← 返回资讯屏轩教育 · 行业资讯

Case Study Practice for Year 7 OCR Biology | Year 7 OCR 生物：案例分析实战演练

2026-07-16 14:15 · 本文部分内容由AI辅助创作

📚 Case Study Practice for Year 7 OCR Biology | Year 7 OCR 生物：案例分析实战演练

Welcome to our collection of engaging case studies designed to help Year 7 students master the OCR Biology syllabus through real-world scenarios. Each case will challenge you to apply your knowledge of cells, ecosystems, human biology and scientific investigation skills to situations you have never seen before - exactly the way OCR examiners like to ask questions.

欢迎来到这个专为七年级学生打造的案例集，通过真实场景帮助你掌握 OCR 生物学大纲。每个案例都将考验你运用细胞、生态系统、人体生物学和科学探究技能的能力，去解决你从未见过的新情境——这正是 OCR 考官最喜欢的出题方式。

This expanded guide takes one classic case study - DDT in a lake - and shows you exactly how to turn a short scenario into a full-mark answer. Along the way you will meet five more cases covering cells, food webs, human biology and practical investigation, plus the data skills and command-word training that tie everything together.

这份扩展版指南以一个经典案例——湖泊中的 DDT——为例，向你展示如何把一个简短的情境题转化为满分答案。同时你还将遇到另外五个案例，涵盖细胞、食物网、人体生物学和实验探究，并配合数据技能与指令词训练，把知识串联成完整体系。

1. Why Case Studies Matter in Year 7 OCR Biology | 为什么案例分析对 Year 7 OCR 生物如此重要

OCR biology questions rarely ask you to simply recall a definition. The examiner gives you a short story - a farmer, a lake, a hospital patient, a greenhouse - and then asks you to use your biology to explain what is happening. This is called 'application', and it is worth the highest marks on any paper.

OCR 生物题目很少只让你背定义。考官会给你一个小故事——一位农民、一片湖泊、一位住院病人、一座温室——然后要求你用生物学知识解释发生了什么。这叫做"应用"，也是整份试卷中分值最高的部分。

Year 7 is the perfect time to practise this skill, because the biology you already know - cells, food chains, organs, respiration - is enough to answer surprisingly sophisticated questions. You do not need more facts; you need to organise the facts you have.

七年级正是练习这项技能的黄金时期，因为你已掌握的生物学知识——细胞、食物链、器官、呼吸作用——足以回答相当有深度的问题。你需要的不是更多事实，而是把已有事实组织起来的能力。

Every case study in this article sits inside one of the four pillars of the Year 7 OCR course: cells and organisation, ecosystems and interdependence, human biology and health, and working scientifically. Use the pillar labels to decide which knowledge to bring out.

本文的每一个案例都归属于 Year 7 OCR 课程的四大支柱之一：细胞与组织、生态系统与相互依存、人体生物学与健康、科学探究方法。你可以用这些支柱标签来判断该调用哪部分知识。

2. The Four-Step Method for Any Case Study | 应对任何案例题的四步法

Before we look at the individual cases, learn a routine. A reliable routine stops you panicking when the scenario looks unfamiliar and stops you wasting marks on irrelevant biology.

在看具体案例之前，先学会一套固定流程。可靠的流程能让你在面对陌生情境时不慌张，也能避免你把分数浪费在无关的生物学内容上。

Command word What the examiner wants 中文含义
Describe A statement of what you observe, no reasons needed 描述：只说你观察到的现象，不需要理由
Explain A chain of cause and effect using biological ideas 解释：用生物学原理串起因果链
Compare Both similarities and differences, ideally in one sentence 比较：既写相同点也写不同点，最好合在一句里
Suggest Apply your knowledge to a new situation, not recall 建议/推测：把知识用到新情境中，不是回忆
Calculate Show working, give the unit, round sensibly 计算：写出过程，标注单位，合理取整

3. Case Study 1: DDT in a Lake Ecosystem | 案例一：湖泊生态系统中的 DDT

A farmer sprayed a pesticide called DDT on his crops to kill insect pests. Heavy rain washed some of the DDT into a nearby lake.

一位农民在庄稼上喷洒了一种名为 DDT 的杀虫剂来杀死害虫。大雨将部分 DDT 冲入了附近的湖泊中。

The lake contained algae (phytoplankton), tiny animals (zooplankton), small fish, larger fish, and finally eagles that ate the large fish.

湖中有藻类（浮游植物）、微小动物（浮游动物）、小鱼、大鱼，最后还有以捕食大鱼为生的鹰。

Over the following months, scientists observed that the number of eagles declined sharply, and their eggshells became very thin and broke easily during incubation.

在接下来的几个月里，科学家观察到鹰的数量急剧减少，它们的蛋壳变得非常薄，孵化时很容易破碎。

Question: Explain why the eagles were harmed even though they were not directly sprayed with DDT.

问题：请解释为什么鹰受到了伤害，即使它们没有被直接喷洒 DDT。

Notice how much information is packed into five sentences. There is a chemical, a route into the water, a food chain with five trophic levels, and an observation about eggshells. A weak answer copies the story back; a strong answer uses the story as evidence for a biological explanation.

注意这五句话里压缩了多少信息：一种化学物质、一条进入水体的途径、一条含五个营养级的食物链，以及关于蛋壳的观察结果。薄弱答案会把故事抄回去；优秀答案则把故事当作证据，构建出生物学解释。

4. Working Through the DDT Answer Step by Step | 逐步拆解 DDT 题的答案

The first key idea is that DDT is a toxic chemical that does not break down easily in the environment. Chemists call this 'persistent' or 'non-biodegradable'. Because bacteria and fungi cannot decompose it, DDT stays in the water and in living tissues for years instead of being broken down and excreted.

第一个核心概念是：DDT 是一种有毒化学物质，在环境中不易分解。化学上称之为"持久性"或"不可生物降解"。由于细菌和真菌无法分解它，DDT 会在水体和生物组织中残留多年，而不会被分解并排出体外。

When algae absorbed DDT from the water, the chemical entered the food chain. The algae did not die immediately, but they stored the DDT in their cells. When zooplankton ate large numbers of algae, they took in all the DDT from every algal cell.

当藻类从水中吸收 DDT 后，这种化学物质便进入了食物链。藻类并未立即死亡，而是把 DDT 储存在细胞内。当浮游动物吃掉大量藻类时，就把每一个藻细胞中的 DDT 都摄入了体内。

This is the crucial step: DDT is fat-soluble, so it is stored in body tissue rather than being broken down or excreted. Each consumer therefore keeps the DDT from everything it eats, and the concentration builds up along the food chain.

这是关键一步：DDT 具有脂溶性，会被储存在身体组织中，而不是被分解或排出。因此每一级消费者都会保留它吃下的所有生物体内的 DDT，浓度便沿着食物链不断累积。

algae → zooplankton → small fish → large fish → eagle

藻类 → 浮游动物 → 小鱼 → 大鱼 → 鹰

Because the eagle is at the top of this food chain, it eats a very large number of large fish over its lifetime. It therefore receives the highest dose of DDT of any organism in the lake - a process called bioaccumulation, or biomagnification up the trophic levels.

由于鹰位于这条食物链的顶端，它一生中会吃掉数量极多的大鱼，因而摄入的 DDT 剂量是湖中所有生物里最高的——这一过程称为生物富集，或沿营养级逐级放大的生物放大作用。

The DDT then affects the eagle's reproduction. It interferes with the way calcium is deposited when the eggshell is formed, so the shell is laid down too thinly and cannot support the developing chick. The thin shells crack during incubation, the embryos die, and fewer young eagles hatch. With fewer chicks surviving each year, the population falls sharply.

随后 DDT 影响了鹰的繁殖。它干扰了蛋壳形成时钙的沉积过程，使蛋壳过薄，无法支撑正在发育的胚胎。薄壳在孵化过程中破裂，胚胎死亡，能成功孵化的幼鹰减少。由于每年存活的幼鸟变少，种群数量便急剧下降。

A full-mark model answer would read something like this: 'DDT is not broken down by decomposers, so it stays in the environment and is absorbed by algae. It is fat-soluble and is not excreted, so it is passed along the food chain and becomes more concentrated at each trophic level. The eagle is the top consumer, so it takes in the greatest amount. The DDT disrupts calcium deposition in the eggshell, making the shell too thin, so it breaks during incubation and fewer chicks hatch, causing the population to decline.'

满分答案示范如下："DDT 不能被分解者分解，因此在环境中长期存在并被藻类吸收。它具有脂溶性且不被排出，于是沿食物链传递，并在每个营养级进一步浓缩。鹰是顶级消费者，因此摄入量最大。DDT 干扰蛋壳中钙的沉积，使蛋壳过薄，孵化时破裂，成功孵化的幼鸟减少，导致种群数量下降。"

Questions like this often then ask you to suggest one way the farmer could reduce the problem. Good suggestions include using a biodegradable pesticide, spraying before heavy rain is forecast, leaving a buffer strip of untreated land beside the lake, or using biological control such as ladybirds that eat aphids.

这类题目常常还会要求你提出一个减少危害的建议。可行的答案包括：改用可生物降解的杀虫剂；在预报有暴雨前不喷药；在湖边留出未经施药的缓冲带；或采用生物防治，例如用瓢虫吃掉蚜虫。

5. Case Study 2: Cells Under the Microscope | 案例二：显微镜下的细胞

A Year 7 student peels a thin layer of onion epidermis and mounts it on a slide. She also smears some cheek cells from the inside of her mouth onto a second slide. Under the microscope the onion cells look like neat bricks, while the cheek cells are rounded and scattered.

一名七年级学生撕下一层薄薄的洋葱表皮，制成装片；她又从口腔内侧刮取一些上皮细胞涂在第二张载玻片上。在显微镜下，洋葱细胞像整齐的砖块，而口腔上皮细胞则是圆形、分散的。

Question: Give two differences between the two cell types and explain why each difference is useful to the plant.

问题：说出这两种细胞的两个不同点，并解释每个不同点对植物有何用处。

The onion cell has a cellulose cell wall, which makes the cell rigid and gives the plant support. It also has a large permanent vacuole filled with cell sap, which keeps the cell firm and helps store water and dissolved substances. Cheek cells have neither.

洋葱细胞具有纤维素细胞壁，使细胞坚硬，为植物提供支撑。它还有一个充满细胞液的大型永久液泡，使细胞保持饱满，并帮助储存水分与溶解物质。口腔上皮细胞两者都没有。

广告 / Sponsored

牛津AQA国际GCSE生物?OxfordAQA International GCSE Biology (9201): Onl?进口原版
牛津AQA国际GCSE生物?OxfordAQA International GCSE Biology (9201): Onl?进口原版
¥399.0
📱 去京东购买
京东精选

Mature onion epidermis cells do not contain chloroplasts because they are underground and receive no light, so photosynthesis cannot occur there. A leaf cell from the same plant would contain chloroplasts, which absorb light energy for photosynthesis.

成熟的洋葱表皮细胞不含叶绿体，因为它们位于地下、接受不到光照，无法进行光合作用。同一植株的叶细胞则会含有叶绿体，用于吸收光能进行光合作用。

Notice the language pattern the examiner wants: structure, then function, connected by 'so' or 'because'. Saying only 'it has a cell wall' earns one mark; adding 'which is made of cellulose and keeps the cell rigid, supporting the plant' earns the second.

注意考官期望的语言模式：先写结构，再写功能，用 so 或 because 连接。只写"它有细胞壁"得一分；补上"它由纤维素构成，使细胞保持坚硬，从而支撑植物"才能拿到第二分。

6. Case Study 3: Magnification and Scale | 案例三：放大倍数与比例换算

The same student draws one onion cell. On her drawing the cell is 40 mm wide. The actual cell is 0.1 mm wide. She is asked to calculate the magnification of her drawing.

这位学生画出了一个洋葱细胞。在图上，该细胞宽 40 mm；而细胞的真实宽度是 0.1 mm。题目要求她计算这幅图的放大倍数。

magnification = image size ÷ actual size

magnification = 40 mm ÷ 0.1 mm = ×400

Always convert both measurements to the same unit before dividing. Note that 1 mm = 1000 µm, so 0.1 mm = 100 µ the actual size, rearrange the equation to read actual size = image size ÷ magnification.

相除之前务必把两个数据换算成同一单位。记住 1 mm = 1000 µm，所以 0.1 mm = 100 µm。如果题目给出放大倍数而要求真实尺寸，则把公式变形为：真实尺寸 = 图像尺寸 ÷ 放大倍数。

Magnification has no units - it is a ratio. If your answer comes out with 'mm' attached, you have made an error. Writing '×400' or '400 times' both earn the mark, but '400 mm' does not.

放大倍数没有单位——它是一个比值。如果你的答案带了"mm"，说明出错了。写 ×400 或 400 倍都能得分，但写 400 mm 不能得分。

A common trap is forgetting to convert micrometres to millimetres. A cell quoted as 50 µm is 0.05 mm, not 50 mm, and dividing by the wrong value will produce an answer 1000 times too small.

一个常见陷阱是忘记把微米换算成毫米。一个标注为 50 µm 的细胞实际是 0.05 mm，而不是 50 mm；用错数值会让答案相差一千倍。

7. Case Study 4: A Woodland Food Web and Energy Loss | 案例四：林地食物网与能量损失

In a woodland, oak leaves are eaten by caterpillars. Caterpillars are eaten by blue tits, and blue tits are eaten by sparrowhawks. Scientists measured the energy in each trophic level and found that only about 10% of the energy passed from one level to the next.

在一片林地中，橡树叶被毛虫取食，毛虫被蓝山雀取食，蓝山雀又被雀鹰捕食。科学家测量了各营养级的能量，发现只有约 10% 的能量能从一个营养级传递到下一级。

Question: Explain why so much energy is lost, and suggest why food chains rarely have more than five trophic levels.

问题：解释为什么会有如此多的能量损失，并推测为什么食物链很少有超过五个营养级的。

Because roughly 90% of the energy is lost at every transfer, the energy available becomes too small to support another level after about four or five steps. This is also why top predators are rare and need large territories.

由于每一次能量传递大约损失 90%，经过四到五步之后，剩余能量已不足以支撑下一个营养级。这也解释了为什么顶级捕食者数量稀少、需要很大的领地。

ight ask you to calculate efficiency, using energy transferred out ÷ energy taken in × 100%. Always round sensibly and include the % sign.

相关问题还可能要求计算能量传递效率：传递出去的能量 ÷ 摄入的能量 × 100%。注意合理取整并写上百分号。

8. Case Study 5: Exercise and Heart Rate (Human Biology) | 案例五：运动与心率（人体生物学）

A student measured her pulse rate at rest and again straight after running for two minutes. Her resting rate was 72 beats per minute; immediately after exercise it was 132 beats per minute. Ten minutes later it had returned to 78 beats per minute.

一名学生测量了自己静息时和跑两分钟后的脉搏。静息心率为每分钟 72 次；运动后立刻为每分钟 132 次；十分钟后恢复到每分钟 78 次。

Question: Explain why the heart rate increased during exercise.

问题：解释运动时心率为什么会升高。

Muscles need more energy during exercise, so they respire faster. Respiration requires glucose and oxygen and releases energy, so the body needs to deliver oxygen and glucose to the muscles more quickly and remove carbon dioxide more quickly.

运动时肌肉需要更多能量，因此呼吸作用加快。呼吸作用需要葡萄糖和氧气并释放能量，所以身体必须更快地把氧气和葡萄糖输送到肌肉，同时更快地清除二氧化碳。

glucose + oxygen → carbon dioxide + water (+ energy released)

葡萄糖 + 氧气 → 二氧化碳 + 水（+ 释放能量）

The heart therefore contracts faster and more forcefully, increasing cardiac output and pushing more blood per minute through the arteries to the muscles. The breathing rate and depth also increase to take in more oxygen and remove more carbon dioxide.

因此心脏收缩得更快、更有力，心输出量增加，每分钟通过动脉输送到肌肉的血液更多。同时呼吸频率和深度也增加，以摄取更多氧气并排出更多二氧化碳。

If exercise continues vigorously and oxygen supply cannot keep up, muscles respire anaerobically. In humans this produces lactic acid, which builds up and causes cramp and fatigue. This is why the student's pulse stayed slightly above resting level for a few minutes afterwards - extra oxygen was still needed to break down the lactic acid.

如果剧烈运动持续进行、氧气供应跟不上，肌肉就会进行无氧呼吸。在人体中这一过程会产生乳酸，乳酸积累会引起抽筋和疲劳。这就是该学生运动后几分钟内心率仍略高于静息值的原因——身体还需要额外氧气来分解乳酸。

9. Case Study 6: Planning a Fair Test | 案例六：设计公平实验

A group of students wants to find out whether light intensity affects the rate at which pondweed produces oxygen bubbles. They plan to move a lamp different distances from a test tube of pondweed and count the bubbles produced in one minute.

一组学生想探究光照强度是否影响水草产生氧气气泡的速率。他们计划把台灯放在距水草试管不同距离处，并统计一分钟内产生的气泡数。

Question: Identify the independent, dependent and three control variables, and suggest one improvement.

问题：指出自变量、因变量和三个控制变量，并提出一项改进建议。

Variable type In this investigation 中文
Independent Distance of the lamp from the pondweed 自变量：灯到水草的距离
Dependent Number of bubbles per minute 因变量：每分钟气泡数
Control Temperature, CO₂ concentration, same pondweed mass, same time period 控制变量：温度、二氧化碳浓度、水草质量、计时时长

An improvement would be to repeat each distance three times and calculate a mean, which reduces the effect of random error and makes the result more reliable. Another improvement is to use a lamp with a fixed wattage and to place a heat shield or water bath between the lamp and the tube, so temperature does not change as well as light.

一项改进是每个距离重复三次并计算平均值，这能减小随机误差的影响，使结果更可靠。另一项改进是使用功率固定的灯泡，并在灯与试管之间放置隔热板或水浴，以免温度随光照一起发生变化。

Always finish a planning question by considering safety: pondweed in water near mains electricity is a genuine hazard, so check the lamp and leads for damage and keep water away from the plug.

回答实验设计题时一定要以安全考虑收尾：水中的水草靠近市电是真实风险，应检查灯具和电线是否破损，并让水远离插头。

10. Data Skills: Tables, Graphs and Calculations | 数据处理技能：表格、图表与计算

Most case studies finish with data. Examiners test whether you can read a table accurately, plot a graph correctly and perform a simple calculation without losing the unit.

大多数案例题最后都会给数据。考官要检验你能否准确读取表格、正确绘图，并在不丢单位的前提下完成简单计算。