📚 Year 8 Edexcel Biology: Core Knowledge Summary | Year 8 Edexcel 生物：核心知识点梳理
Welcome to your essential guide for Year 8 Edexcel Biology. This article brings together the most important topics you will encounter, from the tiny structures inside cells to the large-scale interactions in ecosystems. Use this summary to reinforce your understanding, clarify difficult concepts, and prepare confidently for your assessments.
欢迎来到 Year 8 Edexcel 生物的核心指南。本文汇集了你将遇到的最重要主题，从细胞内部的微小结构到生态系统中的大规模相互作用。通过这份总结，你可以巩固理解、厘清难懂的概念，并为评估做好充分准备。
1. Cells: The Building Blocks of Life | 细胞：生命的构建块
All living organisms are made of cells. Animal cells contain a nucleus that controls the cell's activities, cytoplasm where chemical reactions take place, a cell membrane that controls the movement of substances, and mitochondria that release energy through respiration. Plant cells have all these parts plus a rigid cell wall made of cellulose, a large permanent vacuole filled with cell sap, and chloroplasts that absorb light for photosynthesis.
所有生物体都由细胞构成。动物细胞包含控制细胞活动的细胞核、发生化学反应的细胞质、控制物质进出的细胞膜，以及通过呼吸作用释放能量的线粒体。植物细胞除了上述结构外，还有由纤维素构成的坚硬细胞壁、充满细胞液的大液泡，以及吸收光能进行光合作用的叶绿体。
Some organisms, like bacteria, are unicellular – they exist as a single cell. Others, like humans and oak trees, are multicellular. In multicellular organisms, cells become specialised to perform particular jobs. For example, red blood cells have no nucleus and are biconcave to carry more oxygen; nerve cells are long and thin to transmit electrical signals; root hair cells have a large surface area to absorb water from the soil.
有些生物，如细菌，是单细胞的——它们以单个细胞的形式存在。其他生物，如人类和橡树，是多细胞的。在多细胞生物中，细胞会特化以执行特定功能。例如，红细胞没有细胞核且呈双凹圆盘状，以便携带更多氧气；神经细胞细长，能传递电信号；根毛细胞具有很大的表面积，可以从土壤中吸收水分。
2. Levels of Organisation: Tissues, Organs and Systems | 组织层次：组织、器官和系统
In multicellular organisms, cells do not work alone. A group of similar cells working together to perform a shared function forms a tissue. For instance, muscle tissue is made of muscle cells that contract to bring about movement. Xylem tissue in plants consists of hollow tubes that transport water and minerals upwards from the roots.
在多细胞生物中，细胞并非单独工作。一组相似细胞共同执行相同功能形成组织。例如，肌肉组织由肌肉细胞组成，可以收缩产生运动。植物中的木质部组织由中空的管道构成，能将水和矿物质从根部向上运输。
Different tissues combine to form an organ. The stomach is an organ that contains muscular tissue to churn food, glandular tissue to produce digestive juices, and epithelial tissue to line its inner surface. In plants, a leaf is an organ made up of epidermis, palisade mesophyll, spongy mesophyll, and vascular tissues.
不同的组织组合形成器官。胃是一个器官，包含用于搅拌食物的肌肉组织、产生消化液的腺体组织以及覆盖内表面的上皮组织。在植物中，叶子是一个器官，由表皮、栅栏组织、海绵组织和维管组织组成。
Organs work together in organ systems. The digestive system includes the mouth, oesophagus, stomach, liver, pancreas, small intestine and large intestine. The circulatory system consists of the heart, blood vessels and blood. Each system depends on others to keep the organism alive and healthy.
器官协同工作构成器官系统。消化系统包括口腔、食道、胃、肝脏、胰腺、小肠和大肠。循环系统由心脏、血管和血液组成。每个系统都相互依赖，共同维持生物体的生存和健康。
3. The Digestive System: Breaking Down Food | 消化系统：分解食物
The food we eat contains large, insoluble molecules that cannot be absorbed directly into the blood. Digestion is the process of breaking these large molecules into smaller, soluble ones. Mechanical digestion begins in the mouth, where teeth chew and grind food. Saliva adds amylase, an enzyme that starts breaking down starch into sugar.
我们吃的食物含有大而不溶的分子，无法直接吸收到血液中。消化就是将这些大分子分解为可溶的小分子的过程。物理性消化从口腔开始，牙齿咀嚼和研磨食物。唾液中含有淀粉酶，这种酶开始将淀粉分解为糖。
In the stomach, food mixes with hydrochloric acid and protease enzymes. The acid kills harmful bacteria and provides the right pH for protease to break proteins into amino acids. The churning action of the stomach walls turns food into a creamy liquid called chyme.
在胃中，食物与盐酸和蛋白酶混合。胃酸杀死有害细菌，并为蛋白酶提供适宜的pH环境，将蛋白质分解为氨基酸。胃壁的搅拌作用使食物变成奶油状的食糜。
Most chemical digestion occurs in the small intestine. Here, enzymes from the pancreas and the intestinal wall complete the breakdown of carbohydrates into simple sugars, proteins into amino acids, and lipids into fatty acids and glycerol. Bile, produced by the liver and stored in the gall bladder, neutralises stomach acid and emulsifies fats, giving enzymes a larger surface area to work on. The small intestine then absorbs these small, soluble products through its walls into the bloodstream.
大部分化学消化发生在小肠。在这里，来自胰腺和小肠壁的酶将碳水化合物彻底分解为单糖，蛋白质分解为氨基酸，脂质分解为脂肪酸和甘油。由肝脏分泌、胆囊储存的胆汁能中和胃酸并乳化脂肪，为酶提供更大的作用表面积。然后，小肠壁将这些可溶的小分子产物吸收进入血液。
4. The Circulatory System and Blood | 循环系统与血液
The circulatory system transports substances around the body. 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. This double circulation ensures efficient delivery of oxygen and removal of carbon dioxide.
循环系统将物质输送到全身。心脏是一个双重泵：右侧将缺氧血泵送到肺部，左侧将富氧血泵送到身体其他部位。这种双循环确保了氧气的有效输送和二氧化碳的排出。
Blood is a tissue consisting of four main components. Red blood cells carry oxygen using haemoglobin. White blood cells fight infection as part of the immune system. Platelets are tiny cell fragments that help blood clot to prevent excessive bleeding. Plasma is the straw-coloured liquid that transports dissolved nutrients, hormones, carbon dioxide, and urea.
血液是一种组织，由四种主要成分组成。红细胞利用血红蛋白携带氧气。白细胞作为免疫系统的一部分抵御感染。血小板是微小的细胞碎片，帮助血液凝固以防止过度出血。血浆是淡黄色的液体，运输溶解的营养物质、激素、二氧化碳和尿素。
Arteries carry blood away from the heart under high pressure and have thick, muscular walls. Veins carry blood back to the heart at lower pressure and contain valves to prevent backflow. Capillaries are tiny, thin-walled vessels where materials are exchanged between the blood and body cells.
动脉在高压下将血液从心脏运出，管壁厚且有肌肉层。静脉在较低压力下将血液送回心脏，管内有瓣膜防止倒流。毛细血管是微小且壁薄的血管，是血液与体细胞进行物质交换的场所。
5. Breathing and Gas Exchange | 呼吸与气体交换
Breathing is the mechanical process of moving air into and out of the lungs. Gas exchange is the diffusion of oxygen from the air into the blood and of carbon dioxide from the blood into the air. This occurs in the alveoli, tiny air sacs at the ends of the bronchioles.
呼吸是空气进出肺部的机械过程。气体交换是指氧气从空气扩散到血液中，以及二氧化碳从血液扩散到空气中的过程。这发生在肺泡中，即细支气管末端的微小气囊。
When you inhale, the diaphragm contracts and flattens, while the intercostal muscles pull the rib cage up and out. This increases the volume of the chest cavity, lowering the pressure and drawing air in. When you exhale, these muscles relax, the diaphragm rises, the rib cage moves down and in, and air is forced out.
吸气时，膈肌收缩并变平，肋间肌将肋骨向上向外拉起。这增加了胸腔容积，降低了压力，将空气吸入。呼气时，这些肌肉放松，膈肌上升，肋骨向下向内移动，空气被挤出。
Alveoli are adapted for efficient gas exchange: they have very thin walls (just one cell thick), a large total surface area, a rich supply of blood capillaries, and a moist lining. Oxygen diffuses from a high concentration in the alveoli to a low concentration in the blood; carbon dioxide diffuses in the opposite direction.
肺泡的结构非常适合高效气体交换：它们有非常薄的壁（仅一个细胞厚），巨大的总表面积，丰富的毛细血管供应，以及湿润的内壁。氧气从肺泡中的高浓度区域扩散到血液中的低浓度区域；二氧化碳则沿相反方向扩散。
6. Respiration: Releasing Energy | 呼吸作用：释放能量
Respiration is a chemical reaction that happens in every living cell to release energy from glucose. It is not the same as breathing. The energy released is used for muscle contraction, maintaining a constant body temperature, building larger molecules, and active transport across cell membranes.
呼吸作用是每个活细胞中发生的化学反应，从葡萄糖中释放能量。它与呼吸（通气）不同。释放的能量用于肌肉收缩、维持恒定体温、构建大分子以及跨越细胞膜的主动运输。
ergy). In symbols: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy). Aerobic respiration takes place continuously in the mitochondria of plant and animal cells.
有氧呼吸利用氧气并释放大量能量。文字方程式为：葡萄糖 + 氧气 → 二氧化碳 + 水（+能量）。符号表示为：C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O（+能量）。有氧呼吸持续在植物和动物细胞的线粒体中进行。
he word equation is: glucose → lactic acid (+ some energy). This type of respiration releases much less energy and causes muscle fatigue. Anaerobic respiration in yeast produces ethanol and carbon dioxide, a process known as fermentation.
剧烈运动时，肌肉可能得不到足够的氧气进行有氧呼吸。这时，它们会转而进行无氧呼吸。文字方程式为：葡萄糖 → 乳酸（+少量能量）。这种呼吸方式释放的能量少得多，并导致肌肉疲劳。酵母的无氧呼吸产生乙醇和二氧化碳，这一过程称为发酵。
7. Photosynthesis: Making Food Using Light | 光合作用：利用光制造养分
Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesise nutrients from carbon dioxide and water. It takes place in the chloroplasts, which contain the green pigment chlorophyll that absorbs light energy. Oxygen is released as a by-product.
光合作用是绿色植物及某些其他生物利用阳光，以二氧化碳和水合成营养物质的过程。它发生在叶绿体中，叶绿体含有能吸收光能的绿色色素叶绿素。氧气作为副产品被释放。
requires light energy, which is trapped by chlorophyll. Glucose produced can be used immediately for respiration, converted into starch for storage, or turned into cellulose and other compounds for growth.
光合作用的总文字方程式为：二氧化碳 + 水 → 葡萄糖 + 氧气。用符号表示：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。该反应需要光能，光能被叶绿素捕获。产生的葡萄糖可以立即用于呼吸作用，转化为淀粉储存，或转变为纤维素和其他化合物用于生长。
Several factors affect the rate of photosynthesis: light intensity, carbon dioxide concentration, and temperature. The leaf is well adapted for photosynthesis; it is broad and flat to capture light, has stomata for gas exchange, and veins to supply water and remove glucose.
影响光合作用速率的因素有：光照强度、二氧化碳浓度和温度。叶片非常适合进行光合作用；它宽而平以捕捉光线，有气孔进行气体交换，有叶脉供应水分并运走葡萄糖。
8. Feeding Relationships: Food Chains | 取食关系：食物链
A food chain shows the feeding relationship between organisms and the transfer of energy from one organism to the next. It always begins with a producer, usually a green plant or alga that makes its own food through photosynthesis. The producer is eaten by a primary consumer (herbivore), which is then eaten by a secondary consumer (carnivore).
食物链显示了生物之间的取食关系以及能量从一个生物传递到下一个生物的过程。它总是从生产者开始，通常是绿色植物或藻类，它们通过光合作用制造自己的食物。生产者被初级消费者（植食动物）吃掉，然后又被次级消费者（肉食动物）吃掉。
arrows represent the direction of energy flow. All food chains have only three or four trophic levels because energy is lost at each stage, mainly through movement, respiration, heat, and waste materials. Predators and prey populations are often interdependent; changes in one population affect the numbers of the other.
例如：草 → 兔 → 狐狸。箭头表示能量流动的方向。所有食物链通常只有三到四个营养级，因为在每一阶段能量都会损失，主要通过运动、呼吸、热量和废物形式消耗。捕食者和猎物的种群数量常常相互依赖；一个种群数量的变化会影响另一个。
Decomposers, such as bacteria and fungi, break down dead organisms and waste materials, returning valuable nutrients to the soil. They are not usually shown in food chains, but they play a vital role in recycling matter within ecosystems.
分解者，如细菌和真菌，分解死亡的生物体和废物，将宝贵的营养物质归还土壤。它们通常不显示在食物链中，但在生态系统的物质循环中发挥着至关重要的作用。
9. Food Webs and Energy Transfer | 食物网与能量传递
In an ecosystem, most organisms eat more than one type of food and can be eaten by several different predators. A food web is a network of interconnected food chains that gives a more realistic picture of feeding relationships. It shows how energy passes through a community.
在生态系统中，大多数生物不止吃一种食物，也可能被几种不同的捕食者吃掉。食物网是由相互关联的食物链组成的网络，更真实地展示了取食关系。它显示了能量如何通过一个群落流动。
Energy transfer between trophic levels is inefficient. Typically, only about 10% of the energy is passed on to the next consumer. The rest is lost as heat, used in respiration, or remains undigested. This explains why there are rarely more than four or five trophic levels and why the number of organisms generally decreases at higher levels. You can represent this using pyramids of numbers or pyramids of biomass.
能量在营养级之间的传递效率很低。通常，只有大约10%的能量传递给下一级消费者。其余能量以热量形式散失、用于呼吸作用或未被消化。这就解释了为什么营养级很少超过四到五个，也解释了为什么生物的数量通常在较高营养级会减少。可以用数量金字塔或生物量金字塔来表示。
A pyramid of biomass is often more accurate because it considers the total mass of living material at each level, whereas a pyramid of numbers may be distorted if the producers are very large or very small. Both pyramids help ecologists understand the structure of an ecosystem.
生物量金字塔通常更为准确，因为它考虑的是每一级生物体的总质量，而数量金字塔在生产者体形巨大或极小时可能出现倒置。这两种金字塔都帮助生态学家理解生态系统的结构。
10. Human Reproduction: Creating New Life | 人类生殖：创造新生命
Reproduction ensures the continuation of a species. Humans reproduce sexually, requiring a male sex cell (sperm) and a female sex cell (ovum or egg). The male reproductive system includes the testes, which produce sperm and the hormone testosterone, and the penis, which delivers sperm into the female's body. Sperm are adapted for swimming with a long tail and contain enzymes to penetrate the egg.
生殖保证了物种的延续。人类进行有性生殖，需要雄性生殖细胞（精子）和雌性生殖细胞（卵子）。男性生殖系统包括产生精子和睾酮激素的睾丸，以及将精子送入女性体内的阴茎。精子适应游动，有长长的尾巴，并含有穿透卵子的酶。
The female reproductive system includes the ovaries, which release eggs and produce oestrogen, the oviducts (fallopian tubes) where fertilisation occurs, the uterus where the baby develops, and the vagina. After intercourse, millions of sperm are released, but only one may successfully fertilise the egg. The fertilised egg, or zygote, implants into the uterus lining and begins to divide and grow.
女性生殖系统包括释放卵子并分泌雌激素的卵巢、发生受精的输卵管（输卵管道）、胎儿发育的子宫，以及阴道。性交后，数百万精子被释放，但只有一个可能成功与卵子结合。受精卵（合子）植入子宫内膜，开始分裂和生长。
The placenta forms within the uterus, allowing the exchange of oxygen, nutrients and waste between mother and foetus without their blood mixing. The amniotic sac surrounds and protects the developing embryo. During birth, the cervix dilates and muscular contractions push the baby out.
胎盘在子宫内形成，允许母体和胎儿之间进行氧气、营养物质和废物的交换，而两者的血液并不混合。羊膜囊包围并保护发育中的胚胎。分娩时，宫颈扩张，肌肉收缩将婴儿推出。
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