📚 IGCSE CCEA Science: Human Body – Key Exam Topics | IGCSE CCEA 科学：人体 考点精讲
The human body is a remarkable collection of interacting systems, each with specialised structures that enable life processes. For IGCSE CCEA Science, you need to master the key organs, tissues, and physiological mechanisms — from digestion and circulation to neural control and reproduction. This revision guide breaks down every major body system into clear, exam-focused explanations, ensuring you understand both the 'what' and the 'why'.
人体是一个由相互作用系统组成的精妙集合，每个系统都具有特化的结构以维持生命过程。针对 IGCSE CCEA 科学考试，你需要掌握关键器官、组织和生理机制——从消化、循环到神经控制和生殖。本复习指南将每一个人体主要系统拆解为清晰、紧扣考点的解释，确保你既理解“是什么”也理解“为什么”。
1. Levels of Organisation | 组织层次
Living organisms are built from progressively complex levels. The basic unit is the cell; specialised cells carrying out particular functions group together to form a tissue. Different tissues work together to form an organ, and several organs cooperate in an organ system. Finally, all the organ systems together make up the entire organism.
生物体由逐级复杂的层次构成。基本单位是细胞；执行特定功能的特化细胞聚集在一起形成组织。不同组织共同工作形成器官，而多个器官合作构成器官系统。最终，所有器官系统共同组成整个生物体。
For example, the stomach is an organ containing muscle tissue (to churn food), glandular epithelial tissue (to secrete enzymes and acid) and connective tissue (to hold it together). The stomach is part of the digestive system.
例如，胃是一个器官，包含肌肉组织（用于搅拌食物）、腺上皮组织（分泌酶和酸）以及结缔组织（将其固定在一起）。胃是消化系统的一部分。
d by asking you to arrange structures in order: cell → tissue → organ → system → organism.
组织层次常考题型是要求你按顺序排列结构：细胞 → 组织 → 器官 → 系统 → 生物体。
2. Digestion and Enzymes | 消化与酶
Physical digestion begins in the mouth with teeth breaking food into smaller pieces, increasing surface area for enzyme action. Chemical digestion then takes over: salivary amylase starts breaking down starch into maltose.
物理消化从口腔开始，牙齿将食物粉碎成更小的颗粒，增加酶作用的表面积。然后化学消化接替进行：唾液淀粉酶开始将淀粉分解为麦芽糖。
In the stomach, gastric juice (containing hydrochloric acid and pepsin) provides an acidic optimum pH for pepsin to break proteins into polypeptides. The acid also kills many bacteria.
在胃中，胃液（含有盐酸和胃蛋白酶）为胃蛋白酶提供了酸性最适pH，将蛋白质分解为多肽。胃酸还能杀灭许多细菌。
The small intestine receives pancreatic juice and bile. Pancreatic amylase continues starch digestion; trypsin (a protease) breaks proteins into peptides; lipase digests fats into fatty acids and glycerol. Bile, produced by the liver and stored in the gall bladder, emulsifies fats into tiny droplets, greatly increasing the surface area for lipase to work.
小肠接收胰液和胆汁。胰淀粉酶继续消化淀粉；胰蛋白酶（一种蛋白酶）将蛋白质分解为肽；脂肪酶将脂肪分解为脂肪酸和甘油。由肝脏产生、储存在胆囊中的胆汁将脂肪乳化成微小液滴，极大地增加了脂肪酶作用的表面积。
The end products of digestion are small, soluble molecules: glucose (from carbohydrates), amino acids (from proteins), fatty acids and glycerol (from fats). Absorption occurs in the ileum, where the lining is folded into villi. Villi have a very large surface area, a thin epithelium (one cell thick) and a rich network of blood capillaries, which absorb glucose and amino acids. Fatty acids and glycerol enter the lacteal (lymph vessel), eventually reaching the bloodstream.
消化的最终产物是小的、可溶性分子：葡萄糖（来自碳水化合物）、氨基酸（来自蛋白质）、脂肪酸和甘油（来自脂肪）。吸收发生在回肠，其内壁折叠成绒毛。绒毛具有很大的表面积、单细胞厚的薄上皮以及丰富的毛细血管网，用于吸收葡萄糖和氨基酸。脂肪酸和甘油进入乳糜管（淋巴管），最终进入血液。
Enzymes are proteins that act as biological catalysts, lowering activation energy. Each enzyme has an active site specific to its substrate. Temperature and pH affect enzyme activity: each enzyme has an optimum temperature (around 37 °C in humans) and an optimum pH. Extremes in temperature or pH denature the enzyme, changing the shape of the active site permanently so the substrate can no longer bind.
酶是充当生物催化剂的蛋白质，可降低活化能。每种酶的活性部位对其底物具有特异性。温度和pH会影响酶活性：每种酶都有最适温度（人体内约37 °C）和最适pH。极端温度或pH会使酶变性，永久改变活性部位的形状，使底物不能再结合。
3. The Heart and Circulation | 心脏与循环
The heart is a muscular organ that pumps blood around the body in a double circulatory system. 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). This separation keeps oxygen-rich blood at high pressure for efficient delivery to tissues.
心脏是一个肌肉器官，通过双循环系统将血液泵送至全身。右侧将缺氧血泵至肺部（肺循环），左侧将含氧血泵至身体其余部分（体循环）。这种分隔使富氧血液保持高压，以高效输送至组织。
The heart has four chambers: right atrium, right ventricle, left atrium and left ventricle. Valves (tricuspid, bicuspid, semi-lunar) prevent backflow of blood. The cardiac muscle of the ventricles is much thicker on the left side because it must generate higher pressure to push blood through the entire systemic circuit.
心脏有四个腔室：右心房、右心室、左心房和左心室。瓣膜（三尖瓣、二尖瓣、半月瓣）防止血液倒流。左心室的心肌比右侧厚得多，因为它必须产生更高的压力将血液泵入整个体循环。
Heart rate is controlled by a pacemaker (sinoatrial node) in the right atrium. A formula you may need to use relates cardiac output, heart rate and stroke volume:
心率由位于右心房的起搏点（窦房结）控制。你可能需要运用一个关于心输出量、心率和每搏输出量的公式：
Cardiac Output (cm³/min) = Heart Rate (bpm) × Stroke Volume (cm³)
The three main types of blood vessels differ in structure to suit their function.
三种主要血管在结构上不同以适应其功能。
| Feature | Artery | Vein | Capillary |
|---|---|---|---|
| Wall | Thick, muscular, elastic | Thinner, less muscular, less elastic | One cell thick (endothelium only) |
| Valves | None (except at base of aorta and pulmonary artery) | Present to prevent backflow | None |
| Lumen | Relatively narrow | Wide | Very narrow (about 1 red blood cell wide) |
| Blood pressure | High | Low | Falling |
| Function | Carry blood away from heart | Carry blood toward heart | Exchange of gases, nutrients and waste |
Arteries withstand high pressure and stretch during ventricular contraction, then recoil to maintain blood flow. Veins contain valves to ensure blood returns to the heart against gravity, and muscle contraction in limbs helps push blood along. Capillaries have very thin walls to minimise diffusion distance, enabling efficient exchange in tissues.
动脉能承受高压并在心室收缩时扩张，然后回弹以维持血流。静脉含有瓣膜以确保血液抵抗重力返回心脏，肢体肌肉的收缩也有助于推动血液。毛细血管的壁极薄，可最大程度缩短扩散距离，从而实现高效的组织交换。
4. Blood and Its Components | 血液及其成分
Blood is a tissue consisting of plasma and three main types of cells: red blood cells (erythrocytes), white blood cells (leucocytes) and platelets (thrombocytes).
血液是一种组织，由血浆和三种主要细胞组成：红细胞（红血球）、白细胞（白血球）和血小板（凝血细胞）。
Red blood cells are biconcave discs with no nucleus, packed with the red pigment haemoglobin. Haemoglobin binds oxygen in the lungs to form oxyhaemoglobin and releases it in respiring tissues. The biconcave shape gives a high surface area to volume ratio for rapid oxygen diffusion.
红细胞是无核的双凹盘状细胞，充满红色色素血红蛋白。血红蛋白在肺中与氧结合形成氧合血红蛋白，并在进行呼吸的组织中释放氧气。双凹形状提供了高表面积体积比，有利于氧气的快速扩散。
White blood cells are larger, have a nucleus and are part of the immune system. Phagocytes engulf and digest pathogens by phagocytosis. Lymphocytes produce antibodies that bind to specific antigens on pathogens, marking them for destruction or neutralising toxins.
白细胞较大，有核，是免疫系统的一部分。吞噬细胞通过吞噬作用吞噬并消化病原体。淋巴细胞产生抗体，与病原体上的特定抗原结合，标记它们以便消灭或中和毒素。
Platelets are small cell fragments that help with blood clotting. At a wound, platelets release chemicals that convert the soluble plasma protein fibrinogen into insoluble fibrin threads, forming a mesh that traps blood cells and forms a clot to prevent blood loss and entry of pathogens.
血小板是小的细胞碎片，有助于血液凝固。在伤口处，血小板释放化学物质，将可溶性血浆蛋白纤维蛋白原转化为不溶性的纤维蛋白丝，形成网络捕获血细胞，形成凝块以防止失血和病原体侵入。
Plasma is the liquid part of blood (about 55%), composed mostly of water. It transports red and white blood cells, platelets, dissolved nutrients (glucose, amino acids, vitamins), carbon dioxide, urea, hormones and heat around the body.
血浆是血液的液体部分（约占55%），主要由水组成。它将红细胞、白细胞、血小板以及溶解的营养物质（葡萄糖、氨基酸、维生素）、二氧化碳、尿素、激素和热量运输到全身。
5. The Respiratory System and Gas Exchange | 呼吸系统与气体交换
The respiratory system includes the nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles and alveoli. Its primary function is to bring air into close contact with blood so that oxygen can diffuse in and carbon dioxide can diffuse out.
呼吸系统包括鼻腔、咽、喉、气管、支气管、细支气管和肺泡。其主要功能是使空气与血液紧密接触，以便氧气可扩散进入，二氧化碳可扩散排出。
The trachea and bronchi are kept open by C-shaped rings of cartilage. They are lined with ciliated epithelial cells and goblet cells that secrete mucus. The mucus traps dust and pathogens, and the cilia beat rhythmically to sweep the mucus up towards the throat, where it is swallowed.
气管和支气管由C形软骨环保持通畅。其内壁衬有纤毛上皮细胞和分泌黏液的杯状细胞。黏液捕获灰尘和病原体，纤毛有节律地摆动，将黏液向上推送至喉部，然后被咽下。
Alveoli are tiny air sacs at the ends of bronchioles, each surrounded by a network of blood capillaries. Gas exchange takes place by diffusion. The alveoli are adapted by having a very large total surface area, moist, thin walls (one cell thick alveolar epithelium and one cell thick capillary endothelium), and a steep concentration gradient maintained by ventilation and blood flow.
肺泡是细支气管末端的微小气囊，每个肺泡周围都环绕着毛细血管网。气体交换通过扩散进行。肺泡具有诸多适应性特征：极大的总表面积、湿润且极薄的壁（单细胞厚的肺泡上皮和单细胞厚的毛细血管内皮），以及通过通气和血流维持的陡峭浓度梯度。
Inspiration (breathing in) is an active process: the diaphragm contracts and flattens, the external intercostal muscles contract, raising the ribcage up and out. The volume of the thorax increases, pressure decreases below atmospheric pressure, and air rushes in. Expiration at rest is largely passive: the diaphragm and intercostal muscles relax, the ribcage moves down and in, volume decreases, pressure increases, and air flows out.
吸气是一个主动过程：膈肌收缩变平，外肋间肌收缩，使胸廓向上向外抬高。胸腔容积增大，压力降至低于大气压，空气涌入。安静状态下的呼气主要是被动的：膈肌和肋间肌松弛，胸廓向下向内移动，容积减小，压力升高，空气流出。
6. Cellular Respiration | 细胞呼吸
Respiration is the process by which cells release energy from organic molecules, usually glucose. It is not the same as breathing. The energy released is used to synthesise ATP, which powers processes such as muscle contraction, active transport and protein synthesis.
呼吸作用是细胞从有机分子（通常是葡萄糖）中释放能量的过程，它不同于“呼吸”的动作。释放的能量用于合成ATP，驱动肌肉收缩、主动运输和蛋白质合成等过程。
Aerobic respiration uses oxygen and fully breaks down glucose into carbon dioxide and water, releasing a large amount of energy. The balanced chemical equation is:
有氧呼吸利用氧气，将葡萄糖完全分解为二氧化碳和水，释放大量能量。配平的化学方程式为：
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy as ATP)
In the absence of oxygen, many cells can respire anaerobically to produce a little energy quickly. In human muscle cells during vigorous exercise, glucose is converted to lactic acid:
在缺氧的情况下，许多细胞可以进行无氧呼吸，迅速产生少量能量。在剧烈运动中，人体肌肉细胞将葡萄糖转化为乳酸：
C₆H₁₂O₆ → 2C₃H₆O₃ + energy
Lactic acid builds up in muscles, causing fatigue and pain; it is later oxid
Published by TutorHao | IGCSE Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图