📚 Year 9 CIE Biology: Quick Reference Handbook of Formulas & Theorems | Year 9 CIE 生物：公式定理速查手册
This quick reference handbook brings together the key equations, principles, and fundamental theorems you will encounter in the Year 9 CIE Biology syllabus. From photosynthesis to genetics, each entry is presented with clear statements and worked examples to help you memorise and apply the concepts accurately during revision and examinations.
本速查手册汇集了 Year 9 CIE 生物课程中最核心的公式、原理和基本定律。从光合作用到遗传学，每个条目都配有清晰的陈述和计算实例，帮助你在复习和考试中准确记忆并灵活运用这些概念。
1. Photosynthesis Equation | 光合作用方程式
Photosynthesis is the process by which green plants trap light energy and convert it into chemical energy stored in glucose. The word and balanced chemical equations summarise the raw materials and products.
光合作用是绿色植物捕获光能并将其转化为储存在葡萄糖中的化学能的过程。文字方程式和配平的化学方程式总结了原料和产物。
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Carbon dioxide and water, in the presence of light and chlorophyll, produce glucose and oxygen. The numbers in the balanced equation show that six molecules of carbon dioxide react with six molecules of water to yield one molecule of glucose and six molecules of oxygen.
二氧化碳和水，在光和叶绿素的作用下，生成葡萄糖和氧气。配平方程式中的数字表明，6 个二氧化碳分子与 6 个水分子反应，产生 1 个葡萄糖分子和 6 个氧分子。
2. Aerobic Respiration Equation | 有氧呼吸方程式
Aerobic respiration releases energy from glucose in the presence of oxygen. It occurs continuously inside the mitochondria of living cells.
有氧呼吸在氧气参与下从葡萄糖中释放能量。它在活细胞的线粒体内持续进行。
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP)
The overall reaction is essentially the reverse of photosynthesis. One glucose molecule and six oxygen molecules are broken down to release six carbon dioxide molecules, six water molecules, and a large amount of energy in the form of ATP.
总反应基本上是光合作用的逆反应。一个葡萄糖分子和六个氧分子被分解，释放出六个二氧化碳分子、六个水分子以及大量以 ATP 形式存在的能量。
3. Anaerobic Respiration in Yeast (Fermentation) | 酵母的无氧呼吸（发酵）
When yeast cells are deprived of oxygen, they respire anaerobically, producing ethanol and carbon dioxide. This process is used in baking and brewing.
当酵母细胞缺少氧气时，它们进行无氧呼吸，产生乙醇和二氧化碳。这一过程被用于烘焙和酿造。
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + energy
No oxygen is required. One glucose molecule is converted into two molecules of ethanol and two molecules of carbon dioxide, releasing a small amount of energy.
该过程不需要氧气。一个葡萄糖分子转化为两个乙醇分子和两个二氧化碳分子，同时释放少量能量。
4. Anaerobic Respiration in Muscles | 肌肉中的无氧呼吸
During vigorous exercise, muscle cells may not receive sufficient oxygen and switch to anaerobic respiration, producing lactic acid.
剧烈运动时，肌肉细胞可能得不到充足的氧气，转而进行无氧呼吸，产生乳酸。
C₆H₁₂O₆ → 2C₃H₆O₃ + energy
Glucose is broken down into lactic acid without the use of oxygen. This provides a rapid burst of energy but can lead to muscle fatigue and an oxygen debt that must be repaid later.
葡萄糖在不消耗氧气的情况下分解为乳酸。这能快速提供能量，但会导致肌肉疲劳，并形成必须在事后偿还的氧债。
5. Magnification Formula | 放大倍数计算公式
The magnification of a biological drawing or micrograph tells you how much larger the image appears compared with the real specimen.
生物绘图或显微照片的放大倍数表示图像比实际标本放大了多少。
Magnification = Image size ÷ Actual size
Always ensure both measurements are in the same unit before dividing. For example, if an image of a cell measures 50 mm and the actual cell is 0.05 mm, the magnification is 50 ÷ 0.05 = 1000×. The formula can be rearranged: Actual size = Image size ÷ Magnification.
在相除之前务必确保两个测量值使用同一单位。例如，若一个细胞的图像长 50 mm，而实际细胞为 0.05 mm，则放大倍数为 50 ÷ 0.05 = 1000×。该公式可变形为：实际尺寸 = 图像尺寸 ÷ 放大倍数。
6. Total Microscope Magnification | 显微镜总放大倍数
A compound microscope uses two lenses: the eyepiece lens and the objective lens. Their individual magnifications multiply to give the total magnification.
复式显微镜使用两个透镜：目镜和物镜。它们各自的放大倍数相乘得到总放大倍数。
Total magnification = Eyepiece magnification × Objective magnification
If the eyepiece lens is 10× and the objective lens is 40×, then the specimen is magnified 10 × 40 = 400 times. This relationship is essential for interpreting observations and calculating sizes.
如果目镜为 10×，物镜为 40×，则标本被放大 10 × 40 = 400 倍。这一关系对于解读观察结果和计算尺寸至关重要。
7. Fick’s Law of Diffusion | 菲克扩散定律
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. Fick’s Law describes the factors affecting the rate of diffusion across a membrane.
扩散是粒子从高浓度区域向低浓度区域的净移动。菲克定律描述了影响跨膜扩散速率的因素。
Rate of diffusion ∝ (Surface area × Concentration difference) ÷ Membrane thickness
The rate is directly proportional to the surface area available for exchange and the concentration gradient, and inversely proportional to the distance (thickness) that particles must travel. Adaptations such as alveoli in the lungs, villi in the small intestine, and flattened leaves maximise the rate using these principles.
扩散速率与可用于交换的表面积和浓度梯度成正比，与粒子必须穿行的距离（膜厚度）成反比。肺中的肺泡、小肠中的绒毛以及扁平的叶片等适应性结构正是利用这些原理来最大化扩散速率。
8. The Lock-and-Key Model of Enzyme Action | 酶作用的锁钥模型
Enzymes are biological catalysts that speed up reactions without being used up. Their action is highly specific and is explained by the lock-and-key model.
酶是生物催化剂，能在不被消耗的情况下加速反应。其作用具有高度特异性，可用锁钥模型解释。
Each enzyme has an active site with a complementary shape to its specific substrate. The substrate fits into the active site like a key into a lock, forming an enzyme-substrate complex. The reaction takes place, and products are released. Denaturation occurs when high temperature or extreme pH changes the shape of the active site permanently, preventing binding.
每种酶都有一个活性部位，其形状与特定的底物互补。底物像钥匙插入锁孔一样嵌入活性部位，形成酶-底物复合物。反应发生，产物被释放。当高温或极端 pH 值永久改变活性部位的形状时，酶会变性，从而无法结合。
9. Mendel’s Law of Segregation | 孟德尔分离定律
Gregor Mendel’s first law explains how alleles separate during gamete formation, ensuring that each gamete carries only one allele for each gene.
格里戈尔·孟德尔的第一定律解释了等位基因在配子形成过程中如何分离，确保每个配子只携带每个基因的一个等位基因。
Every organism possesses two alleles for each trait, located on homologous chromosomes. During meiosis, these alleles segregate so that each gamete receives only one allele. At fertilisation, the offspring thus inherits one allele from each parent. This law underlies the 3:1 phenotypic ratio seen in a monohybrid cross between two heterozygous individuals (e.g., Tt × Tt → 3 tall : 1 short).
每个生物体对每个性状拥有两个等位基因，位于同源染色体上。在减数分裂过程中，这些等位基因分离，使每个配子只获得一个等位基因。受精时，后代从每个亲本继承一个等位基因。这一定律解释了两个杂合子单杂交（如 Tt × Tt → 3 高 : 1 矮）中看到的 3:1 表型比。
10. Mendel’s Law of Independent Assortment | 孟德尔自由组合定律
Mendel’s second law states that alleles for different characteristics are distributed to gametes independently of one another, provided the genes are located on different chromosomes.
孟德尔第二定律指出，控制不同性状的等位基因相互独立地分配到配子中，前提是这些基因位于不同的染色体上。
During metaphase I of meiosis, the orientation of each pair of homologous chromosomes on the spindle is random and does not influence the orientation of other pairs. This creates new combinations of alleles in the gametes. For example, a dihybrid cross of pea plants with genotypes RrYy can produce four types of gametes in equal proportions: RY, Ry, rY, ry, leading to a 9:3:3:1 phenotypic ratio in the offspring.
在减数分裂中期 I，每对同源染色体在纺锤体上的取向是随机的，且不影响其他对的取向。这在配子中产生新的等位基因组合。例如，具有 RrYy 基因型的豌豆植株双因子杂交可产生四种比例均等的配子：RY、Ry、rY、ry，导致后代出现 9:3:3:1 的表型比。
11. Chargaff’s Base Pairing Rules | 查尔加夫碱基配对法则
Erwin Chargaff discovered that in DNA the amount of adenine equals thymine, and the amount of cytosine equals guanine. This complementarity stabilises the double helix and ensures faithful replication.
埃尔文·查尔加夫发现，在 DNA 中腺嘌呤的量等于胸腺嘧啶的量，胞嘧啶的量等于鸟嘌呤的量。这种互补性稳定了双螺旋结构，并确保了忠实的复制。
A = T and G ≡ C
Adenine pairs with thymine via two hydrogen bonds (A=T), while guanine pairs with cytosine via three hydrogen bonds (G≡C). These rules allow one strand to act as a template for building a complementary strand during DNA replication and transcription.
腺嘌呤通过两个氢键与胸腺嘧啶配对（A=T），鸟嘌呤通过三个氢键与胞嘧啶配对（G≡C）。这些法则使一条链能够在 DNA 复制和转录过程中充当构建互补链的模板。
12. The 10% Rule of Energy Transfer in Food Chains | 食物链能量传递的 10% 定律
As energy moves from one trophic level to the next in a food chain, a large proportion is lost through respiration, movement, and undigested material. Typically, only about 10% is passed on.
当能量在食物链中从一个营养级传递到下一营养级时，很大一部分通过呼吸、运动以及未消化的物质而散失。通常只有大约 10% 的能量被传递下去。
This principle explains why food chains rarely exceed four or five trophic levels. The producer level (plants) captures the most energy through photosynthesis. Each subsequent consumer gains only a fraction of the energy stored in the level below. This loss limits the biomass and number of organisms that can be supported at higher trophic levels.
这一原理解释了为什么食物链很少超过四或五个营养级。生产者（植物）通过光合作用捕获最多的能量。随后的每一级消费者仅获得下级所储存能量的一小部分。这种能量损耗限制了更高营养级可支持的生物量和生物数量。
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