📚 Case Study Practice for WJEC Year 11 Biology | WJEC 11年级生物案例分析实战演练
Case studies are a powerful way to apply biological concepts to real-world situations; they train you to think like a scientist, interpret data, evaluate evidence and justify conclusions. This revision guide presents ten detailed case studies spanning the WJEC Year 11 curriculum, with step-by-step analysis to strengthen your exam technique and deepen your understanding of ecology, genetics, disease, cellular processes and more.
案例分析是将生物学概念应用于真实情境的强大方式；它能训练你像科学家一样思考，解读数据、评价证据并论证结论。这份复习指南围绕 WJEC 11 年级大纲设计了十个详细的案例研究，通过逐步分析帮助你提升应试技巧，加深对生态、遗传、疾病、细胞过程等主题的理解。
1. Disappearing Ospreys in a Welsh Estuary | 威尔士河口鱼鹰消失之谜
A local wildlife trust noticed that osprey numbers in a Welsh estuary had fallen from 12 breeding pairs to just 3 pairs over five years. Water samples showed nitrate levels three times higher than the safe threshold. The estuary supports eelgrass, small fish such as sandeels, and the ospreys feed mainly on mullet. Farmers in the surrounding catchment had recently intensified their use of ammonium nitrate fertiliser.
当地野生动物基金会发现，五年内威尔士某河口的鱼鹰数量从 12 对繁殖对下降到仅 3 对。水样检测显示硝酸盐浓度超过安全阈值三倍。河口生态系统包含鳗草、玉筋鱼等小型鱼类，而鱼鹰主要以鲻鱼为食。流域周围农民近期大量使用了硝酸铵肥料。
- Excess fertiliser runs off into streams, causing eutrophication. Nitrates stimulate rapid growth of algae, blocking sunlight to aquatic plants. Eelgrass dies, reducing habitat for sandeels, so mullet populations crash, removing the ospreys' food source.
- 过量化肥流入溪流引发富营养化。 硝酸盐刺激藻类快速繁殖，遮挡了水生植物的阳光。鳗草死亡，玉筋鱼栖息地缩减，导致鲻鱼数量锐减，鱼鹰失去食物来源。
- Leaching of nitrates also poisons drinking water and reduces biodiversity. The trophic cascade shows how human activity at one trophic level can destabilise a whole food web.
- 硝酸盐淋溶还会污染饮用水并降低生物多样性。 这个营养级联反应表明，人类在某一营养级上的活动会破坏整个食物网的稳定。
- Scientific solution: riparian buffer zones of trees and reeds can absorb excess nutrients before they reach the water. The trust can also work with farmers to apply fertiliser only at times of active plant growth to minimise runoff.
- 科学解决方案：河岸缓冲带种植树木和芦苇 可以在营养物质进入水体之前将其吸收。基金会还可建议农民仅在植物活跃生长期施肥，以减少径流。
2. The Peatland Carbon Time Bomb | 泥炭地碳定时炸弹
Welsh peatlands store an estimated 300 million tonnes of carbon. A case study in the Brecon Beacons examined two adjacent bogs: one drained for sheep grazing, the other left intact. Core samples revealed that the drained bog was losing 25 tonnes of CO₂ per hectare per year, while the intact bog was a net carbon sink, accumulating 5 tonnes per hectare per year.
威尔士泥炭地储存了约 3 亿吨碳。对布雷肯比肯斯地区两个相邻沼泽进行研究：一个被排水用于放牧，另一个保持原状。钻探样本显示，排水沼泽每年每公顷释放 25 吨 CO₂，而原状沼泽是净碳汇，每年每公顷累积 5 吨碳。
- Peat forms in waterlogged, anaerobic conditions where decomposition is very slow. Drainage introduces oxygen, allowing aerobic bacteria to decompose stored organic matter rapidly, releasing CO₂.
- 泥炭在积水缺氧条件下形成，分解极其缓慢。 排水引入氧气，好氧细菌快速分解储存的有机物，释放出 CO₂。
- This positive feedback loop links land management to climate change: draining peat releases greenhouse gases, which warm the climate, drying out more peatland.
- 这一正反馈循环 将土地管理与气候变化联系起来：排水释放温室气体，导致气候变暖，进而使更多泥炭地干涸。
- Restoration involves blocking drainage ditches and replanting Sphagnum moss. Sphagnum holds up to 20 times its dry mass in water, creating waterlogged conditions that suppress decomposition and lock away carbon.
- 修复措施包括堵塞排水沟并重新种植泥炭藓。 泥炭藓可吸收相当于自身干重 20 倍的水分，创造积水条件，抑制分解，封存碳元素。
3. Cystic Fibrosis Across Three Generations | 三代囊性纤维化遗传分析
A family genetic history shows that two healthy parents have a child with cystic fibrosis (CF). The mother’s sister also has CF, but the father has no family history of the condition. The parents are expecting a second child and seek genetic counselling. CF is caused by a recessive allele on chromosome 7.
某家族遗传史显示，一对健康夫妇育有一名患囊性纤维化的孩子。母亲的妹妹也患有此病，父亲家族无相关病史。这对夫妇即将迎来第二个孩子，并寻求遗传咨询。囊性纤维化由 7 号染色体上的隐性等位基因引起。
- Since CF is recessive, the affected child has the genotype ff. Both parents must be carriers (Ff) because they are healthy but produced an affected child. The father’s lack of family history simply means no affected relatives were recorded; a carrier can go unnoticed for generations.
- 囊性纤维化是隐性性状，患病孩子的基因型为 ff。 由于父母均健康却生出患病孩子，两人必然都是携带者（Ff）。父亲家族没有病史仅意味着过去没有记录在案的患病亲属；携带者可能数代不被察觉。
- Punnett square for Ff × Ff: 25% chance FF (healthy, non-carrier), 50% chance Ff (healthy carrier), 25% chance ff (affected). So for the second child, the risk of being affected is 1 in 4, regardless of the first child’s status.
- Ff × Ff 的庞尼特方格： 25% 概率 FF（健康非携带者），50% 概率 Ff（健康携带者），25% 概率 ff（患病）。因此第二个孩子的患病风险为 1/4，与第一个孩子的状况无关。
- Prenatal testing such as amniocentesis or chorionic villus sampling can detect the CFTR mutation in fetal cells. Carrier testing can also be offered to extended family members to inform their reproductive choices.
- 产前检测，如羊膜穿刺或绒毛膜采样，可检测胎儿细胞中的 CFTR 基因突变。也可为家族其他成员提供携带者检测，以帮助其做出生育决策。
4. Salmonella Outbreak on a School Trip | 学校旅行中的沙门氏菌暴发
Thirty-two students and four staff on a residential field trip developed diarrhoea, fever and abdominal cramps 24-48 hours after a barbecue. Public health investigators traced the illness to undercooked chicken skewers. Stool cultures confirmed Salmonella enteritidis. One teacher, who had had her gallbladder removed three years earlier, became a chronic carrier and continued to shed bacteria in her faeces for months.
外出实地考察的 32 名学生和 4 名教职员在烧烤后 24–48 小时内出现腹泻、发热和腹部绞痛。公共卫生调查人员将病因追溯至未烤熟的鸡肉串。粪便培养确认了肠炎沙门氏菌。一位三年前切除胆囊的老师成为慢性携带者，持续数月随粪便排出细菌。
- Salmonella is a zoonotic bacterium often found in poultry intestines. Cross-contamination from raw chicken to salad or inadequate cooking (internal temperature below 70 °C) allows the bacteria to survive.
- 沙门氏菌是一种人畜共患细菌，常见于家禽肠道。生鸡肉与沙拉的交叉污染或烹饪不充分（中心温度低于 70 °C）会使细菌存活。
- The immune system responds with inflammation of the gut lining and secretion of fluid, causing diarrhoea. Most people recover within a week without antibiotics; rehydration is the main treatment. Antibiotics are reserved for severe cases to avoid encouraging antibiotic resistance.
- 免疫系统作出反应，引起肠道内膜发炎和液体分泌，导致腹泻。 多数人无需抗生素即可在一周内恢复；补水是主要治疗手段。抗生素仅用于重症患者，以避免助长抗生素耐药性。
- The teacher became a carrier because Salmonella can persist in the gallbladder. Without a gallbladder, bacteria were not trapped and flushed out, but instead established a long-term infection in the bile ducts, leading to prolonged shedding.
- 这位老师成为携带者，是因为沙门氏菌能在胆囊中持续存在。 没有胆囊后，细菌无法被捕获和排出，反而在胆管中形成长期感染，导致持续排菌。
5. Glyphosate Resistance in Field Bindweed | 田旋花对草甘膦的抗性
An arable farm in Pembrokeshire has used glyphosate-based herbicide for twenty years to control weeds. Recently, field bindweed has become increasingly difficult to kill. The farmer sends samples to a university, which confirms that the plants possess an altered EPSPS enzyme that glyphosate cannot bind to. The resistant allele is dominant and spread rapidly in the population.
彭布罗克郡的一家耕地农场使用草甘膦除草剂控制杂草已有二十年。最近，田旋花变得越来越难以杀死。农场主送检样品，大学确认这些植物携带一种已突变的 EPSPS 酶，草甘膦无法与之结合。该抗性等位基因为显性，并在种群中迅速扩散。
- Glyphosate normally inhibits the EPSPS enzyme in the shikimate pathway, blocking synthesis of aromatic amino acids and killing the plant. A spontaneous mutation that alters the shape of the enzyme’s active site prevents herbicide binding, conferring resistance.
- 草甘膦通常抑制莽草酸途径中的 EPSPS 酶， 阻断芳香族氨基酸的合成，导致植物死亡。自发突变改变酶活性位点的形状，阻止除草剂结合，从而赋予抗性。
- Continuous use of a single herbicide exerts strong selection pressure. Resistant plants survive, reproduce and pass the dominant allele to offspring. Over years, the frequency of the resistant allele increases dramatically – a clear case of natural selection driven by human activity.
- 长期使用单一除草剂产生强大的选择压力。 抗性植株存活、繁殖，并将显性等位基因传递给后代。多年后，抗性等位基因频率急剧上升——这是由人类活动驱动的自然选择的典型案例。
- Integrated weed management strategies such as crop rotation, mechanical weeding and alternating herbicides with different modes of action can delay resistance evolution. Genetic engineering of crops to be glyphosate-resistant is not the direct cause of weed resistance; it merely simplifies the selection landscape.
- 综合杂草管理策略， 如轮作、机械除草和交替使用不同作用机制的除草剂，可延缓抗性演化。转基因抗草甘膦作物本身并非杂草抗性的直接原因，它只是简化了选择环境。
6. Respiration Rate in Maggots at Different Temperatures | 不同温度下蛆虫的呼吸速率
Students set up a respirometer with 10 blowfly maggots, soda lime to absorb CO₂, and a coloured liquid manometer. They recorded the distance moved by the liquid in 5 minutes at 5 °C, 15 °C, 25 °C, 35 °C and 45 °C. Results: at 5 °C, 2 mm; 15 °C, 8 mm; 25 °C, 22 mm; 35 °C, 38 mm; 45 °C, 5 mm. At 45 °C the maggots became inactive.
学生用 10 只丽蝇蛆虫搭建呼吸计，内置碱石灰吸收 CO₂，并连接有色液体压力计。他们记录了在 5 °C、15 °C、25 °C、35 °C 和 45 °C 下 5 分钟内液体的移动距离。结果：5 °C 为 2 mm；15 °C 为 8 mm；25 °C 为 22 mm；35 °C 为 38 mm；45 °C 为 5 mm。45 °C 时蛆虫变得不活动。
- Respiration rate increases with temperature up to an optimum because enzymes controlling respiration have more kinetic energy, resulting in more frequent successful collisions between enzyme and substrate. The distance moved by the liquid is directly proportional to oxygen consumption, as the maggots use O₂ and produce CO₂, which is absorbed by soda lime, causing a pressure drop.
- 呼吸速率随温度升高而增加，直至最适温度， 因为控制呼吸的酶获得更多动能，酶与底物成功碰撞的频率增加。液体移动距离与耗氧量成正比，原因是蛆虫消耗 O₂ 并产生 CO₂，后者被碱石灰吸收，导致压力下降。
- Beyond the optimum (around 35 °C), enzymes denature. The active site loses its specific shape, the substrate can no longer bind, and respiration rate drops sharply. At 45 °C the maggots are severely stressed, explaining the very low reading.
- 超过最适温度（约 35 °C）后，酶发生变性。 活性位点失去特定形状，底物无法再结合，呼吸速率急剧下降。45 °C 时蛆虫严重应激，因此读数极低。
- Control variables: maintain equal numbers and life stages of maggots, use the same volume of soda lime, and allow equilibration time at each temperature before recording. A control tube without maggots should be used to correct for pressure changes due to temperature fluctuations.
- 控制变量： 保持蛆虫数量和龄期一致，使用等体积碱石灰，并在每次温度条件下充分平衡后再记录。应设置无蛆虫的对照管，以校正温度波动引起的压力变化。
7. Blood Typing and a Paternity Puzzle | 血型鉴定与亲子关系谜题
A mother with blood type A (genotype Iᴬi) gave birth to a child with blood type O (ii). She named a man with blood type AB (IᴬIᴮ) as the father. He denied paternity. A second man, blood type B (Iᴮi), also claimed to be the father. The court ordered a blood group analysis.
一位血型为 A 型（基因型 Iᴬi）的母亲生下一个 O 型血（ii）的孩子。她指认一名 AB 型血（IᴬIᴮ）的男子为父亲，但该男子否认。另一名 B 型血（Iᴮi）的男子也声称是孩子的父亲。法院下令进行血型鉴定。
- ABO blood type is determined by three alleles: Iᴬ, Iᴮ (co-dominant) and i (recessive). The mother must be Iᴬi to be group A. The child is ii, receiving one i allele from each parent.
- ABO 血型由三个等位基因决定：Iᴬ、Iᴮ（共显性）和 i（隐性）。 母亲必须是 Iᴬi 才是 A 型。孩子为 ii，从父母各获得一个 i 等位基因。
- The man with genotype IᴬIᴮ cannot contribute an i allele because he has only Iᴬ and Iᴮ. Therefore, he cannot be the biological father of a group O child. The man with genotype Iᴮi can contribute an i allele and is compatible with paternity.
- 基因型为 IᴬIᴮ 的男子无法提供 i 等位基因， 因为他只有 Iᴬ 和 Iᴮ。因此，他不可能是 O 型血孩子的生父。基因型为 Iᴮi 的男子可以提供 i 等位基因，符合亲子关系。
- Limitation of blood type evidence: blood groups can only exclude a man, not positively prove paternity because millions of men share compatible genotypes. Modern DNA fingerprinting uses short tandem repeats (STRs) to provide a probability of paternity exceeding 99.99%.
- 血型证据的局限性： 血型鉴定只能排除某男子，不能完全证实亲子关系，因为数以百万计的男性都具有相容的基因型。现代 DNA 指纹鉴定使用短串联重复序列（STR）进行检测，可提供超过 99.99% 的亲子关系概率。
8. The Invasive Signal Crayfish and Native Biodiversity | 入侵物种北美螯虾与本土生物多样性
Signal crayfish (Pacifastacus leniusculus) were introduced to a Welsh river in the 1980s. A recent survey showed that native white-clawed crayfish had disappeared from that stretch, and populations of aquatic plants, invertebrates and small fish had declined by 60%. The signal crayfish carries the crayfish plague pathogen Aphanomyces astaci, to which it is resistant but which is lethal to native crayfish.
北美螯虾于 20 世纪 80 年代被引入威尔士某河流。近期调查显示，该河段的本土白爪螯虾已消失，水生植物、无脊椎动物和小型鱼类的数量下降了 60%。北美螯虾携带螯虾瘟疫病原体 Aphanomyces astaci，自身具有抗性，但对本土螯虾是致命的。
- Invasive species outcompete natives for food and habitat, but here the key impact is disease transmission. The pathogen quickly eliminated the native crayfish, removing a key detritivore and altering the food web.
- 入侵物种在食物和栖息地上胜过本地物种， 但此处最关键的影响在于疾病传播。病原体迅速消灭了本土螯虾，移除了一个关键的食碎屑动物，改变了食物网。
- Trophic cascade effect: without crayfish to break down leaf litter, nutrient cycling slows. Reduced invertebrate numbers impact fish, which then affects predators such as otters and kingfishers.
- 营养级联效应： 没有螯虾分解落叶，营养物质循环减慢。无脊椎动物减少影响鱼类，进而波及水獭和翠鸟等捕食者。
- Biosecurity education is essential: anglers and boat users should check, clean and dry equipment to prevent spreading the plague to isolated native crayfish populations. Trapping signal crayfish can help control numbers but total eradication is unlikely once established.
- 生物安全教育至关重要： 垂钓者和船主应检查、清洁并干燥设备，防止将瘟疫传播到孤立的本土螯虾种群。诱捕北美螯虾有助于控制数量，但一旦建立种群，彻底清除几乎不可能。
9. Mitosis and Cancer in a Sunbed User | 日光浴床使用者的有丝分裂与癌症
A 19-year-old woman used sunbeds weekly for three years and developed a pigmented mole that changed shape and colour. Biopsy revealed malignant melanoma. Pathologists counted the mitotic index – the number of cells in mitosis per 1000 cells – and found it to be 45, compared with fewer than 2 in normal skin.
一名 19 岁女性连续三年每周使用日光浴床，某颗色素痣的形状和颜色发生改变。活检诊断为恶性黑色素瘤。病理学家检测了有丝分裂指数——每 1000 个细胞中处于有丝分裂的细胞数——发现为 45，而正常皮肤中该指数低于 2。
- Ultraviolet (UV) radiation from sunbeds damages DNA in skin cells. If tumour suppressor genes such as p53 are mutated, the cell loses its ability to halt the cell cycle for repair or trigger apoptosis. Uncontrolled mitosis leads to a tumour.
- 日光浴床发出的紫外线会损伤皮肤细胞的 DNA。 若抑癌基因（如 p53）发生突变，细胞将失去暂停细胞周期进行修复或触发细胞凋亡的能力。不受控制的有丝分裂导致肿瘤形成。
- Mitotic index is a quantitative measure of cell division rate. A high mitotic index indicates rapid proliferation and aggressive cancer. It helps oncologists determine the tumour grade and decide on treatment intensity, such as chemotherapy, which targets rapidly dividing cells.
- 有丝分裂指数是衡量细胞分裂速率的定量指标。 高有丝分裂指数说明增殖迅速，癌症侵袭性强。这有助于肿瘤科医生确定肿瘤分级并决定治疗强度，例如针对快速分裂细胞的化疗。
- Prevention is far better than cure: avoid sunbeds, use broad-spectrum sunscreen, and monitor moles using the ABCDE rule (Asymmetry, Border irregularity, Colour variation, Diameter over 6 mm, Evolution). Public health campaigns have led to bans on commercial sunbeds for under-18s in Wales.
- 预防远胜于治疗： 避免使用日光浴床，使用广谱防晒霜，并用 ABCDE 规则（不对称、边缘不规则、颜色多杂、直径超过 6 毫米、演化变化）观察痣的变化。公共卫生宣传已促使威尔士禁止 18 岁以下青少年使用商业日光浴床。
10. Optimising Glasshouse Conditions for Tomato Yield | 优化温室条件以提升番茄产量
A commercial grower in Anglesey grows tomatoes in a glasshouse enriched with extra CO₂ and artificial lighting. Sensors show that at 400 ppm CO₂, light intensity 800 lux and temperature 22 °C, the net rate of photosynthesis is 12 mg glucose dm⁻² h⁻¹. When CO₂ is increased to 800 ppm, with light at 1200 lux and temperature 28 °C, the rate increases to 28 mg glucose dm⁻² h⁻¹. However, raising temperature further to 35 °C drops the rate to 9 mg dm⁻² h⁻¹.
安格尔西的一位商业种植者在温室中额外补充 CO₂ 和人工光照种植番茄。传感器显示，当 CO₂ 浓度为 400 ppm、光照强度 800 lux、温度 22 °C 时，净光合作用速率为 12 mg 葡萄糖 dm⁻² h⁻¹。当 CO₂ 提高至 800 ppm，光照为 1200 lux，温度 28 °C 时，速率上升至 28 mg dm⁻² h⁻¹。然而，将温度进一步提升至 35 °C 时，速率降至 9 mg dm⁻² h⁻¹。
- Photosynthesis is limited by the factor in shortest supply. Initially CO₂ and light were limiting. Boosting both together lifted the rate because the limiting factors were alleviated. The Calvin cycle uses CO₂, so extra CO₂ increases the rate of carbon fixation, provided there is enough ATP and reduced NADP from the light-dependent reactions.
- 光合作用受最少供应因子的限制。 最初 CO₂ 和光强是限制因子。同时提升两者解除了限制，速率得以提高。卡尔文循环需要 CO₂，因此额外 CO₂ 可在有充足 ATP 和还原型 NADP 的前提下提高碳固定速率。
- At 35 °C, the enzyme rubisco starts to denature, and the stomata may close to conserve water, limiting CO₂ entry. Photorespiration also increases, wasting fixed carbon. Hence the dramatic decline.
- 在 35 °C 时，RuBisCO 酶开始变性， 且气孔可能关闭以保存水分，限制了 CO₂ 进入。光呼吸也会加剧，浪费已固定的碳，因此速率急剧下降。
- Economic judgement: the grower must weigh the cost of heating, CO₂ enrichment and supplementary lighting against the increase in yield. Marginal analysis shows that the optimum commercial point is often just below the physiological maximum, where the cost of the next unit of input equals the value of the extra yield it produces.
- 经济考量： 种植者须权衡加温、补充 CO₂ 和人工光照的成本与产量增益。边际分析显示，商业最佳点通常略低于生理最大值，此时下一单位投入的成本恰好等于其所带来额外产出的价值。
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