IGCSE Edexcel Biology: Unit Test Paper | IGCSE Edexcel 生物：单元测试卷

📚 IGCSE Edexcel Biology: Unit Test Paper | IGCSE Edexcel 生物：单元测试卷

This unit test paper is designed to help you revise the core topics of the IGCSE Edexcel Biology syllabus. Each question targets a specific learning outcome and is followed by a detailed answer and explanation in both English and Chinese. Work through the questions, check your answers, and use the explanations to deepen your understanding.

本单元测试卷旨在帮助你复习IGCSE Edexcel生物大纲的核心主题。每一道题针对一个特定的学习目标，并附有中英文详尽的答案与解析。请完成题目，核对答案，并利用解析加深理解。

1. Cell Structure – Multiple Choice | 细胞结构 – 选择题

Question 1: Which of the following structures is found in both plant and animal cells? A. Cell wall, B. Chloroplast, C. Nucleus, D. Permanent vacuole. The correct answer is C, Nucleus. A nucleus is present in almost all eukaryotic cells, including both plant and animal cells. It stores genetic information and controls cellular activities. In contrast, the cell wall, chloroplasts, and a large permanent vacuole are exclusive to plant cells (and some other organisms); animal cells lack these features.

问题1：下列哪种结构同时存在于植物细胞和动物细胞中？A. 细胞壁，B. 叶绿体，C. 细胞核，D. 大液泡。正确答案是C，细胞核。细胞核存在于几乎所有的真核细胞中，包括植物和动物细胞。它储存遗传信息并控制细胞活动。相比之下，细胞壁、叶绿体和大液泡是植物细胞（及部分其他生物）独有的特征，动物细胞缺少这些结构。

2. Movement of Substances – Osmosis | 物质移动 – 渗透

Question 2: A potato cylinder is placed in pure water for 30 minutes. Describe and explain what happens to the mass and texture of the cylinder. Answer: The potato cylinder gains mass and becomes turgid (firmer). Explanation: The cytoplasm of potato cells contains solutes (e.g. sugars and salts) making it have a lower water potential than pure water. Water moves by osmosis from the region of higher water potential (pure water) to the region of lower water potential (inside the cells) through a partially permeable membrane. As water enters, the cells swell and push against the cell walls, increasing turgor pressure and firmness.

问题2：一块马铃薯圆柱在纯水中放置30分钟。描述并解释其质量和质地的变化。答案：马铃薯圆柱质量增加并变得硬挺（更硬）。解释：马铃薯细胞的细胞质中含有溶质（如糖和盐），因此其水势比纯水低。水分通过渗透从水势较高的区域（纯水）穿过部分透性膜向水势较低的区域（细胞内部）移动。水分进入后，细胞膨胀并挤压细胞壁，增加膨压和硬度。

3. Enzymes – Temperature and Activity | 酶 – 温度与活性

Question 3: The table below shows the rate of an enzyme-controlled reaction at different temperatures. Identify the optimum temperature and explain the changes in activity above 40 °C.

问题3：下表显示了不同温度下一种酶促反应的速率。找出最适温度，并解释40 °C以上活性的变化。

Answer: The optimum temperature is approximately 40 °C, as this is where the reaction rate is highest. Above 40 °C, the rate drops sharply because the enzyme molecules denature. High temperatures break the hydrogen bonds maintaining the enzyme’s specific tertiary structure. The active site loses its complementary shape, so the substrate can no longer bind effectively, and the reaction slows or stops. Denaturation is usually irreversible.

答案：最适温度约为40 °C，此时反应速率最高。超过40 °C后，速率急剧下降，因为酶分子发生了变性。高温破坏了维持酶特定三级结构的氢键。活性位点失去互补形状，因此底物无法有效结合，反应

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