📚 GCSE Edexcel Biology: Formula Summary Handbook | GCSE Edexcel 生物：公式汇总手册
This handbook summarises all the essential formulae you need for Edexcel GCSE Biology. Mastering these calculations is crucial for both Paper 1 and Paper 2, as they underpin practical questions, graphical analysis and data-handling tasks. Keep this sheet handy during revision to boost your confidence with numbers in biology.
本手册汇总了 Edexcel GCSE 生物所需的所有重要公式。掌握这些计算对于试卷一和试卷二至关重要，它们是实验题、图表分析和数据处理的基础。复习时随身携带本汇总，能帮你增强生物计算题的信心。
1. Magnification and Actual Size | 放大倍率与真实尺寸
The magnification (M) of a drawing or photo tells you how many times larger the image is compared to the real specimen. It is defined by the equation below, where I is the image size and A is the actual size. Both measurements must be in the same unit, most commonly millimetres (mm) or micrometres (µm).
放大倍率 (M) 表示图像比真实标本大多少倍。公式中 I 为图像尺寸，A 为实际尺寸。两量必须采用相同单位，通常为毫米 (mm) 或微米 (µm)。
M = I / A
Always convert units to match: 1 mm = 1000 µm. For example, an image of a cell is 20 mm wide and the real cell is 0.02 mm; M = 20 / 0.02 = 1000 ×.
务必统一单位：1 mm = 1000 µm。例如，细胞图像宽 20 mm，真实细胞宽 0.02 mm，则 M = 20 / 0.02 = 1000 倍。
If you know M and I, rearrange the formula to calculate the actual size. This is especially useful when working from scaled diagrams in the exam.
若已知 M 和 I，可变换公式求实际尺寸。这在考试中根据比例图计算时非常实用。
A = I / M
Check that your answer has a sensible unit; 0.002 mm is better written as 2 µm. Always show the unit conversion step clearly.
检查答案单位是否合理；0.002 mm 更宜写作 2 µm。务必清楚写出单位换算过程。
2. Total Microscope Magnification | 显微镜总放大倍率
A compound light microscope uses both an eyepiece lens and an objective lens. The total magnification is simply the product of the two magnifications, which allows you to see extremely small structures such as nuclei and mitochondria.
复式光学显微镜同时使用目镜和物镜。总放大倍率就是两者放大倍数的乘积，这使你能够观察到细胞核、线粒体等极微小的结构。
Mtotal = Meyepiece × Mobjective
For instance, a ×10 eyepiece used with a ×40 objective gives a total magnification of 10 × 40 = 400. The eyepiece magnification is usually engraved on the lens barrel.
例如，×10 目镜搭配 ×40 物镜，总放大倍率为 10 × 40 = 400。目镜的放大倍率通常刻在镜筒上。
When calibrating an eyepiece graticule, you must use a stage micrometer to find the value of one graticule unit at each magnification. The total magnification formula helps you check whether you have the correct enlargement for measuring cells accurately.
标定目镜测微尺时，必须使用镜台测微尺确定各放大倍率下一个测微刻度的值。总放大倍率公式有助于检查你的放大倍数是否适合精确测量细胞。
3. Population Density | 种群密度
Population density indicates how crowded a population is within a given area. It is a fundamental concept in ecology, often estimated by random sampling with quadrats.
种群密度表示单位面积内生物的数量拥挤程度。它是生态学的基本概念，常通过样方随机取样来估算。
Density (D) = Number of individuals (N) / Area (A)
Area is typically expressed in square metres (m²). If you place a 0.5 m × 0.5 m quadrat and find 12 daisies, the density is 12 / 0.25 m² = 48 daisies per m². Multiply by the total habitat area to estimate total population.
面积通常以平方米 (m²) 表示。若用 0.5 m × 0.5 m 的样方，数得 12 株雏菊，则密度为 12 / 0.25 m² = 48 株/m²。乘以整个栖息地的面积即可估算总种群数量。
4. Capture-Recapture Method | 标记重捕法
For mobile animals, the Lincoln index (capture-recapture) provides an estimate of population size (N). It relies on the assumption that the ratio of marked to unmarked individuals in the second sample reflects the ratio in the total population.
对于移动活跃的动物，林肯指数（标记重捕法）给出种群数量 (N) 的估算值。其假设第二次样本中标记个体与未标记个体的比例与整个种群中的比例相同。
N = (M × C) / R
Here M is the number of animals first captured and marked, C is the total number caught in the second sample, and R is the number of marked animals recaptured in the second sample. This method assumes no migration, no births or deaths, and that marks are not lost during the study.
M 为初次捕获并标记的动物数量，C 为第二次捕获的总数，R 为第二次捕获中带标记的个体数。该方法假设研究期间无迁入迁出、无出生死亡，且标记不会脱落。
5. Efficiency of Energy Transfer | 能量传递效率
Only a small proportion of the energy at one trophic level is transferred to the next; most is lost through respiration, waste and heat. The percentage efficiency can be calculated with this formula.
一个营养级只有一小部分能量传递到下一个营养级；大部分通过呼吸作用、排泄和热量散失。其效率百分比可用以下公式计算。
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