📚 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.
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。
1. DDT in a Lake Ecosystem | 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。
DDT is a toxic chemical that does not break down easily in the environment. When algae absorbed D
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