📚 Year 8 Cambridge Biology: Formulas and Theorems Quick-Reference Handbook | 剑桥八年级生物：公式定理速查手册
This handbook brings together the essential word equations, formulas and key principles you need to master for Year 8 Cambridge Biology. Use it as a go-to checklist to reinforce your understanding and tackle exam questions with confidence.
本手册汇集了剑桥八年级生物学必须掌握的核心文字方程式、计算公式和重要原理。将它作为速查清单，巩固理解，自信地应对考题。
1. Photosynthesis Word Equation | 光合作用文字方程式
Photosynthesis is the process by which green plants use sunlight to synthesise nutrients from carbon dioxide and water. It produces glucose and releases oxygen as a by-product. The overall word equation is:
光合作用是绿色植物利用阳光将二氧化碳和水合成营养物质的过程。它生成葡萄糖并释放氧气。总文字方程式如下：
carbon dioxide + water → glucose + oxygen
This reaction requires light energy and chlorophyll, and it takes place in chloroplasts.
二氧化碳 + 水 → 葡萄糖 + 氧气
该反应需要光能和叶绿素，在叶绿体中进行。
2. Aerobic Respiration Word Equation | 有氧呼吸文字方程式
Aerobic respiration releases energy from glucose using oxygen. It occurs continuously in the mitochondria of most living cells. The word equation is:
有氧呼吸利用氧气从葡萄糖中释放能量。它在大多数活细胞的线粒体中持续进行。文字方程式为：
glucose + oxygen → carbon dioxide + water (+ energy)
The energy released is used for cellular activities such as muscle contraction, growth and maintaining body temperature.
葡萄糖 + 氧气 → 二氧化碳 + 水 (+ 能量)
释放的能量用于肌肉收缩、生长、维持体温等细胞活动。
3. Anaerobic Respiration in Yeast (Fermentation) | 酵母的无氧呼吸（发酵）
When yeast is deprived of oxygen, it carries out anaerobic respiration, also called fermentation. This produces ethanol and carbon dioxide. The word equation is:
酵母在缺氧时进行无氧呼吸，又称发酵，产生乙醇和二氧化碳。文字方程式：
glucose → ethanol + carbon dioxide (+ some energy)
This process is exploited in baking and brewing, where the carbon dioxide makes dough rise and ethanol contributes to alcoholic drinks.
葡萄糖 → 乙醇 + 二氧化碳 (+ 少量能量)
此过程用于烘焙和酿造——二氧化碳使面团膨胀，乙醇则形成酒精饮料。
4. Anaerobic Respiration in Muscles | 肌肉的无氧呼吸
During vigorous exercise, muscle cells may be short of oxygen. They respire anaerobically, producing lactic acid. The word equation is:
剧烈运动时，肌肉细胞可能缺氧而转为无氧呼吸，产生乳酸。文字方程式：
glucose → lactic acid (+ some energy)
Accumulation of lactic acid causes muscle fatigue and cramps. After exercise, extra oxygen is needed to break down the lactic acid — this is called the oxygen debt.
葡萄糖 → 乳酸 (+ 少量能量)
乳酸堆积导致肌肉疲劳和抽筋。运动后需要额外氧气分解乳酸，这称为氧债。
5. Magnification Formula | 放大倍数公式
To calculate the magnification of a biological drawing or a micrograph, use the formula:
计算生物绘图或显微图像的放大倍数，使用以下公式：
Magnification = Image size ÷ Actual size
Always ensure the image size and the actual size are in the same units (e.g. mm or μm). You can rearrange the formula to find actual size: Actual size = Image size ÷ Magnification.
放大倍数 = 图像尺寸 ÷ 实际尺寸
务必确保图像尺寸与实际尺寸单位一致。公式可变形：实际尺寸 = 图像尺寸 ÷ 放大倍数。
6. Energy Content of Food (Calorimetry) | 食物中的能量（量热法）
A simple calorimeter can estimate the energy content of food by burning a sample and measuring the temperature rise of a known mass of water. The heat energy transferred is:
简易量热器通过燃烧食物样品，测量已知质量水的温升，估算食物所含能量。传递的热能为：
Energy (J) = mass of water (g) × 4.2 (J/g°C) × temperature rise (°C)
To compare different foods fairly, calculate the energy released per gram: Energy per gram = Total energy (J) ÷ mass of food burned (g).
能量 (焦耳) = 水质量 (克) × 4.2 (焦/克·°C) × 温度升高 (°C)
为公平比较不同食物，计算每克释放的能量：每克能量 = 总能量 (J) ÷ 燃烧的食物质量 (g)。
7. Diffusion | 扩散
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, moving down a concentration gradient. It is a passive process — it does not require metabolic energy. Factors that speed up diffusion include a steeper concentration gradient, higher temperature, larger surface area and a shorter diffusion distance.
扩散是粒子从高浓度区域向低浓度区域的净运动，顺浓度梯度进行。这是一个被动过程，不需要代谢能量。加快扩散的因素包括：更陡的浓度梯度、较高温度、较大的表面积以及较短的扩散距离。
Examples in living organisms: oxygen diffusing from alveoli into blood and carbon dioxide diffusing out.
生物体实例：氧气从肺泡扩散入血液，二氧化碳从血液扩散出。
8. Osmosis | 渗透
Osmosis is a special type of diffusion — the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) through a partially permeable membrane.
渗透是一种特殊的扩散——水分子通过半透膜从水势较高（稀溶液）区域向水势较低（浓溶液）区域的净运动。
In plant cells, water entering by osmosis makes the cell turgid and supports the plant. If a plant cell loses water, it becomes flaccid, and the cytoplasm may pull away from the cell wall (plasmolysis). In animal cells, too much water entry can cause the cell to burst (lysis), while water loss causes it to shrink.
在植物细胞中，渗透吸水使细胞硬挺，支撑植株。失水时植物细胞萎蔫，原生质可能与细胞壁分离（质壁分离）。动物细胞中，过多水分进入可使细胞胀破（溶血），失水则导致皱缩。
9. Active Transport | 主动运输
Active transport is the movement of particles against a concentration gradient — from a region of lower concentration to a region of higher concentration. This process requires energy released from respiration and uses carrier proteins in the cell membrane.
主动运输是粒子逆浓度梯度（从低浓度区域向高浓度区域）的运动。该过程需要呼吸作用释放的能量，并利用细胞膜中的载体蛋白。
A key example is the absorption of mineral ions (e.g. nitrate ions) by root hair cells from the soil, where the concentration of minerals inside the cell is already higher.
关键实例是根毛细胞从土壤吸收矿物质离子（如硝酸根离子），而细胞内已有较高的矿物浓度。
10. Enzyme Action: Lock-and-Key Model and Factors | 酶的作用：锁钥模型与影响因素
Enzymes are biological catalysts that speed up chemical reactions without being used up. The lock-and-key model describes enzyme action: the substrate (key) has a shape complementary to the enzyme's active site (lock). An enzyme-substrate complex forms, the reaction takes place, and products are released, leaving the enzyme unchanged.
酶是生物催化剂，加速化学反应而自身不被消耗。锁钥模型描述酶的作用：底物（钥匙）的形状与酶活性位点（锁）互补。形成酶-底物复合物，发生反应，释放产物，而酶保持不变。
Enzyme activity is affected by temperature and pH. Each enzyme has an optimum temperature and optimum pH at which it works fastest. Too high a temperature or extreme pH denatures the enzyme — the active site loses its shape permanently, and the substrate can no longer fit.
酶活性受温度和 pH 影响。每种酶都有使其作用最快的最适温度和最适 pH。温度过高或极端 pH 会使酶变性——活性位点永久丧失形状，底物无法再嵌入。
11. Monohybrid Inheritance and Punnett Squares | 单基因遗传与庞纳特方格
A gene controls a characteristic. Different forms of a gene are called alleles. A dominant allele (represented by a capital letter) masks the effect of a recessive allele (lowercase letter). A Punnett square predicts the genetic outcomes of a cross.
基因控制性状，不同的基因形式称为等位基因。显性等位基因（用大写字母表示）遮盖隐性等位基因（小写字母）的效应。庞纳特方格用于预测杂交的遗传结果。
nts (Aa × Aa). Their gametes carry A or a. The Punnett square shows possible combinations:
例如：两杂合亲本杂交 (Aa × Aa)，其配子带有 A 或 a。庞纳特方格显示可能组合：
| A | a | |
| A | AA | Aa |
| a | Aa | aa |
The expected genotype ratio is 1 AA : 2 Aa : 1 aa. If the trait follows a simple dominant-recessive pattern, the phenotype ratio is 3 : 1.
预期基因型比例为 1 AA : 2 Aa : 1 aa。若性状遵循简单的显隐性规律，表型比例为 3 : 1。
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