Correct Selection and Operation of Laboratory Instruments | A-Level 生物：实验仪器的正确选用与操作

📚 Correct Selection and Operation of Laboratory Instruments | A-Level 生物：实验仪器的正确选用与操作

A-Level Biology requires not only conceptual understanding but also practical competence. Examiners consistently test whether candidates can choose the correct instrument for a given task and operate it with precision. This guide reviews the most common instruments in CIE A-Level Biology practicals, covering selection criteria, setup, correct technique, and common errors.

A-Level 生物不仅考查概念理解，同样考验实验操作能力。考官一贯考察考生能否为特定任务选择正确仪器，并精确操作。本指南系统梳理 CIE A-Level 生物实验中最常用仪器的选择依据、设置方法、正确操作与常见错误。

1. Light Microscope | 光学显微镜

The light microscope is the standard tool for viewing cells and tissues. Choose a compound microscope for stained specimens; phase-contrast or differential interference contrast may be used for living, unstained material, though these are not always available in school laboratories.

光学显微镜是观察细胞与组织的标准工具。染色标本应选用复式光学显微镜；观察活体未染色材料时可用相差显微镜或微分干涉显微镜，但学校实验室不常配备。

Before use, check the eyepiece and objective lenses for dust. Place the slide on the stage, secure it with clips, and turn the objective turret to the lowest magnification. While looking from the side, lower the body tube until the objective is just above the coverslip; then look through the eyepiece and raise the tube slowly using the coarse adjustment knob until the image appears. Fine-tune with the fine adjustment knob only.

使用前检查目镜与物镜是否洁净。将玻片置于载物台上并用弹簧夹固定，把物镜转至最低倍数。从侧面注视，降低镜筒至物镜接近盖玻片；再从目镜观察，用粗准焦螺旋缓慢上升镜筒直至看到图像，最后只用细准焦螺旋微调。

After focusing, adjust the iris diaphragm and condenser to obtain even, proper illumination. Use the eyepiece graticule to measure specimen size, calibrating it against a stage micrometer: each graticule division equals the micrometer reading divided by the number of observed divisions.

对焦后调节光圈与聚光器，使照明均匀、亮度适宜。用目镜测微尺测量标本尺寸，并需用载物台测微尺标定：每格目镜测微尺长度 = 载物台测微尺读数 ÷ 目镜观察格数。

Common errors include using the coarse knob at high magnification (risk of cracking the slide), forgetting to adjust illumination, or measuring without calibration.

常见错误包括：高倍镜下使用粗准焦螺旋（易压碎玻片）、忘记调节照明、以及未标定就进行测量。

2. Micropipette | 微量移液器

Micropipettes deliver precise volumes of 0.5 µL to 1000 µL. Select the pipette whose range brackets your target volume; for example, use a P1000 for 500 µL, not a P200 (overflow risk) or a P20 (too imprecise). Note that 1 µL = 10⁻³ mL = 10⁻⁶ L.

微量移液器可精确移取 0.5 µL 至 1000 µL 的液体。应选择量程覆盖目标体积的移液器：例如移取 500 µL 用 P1000，既不能用 P200（易超量程），也不宜用 P20（精度不足）。注意换算：1 µL = 10⁻³ mL = 10⁻⁶ L。

Operating sequence: set the volume by turning the plunger wheel; attach a fresh tip; press the plunger to the first stop; hold the pipette vertically and immerse the tip 2-3 mm below the liquid surface; release slowly to draw up liquid

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