GCSE CCEA Biology: Calculation Practice | GCSE CCEA 生物：计算题专项训练

📚 GCSE CCEA Biology: Calculation Practice | GCSE CCEA 生物：计算题专项训练

Mastering calculation questions is essential for success in GCSE CCEA Biology. This guide provides focused practice on all major types of numerical problems you will encounter, from magnification to population estimates.

掌握计算题对于 GCSE CCEA 生物考试的成功至关重要。本指南针对你将遇到的所有主要类型数值问题进行专项训练，从放大率到种群估算。

1. Magnification Calculations | 放大率计算

Magnification is how much larger an image appears compared to the actual object. The formula is M = I ÷ A, where M is magnification, I is image size, and A is actual size. Always ensure both I and A are in the same units before calculating.

放大率是指图像相对于实际物体放大了多少。公式为 M = I ÷ A，其中 M 为放大率，I 为图像尺寸，A 为实际尺寸。计算前务必确保 I 和 A 单位相同。

M = I ÷ A

For example, a plant cell image measures 50 mm across, but the actual cell is 0.05 mm wide. Magnification = 50 ÷ 0.05 = 1000×.

例如，一个植物细胞图像宽度为 50 mm，而实际细胞宽 0.05 mm。放大率 = 50 ÷ 0.05 = 1000×。

2. Actual Size Using Magnification | 利用放大率求实际尺寸

If you know the magnification and the image size, rearrange the formula to A = I ÷ M. Measure the image in mm, convert to the desired unit, then divide.

如果已知放大率和图像尺寸，将公式变形为 A = I ÷ M。测量图像尺寸（mm），转换为所需单位，然后除以放大率。

Example: An electron micrograph of a mitochondrion is 80 mm wide at 20000× magnification. Calculate the actual width in µm.

示例：一张线粒体的电子显微照片在 20000× 放大下宽 80 mm。计算实际宽度（µm）。

Convert 80 mm to µm: 80 mm = 80 × 1000 = 80000 µm. Then A = 80000 ÷ 20000 = 4 µm.

将 80 mm 转换为 µm：80 mm = 80 × 1000 = 80000 µm。然后 A = 80000 ÷ 20000 = 4 µm。

3. Unit Conversions in Biology | 生物学中的单位换算

Common units include millimetres (mm), micrometres (µm), and nanometres (nm). You need to convert between them for calculations.

常见单位包括毫米（mm）、微米（µm）和纳米（nm）。计算时需要进行转换。

To convert a larger unit to a smaller unit, multiply by 1000 each step. For example, 0.002 mm → 0.002 × 1000 = 2 µm.

要将较大单位转换为较小单位，每级乘以 1000。例如，0.002 mm → 0.002 × 1000 = 2 µm。

4. Percentage Change in Mass (Osmosis) | 质量变化百分比（渗透作用）

When investigating osmosis, you often calculate the percentage change in mass of potato cylinders. Formula: % change = (final mass – initial mass) ÷ initial mass × 100.

在研究渗透作用时，常常计算土豆圆柱体的质量变化百分比。公式：变化 % = (最终质量 – 初始质量) ÷ 初始质量 × 100。

% change = (m_final – m_initial) ÷ m_initial × 100

If a potato strip had an initial mass of 5.2 g and a final mass of 5.8 g after soaking in water, % change = (5.8 − 5.2) ÷ 5.2 × 100 = +11.5% (mass gain).

如果一条土豆初始质量为 5.2 g，在水中浸泡后最终质量为 5.8 g，则变化 % = (5.8 – 5.2) ÷ 5.2 × 100 = +11.5%（质量增加）。

5. Energy Content of Food | 食物的能量含量

Burning a food sample heats a known mass of water. Energy transferred (J) = mass of water (g) × 4.2 J/g°C × temperature rise (°C). To find energy per gram, divide by the mass of food burnt.

燃烧食物样品可加热已知质量的水。传递的能量（J）= 水的质量（g）× 4.2 J/g°C × 温度升高值（°C）。要计算每克能量，除以燃烧的食物质量。

E = m_water × 4.2 × ΔT

Then energy per gram = E ÷ mass

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