Case Study Workout for Year 7 Edexcel Biology | 七年级Edexcel生物案例分析实战演练

📚 Case Study Workout for Year 7 Edexcel Biology | 七年级Edexcel生物案例分析实战演练

In Year 7 Edexcel Biology, you are introduced to a wide range of amazing topics – from the microscopic world of cells to the complexity of whole ecosystems. To help you truly understand these ideas, it is essential to practise applying your knowledge to realistic scenarios. This article presents ten mini case studies designed to sharpen your analytical skills. Each case includes a scenario, thought-provoking questions, and detailed explanations in clear, age-appropriate language. Work through them at your own pace, and use them to test your understanding before your exams.

在七年级 Edexcel 生物课程中，你会接触到从微观细胞到整个生态系统的许多奇妙主题。为了帮助你真正理解这些概念，你需要练习将知识应用到真实情境中。本文提供了十个迷你案例，旨在锻炼你的分析能力。每个案例都包含一个场景、引人思考的问题，以及用清晰易懂的语言写出的详细解释。请按照自己的节奏学习，并用它们来检测你考试前的掌握程度。

1. Mystery Microscope Image | 神秘的显微镜图像

Sarah placed a thin slice of an unknown organism under her light microscope. She sketched what she saw: a rectangular shape with a distinct outer wall, a large central vacuole, and several small green discs called chloroplasts. She also noticed a darker round nucleus, but no other organelles were clearly visible.

莎拉将一种未知生物体的薄切片放在光学显微镜下观察。她画下了所看到的结构：一个具有清晰外壁的矩形形状，一个大的中央液泡，以及几个叫作叶绿体的小绿盘。她还注意到了一个颜色较深的圆形细胞核，但没有看到其他细胞器。

Question: How can Sarah tell that this is a plant cell and not an animal cell? List two pieces of evidence from her observation.

问题：莎拉如何判断这是一个植物细胞而不是动物细胞？从她的观察中列出两个证据。

Explanation: The presence of a cell wall is a clear indicator of a plant cell, because animal cells only have a cell membrane. The green chloroplasts are used for photosynthesis and are never found in animal cells. In addition, the large permanent vacuole, which stores cell sap and helps keep the cell firm, is typical of plant cells. Together, these features provide strong evidence.

解释：细胞壁的存在是植物细胞的明显标志，因为动物细胞只有细胞膜。绿色的叶绿体用于光合作用，动物细胞中从未发现过叶绿体。此外，储存细胞液并帮助保持细胞坚挺的大的永久液泡，也是植物细胞的典型特征。这些特征一起提供了有力的证据。

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2. The Unhealthy Diet | 不健康的饮食

Tom is a 12-year-old student who loves fast food. His typical daily meals are: breakfast – sugary cereal with whole milk; lunch – cheeseburger, chips and a fizzy drink; dinner – pepperoni pizza followed by chocolate ice cream. He rarely eats fruit or vegetables and drinks very little water.

汤姆是一个12岁的学生，喜欢快餐。他日常的典型饮食是：早餐——含糖谷物加全脂牛奶；午餐——芝士汉堡、薯条和汽水；晚餐——意大利辣香肠披萨，随后吃巧克力冰淇淋。他很少吃水果和蔬菜，喝水也非常少。

Question: Which essential nutrients and food groups are missing or insufficient in Tom’s diet? Predict two possible health problems he might face.

问题：汤姆的饮食中缺少或不足哪些必需的营养物质和食物类别？预测他可能面临的两个健康问题。

Explanation: Tom’s diet is high in fats, sugars and salt but low in dietary fibre, vitamins and minerals. He is not consuming enough fruit and vegetables, which provide vitamin C for healthy skin and immunity, and fibre for healthy digestion. A lack of iron-rich foods could lead to anaemia, making him feel tired. Over time, excessive sugar and fat can lead to obesity, tooth decay and even type 2 diabetes. Drinking more water, adding a side salad and replacing the fizzy drink with a piece of whole fruit would make his meals much healthier.

解释：汤姆的饮食含有大量脂肪、糖分和盐，但缺乏膳食纤维、维生素和矿物质。他没有摄入足够的水果和蔬菜，而蔬果能提供维持皮肤和免疫力健康的维生素C，以及促进健康消化的纤维。缺少富含铁的食物可能导致贫血，使他感到疲倦。长期摄入过量的糖和脂肪会导致肥胖、蛀牙甚至2型糖尿病。多喝水、增加一份配菜沙拉以及用整个水果代替汽水，都会让他的饮食健康得多。

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3. Food Chain Puzzle | 食物链谜题

A pond ecosystem contains the following organisms: algae, water fleas (Daphnia), small fish such as sticklebacks, and a grey heron that visits daily. Sunlight reaches the surface of the pond, allowing algae to thrive. A scientist drawing a food web for the pond has recorded these feeding relationships.

一个池塘生态系统中生活着以下生物：藻类、水蚤、像刺鱼这样的小鱼，以及每天光顾的灰鹭。阳光照射到池塘表面，使藻类得以茂盛生长。一位科学家为这个池塘绘制食物网时记录了这些摄食关系。

Question: Construct a simple food chain that starts with the Sun. Explain what would happen to the population of sticklebacks if all the water fleas died from a disease.

问题：构建一条以太阳为起点的简单食物链。解释如果所有水蚤都因疾病而死亡，刺鱼的数量会发生什么变化。

Explanation: The food chain is: Sun → algae → water flea → stickleback → heron. Algae are producers that trap sunlight energy for photosynthesis. Water fleas are primary consumers. If water fleas were wiped out, sticklebacks would lose their main food source, so their population would decrease due to starvation. This might also affect the heron, which could lose one of its prey species. Food webs help us understand how dependent species are on one another.

解释：食物链为：太阳 → 藻类 → 水蚤 → 刺鱼 → 苍鹭。藻类是能捕获阳光进行光合作用的生产者。水蚤是初级消费者。如果水蚤灭绝，刺鱼将失去主要食物来源，因此它们的数量会因饥饿而减少。这也可能会影响苍鹭，因为它们失去了一个猎物物种。食物网帮助我们理解物种之间如何相互依赖。

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4. Investigating Variation in Our Class | 调查班级中的变异

Miss Khan asked her Year 7 class to measure their hand spans – the distance from the tip of the thumb to the tip of the little finger when the hand is fully stretched – to the nearest millimetre. The results are shown below: 152, 168, 145, 177, 161, 154, 170, 163, 148, 175 (mm). She wants students to identify the type of variation and suggest a suitable graph.

汗老师要求她七年级的学生测量自己的手掌跨度——即手掌完全伸展时从拇指尖到小指尖的距离，精确到毫米。结果如下：152, 168, 145, 177, 161, 154, 170, 163, 148, 175 (毫米)。她希望学生确定这是哪种变异类型，并建议一种合适的图表。

Question: What type of variation does hand span show? What graph would you draw to display these measurements? Calculate the range.

问题：手掌跨度显示的是哪种变异？你会绘制什么图来展示这些测量数据？计算全距。

Explanation: Hand span is an example of continuous variation, because it can take any numerical value within a range, and there are no distinct categories. A histogram or a frequency diagram is the most suitable for continuous data. The range is the difference between the largest and smallest values: 177 – 145 = 32 mm. Continuous variation is usually influenced by both genes and environment – for instance, nutrition during growth can affect hand size.

解释：手掌跨度是连续变异的一个例子，因为它可以取一个范围内的任何数值，不存在明显的分类。直方图或频率图最适合连续数据。全距是最大值与最小值之差：177 – 145 = 32 毫米。连续变异通常受基因和环境共同影响——例如，生长期间的营养状况可能影响手的大小。

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5. Yeast Respiration Experiment | 酵母呼吸实验

A group of students set up two flasks. Flask A contained yeast, glucose and warm water. Flask B contained yeast, warm water but no sugar. A balloon was secured over the mouth of each flask. After 30 minutes, the balloon on Flask A had inflated noticeably, but the balloon on Flask B remained flat. The temperature in both flasks remained constant at 30 °C.

一组学生准备了两个烧瓶。烧瓶A装有酵母、葡萄糖和温水。烧瓶B装有酵母、温水但不加糖。每个烧瓶口都套上了一个气球。30分钟后，烧瓶A上的气球明显膨胀，而烧瓶B上的气球仍然扁平。两个烧瓶的温度都保持在30 °C。

Question: Which substance is the independent variable? What gas caused the balloon to inflate, and why was Flask B included? Write a word equation for the process occurring in Flask A.

问题：哪个物质是自变量？什么气体使气球膨胀，为什么设置烧瓶B？写出烧瓶A中发生过程的文字方程式。

Explanation: The independent variable is the presence or absence of glucose. Yeast cells use glucose in respiration, releasing carbon dioxide (CO₂) gas, which filled the balloon. Flask B was the control experiment – it showed that without sugar, no gas was produced, confirming that glucose was necessary. The word equation for anaerobic respiration in yeast is: glucose → ethanol + carbon dioxide (+ some energy). Notice that this process does not require oxygen, which is why it is called anaerobic respiration.

解释：自变量是葡萄糖的有无。酵母细胞利用葡萄糖进行呼吸，释放出二氧化碳气体，充满了气球。烧瓶B是对照实验——它表明没有糖就没有气体产生，从而证实葡萄糖是必需的。酵母无氧呼吸的文字方程式为：葡萄糖 → 乙醇 + 二氧化碳（+ 少许能量）。注意此过程不需要氧气，因此被称为无氧呼吸。

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6. Flower Dissection Detective | 花朵解剖侦探

Amar dissected a lily and carefully separated its parts. He found a green outer ring of leaf-like structures, large brightly coloured petals, several stalk-tipped structures with yellow powdery heads, and a central structure with a sticky top, a slender stalk and a swollen base. He labelled them A, B, C and D, but forgot to write the correct names.

阿马尔解剖了一朵百合花，并仔细分开了各个部分。他发现了一圈绿色的叶状结构、大而鲜艳的花瓣、几根顶端带有黄色粉末状头部的柄状结构，以及一个中心结构，其顶部有黏性，中间是一根纤细的柄，基部膨大。他把它们标注为A、B、C和D，但忘了写出正确的名称。

Question: Match these labels to: sepal, petal, stamen and carpel. Then state which part produces pollen and which part contains ovules.

问题：将这些标签匹配到：花萼、花瓣、雄蕊和雌蕊。然后说明哪个部分产生花粉，哪个部分含有胚珠。

Explanation: The green outer ring is the sepal, which protects the flower bud. The brightly coloured parts are petals, intended to attract insects for pollination. The structures with yellow powdery heads are stamens – each anther produces pollen grains. The central structure with sticky top (stigma), slender stalk (style) and swollen base (ovary) is the carpel. The ovary contains ovules, which after fertilisation will develop into seeds. This layout ensures efficient insect pollination.

解释：绿色外环是花萼，用来保护花蕾。颜色鲜艳的部分是花瓣，用来吸引昆虫传粉。带有黄色粉末头部的结构是雄蕊——每个花药都能产生花粉粒。具有黏性顶部（柱头）、细长柄（花柱）和膨大基部（子房）的中心结构是雌蕊。子房含有胚珠，受精后胚珠将发育成种子。这种构造确保了高效的昆虫传粉。

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7. Classifying Organisms with a Key | 用检索表对生物进行分类

The teacher gave students four animal cards: frog, crocodile, golden eagle and dolphin. A simple dichotomous key was written on the board:

1a. Has feathers … go to 2
1b. Does not have feathers … go to 3
2a. Can fly long distances over water … golden eagle
2b. Cannot fly … (not present)
3a. Has scales and lays eggs on land … crocodile
3b. Does not have scales … go to 4
4a. Breathes air through lungs and gives birth to live young … dolphin
4b. Moist skin, begins life in water … frog

老师给了学生四张动物卡片：青蛙、鳄鱼、金雕和海豚。一块白板上写着一个简单的二叉式检索表：

1a. 有羽毛 …… 转到2
1b. 没有羽毛 …… 转到3
2a. 可以长距离在水面上飞行 …… 金雕
2b. 不能飞行 ……（无）
3a. 有鳞片，在陆地上产卵 …… 鳄鱼
3b. 没有鳞片 …… 转到4
4a. 用肺呼吸空气并胎生产仔 …… 海豚
4b. 皮肤湿润，生命初期生活在水里 …… 青蛙

Question: Use the key to identify an animal that has moist skin and begins life in water. Explain why keys are useful for biologists.

问题：使用检索表识别一种皮肤湿润、生命初期生活在水中的动物。解释为什么检索表对生物学家非常有用。

Explanation: Following the key: 1b (no feathers) → 3b (no scales) → 4b (moist skin, begins life in water) identifies the animal as a frog. Identification keys allow scientists to name organisms accurately without needing an expert for every species. They use observable features, making classification consistent. Keys can also be updated as new species are discovered.

解释：按照检索表：1b（无羽毛）→ 3b（无鳞片）→ 4b（皮肤湿润，初期生活在水里）将该动物鉴定为青蛙。检索表使科学家能够准确地对生物进行命名，而不需要每个物种都有专家在场。它们利用可观察的特征，使分类保持一致。当发现新物种时，检索表也可以更新。

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8. The Spread of Infection | 感染的传播

During a flu outbreak, Year 7 students carried out a hand-hygiene investigation. They sprinkled a harmless fluorescent powder onto the hands of a student volunteer, who then coughed (covering the mouth incorrectly with a hand) and immediately touched a shared door handle, a keyboard and a friend’s pen. Using an ultraviolet lamp, they traced the powder’s spread to many surfaces and other students’ hands.

在一次流感爆发期间，七年级学生进行了一项手部卫生调查。他们将无害的荧光粉末撒在一名志愿者学生的手上，该学生随后咳嗽（错误地用手捂住嘴），并立即触摸了共用的门把手、键盘和一位朋友的笔。他们使用紫外线灯追踪到粉末扩散到许多表面和其他学生的手上。

Question: What do the powder particles represent? List two ways students could reduce the spread of microbes at school.

问题：这些粉末微粒代表什么？列出学生们在学校减少微生物传播的两种方法。

Explanation: The powder represents microbes such as viruses or bacteria that can cause disease. This model shows how easily pathogens spread from hands to surfaces and then to other people, a process called indirect transmission. To reduce spread, students should wash hands with soap and warm water for at least 20 seconds after coughing or sneezing, and use a tissue to catch droplets – followed by binning the tissue. Vaccination also helps protect individuals and the community by building immunity.

解释：粉末代表可以致病的微生物，如病毒或细菌。这个模型显示了病原体多么容易从手传播到物体表面，再传播给其他人，这一过程叫作间接传播。为减少传播，学生们应在咳嗽或打喷嚏后用肥皂和温水洗手至少20秒，并使用纸巾接住飞沫——随后把纸巾扔进垃圾桶。接种疫苗也有助于通过建立免疫力来保护个人和社区。

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9. Blood Flow Journey | 血流之旅

Imagine you are a red blood cell starting in the right atrium of the heart. Your job is to collect oxygen from the lungs and deliver it to the muscles of the leg. Think carefully about the route you must take through the four chambers of the heart and the blood vessels.

想象你是一个红细胞，从心脏的右心房出发。你的任务是从肺部收集氧气，并将其输送到腿部肌肉。仔细思考你通过心脏四个腔室和血管所必须经过的路线。

Question: Name the chambers and major blood vessels, in order, that the red blood cell passes through before reaching the leg muscles. Explain why the blood must travel to the lungs.

问题：按顺序说出红细胞在到达腿部肌肉之前所经过的腔室和主要血管的名称。解释为什么血液必须经过肺部。

Explanation: The correct route is: right atrium → right ventricle → pulmonary artery → lungs (where gas exchange occurs) → pulmonary vein → left atrium → left ventricle → aorta → arteries to the leg → leg muscles. The blood travels to the lungs to release carbon dioxide and pick up oxygen. This oxygen-rich blood is then pumped by the left side of the heart to the body. This double circulatory system ensures that oxygen is delivered efficiently to working muscles.

解释：正确的路线是：右心房 → 右心室 → 肺动脉 → 肺部（发生气体交换） → 肺静脉 → 左心房 → 左心室 → 主动脉 → 通往腿部的动脉 → 腿部肌肉。血液去往肺部是为了排出二氧化碳并装载氧气。然后，充满氧气的血液由左心脏泵向全身。这种双循环系统确保了氧气高效地输送到工作中的肌肉。

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10. Seed Dispersal Challenge | 种子传播挑战

Four seeds were found on the school field: a dandelion ‘clock’ with a parachute of fluffy hairs; a smooth coconut; a sticky burdock burr with tiny hooks; and a pea pod that twists and splits open when dry. The students hypothesised about how each seed is dispersed from the parent plant.

在学校操场上发现了四种种子：带有绒毛降落伞的蒲公英‘钟’；光滑的椰子；带有微小钩子的牛蒡刺果；以及干燥时会扭动裂开的豌豆荚。学生们对每种种子是如何从母株传播开来的提出了假设。

Question: Match each seed to its most likely dispersal method: wind, water, animal (internal/external) or mechanical. Explain one advantage of seed dispersal for the survival of the plant species.

问题：将每种种子与其最可能的传播方式配对：风、水、动物（内部/外部）或机械。解释种子传播对植物物种生存的一个优势。

Explanation: The dandelion uses wind dispersal – its parachute catches the breeze. The coconut floats and is dispersed by water, often travelling to new islands. The burdock attaches to animal fur via its hooks (external animal dispersal). The pea pod uses mechanical dispersal: the pod explodes to fling seeds away. Dispersal reduces competition between parent plant and offspring for light, water and nutrients, and helps the species colonise new habitats. Without dispersal, seedlings might all grow in a small, crowded area and struggle to survive.

解释：蒲公英利用风传播——它的降落伞能抓住微风。椰子能漂浮并通过水传播，常常漂流到新的岛屿。牛蒡通过小钩子附着在动物毛皮上（动物外部传播）。豌豆荚使用机械传播：豆荚爆裂将种子弹射出去。传播减少了母株与后代对光线、水分和养分的竞争，并帮助物种开拓新的栖息地。如果没有传播，幼苗可能全部生长在一块拥挤的小区域里，难以存活。

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