📚 Breathing and Gas Exchange | 呼吸与气体交换
Breathing is the process of moving air into and out of the lungs. It supplies oxygen for respiration and removes carbon dioxide. In KS3 CIE science, you need to understand the organs involved, how ventilation works, and how gases are exchanged in the alveoli.
呼吸是将空气吸入和排出肺部的过程。它为呼吸作用提供氧气，并排出二氧化碳。在 KS3 CIE 科学中，你需要了解相关器官、通气机制以及肺泡内气体交换的方式。
1. Why We Breathe | 我们为什么呼吸
Every cell in your body needs energy to stay alive, grow and repair itself. This energy is released from nutrients such as glucose during a process called respiration.
身体中的每个细胞都需要能量来维持生命、生长和修复。这种能量是在一个叫做呼吸作用的过程中，从葡萄糖等营养物质中释放出来的。
Respiration uses oxygen and produces carbon dioxide as a waste product. Breathing brings in the oxygen and removes the carbon dioxide from the body.
呼吸作用消耗氧气并产生二氧化碳废气。呼吸将氧气带入体内，并将二氧化碳排出体外。
If oxygen supply stops for more than a few minutes, cells cannot release enough energy and can be damaged. This is why breathing is essential for life.
如果氧气供应停止超过几分钟，细胞就无法释放足够的能量并可能受损。这就是呼吸对生命至关重要的原因。
2. The Human Breathing System | 人体呼吸系统
The main organs of the human breathing system are the nose, trachea, bronchi, bronchioles, lungs and diaphragm.
人体呼吸系统的主要器官包括鼻子、气管、支气管、细支气管、肺和膈肌。
The trachea splits into two bronchi, one for each lung. Inside the lungs, the bronchi divide into smaller tubes called bronchioles, which end in tiny air sacs called alveoli.
气管分叉为两根支气管，分别连接左右肺。在肺内，支气管分成更小的细支气管，细支气管末端是微小的气囊，叫做肺泡。
The lungs are protected by the ribcage, and the diaphragm is a sheet of muscle that separates the chest cavity from the abdomen.
肺由胸廓保护，膈肌是一层将胸腔与腹腔分开的肌肉。
3. Pathway of Air | 空气的路径
Air enters through the nose or mouth, where it is warmed, moistened and filtered by hairs and mucus in the nasal passages.
空气通过鼻子或口腔进入，在鼻腔中被鼻毛和黏液加热、湿润并过滤。
The air then travels down the trachea, through the bronchi and bronchioles, and finally reaches the alveoli in the lungs.
然后空气向下经过气管、支气管和细支气管，最终到达肺内的肺泡。
The epiglottis is a flap of tissue that closes over the trachea when you swallow, preventing food and drink from entering the airways.
会厌是一块组织瓣，当你吞咽时会盖住气管，防止食物和饮料进入气道。
The trachea and bronchi are supported by rings of cartilage, which keep the airways open during breathing movements.
气管和支气管由软骨环支撑，在呼吸运动时保持气道畅通。
4. Ventilation: Breathing In | 通气：吸气
Breathing in is called inhalation or inspiration. During quiet breathing, it is an active process that requires muscle contraction.
吸气称为吸入。在平静呼吸时，这是一个需要肌肉收缩的主动过程。
When you inhale, the diaphragm contracts and flattens. The intercostal muscles between the ribs contract and lift the ribcage up and outwards.
当你吸气时，膈肌收缩并变平。肋骨之间的肋间肌收缩，使胸廓向上和向外抬起。
These movements increase the volume of the chest cavity. As the volume increases, the pressure inside the lungs drops below atmospheric pressure, so air rushes in.
这些运动增大了胸腔的容积。容积增大时，肺内压力下降到低于大气压，因此空气被吸入。
The lungs themselves do not have muscles; they expand and contract because of the movements of the diaphragm and ribcage.
肺本身没有肌肉；它们因膈肌和胸廓的运动而扩张和收缩。
5. Ventilation: Breathing Out | 通气：呼气
Breathing out is called exhalation or expiration. At rest it is mostly a passive process, meaning it does not require much muscle contraction.
呼气称为呼出。在安静状态下，它主要是一个被动过程，意味着不需要太多肌肉收缩。
When you exhale, the diaphragm relaxes and moves back into a dome shape. The intercostal muscles relax, so the ribcage moves down and inwards.
当你呼气时，膈肌放松并恢复成穹顶形。肋间肌放松，使胸廓向下和向内移动。
These changes reduce the volume of the chest cavity. The pressure inside the lungs rises above atmospheric pressure, so air is pushed out of the lungs.
这些变化减小了胸腔的容积。肺内压力升高到高于大气压，因此空气被推出肺部。
During forced breathing, such as during exercise, extra muscles in the abdomen can also help push air out more quickly.
在用力呼吸时，例如运动时，腹部的额外肌肉也可以帮助更快地排出空气。
6. Gas Exchange in the Alveoli | 肺泡内的气体交换
Gas exchange happens in the alveoli. Oxygen moves from the air inside the alveoli into the blood, and carbon dioxide moves from the blood into the alveoli.
气体交换发生在肺泡内。氧气从肺泡内的空气进入血液，二氧化碳从血液进入肺泡。
Gases move by diffusion, which is the net movement of particles from a region of higher concentration to a region of lower concentration.
气体通过扩散运动，即粒子从高浓度区域向低浓度区域的净移动。
Inhaled air has a higher oxygen concentration than the blood arriving at the lungs, so oxygen diffuses into the blood. The blood arriving at the lungs has a higher carbon dioxide concentration than the alveolar air, so carbon dioxide diffuses out.
吸入空气中的氧气浓度高于到达肺部的血液，因此氧气扩散进入血液。到达肺部的血液中二氧化碳浓度高于肺泡空气，因此二氧化碳扩散出来。
This exchange happens continuously because breathing keeps bringing fresh air into the alveoli and the blood keeps flowing through the capillaries around them.
这种交换持续进行，因为呼吸不断将新鲜空气送入肺泡，而血液不断流经肺泡周围的毛细血管。
7. Adaptations of the Alveoli | 肺泡的适应性特征
Alveoli are well adapted for efficient gas exchange. They are tiny and very numerous, giving the lungs a huge total surface area.
肺泡非常适合高效气体交换。它们微小且数量极多，为肺提供了巨大的总表面积。
Each alveolus has a wall that is only one cell thick, so the diffusion distance for gases is very short.
每个肺泡壁只有一层细胞厚，因此气体扩散距离非常短。
The alveoli are covered with a dense network of capillaries, and their inner surface is moist. These features help oxygen and carbon dioxide dissolve and diffuse rapidly.
肺泡表面覆盖着密集的毛细血管网，内表面湿润。这些特征有助于氧气和二氧化碳快速溶解和扩散。
A large surface area, a short diffusion distance and a good blood supply all increase the rate of gas exchange.
大的表面积、短的扩散距离和良好的血液供应都能提高气体交换速率。
8. Breathing vs Respiration | 呼吸与呼吸作用
Do not confuse breathing with respiration. Breathing is the movement of air into and out of the lungs. It is a physical process that can be observed.
不要将呼吸与呼吸作用混淆。呼吸是空气进出肺部的运动，是一种可以观察到的物理过程。
Respiration is a chemical process that happens inside cells. It releases energy from glucose using oxygen and produces carbon dioxide and water as waste products.
呼吸作用是发生在细胞内部的化学过程。它利用氧气从葡萄糖中释放能量，并产生二氧化碳和水作为废物。
The word equation for aerobic respiration is: glucose + oxygen → carbon dioxide + water (+ energy).
有氧呼吸的文字方程为：葡萄糖 + 氧气 → 二氧化碳 + 水（+ 能量）。
glucose + oxygen → carbon dioxide + water (+ energy)
Breathing brings the oxygen needed for respiration into the body and removes the carbon dioxide produced by it.
呼吸将呼吸作用所需的氧气带入体内，并排出呼吸作用产生的二氧化碳。
9. Gas Transport in the Blood | 血液中气体的运输
Oxygen is carried in the blood by red blood cells. Inside red blood cells, oxygen binds to a substance called haemoglobin, forming oxyhaemoglobin.
氧气由血液中的红细胞运输。在红细胞内，氧气与一种叫做血红蛋白的物质结合，形成氧合血红蛋白。
Most carbon dioxide is carried in the blood plasma as dissolved carbon dioxide or as hydrogen carbonate ions. A small amount binds to haemoglobin.
大部分二氧化碳以溶解的二氧化碳或碳酸氢根离子的形式在血浆中运输。少量与血红蛋白结合。
Red blood cells are biconcave discs with no nucleus, which gives them more space to carry oxygen. They contain haemoglobin, which can bind oxygen reversibly.
红细胞是双凹圆盘状，没有细胞核，这为携带氧气提供了更多空间。它们含有可逆结合氧气的血红蛋白。
The blood flowing away from the lungs is bright red because it is rich in oxygen. Blood returning to the lungs is darker red because it carries more carbon dioxide and less oxygen.
从肺部流出的血液呈鲜红色，因为它富含氧气。回到肺部的血液呈深红色，因为它携带更多的二氧化碳和更少的氧气。
10. Exercise and Breathing Rate | 运动与呼吸频率
During exercise, muscles contract more often and need more energy. This means they carry out more respiration and use more oxygen.
运动时，肌肉收缩更频繁，需要更多能量。这意味着它们进行更多呼吸作用并消耗更多氧气。
The breathing rate and the depth of each breath increase during exercise. This brings more oxygen into the lungs and removes more carbon dioxide.
运动时呼吸频率和每次呼吸的深度都会增加。这使更多氧气进入肺部，并排出更多二氧化碳。
The heart rate also increases, so blood flows faster and carries gases more quickly between the lungs and muscles.
心率也会增加，因此血液流动更快，在肺和肌肉之间更快地运输气体。
After exercise, the breathing rate stays high for a while to repay the oxygen debt and remove extra carbon dioxide produced by the muscles.
运动后，呼吸频率会在一段时间内保持较高，以偿还氧债并排出肌肉产生的额外二氧化碳。
11. Lung Health and Smoking | 肺部健康与吸烟
Smoking damages the breathing system. Cigarette smoke contains tar, nicotine, carbon monoxide and many harmful chemicals.
吸烟会损害呼吸系统。香烟烟雾中含有焦油、尼古丁、一氧化碳和许多有害化学物质。
Tar sticks to the lining of the airways and damages cilia, the tiny hairs that normally remove mucus and trapped dust. This leads to a build-up of mucus and a smoker’s cough.
焦油黏附在气道内壁，损害纤毛——那些通常会清除黏液和捕获灰尘的微小毛发。这导致黏液堆积和吸烟者咳嗽。
Carbon monoxide reduces how much oxygen the blood can carry, and smoking increases the risk of lung cancer, COPD and infections.
一氧化碳降低血液输送氧气的能力，吸烟还会增加肺癌、慢性阻塞
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