📚 CIE Lower Secondary Science Stage 8: Core Concepts | CIE 初中科学第八阶段：核心概念
This article provides a structured revision guide for CIE Lower Secondary Science Stage 8. It summarises the major biology, chemistry and physics topics from the Learner's Book, with key definitions and exam tips.
本文为 CIE 初中科学第八阶段提供结构化复习指南，归纳学习者用书中的主要生物、化学和物理主题，并给出关键定义与考试技巧。
1. Cells and Life Processes | 细胞与生命过程
Stage 8 revisits cells and focuses on how structures relate to functions. A plant cell has a rigid cell wall, chloroplasts for photosynthesis and a large permanent vacuole for support and storage. An animal cell has a flexible cell membrane, no chloroplasts and usually small temporary vacuoles.
第八阶段重新学习细胞，重点关注结构如何与功能相关。植物细胞有坚硬的细胞壁、进行光合作用的叶绿体以及用于支撑和储存的大液泡。动物细胞有柔韧的细胞膜，没有叶绿体，通常只有小的临时液泡。
The nucleus controls the cell and contains genetic material; the cytoplasm is where many chemical reactions occur; mitochondria release energy during respiration. Learners should be able to label diagrams and explain why each part is essential.
细胞核控制细胞并含有遗传物质；细胞质是许多化学反应发生的场所；线粒体在呼吸作用中释放能量。学习者应能标注结构图并解释每个部分为何重要。
2. Nutrition and Digestion | 营养与消化
The digestive system is a muscular tube from the mouth to the anus. Mechanical digestion breaks food into smaller pieces, while chemical digestion uses enzymes to break bonds in large molecules.
消化系统是一条从口腔到肛门的肌肉管道。机械消化将食物分解成小块，而化学消化利用酶打断大分子中的化学键。
Key enzymes include amylase (carbohydrates to simple sugars), protease (proteins to amino acids) and lipase (fats to fatty acids and glycerol). Bile helps to emulsify fats but is not an enzyme.
关键酶包括淀粉酶（碳水化合物分解为单糖）、蛋白酶（蛋白质分解为氨基酸）和脂肪酶（脂肪分解为脂肪酸和甘油）。胆汁帮助乳化脂肪，但不是酶。
Absorption mainly occurs in the small intestine, where villi provide a large surface area. Water is absorbed in the large intestine.
吸收主要发生在小肠，绒毛提供了巨大的表面积。水分在大肠中被吸收。
3. Circulatory and Respiratory Systems | 循环系统与呼吸系统
Blood consists of plasma, red blood cells, white blood cells and platelets. Red blood cells contain haemoglobin, which binds oxygen; white blood cells defend against pathogens; platelets help blood clot.
血液由血浆、红细胞、白细胞和血小板组成。红细胞含有血红蛋白，能与氧气结合；白细胞抵御病原体；血小板帮助血液凝固。
The heart pumps blood through arteries, veins and capillaries. Arteries carry blood away from the heart under high pressure; veins return blood to the heart and have valves; capillaries allow exchange of substances.
心脏将血液泵入动脉、静脉和毛细血管。动脉在高压下将血液导出心脏；静脉将血液送回心脏并具有瓣膜；毛细血管进行物质交换。
In the lungs, oxygen diffuses from alveoli into blood, and carbon dioxide diffuses from blood into alveoli. The alveoli are thin, moist and surrounded by capillaries to maximise diffusion.
在肺部，氧气从肺泡扩散入血液，二氧化碳从血液扩散入肺泡。肺泡薄、湿润且被毛细血管包围，以最大程度促进扩散。
4. Respiration | 呼吸作用
ergy. The word equation is glucose + oxygen → carbon dioxide + water (energy is released).
有氧呼吸需要氧气，释放的能量相对较多。文字方程式为：葡萄糖 + 氧气 → 二氧化碳 + 水（释放能量）。
ethanol + carbon dioxide. Less energy is released, and lactic acid causes muscle fatigue.
无氧呼吸在氧气供应不足时进行。在肌肉细胞中，葡萄糖 → 乳酸；在酵母中，葡萄糖 → 乙醇 + 二氧化碳。释放的能量较少，乳酸会引起肌肉疲劳。
Respiration should not be confused with breathing. Breathing is the physical movement of air in and out; respiration is the chemical release of energy in cells.
呼吸作用不应与呼吸相混淆。呼吸指空气进出肺部的物理运动；呼吸作用是细胞中释放能量的化学过程。
5. Reproduction in Plants | 植物生殖
Flowers contain male and female reproductive organs. The stamen produces pollen; the carpel contains the ovary, style and stigma. Pollination transfers pollen from an anther to a stigma.
花包含雄性和雌性生殖器官。雄蕊产生花粉；雌蕊包含子房、花柱和柱头。传粉将花粉从花药传递到柱头。
Insect-pollinated flowers are often brightly coloured, scented and produce nectar; wind-pollinated flowers usually have small, dull petals and produce large amounts of lightweight pollen.
虫媒花通常颜色鲜艳、有香味并产生花蜜；风媒花通常花瓣小、颜色暗淡，并产生大量轻质花粉。
After fertilisation, the ovule becomes a seed and the ovary becomes a fruit. Seeds need water, oxygen and a suitable temperature for germination; some also need light or scarification.
受精后，胚珠发育成种子，子房发育成果实。种子萌发需要水分、氧气和适宜的温度；有些种子还需要光照或破皮处理。
6. Chemical Reactions | 化学反应
A chemical change produces new substances with different properties. Evidence includes a permanent colour change, a gas given off, a precipitate forming, or an energy change such as heat or light.
化学变化会生成性质不同的新物质。证据包括永久性颜色变化、放出气体、生成沉淀，或产生热、光等能量变化。
Word equations summarise reactions. Example
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