AS CAIE Biology: Case Study Practice Drills | AS CAIE 生物：案例分析实战演练

📚 AS CAIE Biology: Case Study Practice Drills | AS CAIE 生物：案例分析实战演练

Case study practice is a vital component of AS Level Biology (CAIE). It trains you to interpret data, design experiments, and apply theoretical knowledge to real-world scenarios. This article provides a series of drill exercises covering key syllabus topics, each with a step-by-step analysis to build your confidence for Paper 2 and Paper 3.

案例分析练习是AS生物（CAIE）的重要组成部分。它能训练你解读数据、设计实验，并将理论知识应用于实际情境。本文提供一系列涵盖核心大纲主题的演练，每个案例均附带逐步分析，以增强你应对Paper 2和Paper 3的信心。

1. Enzyme Activity: Effect of pH | 酶活性：pH的影响

An experiment was conducted to investigate the effect of pH on catalase activity using potato extract. The volume of oxygen produced in 30 seconds was recorded at different pH values. The raw data are shown in the table below.

一个利用土豆提取物探究pH对过氧化氢酶活性影响的实验，记录了在不同pH值下30秒内产生的氧气体积。原始数据如上表所示。

Calculate the rate of reaction for each pH by dividing the volume of oxygen by 30 s. The highest rate occurs at pH 7, producing 9.5 cm³ O₂. This value represents the optimum pH for catalase. Around this pH, the enzyme’s active site has the ideal shape for the substrate, hydrogen peroxide, to bind.

通过将氧气体积除以30秒，计算每个pH值的反应速率。最高速率出现在pH 7，产生9.5 cm³ O₂，此值代表过氧化氢酶的最适pH。在该pH附近，酶的活性位点具有与底物过氧化氢结合的理想形状。

At pH values far from the optimum, the excess H⁺ or OH⁻ ions disrupt the hydrogen bonds and ionic interactions that maintain the tertiary structure of the enzyme. This leads to changes in the shape of the active site, so the substrate can no longer fit; the enzyme is denatured. Extreme pH causes irreversible denaturation, while small shifts may only reduce activity temporarily.

在远离最适pH的数值下，过量的H⁺或OH⁻会破坏维持酶三级结构的氢键和离子相互作用。这导致活性位点形状改变，底物不再能嵌合，酶发生变性。极端pH引起不可逆变性的，而小幅变化可能仅暂时降低活性。

2. Osmosis and Water Potential in Potato Strips | 土豆条的渗透作用与水势

Potato strips of equal mass were placed in a series of sucrose solutions (0.0 to 1.0 mol dm⁻³) for one hour. The percentage change in mass was calculated and plotted against sucrose concentration. The data are summarised below.

取等质量的土豆条，在不同浓度的蔗糖溶液（0.0 至 1.0 mol dm⁻³）中浸泡一小时。计算质量变化的百分比，并以此对蔗糖浓度作图。数据汇总如上。

The graph of percentage change against concentration crosses the zero line at approximately 0.32 mol dm⁻³. This is the sucrose concentration that has the same water potential as the potato cells, so there is no net movement of water. At lower concentrations, water

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