Edexcel (B) Biology A-Level CP07 蝗虫气体交换系统实验全攻略 | Gas Exchange System – Locust Dissection Guide

📌 引言 | Introduction

在 Edexcel (B) Biology A-Level 课程中，CP07（Core Practical 7）是一个让学生”又爱又恨”的实验——蝗虫气体交换系统的解剖与观察。这个实验不仅考察你对昆虫呼吸系统的理论知识，更重要的是检验你的动手操作能力、科学绘图规范以及实验安全习惯。很多同学在考试中因为细节扣分，而这些恰恰是可以通过充分准备来避免的。本文将从昆虫气体交换系统原理、解剖实操步骤、科学绘图技巧以及考试常见失分点四个方面，为你提供一份详尽的中英双语学习指南。

In the Edexcel (B) Biology A-Level syllabus, CP07 (Core Practical 7) is a practical that students find both fascinating and challenging — the dissection and observation of a locust’s gas exchange system. This experiment tests not only your knowledge of insect respiratory systems but, more importantly, your practical skills, scientific drawing standards, and laboratory safety habits. Many students lose marks on details that can easily be avoided with proper preparation. This article provides a comprehensive bilingual study guide covering the principles of insect gas exchange, dissection procedures, scientific drawing techniques, and common exam pitfalls.

🔬 核心知识点一：昆虫气体交换系统概述 | Core Concept 1: Overview of Insect Gas Exchange

昆虫的气体交换系统与哺乳动物截然不同。哺乳动物依赖肺和血液循环中的血红蛋白来运输氧气，而昆虫采用的是气管系统（tracheal system）——一种由外骨骼内陷形成的精细管道网络，将空气直接输送到每一个细胞的附近。

蝗虫（locust）作为典型的昆虫代表，其气体交换系统主要由三部分组成：(1) 气门（spiracles）——位于胸部和腹部两侧的小孔，是空气进出的门户，通常配有瓣膜以控制开合并减少水分流失；(2) 气管（tracheae）——由气门向内延伸的管道，管壁由几丁质螺旋加厚支撑，防止塌陷；(3) 微气管（tracheoles）——气管的末端分支，直径小于1微米，直接穿透到肌肉细胞附近，实现氧气与二氧化碳的扩散交换。理解这个结构层次是掌握整个 CP07 实验的理论基础。

The gas exchange system of insects is fundamentally different from that of mammals. While mammals rely on lungs and haemoglobin in the bloodstream to transport oxygen, insects use a tracheal system — an intricate network of tubes formed by invaginations of the exoskeleton, delivering air directly to nearly every cell in the body.

A locust, as a representative insect, has a gas exchange system consisting of three main components: (1) Spiracles — small openings along the thorax and abdomen, serving as gateways for air, typically equipped with valves to regulate opening/closing and minimise water loss; (2) Tracheae — tubes extending inward from the spiracles, reinforced with spiral thickening of chitin to prevent collapse; (3) Tracheoles — the terminal branches of tracheae, less than 1 micrometre in diameter, penetrating close to muscle cells to facilitate diffusion of oxygen and carbon dioxide. Understanding this structural hierarchy is the theoretical foundation for mastering the entire CP07 practical.

🦗 核心知识点二：蝗虫解剖实操技能 | Core Concept 2: Locust Dissection Practical Skills

CP07 实验的核心操作是对蝗虫进行解剖，以观察其内部气管系统。实验前必须做好充分准备：第一步——将蝗虫放入装有乙醇或乙酸乙酯的密封容器中进行安乐死，遵循动物实验伦理规范；第二步——用昆虫针将蝗虫固定在解剖盘上，腹部朝上，确保标本稳固；第三步——在解剖显微镜下，使用精细剪刀沿蝗虫腹部中线小心剪开外骨骼，注意力度控制，避免损伤内部器官。

解剖完成后，需要在标本上加水覆盖（flood with water），这一步经常被忽略但却至关重要——水面覆盖可以减少光线折射引起的视觉扭曲，使银白色的气管在深色背景下更加清晰可见。你会看到一条条闪烁着银色光泽的细管从气门向内延伸，分支到各个组织——这就是气管系统。如果条件允许，可以尝试用亚甲蓝（methylene blue）染色来增强对比度。整个过程中，务必佩戴护目镜和手套，确保实验安全。

The core operation of the CP07 practical involves dissecting a locust to observe its internal tracheal system. Adequate preparation before the experiment is essential: Step 1 — humanely euthanise the locust in a sealed container with ethanol or ethyl acetate, following ethical guidelines for animal experimentation; Step 2 — pin the locust onto a dissection board using insect pins, ventral side up, ensuring the specimen is secure; Step 3 — under a dissecting microscope, use fine scissors to carefully cut along the midline of the abdomen through the exoskeleton, controlling pressure to avoid damaging internal organs.

After dissection, the specimen must be flooded with water — a step often overlooked but absolutely critical. The water layer reduces visual distortion caused by light refraction, making the silvery-white tracheae far more visible against the darker background. You will see shimmering silver tubes extending inward from the spiracles, branching into various tissues — this is the tracheal system. If available, methylene blue staining can be used to enhance contrast. Throughout the procedure, always wear goggles and gloves for safety.

✏️ 核心知识点三：科学绘图规范 | Core Concept 3: Scientific Drawing Standards

科学绘图（scientific drawing）是 A-Level 生物考试中的高频评分项，但也是中国学生容易失分的环节。记住以下铁律：

① 大小要求：图必须占据给定空间至少一半。太小的图不仅不美观，更重要的是无法清晰展示结构细节，考试会被直接扣分。② 线条要求：使用铅笔绘制，单条连续线（single continuous lines），不要使用素描式的短线段拼接。线条必须清晰、准确，不允许任何阴影（no shading）。③ 标注线：用直尺画标注线，线端不加箭头（no arrows），确保不同标注线之间互不交叉。标注文字写在标注线的末端。④ 标题：每张图需要有清晰的标题，说明观察的是什么、放大倍数是多少。

Scientific drawing is a high-frequency assessment criterion in A-Level Biology exams, yet it is an area where many international students lose marks. Remember these golden rules:

① Size requirement: Your drawing must occupy at least half the space provided. A drawing that is too small is not only unaesthetic but, more critically, fails to display structural details clearly — and will be penalised directly in the exam. ② Line quality: Draw using a pencil with single continuous lines — avoid sketchy, multiple short strokes. Lines must be clear and precise, with absolutely no shading allowed. ③ Label lines: Draw label lines using a ruler, with no arrows at the ends. Ensure different label lines do not cross each other. Write the label text at the end of each label line. ④ Title: Every drawing must have a clear title indicating what is being observed and the magnification used.

🧪 核心知识点四：显微镜操作与观察技巧 | Core Concept 4: Microscope Operation & Observation Tips

在正式将蝗虫放到显微镜下之前，有几个关键准备步骤。首先，必须去除外骨骼（remove the exoskeleton）的部分区域，因为蝗虫的几丁质外壳厚重且不透明，直接观察无法看到内部结构。其次，如前所述，用水覆盖标本（flood the specimen with water）——这个操作不只是为了光学效果，也防止标本在强光照射下过快干燥。

在观察时，从低倍镜开始（如×40），先定位气门和气囊的宏观位置，然后逐步切换到高倍镜（×100或×400）观察微气管的分支细节。注意：高倍镜下视野较暗，适当调节光圈和光源角度。你可能会看到气管壁上的螺旋加厚结构——这是几丁质形成的特征性环纹，用来支撑管道保持通畅。如果能在图中准确描绘出这些螺旋纹，会给考官留下深刻印象。

Before viewing the locust under the microscope, several critical preparatory steps are required. First, you must remove sections of the exoskeleton, as the locust’s chitinous outer layer is thick and opaque — direct observation cannot reveal internal structures. Second, as mentioned above, flood the specimen with water — this step serves not only optical purposes but also prevents the specimen from drying out too quickly under intense illumination.

During observation, begin at low magnification (e.g., ×40) to locate spiracles and air sacs at the macro level, then progressively switch to higher magnification (×100 or ×400) to observe the branching details of tracheoles. Note: at high magnification the field of view becomes darker — adjust the diaphragm and light source angle accordingly. You may observe the spiral thickening on the tracheal walls — characteristic rings of chitin that support the tubes and keep them patent. Accurately depicting these spiral rings in your drawing will leave a strong impression on examiners.

📝 核心知识点五：考试常见错误与避坑指南 | Core Concept 5: Common Exam Mistakes & How to Avoid Them

根据历年考试反馈，CP07 相关题目中最常见的失分点包括：(1) 标注线交叉——这是机械性扣分，一旦出现标注线交叉，不管内容多好都会扣分，务必先用铅笔轻轻勾勒标注线路径再落笔；(2) 图中的阴影——很多同学不自觉地用铅笔侧锋在结构边缘涂抹阴影，这在科学绘图中是绝对不允许的；(3) 图太小——如果整张图只占了给定空间的三分之一，说明你对自己观察到的东西不够自信，趁早重画；(4) 忘记标题和放大倍数——这两个遗漏会让考官认为你缺乏基本的科学素养；(5) 安全措施描述缺失——在实验设计题中，如果要求你写一个完整的实验流程，不要忘记提到护目镜、手套和蝗虫的安乐死处理。

Based on past examiners’ reports, the most common mistakes on CP07-related questions include: (1) Crossing label lines — this incurs a mechanical penalty; regardless of content quality, crossing lines lose marks, so lightly sketch label line paths in pencil before committing; (2) Shading in the drawing — many students unconsciously use the side of the pencil to shade edges of structures, which is absolutely forbidden in scientific drawing; (3) Drawing too small — if the entire drawing occupies only a third of the space provided, it signals a lack of confidence in your observations — redraw it while you can; (4) Missing title and magnification — these two omissions indicate to examiners a lack of basic scientific literacy; (5) Missing safety precautions — in experimental design questions asking for a full method, do not forget to mention goggles, gloves, and humane euthanasia of the locust.

📚 学习建议 | Study Recommendations

掌握 CP07 气体交换实验，建议采用”三步法“：(1) 理论学习——先理解 tracheal system 的三级结构（spiracles → tracheae → tracheoles），能用流程图画出气体交换的全过程；(2) 动手实操——至少完整进行两次解剖练习，第一次熟悉步骤，第二次专注于绘图质量；(3) 模拟考试——在规定时间内完成一张科学绘图并标注，然后对照评分标准自我检查。同时，建议将本次实验与哺乳动物（如人类）的气体交换系统进行比较，这种跨物种的对比分析是 A-Level 高分答案的标志。

To master the CP07 gas exchange practical, adopt a three-step approach: (1) Theory — first understand the three-tier structure of the tracheal system (spiracles → tracheae → tracheoles) and be able to diagram the entire gas exchange process with a flow chart; (2) Hands-on practice — perform at least two complete dissections, the first to familiarise yourself with the procedure, the second to focus on drawing quality; (3) Mock exam — produce a scientific drawing with labels within a time limit, then self-assess against the mark scheme. Additionally, compare this practical with mammalian gas exchange systems (such as the human respiratory system) — cross-species comparative analysis is a hallmark of top-band A-Level answers.

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Edexcel (B) Biology A-Level | CP07 Gas Exchange System – Locust | Flashcards & Study Guide