Tackling the Experimental Design Question in OCR A-Level Biology June 2023 Paper 2 | 攻克OCR A-Level生物2023年6月试卷2实验设计题

📚 Tackling the Experimental Design Question in OCR A-Level Biology June 2023 Paper 2 | 攻克OCR A-Level生物2023年6月试卷2实验设计题

Among the most demanding items in the June 2023 OCR A-Level Biology Paper 2 was the planning exercise, where candidates had to design a field investigation into species diversity. This article unpacks a model answer structure and highlights the assessment objectives that examiners look for, from variable control to statistical reasoning.

在2023年6月OCR A-Level生物学试卷2中，最具挑战性的题目之一是规划练习，要求考生设计一项物种多样性野外调查。本文解析了标准答案结构，并强调考官所关注的评估目标，从变量控制到统计推理。

1. Decoding the Question Stem | 解读题干信息

Start by dissecting the question to extract the organism, habitat, and most importantly the independent variable (the factor you deliberately change). In the June 2023 paper, many students were tasked with comparing mown and unmown grassland.

首先解剖题目，提取生物、栖息地，最重要的是自变量（你特意改变的因素）。在2023年6月的试卷中，许多学生被要求比较割草和未割草草地。

Next, identify the dependent variable: a measure of diversity such as species richness or Simpson’s Index. The dependent variable must be quantifiable and appropriate for the hypothesis.

接着，识别因变量：多样性度量，如物种丰富度或辛普森指数。因变量必须可量化且适合假设。

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2. Formulating a Testable Hypothesis | 建立可检验的假设

Translate the aim into a precise hypothesis that predicts the relationship. For example: ‘The mean Simpson’s Index of Diversity (D) will be significantly higher in unmown grassland than in regularly mown grassland.’

将目的转化为精确预测关系的假设。例如：‘未割草草地的平均辛普森多样性指数（D）将显著高于定期割草的草地。’

Avoid vague statements. Use operational terms that directly link to your planned measurements.

避免模糊陈述。采用直接联系到计划测量的操作性术语。

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3. Identifying and Controlling Variables | 识别与控制变量

List the abiotic and biotic factors that must be kept constant to ensure a fair test. Create a concise control table in your answer.

列出为保公平测试必须保持恒定的非生物和生物因素。在答案中创建简明的控制表格。

For a grassland investigation, controlled variables include soil pH (test and choose areas with similar pH), light intensity, soil moisture, slope aspect, and grazing by herbivores. Use a table with columns for the variable, how it is controlled, and why it matters.

对于草地调查，控制变量包括土壤pH（检测并选择pH相似的区域）、光照强度、土壤湿度、坡向和植食动物放牧。使用表格，列包括变量、如何控制及其重要性。

In the June 2023 exam, candidates who simply stated ‘same soil type’ without specifying how to verify or standardise it lost marks. Be explicit.

在2023年6月考试中，仅写“相同土壤类型”而未说明如何验证或标准化的考生失分。务必明确。

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4. Selecting Appropriate Apparatus and Sampling Techniques | 选择仪器与取样技术

Choose a quadrat of suitable size (e.g., 0.5 m × 0.5 m) and justify your choice. To avoid bias, use a random number generator to determine coordinates within each sampling zone.

选择合适大小的样方（如0.5m × 0.5m）并说明理由。为避免偏差，使用随机数生成器确定每个采样区内的坐标。

Carry an identification key (or app) to reliably name plant species. A point frame or percentage cover grid improves accuracy over simple presence/absence recording. State that you will repeat measurements across multiple quadrats in each area.

携带分类鉴定检索表（或应用程序）以可靠地给植物物种命名。点框或百分盖度网格比单纯的存在/缺失记录更精确。说明将在每个区域的多个样方中重复测量。

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5. Designing a Standardised Procedure | 设计标准化步骤

Present a logical, numbered method. Begin with site selection: ‘Locate a mown field and an adjacent unmown field of similar size and soil type.’ Then detail your sampling effort: ‘Place 15 randomly positioned quadrats in each field. In each quadrat, identify all plant species and estimate percentage cover to the nearest 5% using a gridded quadrat.’

呈现逻辑清晰的编号方法。从选址开始：‘选定一片割草田和相邻的一片大小、土壤类型相似的未割草田。’然后详述采样量：‘每块田地放置15个随机定位的样方。在每个样方内，鉴定所有植物物种，并使用网格样方估计百分盖度至最接近5%。’

Ensure timing is consistent: ‘Carry out all sampling between 10:00 and 14:00 on the same day to minimise diurnal variation.’ This shows awareness of environmental control.

确保时间一致：‘在同一天上午10点至下午2点之间完成所有采样，以最小化日变化。’这体现了对环境控制的意识。

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6. Ensuring Reliability, Accuracy and Validity | 确保信度、准确度与效度

Reliability comes from large sample sizes (15+ quadrats per zone) and repeating the investigation at different times of the year if required. Accuracy is improved by calibrating any instruments and cross‑checking identifications with a second observer.

信度来自大样本量（每区15+样方）以及若需在不同季节重复调查。准确度通过校准任何仪器并与第二位观察者交叉核对鉴定来提高。

Validity is maintained by strictly controlling the mowing regime as the only difference between the two areas. Mention that you would measure soil pH in each quadrat to confirm it is not a confounding variable.

效度通过严格控制割草制度作为两区唯一差异来保持。提及将在各样方测量土壤pH以确认它不是混淆变量。

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7. Risk Assessment and Ethical Considerations | 风险评估与伦理考量

Address safety: uneven ground could cause trips; long grass may harbour ticks – wear appropriate footwear and cover legs. Identify allergies to pollen and suggest carrying antihistamines.

处理安全：地面不平可能导致绊倒；高草可能藏有蜱虫——穿合适的鞋并遮盖腿部。识别花粉过敏并建议携带抗组胺药。

From an ethical standpoint, minimise disturbance: avoid stepping inside quadrats before recording, and do not uproot plants. If any mobile organisms are accidentally captured, release them immediately at the point of collection.

从伦理角度，最小化干扰：避免在记录前踏入样方内，不要连根拔起植物。若意外捕获任何活动生物，立即在采集点释放。

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8. Data Recording and Presentation | 数据记录与呈现

Show a sample results table with headings: Quadrat number, Species present, Total number of individuals (if counting), and Calculated Simpson’s Index (D) for each quadrat. In the exam, drawing a properly ruled table with units gains credit.

展示示例结果表，标题为：样方编号、存在物种、个体总数（若计数）、各样方计算的辛普森指数（D）。考试中绘制规范带单位的表格可获得分数。

Explain that you will calculate the mean D for each treatment and produce a bar chart comparing mown vs. unm

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