📚 KS3 AQA Biology: Quick Formulas & Principles Reference | KS3 AQA 生物：公式定理速查手册
This quick reference guide summarises the essential formulas, equations and key principles you need to master for the KS3 AQA Biology syllabus. From calculating magnification to understanding energy transfers, each topic is explained clearly with English and Chinese support.
本速查手册汇总了 KS3 AQA 生物课程中需要掌握的核心公式、方程式与重要原理。从放大倍数的计算到能量传递的理解，每个主题均配有英文与中文双语讲解。
1. Magnification Formula | 放大倍数公式
When using a microscope, you can calculate how much larger an image appears compared to the real object. The formula is:
使用显微镜时，可以计算图像比实际物体放大了多少。公式为：
Magnification = image size ÷ actual size
You can rearrange the formula to find image size or actual size: Image size = Magnification × Actual size; Actual size = Image size ÷ Magnification. Always ensure the units are the same (e.g. both in millimetres or micrometres). If the image size is 50 mm and the actual size is 0.5 mm, the magnification = 50 ÷ 0.5 = 100×.
该公式可以变形为：图像大小 = 放大倍数 × 实际大小；实际大小 = 图像大小 ÷ 放大倍数。注意单位必须统一（如均为毫米或微米）。若图像大小为 50 mm，实际大小为 0.5 mm，则放大倍数 = 50 ÷ 0.5 = 100倍。
2. Estimating Population Size | 种群大小估算
To estimate the number of organisms in a large area, ecologists often use sampling techniques. For stationary organisms, the mean number per quadrat is multiplied by the total area. For mobile animals, the capture-mark-recapture formula is used:
要估算大面积内的生物数量，生态学家常采用取样技术。针对固着生物，先计算每个样方内的平均个体数，再乘以总面积。针对移动动物，则使用标志重捕法公式：
Population estimate = (C₁ × C₂) ÷ M
Where C₁ = number captured and marked in the first sample, C₂ = total captured in the second sample, M = number of marked animals recaptured in the second sample. This method assumes that marked individuals mix randomly and that no births or deaths occur between samples.
其中 C₁ = 第一次捕获并标记的个体数，C₂ = 第二次捕获的总数，M = 第二次捕获中含有标记的个体数。该方法假设标记个体均随机混合，且两次取样间无出生或死亡。
3. Photosynthesis Equation | 光合作用方程式
Plants make their own food using light energy. The process takes place in chloroplasts and requires carbon dioxide and water. The word equation is:
植物利用光能制造食物。该过程发生在叶绿体中，需要二氧化碳和水。文字方程式如下：
carbon dioxide + water → glucose + oxygen
The balanced chemical equation (with light and chlorophyll as conditions) is:
配平后的化学方程式（光照与叶绿素为条件）：
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Glucose is used immediately for energy, converted into cellulose for cell walls, or stored as starch. Oxygen is released as a by-product. You can test for starch using iodine solution (turns blue-black) and for oxygen using a glowing splint (relights).
葡萄糖可立即用于能量、转化为纤维素构成细胞壁或以淀粉形式储存。氧气作为副产品释放。可使用碘液检测淀粉（变蓝黑色），用带火星的木条检测氧气（复燃）。
4. Aerobic Respiration Equation | 有氧呼吸方程式
Aerobic respiration releases energy from glucose when oxygen is available. It takes place in mitochondria. The overall word equation is:
有氧呼吸在氧气充足时从葡萄糖中释放能量，发生在线粒体中。总文字方程式为：
glucose + oxygen → carbon dioxide + water (+ energy)
The balanced symbol equation is:
配平后的符号方程式：
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
This process is exothermic; the energy released is used for muscle contraction, maintaining body temperature and building larger molecules. Carbon dioxide can be tested with limewater (turns cloudy).
该过程放热；释放的能量用于肌肉收缩、维持体温及构建大分子。可用石灰水检测二氧化碳（变浑浊）。
5. Anaerobic Respiration in Animals | 动物无氧呼吸方程式
During vigorous exercise, muscles may not get enough oxygen and switch to anaerobic respiration. This releases less energy and produces lactic acid:
剧烈运动时，肌肉可能供氧不足而进行无氧呼吸，释放较少能量并产生乳酸：
glucose → lactic acid (+ small amount of energy)
Lactic acid build-up causes muscle fatigue and cramps. After exercise, extra oxygen is needed to break down the lactic acid into carbon dioxide and water; this is called oxygen debt.
乳酸堆积会导致肌肉疲劳和抽筋。运动后需要额外氧气将乳酸分解为二氧化碳和水，这称为氧债。
6. Anaerobic Respiration in Plants & Yeast | 植物与酵母的无氧呼吸
Plants and yeast undergo fermentation when oxygen is low. The equation is:
植物和酵母在缺氧时进行发酵，方程式为：
glucose → ethanol + carbon dioxide (+ some energy)
This process is used in baking (carbon dioxide makes dough rise) and in brewing (ethanol is the alcohol in drinks). Unlike animal anaerobic respiration, no lactic acid is produced.
该过程用于烘焙（二氧化碳使面团膨起）和酿造（乙醇即为酒类饮品中的酒精）。与动物无氧呼吸不同，不产生乳酸。
7. Energy Transfer in Food Chains | 食物链中的能量传递
Energy flows through food chains, but only about 10% is passed from one trophic level to the next. The rest is lost through movement, heat, respiration and undigested material. This limits the length of food chains.
能量沿食物链流动，但大约只有10%从一营养级传递至下一级。其余通过运动、产热、呼吸及未消化物质散失，这限制了食物链的长度。
If a plant stores 1000 kJ of energy, a herbivore eating it might gain only 100 kJ; a carnivore eating that herbivore might receive just 10 kJ. This principle explains why biomass pyramids usually show decreasing mass at higher levels.
若植物储存 1000 kJ 能量，植食动物摄食后可能仅获得 100 kJ；以该植食动物为食的肉食动物可能只得到 10 kJ。该原理解释了为何生物量金字塔通常在较高营养级表现为质量递减。
8. Enzyme Action: Lock and Key Model | 酶作用：锁钥模型
Enzymes are biological catalysts that speed up reactions without being used up. The lock-and-key model states that each enzyme has an active site with a specific shape. The substrate fits exactly into the active site, like a key fits a lock, forming an enzyme-substrate complex.
酶是生物催化剂，能在不被消耗的情况下加速反应。锁钥模型指出，每种酶的活性位点具有特定形状，底物可与活性位点精确契合，如同钥匙插入锁中，形成酶-底物复合物。
Once the reaction occurs, the product is released and the enzyme can be reused. High temperatures or extreme pH can denature the enzyme, changing the shape of the active site so the substrate no longer fits. Each enzyme works best at its optimum temperature and pH.
反应发生后，产物释放，酶可被重复利用。高温或极端pH可使酶变性，改变活性位点形状，底物不再匹配。每种酶有其最适温度与pH。
9. Diffusion and Osmosis Principles | 扩散与渗透原理
Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration, down a concentration gradient, without using energy. Examples include oxygen moving from blood into cells and carbon dioxide moving out of cells.
扩散是粒子从高浓度区域向低浓度区域的净移动，顺浓度梯度，不消耗能量。例如氧气从血液进入细胞，二氧化碳从细胞排出。
Osmosis is a special type of diffusion: the movement of water molecules through a partially permeable membrane from a region of higher water potential (dilute solution) to a region of lower water potential (more concentrated solution). This is important in plant root hair cells and animal cells placed in different solutions.
渗透是一种特殊的扩散：水分子通过部分透性膜从较高水势（稀溶液）向较低水势（较浓溶液）移动。这对植物根毛细胞和处于不同溶液中的动物细胞至关重要。
10. Cell Division: Mitosis Overview | 细胞分裂：有丝分裂概述
Mitosis produces two genetically identical daughter cells and is used for growth, repair and asexual reproduction. Before division, the DNA replicates so each chromosome consists of two identical chromatids. The main stages are prophase (chromosomes condense), metaphase (chromosomes line up at the equator), anaphase (chromatids are pulled apart) and telophase (new nuclei form).
有丝分裂产生两个遗传完全相同的子细胞，用于生长、修复和无性繁殖。分裂前DNA复制，每条染色体由两个相同的染色单体组成。主要阶段为前中期：前期（染色体凝缩），中期（染色体排列在赤道板），后期（染色单体被拉向两极）和末期（新核膜形成）。
Cytokinesis then splits the cytoplasm, resulting in two identical cells. This ensures that each new cell receives the same number of chromosomes as the original parent cell.
随后胞质分裂，形成两个相同的细胞。这确保每个新细胞获得与亲代细胞相同数量的染色体。
11. Inheritance: Punnett Square Method | 遗传：庞纳特方格法
A Punnett square predicts the possible genotypes of offspring from a genetic cross. For a monohybrid cross between two heterozygous parents (Aa × Aa), where ‘A’ is the dominant allele and ‘a’ the recessive:
庞纳特方格可预测杂交后代的可能基因型。以两个杂合亲本（Aa × Aa）的单因子杂交为例，设 ‘A’ 为显性等位基因，’a’ 为隐性等位基因：
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