📚 Differences between Animal and Plant Cells | 动物细胞与植物细胞的差异
In A-Level Biology, one of the first structural comparisons you must master is that between animal and plant cells. Both are eukaryotic, sharing a membrane-bound nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, ribosomes and a cytoskeleton, yet their divergent lifestyles have produced distinctive organelles and specialisations. Understanding these differences is not just a memory exercise; it explains how plants capture light energy, maintain turgor, build multicellular tissues and divide without centrioles.
在 A-Level 生物课程中，你必须掌握的首批结构比较之一就是动物细胞与植物细胞的差异。两者都是真核细胞，都拥有具膜细胞核、线粒体、内质网、高尔基体、核糖体和细胞骨架，但不同的生活方式造就了独特的细胞器和特化结构。理解这些差异不仅是记忆练习，还能解释植物如何捕获光能、维持膨压、构建多细胞组织以及在没有中心粒的情况下完成分裂。
1. Core Similarities as Eukaryotic Cells | 真核细胞的共同基础
Animal and plant cells both belong to the domain Eukarya, so their genetic material is enclosed within a nuclear envelope and their cytoplasm contains a variety of membrane-bound compartments. Common organelles include mitochondria for aerobic respiration, rough and smooth endoplasmic reticulum for protein and lipid synthesis, Golgi apparatus for modification and packaging, and 80S ribosomes for translation. The presence of these shared features means that many metabolic pathways, such as glycolysis, the Krebs cycle and protein secretion, operate on the same principles in both cell types.
动物细胞和植物细胞都属于真核生物域，因此它们的遗传物质被核膜包裹，细胞质中含有多种具膜区室。共同细胞器包括用于有氧呼吸的线粒体、用于蛋白质和脂质合成的粗面与滑面内质网、用于修饰和包装的高尔基体，以及用于翻译的 80S 核糖体。这些共同特征意味着许多代谢途径，如糖酵解、克雷布斯循环和蛋白质分泌，在两种细胞中遵循相同的原理。
From an evolutionary perspective, these commonalities suggest a shared eukaryotic ancestor. In both kingdoms, the plasma membrane is a phospholipid bilayer with embedded proteins, and the cytoskeleton provides internal organisation, intracellular transport and mechanical support. Exam questions often begin by asking for similarities before moving to differences, so keep this common toolkit clearly in mind.
从进化角度看，这些共同点表明它们拥有共同的 eukaryotic 祖先。在动物和植物界中，质膜都是嵌入蛋白质的磷脂双分子层，细胞骨架负责内部组织、胞内运输和机械支撑。考试题常常先要求列出相似点，再转向差异，因此要牢记这套共同的基本结构。
2. Cell Wall: Rigid Cellulose vs Flexible Surface | 细胞壁：刚性纤维素与柔性表面
The most conspicuous structural difference is that plant cells possess a cellulose cell wall outside the plasma membrane, whereas animal cells lack a cell wall and are bounded only by a flexible plasma membrane. This wall is composed of cellulose microfibrils embedded in a matrix of hemicellulose, pectin and sometimes lignin, giving the plant cell high tensile strength and resistance to osmotic swelling.
最显著的结构差异是植物细胞在质膜外具有纤维素细胞壁，而动物细胞没有细胞壁，仅由柔性质膜包裹。该细胞壁由嵌入半纤维素、果胶以及有时木质素基质中的纤维素微纤丝组成，赋予植物细胞很高的抗拉强度和抵抗渗透膨胀的能力。
The cell wall is fully permeable to water and dissolved substances, so it does not control entry in the way the plasma membrane does. Adjacent plant cells are glued together by the middle lamella, a pectin-rich layer. Animal cells instead rely on an extracellular matrix containing collagen and glycoproteins, which is not a rigid wall but still provides adhesion and signalling. In exam answers, avoid saying that animal cells have a cell wall; they have a cell surface membrane only.
细胞壁对水和溶解物质完全通透，因此它不像质膜那样控制物质进出。相邻植物细胞由富含果胶的胞间层粘合在一起。动物细胞则依赖含有胶原蛋白和糖蛋白的细胞外基质，它不是刚性壁，但仍提供粘附与信号传导。在考试答案中，不要说动物细胞有细胞壁；它们只有细胞表面膜。
3. Chloroplasts: Solar Power Stations | 叶绿体：太阳能发电站
Plant cells and some algae contain chloroplasts, the double-membrane organelles that carry out photosynthesis. Chloroplasts contain thylakoid membranes stacked into grana, where light-dependent reactions occur, and a stroma where the Calvin cycle fixes carbon dioxide. The green pigment chlorophyll absorbs mainly red and blue light, reflecting green wavelengths. Animal cells never contain chloroplasts, so they are heterotrophic and must obtain organic nutrients from their diet.
植物细胞和一些藻类含有叶
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