Year 9 Edexcel Biology: Formula and Theorem Quick Reference Guide | Edexcel Year 9 生物公式定理速查手册

📚 Year 9 Edexcel Biology: Formula and Theorem Quick Reference Guide | Edexcel Year 9 生物公式定理速查手册

This quick reference guide collates the essential formulas, principles, and key relationships you need to master for Year 9 Edexcel Biology. From microscopy calculations to inheritance patterns, each entry is written in clear, student-friendly language to help you revise effectively and apply your knowledge accurately in exams.

本速查手册汇集了Edexcel Year 9 生物学中必须掌握的公式、原理与关键关系。从显微镜计算到遗传规律，每一条都以清晰易懂的语言撰写，帮助你高效复习，在考试中准确应用所学知识。

1. Microscopy Formula | 显微镜公式

The total magnification of a light microscope is calculated by multiplying the magnification of the eyepiece lens by the magnification of the objective lens. This simple relationship allows you to switch between low‑power and high‑power observation while keeping track of how much an image is enlarged.

光学显微镜的总放大倍数等于目镜放大倍数乘以物镜放大倍数。这一简单关系让你在低倍与高倍观察之间切换时，能清楚知道图像被放大了多少倍。

Total Magnification = Eyepiece Magnification × Objective Magnification

总放大倍数 = 目镜放大倍数 × 物镜放大倍数

If you need to calculate the actual size of a specimen viewed under the microscope, rearrange the formula: Actual Size = Image Size ÷ Total Magnification. Remember to convert all measurements to the same unit (usually micrometres or millimetres) before calculating.

如果需要计算在显微镜下观察的标本实际大小，可变形使用公式：实际大小 = 图像大小 ÷ 总放大倍数。计算前记得将所有测量值转换为相同单位（通常为微米或毫米）。

Always check that your answer has the correct unit and is sensible for the type of cell or structure you are measuring. For example, a typical plant cell is about 50–100 µm in length, while a bacterium is only 1–2 µm.

始终检查答案是否带有正确单位，并且数值对你所测量的细胞或结构是否合理。例如，一个典型的植物细胞长度约为 50–100 µm，而一个细菌只有 1–2 µm。

2. Cell Size and Surface Area to Volume Ratio | 细胞大小与表面积体积比

As a cell or an organism grows larger, its volume increases more rapidly than its surface area. This relationship is crucial for understanding why cells are microscopic and why organisms need specialised exchange surfaces and transport systems.

随着细胞或生物体变大，其体积的增速快于表面积的增速。这一关系对理解为什么细胞是微观的、以及为什么生物体需要特化的交换表面和运输系统至关重要。

The surface area to volume ratio (SA:V) is calculated by dividing the total surface area of a shape by its volume. For a cube of side length x, surface area = 6x², volume = x³, so SA:V = 6/x. As x increases, the SA:V ratio decreases.

表面积与体积之比 (SA:V) 通过将形状的总表面积除以其体积来计算。对于边长为 x 的立方体，表面积 = 6x²，体积 = x³，因此 SA:V = 6/x。随着 x 增大，SA:V 比值减小。

Single‑celled organisms can rely on diffusion across their cell membrane because their SA:V ratio is large. In contrast, large multicellular organisms have a small SA:V ratio and therefore require adaptations such as alveoli in lungs, villi in the small intestine, and root hair cells in plants to increase surface area.

单细胞生物可以依赖物质通过细胞膜的扩散，因为它们的 SA:V 比值大。相比之下，大型多细胞生物的 SA:V 比值小，因此需要适应结构，如肺中的肺泡、小肠中的绒毛和植物中的根毛细胞来增大表面积。

3. Diffusion, Osmosis, and Active Transport | 扩散、渗透与主动运输

These three fundamental processes govern how substances move into and out of cells. Understanding the differences between them is essential for explaining nutrient uptake, gas exchange, and water balance.

这三个基本过程支配着物质进出细胞的方式。理解它们之间的差异对于解释营养吸收、气体交换和水分平衡至关重要。

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 that does not require energy. Carbon dioxide entering a leaf through stomata and oxygen diffusing into blood from alveoli are examples.

扩散是粒子从高浓度区域净移动到低浓度区域，沿浓度梯度进行。这是一种被动过程，不需要能量。二氧化碳通过气孔进入叶片和氧气从肺泡扩散到血液都是例子。

Osmosis is a special case of diffusion: the net movement of water molecules from a region of high water potential (dilute solution) to a region of low water potential (concentrated solution) through a partially permeable membrane. It continues until the water potential is equal on both sides. Osmosis explains why plant cells become turgid in pure water and plasmolysed in concentrated salt solution.

渗透是扩散的一种特殊情况：水分子从高水势（稀溶液）区域通过部分透性膜净移动到低水势（浓溶液）区域。直到膜两侧水势相等。渗透解释了植物细胞在纯水中变得硬挺（质壁分离复原），在浓盐溶液中发生质壁分离。

Active transport moves substances against a concentration gradient, from a lower to a higher concentration. This process requires energy from respiration and uses carrier proteins in the cell membrane. Root hair cells absorb mineral ions from the soil by active transport, even when soil ion concentration is lower than inside the root.

主动运输 使物质逆着浓度梯度移动，即从低浓度到高浓度。该过程需要呼吸作用提供的能量，并利用细胞膜上的载体蛋白。根毛细胞通过主动运输从土壤中吸收矿质离子，即使土壤中离子浓度低于根内。

Process	Energy required?	Direction of movement
Diffusion	No	High to low concentration
Osmosis	No	High to low water potential
Active transport	Yes (ATP)	Low to high concentration

Table: Summary of transport processes.

4. Enzyme Action and Lock-and-Key Model | 酶的作用与锁钥模型

Enzymes are biological catalysts that speed up chemical reactions without being used up. They are globular proteins with a specific three‑dimensional shape that is vital for their function. The active site of an enzyme has a shape complementary to the substrate, like a key fitting a lock.

酶是生物催化剂，能加快化学反应而本身不被消耗。酶是具有特定三维形状的球状蛋白，其形状对功能至关重要。酶的活性位点具有与底物互补的形状，就像钥匙插入锁孔一样。

According to the lock‑and‑key hypothesis, the substrate molecule fits precisely into the active site, forming an enzyme‑substrate complex. The reaction takes place, converting substrate into product(s), which are then released. The enzyme remains unchanged and can catalyse further reactions.

根据锁钥假说，底物分子精确地嵌入活性位点，形成酶‑底物复合物。反应发生，底物转化为产物，然后被释放。酶保持不变，可继续催化更多反应。

Enzyme activity is affected by temperature and pH. At low temperatures, collisions between enzyme and substrate are infrequent. As temperature rises, activity increases up to an optimum (around 37°C for human enzymes). Above the optimum, the enzyme denatures: its active site loses shape and can no longer bind the substrate. Each enzyme also has an optimum pH; extremes of pH cause denaturation.

酶活性受温度和pH 影响。低温时，酶与底物碰撞频率低。随着温度升高，活性增加，直至达到最适温度（人体酶约为37°C）。超过最适温度，酶变性：活性位点形状改变，无法再结合底物。每种酶还有最适 pH；极端 pH 会导致变性。

The formula to calculate the rate of an enzyme‑controlled reaction from experimental data is:

Rate of Reaction = 1 ÷ Time taken for substrate to disappear (or product to appear)

反应速率 = 1 ÷ 底物消失（或产物出现）所需的时间

When plotting a graph, rate is often measured as the change in product concentration per unit time.

5. Photosynthesis Equation | 光合作用方程式

Photosynthesis is the process by which green plants and some other organisms use light energy to convert carbon dioxide and water into glucose and oxygen. Chlorophyll in chloroplasts captures light energy. The balanced word equation is fundamental to Year 9 Biology.

光合作用是绿色植物和某些其他生物利用光能，将二氧化碳和水转化为葡萄糖和氧气的过程。叶绿体中的叶绿素捕获光能。配平的词汇方程式是 Year 9 生物学的基础内容。

Carbon Dioxide + Water → Glucose + Oxygen

二氧化碳 + 水 → 葡萄糖 + 氧气

Light energy is written above the arrow because it is required but is not a reactant. Chlorophyll can also be written above the arrow as the catalyst.

The chemical symbols for photosynthesis are: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Year 9 students are expected to be able to write the word equation and recognise the chemical symbols. Glucose is used by the plant for respiration, converted into starch for storage, or combined with other elements to make cellulose, proteins, and lipids.

光合作用的化学符号式为：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。Year 9 学生应能写出词汇方程式并识别化学符号。植物利用葡萄糖进行呼吸作用，将其转化为淀粉储存，或结合其他元素合成纤维素、蛋白质和脂质。

6. Factors Affecting Photosynthesis | 影响光合作用的因素

The rate of photosynthesis is limited by the factor at the lowest level relative to the plant’s needs — this is the law of limiting factors. The three main factors are light intensity, carbon dioxide concentration, and temperature.

光合作用的速率受限于相对于植物需求水平最低的因素——这就是限制因子定律。三个主要因素分别是光照强度、二氧化碳浓度和温度。

As light intensity increases, the rate of photosynthesis rises proportionally until another factor becomes limiting. At low CO₂ levels, the rate is slowed, and increasing CO₂ can raise the rate until light or temperature becomes the new limiting factor. Temperature affects the enzymes involved; the rate increases with temperature up to an optimum (around 25–30°C for many plants), after which enzymes denature and the rate drops sharply.

随着光照强度增加，光合作用速率成比例上升，直到另一因素成为限制因子。在低 CO₂ 水平下，速率减慢，提高 CO₂ 可以增加速率，直到光照或温度成为新的限制因子。温度影响相关酶；速率随温度上升直至最适值（许多植物约为 25–30°C），之后酶变性，速率急剧下降。

While there is no one single formula, the relationship can be summarised as:

Rate ∝ Limiting Factor (up to a maximum)

In controlled experiments, the rate of photosynthesis is often measured by counting oxygen bubbles produced by pondweed or by measuring the change in pH due to CO₂ uptake.

7. Aerobic and Anaerobic Respiration | 有氧呼吸与无氧呼吸

Respiration is the process that releases energy from glucose in all living cells. It is not the same as breathing. The energy released is used to power metabolic reactions, muscle contraction, active transport, and maintaining body temperature in mammals.

呼吸作用是所有活细胞从葡萄糖中释放能量的过程。它与呼吸（气体交换）不同。释放的能量用于驱动代谢反应、肌肉收缩、主动运输以及维持哺乳动物的体温。

Aerobic respiration requires oxygen and produces a large amount of energy. The word equation is:

Glucose + Oxygen → Carbon Dioxide + Water (+ Energy)

葡萄糖 + 氧气 → 二氧化碳 + 水 (+ 能量)

The chemical equation is: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy as ATP). The energy released is about 2900 kJ per mole of glucose.

Anaerobic respiration takes place without oxygen and releases much less energy. In animal cells, the equation is:

Glucose → Lactic Acid (+ Energy)

葡萄糖 → 乳酸 (+ 能量)

In plant and yeast cells, anaerobic respiration produces ethanol and carbon dioxide instead of lactic acid; this is also called fermentation:

Glucose → Ethanol + Carbon Dioxide (+ Energy)

葡萄糖 → 乙醇 + 二氧化碳 (+ 能量)

8. DNA and the Genetic Code | DNA 与遗传密码

DNA (deoxyribonucleic acid) is the molecule that carries genetic information. It has a double helix structure made up of two strands coiled around each other. The strands are formed by alternating sugar (deoxyribose) and phosphate groups, with nitrogenous bases attached to the sugars.

DNA（脱氧核糖核酸）是携带遗传信息的分子。它具有双螺旋结构，由两条相互缠绕的链构成。链由交替的糖（脱氧核糖）和磷酸基团组成，含氮碱基连接在糖上。

There are four bases in DNA: adenine (A), thymine (T), cytosine (C), and guanine (G). The bases pair specifically: A always pairs with T (via two hydrogen bonds), and C always pairs with G (via three hydrogen bonds). This is known as complementary base pairing.

DNA 中有四种碱基：腺嘌呤 (A)、胸腺嘧啶 (T)、胞嘧啶 (C) 和鸟嘌呤 (G)。碱基特异性配对：A 总是与 T 配对（通过两个氢键），C 总是与 G 配对（通过三个氢键）。这被称为互补碱基配对。

A gene is a section of DNA that codes for a specific protein. The sequence of bases determines the order of amino acids in a protein, which then determines the protein’s shape and function. Although we do not calculate protein sequences at Year 9, understanding the base‑pairing rule is essential for grasping DNA replication and protein synthesis later.

基因是一段编码特定蛋白质的 DNA 片段。碱基序列决定了蛋白质中氨基酸的顺序，从而决定了蛋白质的形状和功能。虽然 Year 9 不计算蛋白质序列，但理解碱基配对规则对以后掌握 DNA 复制和蛋白质合成至关重要。

9. Monohybrid Inheritance and Mendel’s Laws | 单基因遗传与孟德尔定律

Gregor Mendel’s experiments with pea plants established the fundamental principles of inheritance. A monohybrid cross investigates the inheritance of a single characteristic determined by one gene with two alleles — one dominant and one recessive.

格雷戈尔·孟德尔用豌豆植物进行的实验确立了遗传的基本原理。单基因杂交研究由一个基因决定的单一性状的遗传，该基因有两个等位基因——一个显性，一个隐性。

Key definitions to remember:

Allele: a version of a gene.
Dominant allele: always expressed when present; represented by a capital letter (e.g. B for brown eyes).
Recessive allele: only expressed when two copies are present; represented by a lowercase letter (e.g. b for blue eyes).
Homozygous: having two identical alleles (BB or bb).
Heterozygous: having two different alleles (Bb).
Genotype: the combination of alleles an organism has.
Phenotype: the observable characteristic.

需要记住的关键定义：

等位基因：基因的一种形式。
显性等位基因：只要存在就会表现出来；用大写字母表示 (如 B 代表棕色眼睛)。
隐性等位基因：仅当存在两个拷贝时才表现出来；用小写字母表示 (如 b 代表蓝色眼睛)。
纯合子：具有两个相同等位基因 (BB 或 bb)。
杂合子：具有两个不同等位基因 (Bb)。
基因型：一个生物体具有的等位基因组合。
表型：可观察到的特征。

In a classic monohybrid cross between two heterozygous parents (Bb × Bb), the expected ratio of dominant to recessive phenotype in the offspring is 3 : 1. Use a Punnett square to predict the probability of each genotype:

在经典的杂合子双亲杂交 (Bb × Bb) 中，子代显性表型与隐性表型的预期比例为 3:1。使用邦尼特方格预测每种基因型的概率：

Bb × Bb → 1 BB : 2 Bb : 1 bb (genotypic ratio) → 3 dominant : 1 recessive (phenotypic ratio)

Bb × Bb → 1 BB : 2 Bb : 1 bb (基因型比) → 3 显性 : 1 隐性 (表型比)

10. Cell Division – Mitosis | 细胞分裂 – 有丝分裂

Mitosis is the type of cell division that produces two genetically identical daughter cells from one parent cell. It is used for growth, repair, and asexual reproduction. The chromosome number is maintained: in humans, a diploid cell (46 chromosomes) divides to produce two diploid cells (each with 46).

有丝分裂是一种细胞分裂方式，由一个母细胞产生两个遗传完全相同的子细胞。它用于生长、修复和无性生殖。染色体数目 保持不变：在人类中，一个二倍体细胞 (46条染色体) 分裂产生两个二倍体细胞 (每个46条)。

Before mitosis begins, during interphase, the DNA replicates so that each chromosome consists of two identical chromatids held together at a centromere. The stages of mitosis (prophase, metaphase, anaphase, telophase) ensure that each new nucleus receives an exact copy of the parent cell’s DNA. Cytokinesis then splits the cytoplasm, resulting in two separate cells.

在有丝分裂开始前的间期，DNA 进行复制，使每条染色体由两个相同的染色单体组成，在着丝粒处相连。有丝分裂的各阶段（前期、中期、后期、末期）确保每个新细胞核获得母细胞 DNA 的精确副本。随后细胞质分裂（胞质分裂），形成两个独立的细胞。

No single formula governs mitosis, but the concept of chromosome number constancy is a fundamental principle:

Diploid (2n) Parent Cell → Mitosis → 2 × Diploid (2n) Daughter Cells

二倍体 (2n) 母细胞 → 有丝分裂 → 2 个二倍体 (2n) 子细胞

11. Food Chains and Energy Transfer | 食物链与能量传递

A food chain shows the flow of energy from one organism to another. Energy enters most ecosystems as sunlight and is captured by producers (green plants) during photosynthesis. At each trophic level, only a proportion of the energy is passed on; the rest is lost as heat from respiration, used in growth, or remains undigested as waste.

食物链显示能量从一个生物体到另一个生物体的流动。能量在大多数生态系统中以阳光的形式进入，由生产者（绿色植物）通过光合作用捕获。在每个营养级，只有一部分能量被传递；其余能量以呼吸作用产生的热量散失、用于生长或作为未消化的废物排出。

A key principle is the Law of Conservation of Energy, applied biologically: energy is not created or destroyed, but it is transferred and eventually lost as heat. Typically, only about 10% of the energy at one trophic level is converted into biomass at the next level. This is why food chains rarely exceed four or five trophic levels.

一个关键原理是能量守恒定律在生物学中的应用：能量不会凭空产生或消失，而是被传递并最终以热量形式散失。通常，一个营养级中只有大约 10% 的能量转化为下一个营养级的生物质。这就是食物链很少超过四到五个营养级的原因。

Energy transfer efficiency can be calculated as:

Efficiency (%) = (Energy incorporated into biomass at higher level ÷ Energy in biomass at lower level) × 100

效率 (%) = (较高营养级生物质中的能量 ÷ 较低营养级生物质中的能量) × 100

This formula is not always required for Year 9, but grasping the efficiency concept helps explain pyramid diagrams and why there are fewer top predators.

12. Sampling Techniques and Population Estimates | 采样技术与种群估计

Ecologists use sampling to estimate the population size and distribution of organisms in a habitat. Two key pieces of equipment are the quadrat (a square frame used to count plants or slow‑moving animals) and a transect (a line along which samples are taken to show changes in distribution).

生态学家采用采样方法来估算栖息地中生物体的种群大小与分布。两种关键工具是样方（用于计算植物或缓慢移动动物数量的正方形框）和样线（沿一条线进行采样以显示分布变化）。

To estimate a population using quadrats, follow these steps:

Randomly place several quadrats in the habitat.
Count the number of organisms inside each quadrat.
Calculate the mean number per quadrat.
Multiply the mean by the total area of the habitat divided by the area of one quadrat.

使用样方估算种群大小的步骤：

在栖息地随机放置若干样方。
计数每个样方内的生物体数量。
计算每个样方的平均数。
用平均数乘以栖息地总面积除以单个样方面积得到的商。

The formula is:

Estimated Population = Mean number per quadrat × (Total habitat area ÷ Area of one quadrat)

估算种群数量 = 每样方平均数量 × (栖息地总面积 ÷ 单个样方面积)

This method is based on the principle that the sample is representative, so random placement and sufficient number of quadrats are essential for accuracy.

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Year 9 Edexcel Biology: Formula and Theorem Quick Reference Guide | Edexcel Year 9 生物公式定理速查手册