📚 KS3 CIE Biology: Core Knowledge Review | KS3 CIE 生物：核心知识点梳理
This comprehensive revision guide distils the essential concepts covered in the KS3 Cambridge IGCSE Biology curriculum. From the microscopic world of cells to the grand scale of ecosystems, each section provides concise bilingual explanations to reinforce understanding and prepare students for progression to IGCSE level.
本综合复习指南提炼了 KS3 剑桥 IGCSE 生物课程涵盖的核心概念。从微观的细胞世界到宏观的生态系统，每个部分都提供简洁的双语解释，以加深理解，为学生顺利过渡到 IGCSE 阶段做好准备。
1. Cell Structure and Function | 细胞结构与功能
All living organisms are composed of cells, the fundamental units of life. The cell theory states that cells arise from pre-existing cells and are the site of all life processes.
所有生物体都由细胞构成，细胞是生命的基本单位。细胞学说指出，细胞来自已有的细胞，是一切生命活动的场所。
Cells can be classified as prokaryotic (lacking a true nucleus, e.g. bacteria) or eukaryotic (possessing a membrane-bound nucleus, e.g. plant and animal cells).
细胞可分为原核细胞（无真正的细胞核，如细菌）和真核细胞（有膜包被的细胞核，如动植物细胞）。
Plant cells have a rigid cellulose cell wall, a large permanent vacuole and chloroplasts for photosynthesis, whereas animal cells lack these structures.
植物细胞有坚硬的纤维素细胞壁、一个大的中央液泡以及进行光合作用的叶绿体，而动物细胞没有这些结构。
Nucleus – controls cell activities and contains genetic material (DNA).
细胞核 – 控制细胞活动，含有遗传物质（DNA）。
Cytoplasm – site of chemical reactions.
细胞质 – 化学反应的场所。
Cell membrane – selectively controls entry and exit of substances.
细胞膜 – 选择性地控制物质的进出。
Mitochondria – release energy through aerobic respiration.
线粒体 – 通过有氧呼吸释放能量。
Ribosomes – protein synthesis.
核糖体 – 合成蛋白质。
2. Levels of Organisation | 组织的层次
Cells with similar structure and function group together to form tissues. Examples include muscle tissue in animals and xylem tissue in plants.
结构和功能相似的细胞聚集在一起形成组织。例如动物的肌肉组织和植物的木质部组织。
Organs are structures composed of different tissues working together to perform specific functions. The heart is an organ made of muscle, nerve and connective tissues.
器官是由不同组织协同工作以执行特定功能的结构。心脏是由肌肉、神经和结缔组织构成的器官。
Organ systems consist of multiple organs that collaborate to carry out major functions. The digestive system, for example, includes the stomach, intestines and liver.
器官系统由多个器官组成，这些器官协同完成重要功能。例如消化系统包括胃、肠和肝。
In plants, leaves, stems and roots form organ systems that support photosynthesis, transport and anchorage.
在植物中，叶、茎和根构成器官系统，分别支持光合作用、运输和固定。
3. The Digestive System | 消化系统
The digestive system breaks down large, insoluble food molecules into small, soluble ones that can be absorbed into the blood. This process involves both mechanical digestion (chewing, churning) and chemical digestion (enzymes).
消化系统将大的、不溶性食物分子分解为可溶的小分子，以便吸收进入血液。这一过程包括物理性消化（咀嚼、搅拌）和化学性消化（酶）。
Key enzymes include amylase (breaks down starch into maltose), protease (proteins into amino acids) and lipase (fats into fatty acids and glycerol). Bile, produced by the liver, emulsifies fats to increase their surface area for enzyme action.
主要的酶包括淀粉酶（将淀粉分解为麦芽糖）、蛋白酶（将蛋白质分解为氨基酸）和脂肪酶（将脂肪分解为脂肪酸和甘油）。肝脏分泌的胆汁能乳化脂肪，增大其表面积，利于酶的作用。
| Enzyme | Site of production | Substrate | Products |
|---|---|---|---|
| Amylase | Salivary glands, pancreas | Starch | Maltose |
| Protease | Stomach, pancreas | Protein | Amino acids |
| Lipase | Pancreas | Fats | Fatty acids + glycerol |
The small intestine is the primary site of absorption, where finger-like villi provide a large surface area to maximise uptake of nutrients into the bloodstream.
小肠是吸收的主要场所，其内壁的指状绒毛提供了巨大的表面积，最大程度地促进营养物质进入血液。
4. The Circulatory System | 循环系统
The circulatory system transports oxygen, nutrients, hormones and waste products around the body. In humans, it is a double circulation system consisting of the heart, blood vessels and blood.
循环系统负责在全身运输氧气、营养物质、激素和废物。人类具有双循环系统，由心脏、血管和血液组成。
The heart has four chambers: right atrium, right ventricle, left atrium and left ventricle. The right side pumps deoxygenated blood to the lungs (pulmonary circulation), while the left side pumps oxygenated blood to the rest of the body (systemic circulation).
心脏有四个腔室：右心房、右心室、左心房和左心室。右侧将缺氧血泵送至肺部（肺循环），左侧将富氧血泵送至全身各处（体循环）。
Arteries carry blood away from the heart under high pressure and have thick muscular walls. Veins return blood to the heart and contain valves to prevent backflow. Capillaries are tiny, one-cell-thick vessels where exchange of substances occurs.
动脉将血液带离心脏，血压高，管壁厚而富有肌肉。静脉将血液送回心脏，内有瓣膜防止倒流。毛细血管是极薄的单层细胞管道，在此进行物质交换。
Blood components include:
血液的成分包括：
Red blood cells – transport oxygen using haemoglobin.
红细胞 – 利用血红蛋白运输氧气。
White blood cells – defend against pathogens.
白细胞 – 防御病原体。
Platelets – involved in blood clotting.
血小板 – 参与血液凝固。
Plasma – liquid carrying dissolved substances and cells.
血浆 – 运输溶解物质和细胞的液体。
5. The Respiratory System | 呼吸系统
The respiratory system facilitates gas exchange: taking in oxygen for aerobic respiration and removing carbon dioxide. Air enters through the trachea, which splits into two bronchi leading to the lungs.
呼吸系统负责气体交换：吸入氧气用于有氧呼吸，排出二氧化碳。空气通过气管进入，气管分支为两根支气管通向双肺。
Bronchi divide into smaller bronchioles, ending in clusters of alveoli. Alveoli have thin walls, a large surface area and a rich capillary network, which enables efficient diffusion of gases.
支气管分支为更小的细支气管，末端成簇的肺泡。肺泡壁很薄，表面积大且密布毛细血管网，有利于气体的高效扩散。
Ventilation involves the diaphragm and intercostal muscles. During inhalation, the diaphragm contracts and moves downwards, the ribcage moves up and out, reducing pressure and drawing air in. Exhalation is largely passive as muscles relax.
肺通气涉及膈肌和肋间肌。吸气时，膈肌收缩下移，肋骨上提外扩，胸腔体积增大，压力降低，空气进入。呼气主要是肌肉舒张的被动过程。
6. Plant Nutrition and Photosynthesis | 植物营养与光合作用
Plants are autotrophs, meaning they produce their own food through photosynthesis. This process uses light energy to convert carbon dioxide and water into glucose and oxygen.
植物是自养生物，它们通过光合作用制造自己的食物。该过程利用光能将二氧化碳和水转化为葡萄糖和氧气。
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Photosynthesis occurs in chloroplasts, which contain the pigment chlorophyll that captures light energy. The rate of photosynthesis is affected by light intensity, carbon dioxide concentration and temperature.
光合作用在叶绿体中进行，叶绿体含有的叶绿素能捕获光能。光合作用速率受光照强度、二氧化碳浓度和温度的影响。
Leaves are adapted for photosynthesis with a broad, flat blade, a transparent upper epidermis, and stomata on the lower surface to allow gas exchange. Xylem transports water from the roots, while phloem moves glucose away to other parts of the plant.
叶片适应光合作用的结构特征包括宽阔扁平的叶片、透明的上表皮以及下表皮的气孔供气体交换。木质部从根部输送水分，韧皮部则将葡萄糖运至植物其他部位。
Plants also require mineral ions, such as nitrates for protein synthesis and magnesium for chlorophyll production. Deficiency leads to stunted growth or chlorosis.
植物还需要矿物质离子，如硝酸盐用于合成蛋白质，镁用于合成叶绿素。缺乏时会导致生长迟缓或萎黄病。
7. Reproduction in Humans | 人类生殖
Humans reproduce sexually, involving the fusion of male and female gametes. Male gametes are sperm, produced in the testes; female gametes are eggs (ova), released from the ovaries.
人类有性生殖涉及雌雄配子的融合。雄配子是精子，在睾丸中产生；雌配子是卵子，从卵巢中排出。
The male reproductive system includes the testes, sperm ducts, prostate gland and penis. The female system includes the ovaries, oviducts (fallopian tubes), uterus, cervix and vagina.
男性生殖系统包括睾丸、输精管、前列腺和阴茎。女性系统包括卵巢、输卵管、子宫、子宫颈和阴道。
Fertilisation occurs in the oviduct when a sperm fuses with an egg to form a zygote. The zygote divides and implants in the lining of the uterus, where it develops into an embryo and later a fetus.
受精发生在输卵管中，精子与卵子融合形成受精卵。受精卵分裂并植入子宫内膜，发育成胚胎，继而成为胎儿。
The menstrual cycle prepares the uterus for implantation. If fertilisation does not occur, the thickened lining is shed during menstruation. The placenta provides oxygen and nutrients to the fetus and removes waste via the umbilical cord.
月经周期使子宫为着床做好准备。若未发生受精，增厚的内膜将在月经期间脱落。胎盘通过脐带向胎儿提供氧气和营养，并带走代谢废物。
8. Reproduction in Plants | 植物生殖
Flowers are the reproductive organs of many plants. A typical flower consists of sepals, petals, stamens (male parts) and carpels (female parts).
花是许多植物的生殖器官。一朵典型的花由萼片、花瓣、雄蕊（雄性部分）和心皮（雌性部分）组成。
Each stamen has an anther that produces pollen grains containing the male gametes. The carpel comprises the stigma, style and ovary; the ovary contains ovules, each with a female gamete.
每个雄蕊有一个花药，产生含有雄配子的花粉粒。雌蕊包括柱头、花柱和子房；子房内含胚珠，每个胚珠中含一个雌配子。
Pollination is the transfer of pollen from anther to stigma. It can be wind-pollinated or insect-pollinated. Fertilisation occurs when the pollen tube grows down the style and the male nucleus fuses with the ovum inside the ovule, forming a zygote that develops into an embryo within a seed.
传粉是花粉从花药传到柱头的过程。可以是风媒传粉或虫媒传粉。受精时，花粉管沿花柱生长，雄配子与胚珠内的卵细胞融合，形成受精卵，进而发育为种子里面的胚。
After fertilisation, the ovary develops into a fruit, which aids seed dispersal. Seeds can be dispersed by wind, water, animals or mechanical ejection.
受精后，子房发育成果实，辅助种子传播。种子可通过风、水、动物或机械弹射的方式传播。
9. Genetics and Inheritance | 遗传与遗传
Genetic information is carried on chromosomes found in the nucleus. A gene is a section of DNA that codes for a particular protein, determining characteristics.
遗传信息由细胞核内的染色体携带。基因是编码特定蛋白质的 DNA 片段，决定生物性状。
Humans have 46 chromosomes (23 pairs). Gametes contain 23 single chromosomes, so that fertilisation restores the full number. Alleles are different versions of the same gene; they can be dominant or recessive.
人类有 46 条染色体（23 对）。配子含有 23 条单染色体，因此受精后染色体数恢复正常。等位基因是同一基因的不同形式，可以是显性或隐性。
If a dominant allele is present, it masks the effect of the recessive allele. Genetic diagrams (Punnett squares) can predict the probability of offspring inheriting certain traits. For example, a cross between two heterozygous parents (Bb) yields a 3:1 ratio of dominant to recessive phenotype.
若存在显性等位基因，便会掩盖隐性等位基因的效应。遗传图解（旁氏表）可预测后代遗传特定性状的概率。例如，两个杂合子（Bb）亲本杂交，产生显性表型与隐性表型的比例为 3:1。
10. Ecology and Interdependence | 生态与相互依存
Ecology studies the interactions between organisms and their environment. A habitat is the place where an organism lives, while a population is a group of the same species in an area. A community consists of all populations in a habitat, and an ecosystem includes both the community and the abiotic factors.
生态学研究生物与其环境之间的相互作用。栖息地是生物居住的地方，种群是同一区域内同一物种的集合。群落包含栖息地中的所有种群，生态系统则包括群落与非生物因子。
Food chains show the transfer of energy from producers (plants) to primary consumers (herbivores) and then to secondary consumers (carnivores). Food webs are interconnected food chains that better represent the complexity of feeding relationships.
食物链显示能量从生产者（植物）传递至初级消费者（草食动物），再至次级消费者（肉食动物）。食物网是由多条食物链交织而成，更能反映取食关系的复杂性。
The carbon cycle recycles carbon through photosynthesis, respiration, decomposition and combustion. Nitrogen is also cycled through nitrogen fixation, nitrification and denitrification, driven largely by microorganisms.
碳循环通过光合作用、呼吸作用、分解和燃烧使碳元素循环。氮通过固氮作用、硝化作用和反硝化作用循环，主要由微生物驱动。
11. Microorganisms and Disease | 微生物与疾病
Microorganisms include bacteria, viruses, fungi and protoctists. Many are harmless or beneficial, but some are pathogens that cause infectious diseases.
微生物包括细菌、病毒、真菌和原生生物。许多微生物无害甚至有益，但也有一些是引起传染病的病原体。
Pathogens can spread through direct contact, airborne droplets, contaminated food or water, and vectors such as mosquitoes. The body has several defence mechanisms: skin as a barrier, white blood cells that engulf pathogens, and the production of antibodies.
病原体可通过直接接触、空气飞沫、污染的食物或水以及蚊虫等媒介传播。人体具有多种防御机制：皮肤作为屏障，白细胞吞噬病原体，以及产生抗体。
Vaccination introduces a harmless form of a pathogen, stimulating the immune system to produce memory cells, which provide long-term protection without causing illness. Antibiotics can kill bacteria but are ineffective against viruses.
疫苗接种引入无害的病原体形式，刺激免疫系统产生记忆细胞，从而在不着病的情况下提供长期保护。抗生素能杀灭细菌，但对病毒无效。
12. Evolution and Natural Selection | 进化与自然选择
Evolution is the gradual change in inherited traits within a population over generations. The theory of evolution by natural selection was proposed by Charles Darwin.
进化是指种群内的遗传性状在世代间逐渐改变的过程。自然选择进化论由查尔斯·达尔文提出。
Natural selection operates on variation within a species. Individuals with traits better suited to their environment are more likely to survive and reproduce, passing their advantageous alleles to the next generation. Over time, this leads to adaptation and eventually speciation.
自然选择作用于物种内部的变异。具有更适应环境性状的个体更可能存活并繁殖，将有利等位基因传给下一代。随着时间的推移，这会导致适应，最终形成新物种。
Evidence for evolution comes from fossils, which show how species have changed, and from comparing DNA and anatomical structures. The fossil record demonstrates a progression from simpler to more complex organisms.
进化的证据来自化石（显示物种如何变化）以及 DNA 和解剖结构的比较。化石记录展现了从简单生物到更复杂生物的演变过程。
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