Cambridge AS Biology Practical Skills (P1) | 剑桥 AS 生物实验技能 (P1)

📚 Cambridge AS Biology Practical Skills (P1) | 剑桥 AS 生物实验技能 (P1)

Cambridge International AS & A Level Biology assesses practical skills through the Advanced Practical Skills paper and through experimental contexts embedded in theory papers. Chapter P1 focuses on the core experimental techniques, measurement skills, data handling and planning skills that students need for reliable investigations.

剑桥国际 AS 与 A Level 生物考试通过高级实验技能试卷以及理论卷中的实验情境来考查实验能力。P1 章节重点训练核心实验操作、测量技能、数据处理和实验设计能力，帮助学生完成可靠、可重复的探究。

1. Safety in the Biology Laboratory | 生物实验室安全

Always wear eye protection when using reagents such as Benedict’s solution, biuret reagent, iodine solution or when heating liquids. Tie back long hair, keep the work area clear, and report any spillage or broken glass immediately.

使用本尼迪克特试剂、双缩脲试剂、碘液或加热液体时，必须始终佩戴护目镜。长发应束起，工作台面保持整洁，如发生液体溢出或玻璃破碎，应立即报告。

Use a water bath or electric heater rather than an open flame when heating ethanol or other flammable substances.
加热乙醇等易燃物质时，使用水浴或电加热器，不要使用明火。
Wash hands after handling biological material, enzymes or stains.
接触生物材料、酶或染色剂后要洗手。
Follow school rules for disposal of sharps, chemicals and biological waste.
按照学校规定处置锐器、化学品和生物废弃物。

2. Independent, Dependent and Controlled Variables | 自变量、因变量与控制变量

In any investigation, the independent variable is the factor you deliberately change, the dependent variable is the factor you measure, and controlled variables are kept constant to make the test fair.

在任何实验中，自变量是人为改变的因素，因变量是要测量的因素，控制变量则是保持恒定的因素，以保证实验公平。

For example, when investigating the effect of temperature on enzyme activity, temperature is the independent variable, the time taken for starch to disappear is the dependent variable, and enzyme concentration, substrate concentration and pH are controlled variables.

例如，研究温度对酶活性的影响时，温度是自变量，淀粉消失所需时间或因变量，酶浓度、底物浓度和 pH 都是控制变量。

State the independent variable with a suitable range and at least five intervals.
明确自变量的取值范围，并至少设置五个间隔。
Measure the dependent variable quantitatively rather than by subjective judgement where possible.
尽可能用定量方法测量因变量，而不是主观判断。
List controlled variables and explain how each one is kept constant.
列出控制变量，并说明如何使每个变量保持恒定。

3. Making Accurate Measurements | 精确测量

Select the most appropriate instrument for each measurement: use a syringe or measuring cylinder for liquid volumes, a balance for mass, a thermometer for temperature and a colorimeter for absorbance or transmission.

每次测量都要选择最合适的仪器：测量液体体积用注射器或量筒，测量质量用天平，测量温度用温度计，测量吸光度或透光率用比色计。

Record every reading to the resolution of the instrument. For example, a thermometer graduated in 0.5 °C intervals should be read to the nearest 0.5 °C, and a measuring cylinder graduated every 1 cm³ should be read from the bottom of the meniscus to the nearest 0.5 cm³.

读数时要记录到仪器的分度值精度。例如，分度值为 0.5 °C 的温度计应读到 0.5 °C；分度值为 1 cm³ 的量筒应从弯液面底部读到 0.5 cm³。

Measurement	Suitable instrument	Typical resolution
Volume	Syringe or measuring cylinder	0.1-1 cm³
Mass	Digital balance	0.01 g or 0.001 g
Temperature	Liquid-in-glass thermometer	0.5 °C or 1 °C
Absorbance	Colorimeter	0.01 absorbance units

4. Microscopy and Calibration | 显微镜使用与校准

Prepare temporary mounts by placing a thin specimen in a drop of water or stain on a slide and lowering a coverslip at an angle to avoid air bubbles. Start with the low-power objective, focus using the coarse adjustment, then move to high power and use the fine adjustment only.

制作临时装片时，将薄的材料放在载玻片的水滴或染液中，用镊子将盖玻片倾斜放下以避免气泡。先用低倍物镜，用粗准焦螺旋调焦，再换高倍物镜，只用细准焦螺旋调焦。

To measure cells, calibrate the eyepiece graticule using a stage micrometer. The calibration factor is found by dividing the known length of the stage micrometer divisions by the number of graticule divisions that coincide with them.

测量细胞时，需要用镜台测微尺对目镜测微尺进行校准。校准系数等于镜台测微尺已知长度除以对应的目镜测微尺格数。

actual length = number of graticule divisions × calibration factor

If a cell spans 4 graticule divisions and the calibration factor is 2.5 μm per division, the actual cell length is 4 × 2.5 = 10 μm.

如果细胞占据 4 个目镜测微尺格，校准系数为每格 2.5 μm，则细胞实际长度 = 4 × 2.5 = 10 μm。

5. Biological Drawing Skills | 生物绘图技巧

Make drawings with a sharp HB pencil on plain paper. Use clear, continuous lines without shading, and do not use colour. Label structures with straight ruling lines and write labels outside the drawing.

生物绘图应使用削尖的 HB 铅笔在无格纸上绘制。线条清晰、连续，不涂阴影，不使用颜色。用直线标注结构，将标签写在图的外侧。

Draw only what is visible under the microscope, not textbook features.
只画出显微镜下真实观察到的结构，不要照教科书添加。
Show correct proportions and include a title and magnification or scale bar.
比例要准确，并注明图题和放大倍数或比例尺。
Include a sharp outline of cell walls or membranes where visible.
可见的细胞壁或细胞膜要用清晰的轮廓表现。

6. Reagent Tests for Biological Molecules | 生物分子试剂检测

The standard food tests are frequently assessed in practical work. They give qualitative or semi-quantitative results and must be carried out with appropriate safety precautions, especially when heating.

标准食物检测是实验考查中的常见内容。这些检测可给出定性或半定量结果，操作时必须采取适当的安全措施，尤其是加热时。

Molecule	Reagent	Procedure	Positive result
Reducing sugar	Benedict’s solution	Heat in a water bath for 5 minutes	Blue → green → yellow → orange → brick red
Starch	Iodine in potassium iodide	Add a few drops to the sample	Orange-brown → blue-black
Protein	Biuret reagent	Add reagent and mix at room temperature	Blue → lilac/purple
Lipid	Ethanol + water	Shake sample with ethanol, then pour into water	Cloudy white emulsion

For non-reducing sugars such as sucrose, first boil with dilute hydrochloric acid to hydrolyse the glycosidic bond, neutralise with sodium hydrogencarbonate, then carry out the Benedict’s test.

对于蔗糖等非还原糖，应先用稀盐酸煮沸以水解糖苷键，再用碳酸氢钠中和，然后进行本尼迪克特测试。

7. Enzyme-Controlled Reactions | 酶控制反应

Enzyme practicals often use catalase from potato or liver, or amylase from germinating seeds. You can measure the time taken for a product to appear or for a substrate to disappear.

酶实验常用马铃薯或肝脏中的过氧化氢酶，或萌发种子中的淀粉酶。可以测量产物出现所需的时间，或底物消失所需的时间。

For amylase and starch, remove samples at regular intervals and add iodine solution. The reaction is complete when the iodine no longer turns blue-black, showing that all starch has been digested.

对于淀粉酶和淀粉，定时取样并加入碘液。当碘液不再变蓝黑色时，说明所有淀粉已被分解，反应结束。

Use buffer solutions to maintain pH and a thermostatically controlled water bath for temperature.
使用缓冲溶液维持 pH，并使用恒温水浴控制温度。
Keep enzyme and substrate solutions separate until the start, then mix and immediately start timing.
酶和底物溶液在开始时才混合，混合后立即开始计时。
Repeat each condition two or three times and calculate a mean.
每个条件重复两到三次，并计算平均值。

8. Osmosis and Water Potential | 渗透作用与水势

A common osmosis investigation uses potato or carrot cylinders placed in sucrose or sodium chloride solutions of different concentrations. The change in mass or length shows whether water entered or left the tissue by osmosis.

常见的渗透作用实验使用马铃薯或胡萝卜圆柱体，放入不同浓度的蔗糖或氯化钠溶液中。质量或长度的变化可以显示水分通过渗透作用进入还是离开组织。

Blot the cylinders dry before weighing, use the same surface area and volume for each piece, and measure the initial and final mass accurately.

称量前应吸干圆柱体表面液体，每块材料的表面积和体积保持一致，并准确测量初始质量和最终质量。

percentage change in mass = (final mass − initial mass) / initial mass × 100%

Plotting percentage change in mass against solute concentration allows you to estimate the water potential of the tissue at the point where the graph crosses the x-axis.

以质量变化百分率对溶质浓度作图，曲线与 x 轴交点处的浓度可用于估算组织的水势。

9. Recording Data and Designing Tables | 数据记录与表格设计

A well-designed results table has ruled lines, an appropriate title, and column headings that show both the quantity and the unit, separated by a slash or written in the form quantity / unit.

设计良好的结果表应有边框线、合适的表题，并在每列表头中注明物理量和单位，用斜线分隔或写成“物理量 / 单位”的形式。

Place the independent variable in the first column and the dependent variable in later columns.
将自变量放在第一列，因变量放在后续列中。
Record raw data to the correct number of decimal places and do not write units inside the body of the table.
原始数据要保留正确的小数位数，表格主体内不要写单位。
Leave a column for calculated values such as means or rates.
预留一列用于填写平均值或速率等计算值。

10. Graphs and Data Analysis | 图表与数据分析

Plot the independent variable on the x-axis and the dependent variable on the y-axis. Choose scales that use more than half of the graph grid, plot points with small crosses, and draw a smooth curve or straight line of best fit.

作图时，将自变量放在 x 轴，因变量放在 y 轴。坐标轴刻度应使用超过一半的方格区域，用小叉号描点，并绘制平滑曲线或最佳拟合直线。

Label both axes with quantity and unit.
两个坐标轴都要标注物理量和单位。
If one graph shows a clear linear relationship, use a ruler to draw the best-fit straight line through the points.
若图像呈明显线性关系，用直尺画一条穿过各点的最佳拟合直线。
Identify anomalous points and either repeat the measurement or exclude them from the line of best fit.
识别异常点，重复测量或将其排除在最佳拟合线之外。

Rates can be calculated from the gradient of a graph or from the reciprocal of time. For example, enzyme activity can be expressed as 1 ÷ time taken for the reaction to finish.

速率可通过图像斜率或时间的倒数来计算。例如，酶活性可表示为 1 ÷ 反应完成所需时间。

11. Errors, Limitations and Evaluation | 误差、局限与评价

Random errors cause readings to scatter unpredictably and can be reduced by repeating measurements and calculating means. Systematic errors cause all readings to deviate in the same direction and can be reduced by calibrating instruments or changing technique.

随机误差使读数无规律地分散，可通过重复测量并取平均值来减小。系统误差使所有读数向同一方向偏离，可通过校准仪器或改进操作方法来减小。

Colour-change end-points are subjective; using a colorimeter improves objectivity.
颜色变化终点受主观判断影响；使用比色计可提高客观性。
Temperature may fluctuate during the experiment; use a water bath and monitor at regular intervals.
实验过程中温度可能波动；使用水浴并定期监测温度。
Sample sizes may vary; cut material to the same dimensions and use equal volumes.
样品大小可能不同；将材料切成相同尺寸并使用相同体积。

12. Planning an Investigation | 设计实验

A complete plan should include a clear hypothesis, the independent and dependent variables, key controlled variables, the range and number of values tested, the number of repeats, a stepwise method, a risk assessment and a blank results table.

完整的实验设计应包括明确的假设、自变量和因变量、关键控制变量、测试范围与取点数、重复次数、分步骤方法、风险评估以及空白结果表。

When writing a method, use precise quantities, timings and apparatus so that another student could repeat the procedure exactly. State how you will record results and how you will analyse them.

书写方法时应给出精确的用量、时间和仪器，使其他学生能够完全重复实验。还要说明如何记录和分析结果。

hypothesis → variables → apparatus → method → results table → analysis → evaluation

If planning an investigation on the effect of pH on amylase, you could set the pH at 4, 5, 6, 7, 8 and 9 using buffer solutions, keep starch and amylase concentrations constant, sample every 30 seconds for iodine tests, record the time for starch to disappear, and repeat each pH three times.

如果设计一个 pH 对淀粉酶活性影响的实验，可以用缓冲溶液将 pH 设为 4、5、6、7、8、9，保持淀粉和淀粉酶浓度恒定，每隔 30 秒取样用碘液检测，记录淀粉消失的时间，每个 pH 重复三次。

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Cambridge AS Biology Practical Skills (P1) | 剑桥 AS 生物实验技能 (P1)