。酸性条件会破坏种皮并抑制酶活性。为提高有效性，实验应重复进行，并保持光照、温度、水量等控制变量不变。
7. Heat Conduction in Metals | 金属中的热传导
Identical rods of copper, iron and aluminium were coated with a thin layer of wax at one end. The other ends were heated evenly with a Bunsen burner. The time for the wax to melt was recorded as a measure of thermal conductivity.
在铜、铁、铝的相同棒材一端涂上薄蜡层。另一端用本生灯均匀加热。记录蜡熔化的时间，以此衡量导热性。
| Metal | Time for wax to melt (s) |
|---|---|
| Copper | 12 |
| Aluminium | 18 |
| Iron | 35 |
Copper, with the shortest melting time, is the best conductor among the three. Heat travels through metals by the vibration of atoms and the movement of free electrons; copper’s high density of free electrons accounts for its superior conductivity.
铜的熔化时间最短，是三者中最佳导热体。热量在金属中通过原子振动和自由电子运动传递；铜的高自由电子密度使其具有优异的导热性。
8. Yeast Respiration and Sugar Type | 酵母呼吸作用与糖类
Yeast was mixed with equal masses of glucose, sucrose and starch in separate fermentation tubes, each fitted with a balloon to capture CO₂. The increase in balloon circumference after 20 minutes was measured.
酵母分别与等质量的葡萄糖、蔗糖和淀粉混合在单独的发酵管中，每管套一个气球来收集二氧化碳。20分钟后测量气球周长的增加量。
| Sugar | Circumference increase (cm) |
|---|---|
| Glucose | 7.5 |
| Sucrose | 4.2 |
| Starch | 0.5 |
Glucose produces the most CO₂ because it is a monosaccharide that yeast can directly use in respiration. Sucrose must first be broken down by an enzyme, so respiration is slower. Starch is a polysaccharide that yeast lacks the enzymes to digest quickly, explaining
Published by TutorHao | Year 9 Science Revision Series | aleveler.com
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