📚 Year 9 AQA Biology Core Knowledge Review | Year 9 AQA 生物核心知识点梳理
This revision guide covers the essential topics in the Year 9 AQA Biology curriculum. You will review key concepts about cells, organisation, body systems, photosynthesis, respiration, reproduction, genetics, evolution, and ecosystems to build a strong foundation for GCSE Biology.
本复习指南涵盖 Year 9 AQA 生物课程的核心主题。你将回顾细胞、组织层次、身体系统、光合作用、呼吸作用、生殖、遗传、进化以及生态系统等关键概念，为 GCSE 生物的学习打下坚实基础。
1. Cells – The Building Blocks | 细胞——生命的基本单位
All living organisms are made up of cells. The cell is the smallest unit that can carry out all life processes.
所有生物都是由细胞构成的。细胞是能够进行所有生命活动的最小单位。
Animal and plant cells share several common structures: the cell membrane controls what enters and leaves the cell; the cytoplasm is a jelly-like substance where chemical reactions occur; the nucleus contains genetic material (DNA) and controls the cell's activities; mitochondria are the sites of aerobic respiration, releasing energy; and ribosomes are where proteins are synthesised.
动物细胞和植物细胞具有一些共同的结构：细胞膜控制物质的进出；细胞质是发生化学反应的胶状物质；细胞核含有遗传物质（DNA）并控制细胞的活动；线粒体是有氧呼吸的场所，释放能量；核糖体是合成蛋白质的地方。
Plant cells also have a rigid cell wall made of cellulose for support, a large permanent vacuole containing cell sap that helps maintain turgor pressure, and chloroplasts that absorb light energy for photosynthesis.
植物细胞还具有由纤维素组成的坚硬细胞壁，起支撑作用；含有细胞液的大液泡，有助于维持膨压；以及吸收光能进行光合作用的叶绿体。
Bacterial cells are prokaryotic: they lack a true nucleus; instead, the genetic material is a single loop of DNA found in the cytoplasm. They also have a cell wall, cell membrane, cytoplasm, and sometimes plasmids (small rings of DNA) and flagella for movement.
细菌细胞是原核生物：它们没有真正的细胞核，遗传物质是位于细胞质中的一个环状 DNA。它们也具有细胞壁、细胞膜、细胞质，有时还有质粒（小环状 DNA）和用于运动的鞭毛。
2. Cell Specialisation | 细胞的分化
In multicellular organisms, cells differentiate to become specialised for particular functions. The structure of each specialised cell is adapted to its job.
在多细胞生物体中，细胞通过分化变得特化以执行特定的功能。每种特化细胞的结构都适应其功能。
Examples include: Sperm cells have a tail (flagellum) for swimming, many mitochondria for energy, and an acrosome containing enzymes to penetrate the egg. Nerve cells (neurons) are long and have branched endings to transmit electrical signals quickly. Muscle cells contain many protein fibres that can contract and many mitochondria for energy.
例子包括：精子细胞有用于游动的尾部（鞭毛）、提供能量的大量线粒体，以及含有酶以穿透卵子的顶体。神经细胞（神经元）较长且有分支末梢，可以快速传递电信号。肌肉细胞含有许多能够收缩的蛋白质纤维和大量提供能量的线粒体。
In plants, root hair cells have a large surface area to increase absorption of water and minerals. Xylem vessels are hollow, dead cells with lignified walls that form tubes for water transport. Palisade mesophyll cells are packed with chloroplasts to maximise light absorption for photosynthesis.
在植物中，根毛细胞具有较大的表面积，以增加水分和矿物质的吸收。木质部导管是中空的死细胞，木质化的细胞壁形成输送水分的管道。栅栏叶肉细胞充满叶绿体，以最大化光合作用的光吸收。
3. Levels of Organisation | 组织层次
Cells of the same type group together to form a tissue. A tissue is a group of similar cells working together to carry out a specific function, such as muscular tissue or xylem tissue.
相同类型的细胞聚集在一起形成组织。组织是一群相似的细胞
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