📚 Case Study Practice for Year 7 WJEC Biology | 七年级WJEC生物案例分析实战演练
In biology, a case study is like being a detective. You look at real-world situations or experimental data, use scientific methods to analyse the evidence, and draw logical conclusions. This article will guide you through several practical case studies, helping you build the skills needed to tackle WJEC Year 7 biology assessments. Each example focuses on key topics: ecosystems, healthy diets, plant growth, and microorganisms.
在生物学中，案例分析就像当一名侦探。你需要观察真实世界的情景或实验数据，运用科学方法分析证据，并得出合乎逻辑的结论。本文将通过几个实际案例演练，帮助你建立应对 WJEC 七年级生物评估所需的技能。每个案例都围绕关键主题：生态系统、健康饮食、植物生长和微生物。
1. What is a Case Study in Biology? | 什么是生物学案例分析？
A case study involves collecting data, identifying patterns, and explaining results using your knowledge of biology. You do not need to carry out the experiment yourself. Instead, you are given information – such as tables, graphs, or descriptions – and you must interpret them correctly.
案例分析涉及收集数据、识别模式，并运用生物学知识解释结果。你不需要亲自做实验，而是会得到一些信息——比如表格、图表或文字描述——然后你必须正确解读它们。
Common skills tested include: describing trends, calculating changes, spotting anomalies, and suggesting improvements to experiments. WJEC exams often ask questions like "What conclusion can you draw from these results?" or "How could the investigation be made more reliable?"
常考的技能包括：描述趋势、计算变化、发现异常值，以及提出实验改进建议。WJEC 考试经常会问：“从这些结果中你可以得出什么结论？”或者“如何使这项调查更可靠？”
2. The Scientific Method in Action | 实践中的科学方法
Every good case study follows a logical process: observe, question, hypothesise, predict, test, analyse, conclude, and evaluate. When you work through a case, you are often conducting the 'analyse', 'conclude', and 'evaluate' steps on data someone else has gathered.
每个好的案例分析都遵循一个逻辑过程：观察、提问、假设、预测、测试、分析、结论和评估。当你处理一个案例时，通常是在对别人收集的数据进行“分析”、“得出结论”和“评估”这些步骤。
Let's practise with a simple everyday scenario: you notice that bread goes mouldy faster in a warm kitchen than in a fridge. Your hypothesis might be 'Microorganisms grow more quickly at higher temperatures.' The case study provides the data to test this idea, and you draw conclusions from it.
我们用一个简单的日常场景来练习：你注意到面包在温暖的厨房里比在冰箱里更快发霉。你的假设可能是“微生物在较高温度下生长得更快”。案例分析提供了数据来检验这个想法，你则从中得出结论。
3. Case Study 1: Pond Ecosystem Investigation | 案例1：池塘生态系统调查
A student took water samples from three different ponds (A, B, and C) and counted the number of mayfly nymphs, freshwater shrimps, and rat-tailed maggots in each. Rat-tailed maggots can survive in very polluted water, while mayfly nymphs are very sensitive to pollution. The results are shown below.
一名学生从三个不同的池塘（A、B 和 C）采集了水样，并统计了每个池塘中蜉蝣稚虫、淡水虾和鼠尾蛆的数量。鼠尾蛆能在污染严重的水中生存，而蜉蝣稚虫对污染非常敏感。结果如下表所示。
| Organism / 生物 | Pond A / 池塘A | Pond B / 池塘B | Pond C / 池塘C |
|---|---|---|---|
| Mayfly nymph / 蜉蝣稚虫 | 15 | 2 | 18 |
| Freshwater shrimp / 淡水虾 | 22 | 8 | 20 |
| Rat-tailed maggot / 鼠尾蛆 | 0 | 12 | 1 |
What patterns can you see? Pond B has very few mayfly nymphs but the highest number of rat-tailed maggots. Pond A and C have many mayfly nymphs and shrimps but almost no rat-tailed maggots. This data suggests Pond B is more polluted than the others.
你能看到什么模式？池塘 B 的蜉蝣稚虫很少，但鼠尾蛆数量最多。池塘 A 和 C 有很多蜉蝣稚虫和淡水虾，但几乎没有鼠尾蛆。这些数据表明池塘 B 比其他池塘污染更严重。
4. Data Analysis for the Pond Ecosystem | 池塘生态系统数据分析
ymphs + freshwater shrimps) in each pond is: Pond A = 37, Pond B = 10, Pond C = 38. The total tough organisms (rat-tailed maggots) is: Pond A = 0, Pond B = 12, Pond C = 1.
为了加强分析，你可以计算一些简单的统计数据。例如，每个池塘中对污染敏感的生物（蜉蝣稚虫 + 淡水虾）总数：池塘 A = 37，池塘 B = 10，池塘 C = 38。耐污生物（鼠尾蛆）总数：池塘 A = 0，池塘 B = 12，池塘 C = 1。
Now look at the ratio of sensitive to tolerant organisms. In Pond B, the ratio is 10:12 (about 0.83), while in Pond A it is 37:0 (infinite, but essentially no tolerant organisms). This quantitative approach makes the pollution claim much stronger. Always use data from the table to back up your points.
现在看敏感生物与耐污生物的比例。在池塘 B 中，比例是 10:12（约 0.83），而在池塘 A 中是 37:0（无穷大，但基本上没有耐污生物）。这种定量方法使污染的说法更有力。始终使用表格中的数据来支持你的观点。
5. Drawing Conclusions from the Pond Data | 从池塘数据得出结论
From the evidence, a valid conclusion is: 'Pond B shows signs of organic pollution because it contains very few pollution-sensitive invertebrates and a high number of rat-tailed maggots, which are adapted to low-oxygen, polluted conditions. Ponds A and C appear to be cleaner.'
根据证据，一个有效的结论是：“池塘 B 显示出有机污染的迹象，因为它含有极少数对污染敏感的无脊椎动物，以及大量适应低氧污染环境的鼠尾蛆。池塘 A 和 C 似乎更清洁。”
You might also evaluate the investigation. Was one sample from each pond enough? Perhaps the student should take multiple samples from different parts of each pond to get a more reliable estimate. Also, other factors like temperature or season could affect numbers. A good evaluator always considers limitations.
你还可以对调查进行评估。每个池塘只采一个样足够吗？也许学生应该从每个池塘的不同位置采集多个样本，以获得更可靠的估计。此外，温度或季节等其他因素也可能影响数量。一个好的评估者总是会考虑局限性。
6. Case Study 2: Healthy Diet Analysis | 案例2：健康饮食分析
Tom is a Year 7 student who eats the following on a typical day: breakfast – a bowl of sugary cereal with milk; snack – crisps; lunch – chips, burger, and fizzy drink; dinner – pizza and ice cream. His doctor says he needs a more balanced diet. The table shows his daily intake compared with recommended amounts for boys aged 11-12.
汤姆是一名七年级学生，他典型的一日饮食如下：早餐——一碗含糖麦片加牛奶；零食——薯片；午餐——薯条、汉堡和汽水；晚餐——披萨和冰淇淋。他的医生说他需要更均衡的饮食。下表显示了他的每日摄入量与 11-12 岁男孩推荐量的对比。
| Nutrient / 营养素 | Tom's intake / 汤姆的摄入 | Recommended daily / 每日推荐 |
|---|---|---|
| Energy (kJ) / 能量 (千焦) | 11 500 kJ | 8 800 kJ |
| Protein / 蛋白质 | 85 g | 50 g |
| Carbohydrate / 碳水化合物 | 380 g | 280 g |
| Fat / 脂肪 | 110 g | 70 g |
| Fibre / 纤维 | 8 g | 25 g |
| Vitamin C / 维生素C | 25 mg | 35 mg |
Identify three problems with Tom's diet based on the data. For example, his energy intake is 11 500 kJ, which is 2 700 kJ above the recommended 8 800 kJ. This excess energy can lead to weight gain if not used by physical activity.
根据数据，找出汤姆饮食中的三个问题。例如，他的能量摄入是 11 500 千焦，比推荐的 8 800 千焦高出 2 700 千焦。如果这些多余的能量没有被体力活动消耗掉，可能导致体重增加。
7. Calculating Energy Needs and Deficiencies | 计算能量需求和缺乏
entage excess or deficit using simple division. For energy: (11 500 - 8 800) ÷ 8 800 × 100% ≈ 30.7% above recommendation. For fibre: (8 - 25) ÷ 25 × 100% = -68%, meaning Tom gets only 32% he fibre he needs. Fibre is vital for healthy digestion; low fibre may cause constipation.
你可以用简单的除法计算超出或缺乏的百分比。对于能量：(11 500 - 8 800) ÷ 8 800 × 100% ≈ 30.7%，高于推荐量。对于纤维：(8 - 25) ÷ 25 × 100% = -68%，意味着汤姆只摄入了所需纤维的 32%。纤维对健康消化至关重要；纤维不足可能导致便秘。
His fat intake is 110 g against a recommendation of 70 g, which is 57% too high. Too much saturated fat is linked to higher cholesterol levels and heart problems later in life. Also, his vitamin C is slightly low (25 mg vs 35 mg). To improve, Tom should swap crisps for fruit, replace fizzy drinks with water, and choose wholemeal options.
他的脂肪摄入量是 110 克，而推荐量是 70 克，超出 57%。过多的饱和脂肪与较高的胆固醇水平和日后的心脏问题有关。此外，他的维生素 C 略低（25 毫克对比 35 毫克）。为了改善，汤姆应该用水果代替薯片，用白水代替汽水，并选择全麦食品。
8. Case Study 3: Plant Growth Experiment | 案例3：植物生长实验
A group of students investigated whether adding coffee grounds to soil affects the growth of cress seedlings. They set up three pots: Pot X (no coffee grounds), Pot Y (20 g coffee grounds mixed with soil), and Pot Z (50 g coffee grounds). They planted 10 seeds in each pot, gave them the same water and light, and measured the average seedling height after 10 days.
一组学生研究了在土壤中添加咖啡渣是否会影响水芹幼苗的生长。他们设置了三个花盆：盆 X（无咖啡渣），盆 Y（20 克咖啡渣与土壤混合），盆 Z（50 克咖啡渣）。每个盆中播种 10 粒种子，给予相同的水分和光照，并在 10 天后测量平均幼苗高度。
| Pot / 盆 | Coffee grounds / 咖啡渣 | Mean height / 平均高度 (mm) |
|---|---|---|
| X | 0 g | 42 mm |
| Y | 20 g | 66 mm |
| Z | 50 g | 35 mm |
The results show that a moderate amount of coffee grounds (Pot Y) increased growth to 66 mm compared to 42 mm in the control (Pot X). However, too much coffee grounds (Pot Z) actually reduced growth to 35 mm, even below the control. This suggests coffee grounds may provide nutrients but can become harmful in high concentrations, possibly due to caffeine or acidity.
结果显示，中等量的咖啡渣（盆 Y）使生长高度增加到 66 毫米，而对照组（盆 X）为 42 毫米。然而，过多的咖啡渣（盆 Z）实际上将生长降低到 35 毫米，甚至低于对照组。这表明咖啡渣可能提供营养，但在高浓度下可能有害，可能是由于咖啡因或酸性的原因。
9. Identifying Variables in the Experiment | 识别实验中的变量
In any investigation, correctly identifying independent, dependent, and control variables is crucial. In this plant experiment, the independent variable (what the students changed) is the mass of coffee grounds added (0 g, 20 g, 50 g).
在任何调查中，正确识别自变量、因变量和控制变量至关重要。在这个植物实验中，自变量（学生改变的量）是添加的咖啡渣质量（0 克、20 克、50 克）。
The dependent variable (what they measure) is the average height of seedlings after 10 days. Control variables (what must be kept the same) include: type of seed, amount of water, volume of soil, light intensity, temperature, and size of pots. If these were not controlled, we couldn't be sure that coffee grounds caused the difference.
因变量（他们测量的是什么）是 10 天后幼苗的平均高度。控制变量（必须保持不变的量）包括：种子类型、水量、土壤体积、光照强度、温度以及花盆大小。如果不控制这些变量，我们就无法确定是咖啡渣导致了差异。
10. Presenting Results Effectively | 有效呈现结果
Data is often clearer when shown in a graph. For the plant experiment, you would plot a bar chart with 'Mass of coffee grounds (g)' on the x-axis and 'Mean height (mm)' on the y-axis. Bar charts are used when the independent variable is categoric (like '0 g', '20 g', '50 g'), while line graphs are for continuous data.
用图表展示数据往往更清晰。对于该植物实验，你可以在 x 轴上标绘“咖啡渣质量 (克)”，在 y 轴上标绘“平均高度 (毫米)”的条形图。当自变量是分类变量（如“0 克”、“20 克”、“50 克”）时使用条形图，而线形图适用于连续数据。
If you were to evaluate the method, you could comment: only 10 seeds per pot may not be representative; repeating with larger samples or replicating the entire experiment would increase reliability. Also, recording height every 2 days would give growth rate trends, not just end-point data.
如果要对方法进行评估，你可以评论：每个花盆仅用 10 粒种子可能不具代表性；使用更大样本或重复整个实验会提高可靠性。此外，每 2 天记录一次高度可以得到生长率趋势，而不仅仅是终点数据。
11. Case Study 4: Microorganisms and Food Spoilage | 案例4：微生物与食物腐败
A bakery keeps bread at different temperatures. The manager records how many days until visible mould appears on identical loaves stored at 5°C, 20°C, and 30°C. Data: at 5°C mould appeared after 14 days; at 20°C after 5 days; at 30°C after 2 days. All loaves were in sealed plastic bags and kept in the dark.
一家面包店将面包放在不同温度下储存。经理记录相同面包在 5°C、20°C 和 30°C 下出现可见霉菌所需的天数。数据：5°C 下 14 天后出现霉菌；20°C 下 5 天后；30°C 下 2 天后。所有面包都密封在塑料袋中，并置于暗处。
This is an example of clear negative correlation: as temperature increases, the time to spoilage decreases. Using scientific knowledge, we explain that microorganisms such as mould fungi reproduce fastest at warmer temperatures (within limits). At 5°C, their activity is slowed because the cold reduces enzyme activity and metabolism.
这是一个明显的负相关例子：随着温度升高，腐败时间缩短。运用科学知识，我们解释微生物如霉菌真菌在较暖的温度下（在一定范围内）繁殖最快。在 5°C 时，它们的活动减慢，因为寒冷降低了酶活性和新陈代谢。
12. Review and Self-Assessment Checklist | 复习与自我评估清单
Before attempting a case study in an exam, use this checklist to make sure you are thinking like a biologist. Ask yourself: (1) What is the question or aim? (2) What data is provided? (3) Can I spot a trend, pattern, or anomaly? (4) What science knowledge explains the pattern? (5) Can I calculate rates or percentages? (6) How reliable is the evidence? (7) What improvements would I suggest?
在考试中尝试案例分析之前，使用这份清单确保你像生物学家一样思考。问自己：(1) 问题或目的是什么？(2) 提供了哪些数据？(3) 我能发现趋势、模式或异常值吗？(4) 什么科学知识解释了这个模式？(5) 我能计算比率或百分比吗？(6) 证据有多可靠？(7) 我会提出哪些改进建议？
Practise with past papers or create your own mini case studies from everyday observations. Remember, biologists do not just remember facts; they apply them to understand the living world. Every graph, table, or description is a puzzle waiting to be solved with evidence and logic.
用历年真题练习，或者根据日常观察创建你自己的小案例分析。请记住，生物学家不仅仅是记住事实；他们运用事实来理解生命世界。每一个图表、表格或描述都是一个等待用证据和逻辑来解开的谜题。
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