📚 Year 1 Biology Core Concepts Overview | 一年级生物核心概念总览
Year 1 Biology introduces a wide range of fundamental ideas that explain how living organisms are built, how they obtain energy, how they reproduce and how they defend themselves against disease. This revision guide pulls together the core topics in one place, with each point given in both English and Chinese to support bilingual learners.
一年级生物介绍了一系列基本概念，这些概念解释了生物体如何构建、如何获得能量、如何繁殖以及如何抵御疾病。本复习指南将核心主题汇集在一起，每一点都提供英文和中文对照，以帮助双语学习者。
1. Biological Molecules | 生物分子
All living things are based on carbon-containing compounds, and most large biological molecules are polymers made by joining smaller monomers together through condensation reactions. The reverse process, hydrolysis, breaks polymers back into monomers using water.
所有生物都以含碳化合物为基础，大多数大分子是通过缩合反应将较小的单体连接在一起形成的聚合物。相反的过程——水解——则利用水将聚合物分解回单体。
Carbohydrates include monosaccharides such as glucose, disaccharides such as sucrose and polysaccharides such as starch, glycogen and cellulose. Lipids are hydrophobic molecules; triglycerides form from glycerol and three fatty acids, while phospholipids form cell membranes. Proteins are made from amino acids joined by peptide bonds, and nucleic acids are made from nucleotides joined by phosphodiester bonds.
碳水化合物包括葡萄糖等单糖、蔗糖等二糖以及淀粉、糖原和纤维素等多糖。脂质是疏水分子；甘油三酯由甘油和三个脂肪酸形成，磷脂则构成细胞膜。蛋白质由氨基酸通过肽键连接而成，核酸由核苷酸通过磷酸二酯键连接而成。
2. Cell Structure | 细胞结构
Eukaryotic cells contain membrane-bound organelles, including a nucleus that stores DNA, mitochondria that carry out aerobic respiration, ribosomes that synthesise proteins, and the endoplasmic reticulum and Golgi apparatus that process and package proteins.
真核细胞含有有膜细胞器，包括储存DNA的细胞核、进行有氧呼吸的线粒体、合成蛋白质的核糖体，以及加工和包装蛋白质的内质网和高尔基体。
Plant cells also have chloroplasts for photosynthesis, a cellulose cell wall for support and a large permanent vacuole. Prokaryotic cells, such as bacteria, lack membrane-bound organelles but still carry out all essential life processes using a circular DNA molecule and 70S ribosomes.
植物细胞还具有用于光合作用的叶绿体、用于支撑的纤维素细胞壁和大型永久液泡。原核细胞（如细菌）没有有膜细胞器，但仍利用环状DNA分子和70S核糖体完成所有必需的生命活动。
3. Cell Membranes and Transport | 细胞膜与运输
The cell membrane is described by the fluid mosaic model: a phospholipid bilayer with embedded proteins, cholesterol and glycoproteins. Small non-polar molecules can diffuse directly through the bilayer, while ions and polar molecules need transport proteins.
细胞膜可以用流动镶嵌模型来描述：由磷脂双分子层构成，其中嵌有蛋白质、胆固醇和糖蛋白。小的非极性分子可以直接通过双分子层扩散，而离子和极性分子则需要转运蛋白。
Passive transport includes diffusion, facilitated diffusion through channel or carrier proteins, and osmosis, which is the movement of water from a region of higher water potential to lower water potential across a partially permeable membrane. Active transport uses ATP to move molecules against their concentration gradient, often via carrier proteins.
被动运输包括扩散、通过通道蛋白或载体蛋白的协助扩散，以及渗透作用——水从水势较高的区域穿过半透膜向水势较低的区域移动。主动运输利用ATP使分子逆浓度梯度移动，通常通过载体蛋白完成。
4. Enzymes | 酶
Enzymes are globular proteins that act as biological catalysts by lowering activation energy. Their active site is complementary to a specific substrate, and the induced fit model explains how the active site changes shape slightly to form enzyme-substrate complexes.
酶是球状蛋白质，通过降低活化能起生物催化剂的作用。酶的活性位点与特定底物互补，诱导契合模型解释了活性位点如何轻微改变形状以形成酶-底物复合物。
Temperature, pH, enzyme concentration and substrate concentration affect the rate of enzyme-controlled reactions. At high temperature or extreme pH, hydrogen bonds and ionic interactions break, changing the tertiary structure and denaturing the enzyme. Competitive inhibitors bind at the active site, while non-competitive inhibitors bind elsewhere and change the active site shape.
温度、pH、酶浓度和底物浓度会影响酶促反应的速率。在高温或极端pH下，氢键和离子相互作用被破坏，改变酶的三级结构并使酶变性。竞争性抑制剂结合在活性位点，非竞争性抑制剂结合在其他部位并改变活性位点形状。
5. Nucleic Acids and DNA Replication | 核酸与DNA复制
DNA is a double helix made of two anti-parallel polynucleotide strands. Each nucleotide contains deoxyribose, a phosphate group and one of four bases: adenine, thymine, cytosine or guanine. Adenine pairs with thymine by two hydrogen bonds, and cytosine pairs with guanine by three.
DNA是由两条反向平行的多核苷酸链组成的双螺旋结构。每个核苷酸包含脱氧核糖、一个磷酸基团和四种碱基之一：腺嘌呤、胸腺嘧啶、胞嘧啶或鸟嘌呤。腺嘌呤与胸腺嘧啶通过两个氢键配对，胞嘧啶与鸟嘌呤通过三个氢键配对。
DNA replication is semi-conservative: each new molecule contains one original strand and one newly synthesised strand. DNA helicase unwinds the double helix, and DNA polymerase adds complementary nucleotides in a 5' to 3' direction. The leading strand is synthesised continuously, while the lagging strand forms short Okazaki fragments that are joined by DNA ligase.
DNA复制是半保留的：每个新分子含有一条原始链和一条新合成的链。DNA解旋酶解开双螺旋，DNA聚合酶以5'到3'方向添加互补核苷酸。前导链连续合成，滞后链则形成短的冈崎片段，再通过DNA连接酶连接。
6. Mitosis and the Cell Cycle | 有丝分裂与细胞周期
Mitosis produces two genetically identical diploid daughter cells. It is essential for growth, repair of damaged tissues and asexual reproduction. The cell cycle includes interphase, during which DNA replicates in S phase and the cell grows in G₁ and G₂, followed by mitosis and cytokinesis.
有丝分裂产生两个遗传上相同的二倍体子细胞。它对于生长、受损组织的修复和无性繁殖至关重要。细胞周期包括间期——DNA在S期复制，细胞在G₁期和G₂期生长——随后是有丝分裂和胞质分裂。
The stages of mitosis are prophase, metaphase, anaphase and telophase. During metaphase, chromosomes line up at the equator, and during anaphase sister chromatids are pulled to opposite poles. Cytokinesis then divides the cytoplasm to complete cell division.
有丝分裂的阶段包括前期、中期、后期和末期。在中期，染色体排列在赤道板上；在后期，姐妹染色单体被拉向细胞两极。随后胞质分裂将细胞质分开，完成细胞分裂。
| Stage | 阶段 | Key events | 关键事件 |
|---|---|
| Prophase | 前期 | Chromosomes condense; nuclear envelope breaks down; spindle fibres form | 染色体浓缩；核膜解体；纺锤丝形成 |
| Metaphase | 中期 | Chromosomes align at the equator | 染色体排列在赤道板上 |
| Anaphase | 后期 | Sister chromatids separate to opposite poles | 姐妹染色单体分离并移向两极 |
| Telophase | 末期 | Nuclear envelopes reform; chromosomes decondense | 核膜重新形成；染色体解凝 |
7. The Immune System | 免疫系统
The immune system defends the body against pathogens. Non-specific defences include physical barriers such as skin and chemical barriers such as stomach acid. Specific responses involve white blood cells called lymphocytes and include both cell-mediated and humoral immunity.
免疫系统保护身体免受病原体侵害。非特异性防御包括皮肤等物理屏障和胃酸等化学屏障。特异性反应涉及称为淋巴细胞的白细胞，包括细胞免疫和体液免疫。
Phagocytes carry out phagocytosis, engulfing and digesting pathogens. T lymphocytes respond to antigens presented on body cells and activate other immune cells, while B lymphocytes produce antibodies that bind to specific antigens. After infection, memory cells remain to give a faster secondary response, which is the principle behind vaccination.
吞噬细胞执行吞噬作用，摄取并消化病原体。T淋巴细胞对呈递在体细胞上的抗原作出反应并激活其他免疫细胞，而B淋巴细胞产生与特定抗原结合的抗体。感染后，记忆细胞存留下来以便产生更快的二次反应，这就是疫苗接种的原理。
8. Gas Exchange in Mammals | 哺乳动物的气体交换
Gas exchange in mammals occurs in the alveoli of the lungs. Alveoli provide a large surface area, a thin diffusion barrier, a steep concentration gradient maintained by ventilation and blood flow, and a moist surface for gas dissolution.
哺乳动物的气体交换发生在肺的肺泡中。肺泡提供大的表面积、薄的扩散屏障、通过通气和血流维持的陡峭浓度梯度，以及用于气体溶解的湿润表面。
Ventilation involves the diaphragm and intercostal muscles changing the thoracic cavity volume. During inspiration, the diaphragm contracts and flattens, the ribcage moves up and out, and air enters the lungs. During expiration, these structures relax and air leaves the lungs.
通气涉及膈肌和肋间肌改变胸腔容积。吸气时，膈肌收缩并变平，肋骨上提外移，空气进入肺部。呼气时，这些结构放松，空气离开肺部。
Haemoglobin in red blood cells binds oxygen in the high-oxygen environment of the lung and releases it in respiring tissues. The oxygen dissociation curve is S-shaped, and a shift to the right under conditions such as higher carbon dioxide concentration is called the Bohr effect, which helps supply more oxygen to active tissues.
红细胞中的血红蛋白在肺的高氧环境中结合氧，并在呼吸组织中释放氧。氧解离曲线呈S形，在二氧化碳浓度较高等条件下曲线右移称为玻尔效应，这有助于为活跃组织提供更多氧气。
9. Genetic Information and Protein Synthesis | 遗传信息与蛋白质合成
Genes are sequences of DNA bases that code for proteins. Protein synthesis occurs in two main stages: transcription, in which DNA is copied into messenger RNA, and translation, in which the mRNA sequence is used to assemble a polypeptide at a ribosome.
基因是编码蛋白质的DNA碱基序列。蛋白质合成主要分为两个阶段：转录——将DNA复制为信使RNA；翻译——利用mRNA序列在核糖体上组装多肽。
During transcription, RNA polymerase unwinds the DNA and synthesises pre-mRNA using complementary base pairing. In eukaryotes, introns are removed by splicing before the mature mRNA leaves the nucleus. During translation, transfer RNA molecules carry specific amino acids, and their anticodons pair with codons on mRNA to build the protein.
在转录过程中，RNA聚合酶解开DNA并通过互补碱基配对合成前体mRNA。在真核生物中，内含子通过剪接被去除，成熟的mRNA才离开细胞核。在翻译过程中，转运RNA分子携带特定氨基酸，其反密码子与mRNA上的密码子配对，从而合成蛋白质。
The genetic code is degenerate, meaning most amino acids are coded for by more than one codon, and universal, meaning the same codons specify the same amino acids in almost all organisms.
遗传密码具有简并性，即大多数氨基酸由不止一个密码子编码；同时具有通用性，即几乎所有生物中相同的密码子编码相同的氨基酸。
10. Biodiversity and Classification | 生物多样性与分类
Biodiversity refers to the variety of living organisms in an ecosystem or on Earth. A species is commonly defined as a group of organisms that can interbreed to produce fertile offspring. Classification organises species into hierarchical groups: domain, kingdom, phylum, class, order, family, genus and species.
生物多样性是指生态系统或地球上生物的种类多样性。物种通常被定义为能够交配并产生可育后代的一群生物。分类将物种归入层级系统：域、界、门、纲、目、科、属、种。
Each species is given a binomial name, such as Homo sapiens, consisting of the genus and species. Modern classification increasingly uses DNA sequences and molecular evidence to determine evolutionary relationships, which can reveal connections that are not obvious from physical features alone.
每个物种都有一个双名，例如智人（Homo sapiens），由属名和种加词组成。现代分类越来越依赖DNA序列和分子证据来确定进化关系，这可以揭示仅凭外部特征无法发现的亲缘关系。
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