📚 GCSE AQA Biology: Key Concept Clarifications | GCSE AQA 生物：概念辨析
In GCSE AQA Biology, students often confuse closely related terms, which can lead to avoidable mistakes in exams. This article clarifies the essential differences between common pairs of concepts, helping you to build a more secure understanding and boost your confidence.
在 GCSE AQA 生物中，许多学生容易混淆意思相近的术语，导致考试中不必要的失分。本文将厘清常见概念对之间的关键区别，帮助你建立更扎实的理解并增强信心。
1. Cell Membrane vs Cell Wall | 细胞膜与细胞壁
The cell membrane is a thin, flexible layer that surrounds the cytoplasm of all cells. It is composed of a phospholipid bilayer with embedded proteins and is selectively permeable, meaning it controls which substances can enter or leave the cell.
细胞膜是一层薄而柔韧的结构，包围着所有细胞的细胞质。它由磷脂双分子层及嵌入的蛋白质构成，具有选择通透性，即控制哪些物质可以进出细胞。
The cell wall is a rigid outer covering found in plant cells, bacterial cells and fungal cells, but not in animal cells. It provides structural support and protection, and is fully permeable – it does not regulate the movement of materials.
细胞壁是存在于植物细胞、细菌细胞和真菌细胞的坚硬外层，动物细胞没有。它提供结构支撑和保护，并且是全透性的——它不会调控物质的移动。
In plant cells, the cell wall is made mainly of cellulose (in bacteria and fungi the composition differs). The cell membrane lies just inside the cell wall in these organisms.
在植物细胞中，细胞壁主要由纤维素构成（细菌和真菌的壁成分不同）。这些生物的细胞膜紧贴在细胞壁内侧。
2. Diffusion vs Osmosis | 扩散与渗透
Diffusion is the net movement of particles (molecules or ions) 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 across a membrane or in an open fluid.
扩散是粒子（分子或离子）从较高浓度区域向较低浓度区域的净移动，顺着浓度梯度进行。它是一种被动过程，不需要能量，可以跨膜发生，也可以在没有膜的液体中进行。
Osmosis is a special type of diffusion that involves only water molecules. It occurs across a partially permeable membrane from a dilute solution (high water potential) to a more concentrated solution (low water potential).
渗透是一种特殊类型的扩散，只涉及水分子。它跨过半透膜发生，从稀溶液（高水势）移向较浓溶液（低水势）。
The key difference: diffusion applies
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