📚 KS3 OCR Biology: Formula & Theorem Quick Reference Handbook | KS3 OCR 生物：公式定理速查手册
This handbook brings together the essential formulas, equations and key scientific principles you will encounter in the KS3 OCR Biology course. Use it as a quick refresher to support your revision and build your confidence before assessments.
本手册汇集了 KS3 OCR 生物学课程中的核心公式、方程式和重要科学原理，可作为考前快速复习和巩固理解的速查工具。
1. Microscopy Formulas | 显微镜计算公式
The light microscope is used to view cells and tiny structures. To work out how magnified an image is, you multiply the powers of the two lenses.
光学显微镜用于观察细胞和微小结构。要计算图像的放大倍数，只需将两个镜头的放大倍数相乘。
Total Magnification = Eyepiece Magnification × Objective Magnification
总放大倍数 = 目镜放大倍数 × 物镜放大倍数
When a scale bar or ruler is used, you can find the real size of a specimen by dividing the measured image size by the total magnification. Remember to convert units (1 mm = 1000 µm) if necessary.
当使用比例尺或直尺测量时，可以用测量到的图像尺寸除以总放大倍数来求出标本的实际大小。必要时记住换算单位（1 毫米 = 1000 微米）。
Actual Size = Image Size ÷ Total Magnification
实际大小 = 图像大小 ÷ 总放大倍数
2. Cell Theory | 细胞学说
All living organisms are made up of one or more cells. Cells are the basic building blocks of life and carry out all life processes.
所有生物体都由一个或多个细胞构成。细胞是生命的基本结构和功能单位，进行着一切生命活动。
New cells are produced only from existing cells, by the process of cell division. This principle underpins growth, repair and reproduction in organisms.
新的细胞只能由原有细胞通过细胞分裂产生。这一原理是生物体生长、修复和繁殖的基础。
3. Photosynthesis Equation | 光合作用方程式
Plants and some microorganisms produce their own food using light energy. The word equation summarises the raw materials and products of photosynthesis.
植物和某些微生物利用光能制造自己的养料。下面的文字方程式概括了光合作用的原料和产物。
Carbon Dioxide + Water → Glucose + Oxygen
二氧化碳 + 水 → 葡萄糖 + 氧气
Photosynthesis takes place in the chloroplasts, and chlorophyll absorbs the sunlight needed to drive the reaction. This process stores energy in the glucose molecule.
光合作用在叶绿体中进行，叶绿素吸收阳光驱动反应，将能量储存在葡萄糖分子中。
4. Respiration Equations | 呼吸作用方程式
Respiration is the chemical reaction that releases energy from glucose. It happens in all living cells and can be aerobic (using oxygen) or anaerobic (without oxygen).
呼吸作用是释放葡萄糖中能量的化学反应，发生在所有活细胞中，可分为有氧呼吸（需要氧气）和无氧呼吸（不需要氧气）。
Aerobic: Glucose + Oxygen → Carbon Dioxide + Water (+ Energy)
有氧呼吸：葡萄糖 + 氧气 → 二氧化碳 + 水（+ 能量）
In animals, anaerobic respiration produces lactic acid and a small amount of energy. In yeast and some plants, it produces ethanol and carbon dioxide (fermentation).
在动物体内，无氧呼吸产生乳酸和少量能量；在酵母及某些植物中，则产生乙醇和二氧化碳（发酵）。
Anaerobic (animals): Glucose → Lactic Acid (+ Energy)
无氧呼吸（动物）：葡萄糖 → 乳酸（+ 能量）
Anaerobic (yeast): Glucose → Ethanol + Carbon Dioxide (+ Energy)
无氧呼吸（酵母）：葡萄糖 → 乙醇 + 二氧化碳（+ 能量）
5. Enzyme Principles | 酶的作用原理
Enzymes are biological catalysts made of protein. They speed up chemical reactions by lowering the activation energy, without being used up themselves.
酶是由蛋白质构成的生物催化剂。它们通过降低活化能来加速化学反应，自身在反应中不被消耗。
The lock-and-key model explains enzyme action: the substrate fits into the enzyme’s active site. If the active site changes shape (denatured), the enzyme can no longer work.
“锁钥模型”解释了酶的作用机制：底物与酶的活性部位匹配。如果活性部位形状改变（变性），酶便会失效。
Temperature and pH strongly affect enzyme activity. Each enzyme has an optimum temperature (often around 37 °C in humans) and an optimum pH. Extremes of heat or pH cause irreversible denaturation.
温度和 pH 对酶活性影响重大。每种酶都有其最适温度（人体内常为 37 °C 左右）和最适 pH。极端的温度或 pH 会导致酶永久变性。
6. Digestive System & Nutrient Absorption | 消化系统与营养吸收
Large insoluble food molecules must be broken down into small soluble molecules by digestive enzymes so they can be absorbed into the blood. Amylase breaks down starch into sugars, protease breaks down protein into amino acids, and lipase breaks down fats into fatty acids and glycerol.
大分子不溶性食物必须经消化酶分解为小分子可溶性物质，才能被吸收进入血液。淀粉酶将淀粉分解为糖，蛋白酶将蛋白质分解为氨基酸，脂肪酶将脂肪分解为脂肪酸和甘油。
Absorption mainly occurs in the small intestine. Its inner lining is folded into villi, which greatly increase the surface area for efficient diffusion of nutrients. A thin wall and a dense capillary network also speed up absorption.
吸收主要在小肠进行。小肠内壁具有绒毛状褶皱，极大地增加了营养物质的扩散表面积；其薄壁和丰富的毛细血管网进一步加快了吸收速度。
7. Diffusion and Osmosis Principles | 扩散与渗透原理
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. It is a passive process requiring no energy.
扩散是粒子沿浓度梯度从高浓度区域向低浓度区域的净移动，属于被动运输，无需能量。
Osmosis is a special type of diffusion involving water molecules moving across a selectively permeable membrane from a dilute solution to a more concentrated one. It is crucial for water uptake in plant roots and for cell turgidity.
渗透是扩散的一种特殊形式，指水分子通过选择透过性膜从稀溶液向高浓度溶液移动。它对植物根吸水和细胞保持坚挺至关重要。
8. Ecology: Food Chains and Energy Transfer | 生态学：食物链与能量传递
In a food chain, arrows show the direction of energy flow. Producers (green plants) convert light energy into chemical energy; consumers obtain energy by eating other organisms.
在食物链中，箭头表示能量流动的方向。生产者（绿色植物）将光能转化为化学能；消费者通过捕食其他生物获取能量。
At each trophic level, a large proportion of energy is lost as heat through respiration, movement and metabolic processes. Typically only about 10% of the energy is passed on to the next level. This limits the number of steps in a food chain and explains pyramid-shaped energy pyramids.
每一个营养级都会通过呼吸、运动及代谢等活动以热能形式散失大量能量。通常只有约 10% 的能量传递到下一营养级。这限制了食物链的长度，也解释了为何能量金字塔呈塔形。
Energy transfer efficiency ≈ 10% per trophic level
每营养级能量传递效率约 10%
9. Body Mass Index (BMI) | 身体质量指数 (BMI)
BMI is a simple measure used to assess whether a person’s weight is in a healthy range relative to their height. The formula is easy to apply.
身体质量指数是一个衡量体重相对身高是否处于健康范围的简单指标，其计算公式如下：
BMI = Body Mass (kg) ÷ (Height in metres)²
BMI = 体重 (千克) ÷ (身高 (米))²
A BMI value below 18.5 suggests underweight, 18.5–24.9 is considered healthy, 25–29.9 overweight, and 30 or above indicates obesity. Keep in mind that athletes with high muscle mass may have a high BMI without excess body fat.
BMI 低于 18.5 提示偏瘦，18.5–24.9 为健康范围，25–29.9 为超重，30 及以上为肥胖。但需注意，高肌肉量的运动员可能 BMI 较高而体脂并不超标。
10. Genetics Basics | 遗传学基础定理
Genes, located on chromosomes, carry the instructions for inherited characteristics. Alleles are different versions of a gene. An allele can be dominant (always expressed if present) or recessive (only expressed when two copies are present).
基因位于染色体上，携带遗传特征的指令。等位基因是基因的不同形式。等位基因分为显性（只要存在就会表达）和隐性（仅当两个隐性等位基因同时存在时才表达）。
We use Punnett squares to predict the probability of offspring inheriting certain traits. For example, if both parents are heterozygous (Tt), the expected genotype ratio in offspring is 1 TT : 2 Tt : 1 tt, and the phenotype ratio for a dominant trait is 3 : 1.
我们利用庞纳特方格预测子代遗传特定性状的概率。例如，若双亲均为杂合子 (Tt)，子代基因型比例预计为 1 TT : 2 Tt : 1 tt，若性状完全显性，则表型比例为 3 : 1。
The base-pairing rule in DNA is also a fundamental principle: adenine (A) always pairs with thymine (T), and cytosine (C) pairs with guanine (G). This ensures accurate replication.
DNA 碱基配对法则也是一项基本原理：腺嘌呤 (A) 总是与胸腺嘧啶 (T) 配对，胞嘧啶 (C) 与鸟嘌呤 (G) 配对，从而保证复制的准确性。
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