📚 Year 8 Cambridge Biology: Core Knowledge Overview | Year 8 剑桥生物：核心知识点梳理
In Year 8 Cambridge Biology, you start to explore how living organisms are built from cells and how these units work together to form systems that keep you alive, from digestion to circulation and reproduction. You also begin to examine the wider living world, including how organisms interact in ecosystems, why variation matters, and how microorganisms can be both helpful and harmful. This article brings together all the core knowledge you need, with clear explanations paired in English and Chinese to support bilingual learning.
在 Year 8 剑桥生物课程中，你将逐步探索生物体如何由细胞构成，以及这些基本单位如何协同工作，形成维持生命活动的系统，如消化、循环和生殖。你还将开始审视更广阔的生物世界，包括生物在生态系统中的相互作用、变异的重要性，以及微生物的益处与危害。本文汇集了所有核心知识点，并提供中英双语对照讲解，帮助你更好地理解和记忆。
1. Cells and Organ Systems | 细胞与器官系统
All living organisms are made of cells. Animal cells contain a cell membrane, cytoplasm, and a nucleus. Plant cells have these three parts as well as a cell wall, a large permanent vacuole, and often chloroplasts. The nucleus controls the cell's activities, the cytoplasm is where most chemical reactions occur, and the cell membrane controls what enters and exits the cell. In plants, the cell wall provides structural support, chloroplasts are the sites of photosynthesis, and the vacuole stores cell sap and helps maintain turgor.
所有生物体都由细胞构成。动物细胞包括细胞膜、细胞质和细胞核。植物细胞除了这三者外，还有细胞壁、一个大的中央液泡，并通常含有叶绿体。细胞核控制细胞活动，细胞质是大多数化学反应发生的场所，细胞膜控制物质进出。在植物中，细胞壁提供结构支撑，叶绿体是光合作用的发生场所，液泡储存细胞液并帮助维持细胞膨压。
| Part / 细胞结构 | Animal Cell / 动物细胞 | Plant Cell / 植物细胞 |
|---|---|---|
| Nucleus / 细胞核 | ✓ | ✓ |
| Cytoplasm / 细胞质 | ✓ | ✓ |
| Cell membrane / 细胞膜 | ✓ | ✓ |
| Cell wall / 细胞壁 | ✗ | ✓ |
| Chloroplasts / 叶绿体 | ✗ | ✓ |
| Large vacuole / 大液泡 | ✗ | ✓ |
Cells of similar type work together to form tissues, tissues form organs, and organs work together in organ systems. For example, muscle cells form muscle tissue, which makes up the heart – an organ – which belongs to the circulatory system. Understanding this hierarchy helps you see how the body coordinates functions like movement, nutrition, and gas exchange.
相似类型的细胞共同构成组织，组织形成器官，器官再协同工作构成器官系统。例如，肌细胞构成肌肉组织，肌肉组织构成心脏这一器官，心脏属于循环系统。理解这一层级关系，有助于你认识身体如何协调运动、营养和气体交换等功能。
2. The Digestive System and Nutrition | 消化系统与营养
The digestive system breaks down large, insoluble food molecules into small, soluble ones that can be absorbed into the blood. Food travels from the mouth, down the oesophagus, to the stomach where acid and enzymes begin protein digestion. In the small intestine, food is mixed with digestive enzymes from the pancreas and bile from the liver. Bile neutralises stomach acid and emulsifies fats, while enzymes complete the breakdown. The inner wall of the small intestine is covered with millions of tiny villi, which increase the surface area for efficient absorption of nutrients into the bloodstream.
消化系统将大分子、不溶性的食物分解成小分子、可溶性物质，以便被吸收进入血液。食物从口腔经食道进入胃，胃酸和酶在此开始消化蛋白质。在小肠中，食物与来自胰腺的消化酶以及肝脏分泌的胆汁混合。胆汁能中和胃酸并乳化脂肪，酶则最终完成分解。小肠内壁覆盖着数百万个微小的绒毛，大大增加了吸收营养物质进入血液的表面积。
Enzymes are biological catalysts that speed up digestion without being used up. Amylase breaks down starch into sugars, protease breaks down proteins into amino acids, and lipase breaks down fats into fatty acids and glycerol. A balanced diet, containing carbohydrates, proteins, fats, vitamins, minerals, fibre, and water, provides the energy and raw materials needed for growth and repair.
酶是生物催化剂，能加速消化过程而自身不被消耗。淀粉酶将淀粉分解为糖，蛋白酶将蛋白质分解为氨基酸，脂肪酶将脂肪分解为脂肪酸和甘油。包含碳水化合物、蛋白质、脂肪、维生素、矿物质、膳食纤维和水在内的均衡饮食，为生长和修复提供所需的能量和原材料。
3. Gas Exchange and Breathing | 气体交换与呼吸
Breathing involves the movement of air into and out of the lungs. During inhalation, the diaphragm contracts and flattens, while the intercostal muscles raise the ribcage, increasing the volume of the chest cavity and drawing air in. During exhalation, the diaphragm and intercostal muscles relax, reducing chest volume and pushing air out. Gas exchange happens in the alveoli, tiny air sacs in the lungs surrounded by capillaries.
呼吸涉及空气进出肺部的运动。吸气时，膈肌收缩变平，肋间肌上提肋骨，胸腔容积增大，空气被吸入；呼气时，膈肌和肋间肌放松，胸腔容积减小，空气被排出。气体交换发生在肺泡中，肺泡是肺部被毛细血管包围的微小气囊。
Oxygen diffuses from the alveoli into the blood, where it binds to haemoglobin in red blood cells. Carbon dioxide diffuses from the blood into the alveoli to be breathed out. The process of aerobic respiration, which releases energy from glucose, is summarised by the word equation:
氧气从肺泡扩散进入血液，与红细胞中的血红蛋白结合；二氧化碳则从血液扩散至肺泡，被呼出体外。有氧呼吸从葡萄糖中释放能量，其文字方程式概括如下：
C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + energy
Smoking damages the cilia in the airways, allowing mucus and pathogens to accumulate, and can lead to diseases such as emphysema and lung cancer. It also reduces the oxygen-carrying capacity of the blood due to carbon monoxide poisoning.
吸烟会损害呼吸道中的纤毛，导致黏液和病原体积聚，并可能引发肺气肿和肺癌等疾病。香烟中的一氧化碳还会降低血液的携氧能力。
4. The Circulatory System | 循环系统
The human circulatory system consists of the heart, blood vessels, and blood. The heart is a double pump: the right side pumps deoxygenated blood to the lungs, while the left side pumps oxygenated blood to the rest of the body. Valves inside the heart prevent backflow of blood. Arteries carry blood away from the heart under high pressure and have thick, elastic walls. Veins return blood to the heart and contain valves to prevent backflow. Capillaries are tiny vessels where exchange of gases, nutrients, and waste occurs.
人体循环系统由心脏、血管和血液组成。心脏是一个双泵：右侧将缺氧血泵至肺部，左侧将富氧血泵送至全身各处。心脏内的瓣膜防止血液倒流。动脉将血液从心脏输出，承受较高压力，管壁厚而有弹性；静脉将血液送回心脏，内含瓣膜防止倒流；毛细血管是极细的血管，是气体、营养物质和废物交换的场所。
Blood is composed of plasma, red blood cells, white blood cells, and platelets. Plasma transports dissolved substances such as glucose, urea, and hormones. Red blood cells, which contain haemoglobin, carry oxygen. White blood cells defend the body against pathogens, and platelets are involved in blood clotting.
血液由血浆、红细胞、白细胞和血小板组成。血浆运输葡萄糖、尿素和激素等溶解物质；红细胞含有血红蛋白，负责运输氧气；白细胞抵御病原体入侵；血小板参与凝血过程。
5. Human Reproduction | 人类生殖
The male reproductive system includes the testes, which produce sperm and the hormone testosterone, the sperm ducts, and the penis. The female reproductive system includes the ovaries, which release eggs and produce oestrogen, the oviducts (fallopian tubes), the uterus, and the vagina. Fertilisation occurs when a sperm nucleus fuses with an egg nucleus in an oviduct, forming a zygote.
男性生殖系统包括睾丸（产生精子和雄性激素睾酮）、输精管和阴茎。女性生殖系统包括卵巢（释放卵子并分泌雌激素）、输卵管、子宫和阴道。精子与卵子在输卵管中结合，完成受精，形成受精卵。
The zygote divides repeatedly as it travels to the uterus, becoming an embryo that implants into the uterine lining. The embryo develops into a fetus, surrounded by amniotic fluid that protects it. The placenta allows the exchange of nutrients, oxygen, and waste between the mother and fetus without mixing their blood. During puberty, hormonal changes trigger the development of secondary sexual characteristics.
受精卵在移向子宫的过程中不断分裂，形成胚胎并植入子宫内膜。胚胎发育为胎儿，被羊水保护。胎盘负责母亲与胎儿之间营养物质、氧气和废物的交换，但双方血液并不混合。青春期激素变化会引发第二性征的发育。
6. Plant Reproduction | 植物生殖
Flowers are the reproductive structures of many plants. The male part, the stamen, consists of the anther (which produces pollen) and the filament. The female part, the carpel, consists of the stigma, style, and ovary, which contains ovules. Pollination is the transfer of pollen from the anther to the stigma. This can be carried out by wind, insects, or other animals.
花是许多植物的生殖结构。雄性部分为雄蕊，由花药（产生花粉）和花丝组成；雌性部分为雌蕊，由柱头、花柱和含有胚珠的子房组成。传粉是花粉从花药传播到柱头上的过程，可借助风、昆虫或其他动物完成。
After pollination, a pollen tube grows down the style to deliver the male nucleus to the ovule, where fertilisation takes place. The fertilised ovule develops into a seed, and the ovary becomes a fruit. Seeds are dispersed in various ways – by wind, water, animals, or explosive mechanisms – to reduce competition with the parent plant.
传粉后，花粉管沿花柱向下生长，将雄配子送入胚珠，完成受精。受精的胚珠发育成种子，子房则发育成果实。种子通过风、水、动物或爆裂等方式传播，以减小与母体植株的竞争。
7. Ecosystems and Adaptations | 生态系统与适应
An ecosystem is made up of all the living organisms in an area interacting with each other and with their non-living environment. Energy enters most ecosystems through photosynthesis by producers (green plants). Food chains show the feeding relationships, starting with a producer, followed by primary, secondary, and tertiary consumers, and ending with decomposers. Food webs represent the interconnected food chains in a habitat.
生态系统由某一区域内所有生物及其与非生物环境的相互作用构成。在大多数生态系统中，能量通过生产者（绿色植物）的光合作用进入。食物链显示取食关系，从生产者开始，然后是初级消费者、次级消费者和三级消费者，并以分解者结束。食物网则表示一个栖息地中相互关联的食物链。
Organisms have adaptations that help them survive in their habitats. A camel, for example, has long eyelashes to keep out sand, humps that store fat as an energy reserve, and wide feet for walking on desert sand. Cacti have thick, waxy stems to reduce water loss, spines instead of leaves, and extensive shallow roots to absorb water quickly after rain.
生物体具有适应其特征，帮助它们在栖息地中生存。例如，骆驼有长睫毛阻挡风沙，驼峰储存脂肪作为能量储备，宽大的足便于在沙漠中行走；仙人掌具厚而蜡质的茎以减少水分流失，叶子退化为刺，并有广泛的浅层根系以便雨后迅速吸水。
8. Variation and Classification | 变异与分类
Differences between individuals of the same species are called variation. Some variation is inherited (genetic), such as eye colour or blood group, while some is environmental, such as language spoken or scars. Variation can be continuous, where characteristics can take any value within a range (e.g., height), or discontinuous, where characteristics fall into distinct categories (e.g., tongue rolling ability).
同一物种个体间的差异称为变异。有些变异是遗传的（基因决定），如眼睛颜色或血型；有些则是环境的，如所说的语言或伤疤。变异可以是连续的，即性状在一定范围内可取任意值（如身高），也可以是不连续的，即性状属于明确分类（如卷舌能力）。
Natural selection can lead to changes in the inherited characteristics of a population over time. Classification organises living organisms into groups based on shared features. Vertebrates, for example, are divided into five main classes: fish, amphibians, reptiles, birds, and mammals. Each class has distinct characteristics, such as birds having feathers and laying hard-shelled eggs, while mammals have fur or hair and produce milk for their young.
自然选择可导致种群可遗传特征随时间的推移发生变化。分类是根据共同特征将生物体归类分组。例如，脊椎动物分为五大类：鱼类、两栖动物、爬行动物、鸟类和哺乳动物。每一类都有独特的特征，如鸟类有羽毛并产硬壳卵，哺乳动物具皮毛并能泌乳喂养后代。
9. Microorganisms and Disease | 微生物与疾病
Microorganisms, or microbes, are tiny living things that can only be seen under a microscope. The main groups are bacteria, viruses, and fungi. Bacteria are single-celled organisms with no nucleus; some are harmful, causing diseases like cholera and tuberculosis, but many are essential decomposers. Viruses are even smaller and can only reproduce inside living cells, causing diseases such as influenza and COVID-19. Fungi include yeasts and moulds; some are useful in bread and cheese making, while others can cause infections like athlete's foot.
微生物是需借助显微镜才能看到的微小生物，主要包括细菌、病毒和真菌。细菌是没有细胞核的单细胞生物，部分有害，能引起霍乱和肺结核等疾病，但许多是重要的分解者。病毒更小，只能在活细胞内繁殖，导致流感、COVID-19等疾病。真菌包括酵母菌和霉菌，一些可用于面包和奶酪制作，另一些则会引起足癣等感染。
The body has several defence mechanisms against pathogens: the skin acts as a barrier, mucus traps microbes, and white blood cells can engulf or produce antibodies against them. Vaccination helps the immune system recognise and destroy specific pathogens by exposing the body to a harmless version, building memory cells for faster response upon real infection.
人体具备多种抵御病原体的防御机制：皮肤作为屏障，黏液可捕获微生物，白细胞能吞噬它们或产生相应抗体。疫苗接种通过将无害版本的病原体引入体内，帮助免疫系统识别并摧毁特定的病原体，同时产生记忆细胞，以便在真正感染时能快速反应。
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