📚 IB Biology: Concept Clarifications | IB 生物：概念辨析
Many students struggle with the subtle but critical distinctions in IB Biology. This article clarifies commonly confused concepts, helping you master the subject with confidence. Each section presents paired English and Chinese explanations to reinforce understanding.
许多学生在 IB 生物学中常常混淆一些关键概念。本文厘清这些易混淆的概念，帮助你有信心地掌握这门学科。每个部分都提供成对的英文与中文解释，以加深理解。
1. Diffusion vs. Osmosis | 扩散与渗透
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 and can occur in gases, liquids, or across membranes if the membrane is permeable to the particles.
扩散是粒子从高浓度区域向低浓度区域的净移动，顺着浓度梯度进行。这是一个被动过程，不需要能量，可以发生在气体、液体中，或者如果膜对该粒子是可渗透的，也可以跨膜发生。
Osmosis is a special type of diffusion involving water molecules across a selectively permeable membrane. Water moves from a region of lower solute concentration (higher water potential) to a region of higher solute concentration (lower water potential).
渗透是一种特殊的扩散，涉及水分子通过选择性透过膜的运动。水从溶质浓度较低（水势较高）的区域移动到溶质浓度较高（水势较低）的区域。
2. Active Transport vs. Passive Transport | 主动运输与被动运输
The table below summarises the key differences between active and passive transport mechanisms:
下表总结了主动与被动运输机制的主要区别：
| Feature | Passive Transport | Active Transport |
|---|---|---|
| Energy requirement | No ATP needed | Requires ATP |
| Direction of movement | Down concentration gradient | Against concentration gradient |
| Protein involvement | May use channel or carrier proteins (facilitated diffusion) | Always uses carrier proteins (pumps) |
| Examples | Diffusion, osmosis, facilitated diffusion | Na⁺/K⁺ pump, endocytosis, exocytosis |
In passive transport, substances move freely according to the laws of thermodynamics. Active transport, by contrast, uses metabolic energy to move substances against their gradient, allowing cells to maintain internal concentrations different from the external environment.
在被动运输中，物质根据热力学定律自由移动。相反，主动运输利用代谢能量逆浓度梯度运输物质，使细胞能够维持与外界环境不同的内部浓度。
3. Mitosis vs. Meiosis | 有丝分裂与减数分裂
Mitosis produces two genetically identical diploid daughter cells, essential for growth and repair. Meiosis produces four genetically unique haploid gametes, crucial for sexual reproduction.
有丝分裂产生两个遗传上相同的二倍体子细胞，对生长和修复至关重要。减数分裂产生四个遗传上独特的单倍体配子，对有性生殖至关重要。
| Aspect | Mitosis | Meiosis |
|---|---|---|
| Number of divisions | One | Two (Meiosis I and II) |
| Daughter cell number | 2 | 4 |
| Ploidy | Diploid → Diploid | Diploid → Haploid |
| Genetic variation | None (clones) | High (crossing over, independent assortment) |
| Occurrence | Somatic cells | Germ cells (gonads) |
The reduction in chromosome number during meiosis I is fundamental for maintaining the species' chromosome count across generations. The crossing over in prophase I and independent assortment in metaphase I generate genetic diversity.
减数分裂 I 中染色体数目的减少是维持物种世代间染色体数目恒定的基础。前期 I 的交叉互换和中期 I 的自由组合产生了遗传多样性。
4. DNA Replication, Transcription and Translation | DNA 复制、转录与翻译
DNA replication occurs during the S phase of the cell cycle, producing two identical DNA molecules from one. The enzyme DNA helicase unwinds the double helix, and DNA polymerase synthesises new strands using each original strand as a template.
DNA 复制发生在细胞周期的 S 期，从一个 DNA 分子产生两个相同的 DNA 分子。解旋酶 DNA helicase 解开双螺旋，DNA 聚合酶以每条原始链为模板合成新链。
Transcription is the synthesis of mRNA from a DNA template. RNA polymerase binds to the promoter region, separates the DNA strands, and assembles a complementary mRNA strand (using uracil instead of thymine).
转录是从 DNA 模板合成 mRNA 的过程。RNA 聚合酶与启动子区域结合，解开 DNA 双链，并组装一条互补的 mRNA 链（用尿嘧啶替代胸腺嘧啶）。
Translation occurs at ribosomes, where the mRNA codon sequence is decoded to build a polypeptide. tRNA molecules carry specific amino acids, and their anticodons pair with mRNA codons, enabling the ribosome to form peptide bonds.
翻译发生在核糖体上，mRNA 上的密码子序列被解读以构建多肽。tRNA 分子携带特定的氨基酸，其反密码子与 mRNA 密码子配对，使核糖体能够形成肽键。
Key distinction: replication duplicates the entire genome; transcription copies a single gene into mRNA; translation converts that mRNA sequence into a protein.
关键区别：复制重复整个基因组；转录将一个基因拷贝到 mRNA 中；翻译将该 mRNA 序列转化为蛋白质。
5. Genotype vs. Phenotype | 基因型与表型
The genotype is the genetic constitution of an organism, the set of alleles it possesses for a given trait (e.g., BB, Bb, or bb). The phenotype is the observable characteristic resulting from the interaction of the genotype with the environment (e.g., brown eyes, blue eyes).
基因型是生物体的遗传组成，即其针对某一性状所拥有的等位基因组合（例如 BB、Bb
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