KS3 CIE Breathing and Gas Exchange | KS3 CIE 呼吸与气体交换

📚 KS3 CIE Breathing and Gas Exchange | KS3 CIE 呼吸与气体交换

Breathing is the movement of air into and out of the lungs, and gas exchange is the process by which oxygen enters the blood and carbon dioxide leaves it. This article explains these ideas for the CIE KS3 syllabus, with mark scheme style guidance.

呼吸是空气进出肺部的运动，而气体交换是氧气进入血液、二氧化碳离开血液的过程。本文按照 CIE KS3 大纲解释这些概念，并附评分标准风格的答题指导。

1. Why We Breathe | 呼吸的原因

All living cells need energy to stay alive. This energy is released from glucose during aerobic respiration, which needs oxygen.

所有活细胞都需要能量来维持生命。在需要有氧呼吸过程中，细胞从葡萄糖中释放能量，而这个过程需要氧气。

Aerobic respiration can be written as a word equation:

glucose + oxygen → carbon dioxide + water + energy

葡萄糖 + 氧气 → 二氧化碳 + 水 + 能量

Breathing brings oxygen into the body and removes carbon dioxide, which is a waste product of respiration.

呼吸将氧气带入体内，并排除二氧化碳，而二氧化碳是呼吸作用产生的废物。

Breathing is a mechanical process controlled by muscles.
Respiration is a chemical process that happens inside cells.

呼吸是由肌肉控制的机械过程。
呼吸作用是在细胞内发生的化学过程。

2. The Breathing System | 呼吸系统

The main organs of the breathing system include the trachea, bronchi, bronchioles, lungs, ribs, intercostal muscles and diaphragm.

呼吸系统的主要器官包括气管、支气管、细支气管、肺、肋骨、肋间肌和膈肌。

Part	Function
Trachea	Carries air from the nose and mouth to the lungs.
Bronchi	Two tubes that carry air into each lung.
Bronchioles	Smaller branches that lead to the alveoli.
Alveoli	Tiny air sacs where gas exchange happens.
Diaphragm	Sheet of muscle that changes chest volume.
Intercostal muscles	Muscles between the ribs that move the rib cage.

The trachea is kept open by rings of cartilage. The inside is lined with mucus and cilia, which trap and remove dust and microbes.

气管由软骨环保持通畅。其内壁覆盖着黏液和纤毛，可以捕获并清除灰尘和微生物。

3. Gas Exchange in the Lungs | 肺部气体交换

Gas exchange is the movement of oxygen from the air into the blood, and carbon dioxide from the blood into the air.

气体交换是指氧气从空气进入血液，以及二氧化碳从血液进入空气的过程。

Oxygen moves from the alveoli into the capillaries because there is a higher concentration of oxygen in the alveoli than in the blood.

氧气从肺泡进入毛细血管，因为肺泡中的氧气浓度高于血液中的氧气浓度。

Carbon dioxide moves in the opposite direction because there is a higher concentration of carbon dioxide in the blood than in the alveoli.

二氧化碳朝相反方向移动，因为血液中的二氧化碳浓度高于肺泡中的二氧化碳浓度。

This movement is called diffusion. It does not require energy.

这种移动称为扩散，它不需要能量。

oxygen: alveolus → blood

氧气：肺泡 → 血液

carbon dioxide: blood → alveolus

二氧化碳：血液 → 肺泡

4. The Role of Alveoli | 肺泡的作用

Alveoli are tiny air sacs in the lungs where gas exchange takes place. They are specially adapted for efficiency.

肺泡是肺中进行气体交换的微小气囊，它们经过特殊适应以保证高效。

Each lung contains millions of alveoli.

每个肺包含数百万个肺泡。

Large surface area: more space for diffusion.
Thin walls: only one cell thick, so gases diffuse quickly.
Moist lining: oxygen and carbon dioxide can dissolve before diffusing.
Rich blood supply: maintains a steep concentration gradient.
Good ventilation: fresh air constantly brings oxygen and removes carbon dioxide.

表面积大：为扩散提供更大空间。
壁薄：仅一层细胞厚，气体扩散迅速。
内壁湿润：氧气和二氧化碳可以先溶解再扩散。
血液供应丰富：维持陡峭的浓度梯度。
通气良好：新鲜空气不断带来氧气并带走二氧化碳。

A mark scheme often awards one mark for each correct adaptation and one mark for linking it to faster diffusion.

在评分标准中，通常每个正确的适应特点得一分，如果能将其与扩散加快联系起来再得一分。

5. Ventilation: Inhaling and Exhaling | 通气：吸气和呼气

Ventilation is the movement of air into and out of the lungs. It has two stages: inhalation and exhalation.

通气是空气进出肺部的运动，包括吸气和呼气两个阶段。

Inhalation:

吸气：

The intercostal muscles contract and pull the ribs up and out.
The diaphragm contracts and flattens.
The volume of the chest increases.
The pressure inside the chest decreases below atmospheric pressure.
Air rushes into the lungs.

肋间肌收缩，将肋骨向上向外拉动。
膈肌收缩并变平。
胸腔容积增大。
胸腔内压力降至大气压以下。
空气涌入肺部。

Exhalation:

呼气：

The intercostal muscles relax and the ribs move down and in.
The diaphragm relaxes and curves upward.
The volume of the chest decreases.
The pressure inside the chest increases above atmospheric pressure.
Air is pushed out of the lungs.

肋间肌舒张，肋骨向下向内移动。
膈肌舒张并向上弯曲。
胸腔容积减小。
胸腔内压力升高至大气压以上。
空气被推出肺部。

Remember: breathing in is an active process because muscles contract. Normal breathing out is mostly passive because the muscles relax.

请记住：吸气是主动过程，因为肌肉收缩；正常呼气大多是被动过程，因为肌肉舒张。

6. Measuring Breathing | 测量呼吸

Breathing rate is the number of breaths taken in one minute. It can be measured by counting chest movements.

呼吸频率是每分钟呼吸的次数，可以通过计数胸部运动来测量。

Tidal volume is the volume of air inhaled or exhaled in one normal breath.

潮气量是指一次正常吸气或呼气所吸入或呼出的空气体积。

Breathing rate is calculated using:

呼吸频率的计算方法为：

breathing rate = number of breaths ÷ time in minutes

呼吸频率 = 呼吸次数 ÷ 时间（分钟）

Exercise increases breathing rate and depth. This is because muscle cells respire faster during exercise and need more oxygen.

运动会使呼吸频率和深度增加。这是因为运动时肌肉细胞呼吸作用加快，需要更多氧气。

A simple experiment uses a timer and counts breaths at rest and after exercise. The results usually show a higher rate after exercise.

简单的实验可以用计时器计算静息时和运动后的呼吸次数。结果通常显示运动后呼吸频率更高。

7. Differences Between Inhaled and Exhaled Air | 吸入和呼出气体的差异

Inhaled air and exhaled air have different compositions. The table below shows the typical percentages.

吸入空气和呼出空气的成分不同。下表显示了典型的百分含量。

Gas	Inhaled air	Exhaled air
Oxygen	21%	16%
Carbon dioxide	0.04%	4%
Nitrogen	78%	78%
Water vapour	Variable	Saturated

Exhaled air has less oxygen, more carbon dioxide and more water vapour than inhaled air.

与吸入空气相比，呼出空气中氧气更少、二氧化碳更多、水蒸气也更多。

The amount of nitrogen stays almost the same because it is not used by the body.

氮气的含量几乎不变，因为身体不使用氮气。

You can test exhaled air with limewater: carbon dioxide turns limewater milky or cloudy.

可以用石灰水检测呼出气体：二氧化碳会使石灰水变浑浊或呈乳白色。

8. Aerobic Respiration vs Breathing | 有氧呼吸与呼吸的区别

Breathing and respiration are often confused, but they are not the same.

呼吸（breathing）和呼吸作用（respiration）经常被混淆，但二者并不相同。

Breathing is the movement of air into and out of the lungs. It happens in the breathing system.

呼吸（breathing）是空气进出肺部的运动，发生在呼吸系统中。

Respiration is the chemical release of energy from glucose. It happens in all living cells.

呼吸作用（respiration）是从葡萄糖中释放能量的化学过程，发生在所有活细胞中。

During aerobic respiration, glucose reacts with oxygen to produce carbon dioxide, water and energy.

在有氧呼吸过程中，葡萄糖与氧气反应生成二氧化碳、水和能量。

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 能量

In an exam, if a question asks why we breathe, the answer should mention supplying oxygen for respiration and removing carbon dioxide produced by respiration.

在考试中，如果题目问我们为什么要呼吸，答案应提到为呼吸作用提供氧气，并排除呼吸作用产生的二氧化碳。

9. Common Exam Questions and Mark Scheme | 常见考试题与评分标准

Exam questions on this topic often ask students to describe the pathway of air, explain gas exchange, or compare inhaled and exhaled air.

关于这个主题的考试题通常要求学生描述空气的路径、解释气体交换，或比较吸入与呼出的空气。

Example question 1: Name the structures through which air passes from the nose to the alveoli. (3 marks)

例题1：写出空气从鼻子到肺泡所经过的结构名称。（3分）

Mark scheme: trachea (1), bronchi (1), bronchioles (1).

评分标准：气管（1分），支气管（1分），细支气管（1分）。

Example question 2: Explain how two features of the alveoli make gas exchange efficient. (4 marks)

例题2：解释肺泡的两个特征如何使气体交换高效进行。（4分）

Mark scheme: large surface area for diffusion (1), thin walls for short diffusion distance (1), moist surface for dissolving gases (1), rich blood supply maintains concentration gradient (1). Any two features with explanation = 2 marks each.

评分标准：表面积大有利于扩散（1分），壁薄缩短扩散距离（1分），表面湿润便于气体溶解（1分），丰富血液供应维持浓度梯度（1分）。写出任意两个特征并解释，每个2分。

Example question 3: Describe what happens to the diaphragm during inhalation. (2 marks)

例题3：描述吸气时膈肌发生了什么。（2分）

Mark scheme: it contracts (1), and flattens/moves down (1).

评分标准：膈肌收缩（1分），变平/向下移动（1分）。

Example question 4: Suggest why breathing rate increases during exercise. (2 marks)

例题4：解释为什么运动时呼吸频率会增加。（2分）

Mark scheme: muscles need more oxygen for aerobic respiration (1), more carbon dioxide is produced and must be removed (1).

评分标准：肌肉需要有氧呼吸需要更多氧气（1分），产生更多二氧化碳需要排出（1分）。

10. Summary and Revision Tips | 总结与复习建议

Breathing brings oxygen into the lungs and removes carbon dioxide from the body.

呼吸将氧气带入肺部，并将二氧化碳排出体外。

Gas exchange happens by diffusion in the alveoli, where oxygen moves into the blood and carbon dioxide moves out of the blood.

气体交换通过扩散在肺泡中进行，氧气进入血液，二氧化碳离开血液。

Ventilation involves the ribs, intercostal muscles and diaphragm changing the pressure inside the chest.

通气过程涉及肋骨、肋间肌和膈肌改变胸腔内的压力。

To prepare for CIE KS3 exams, practise drawing simple diagrams of the breathing system and labelling them correctly.

为了准备 CIE KS3 考试，请练习绘制呼吸系统的简图并正确标注。

Use tables to compare inhaled and exhaled air, and make flashcards for key terms such as diffusion, alveolus, trachea, diaphragm and ventilation.

使用表格比较吸入和呼出的空气，并为扩散、肺泡、气管、膈肌和通气等关键词制作闪卡。

Always answer question words exactly: ‘name’ means give a word, ‘describe’ means say what happens, and ‘explain’ means give reasons.

务必准确回应题目指令词：“写出”意味着给出名词，“描述”意味着说明发生了什么，“解释”意味着给出原因。

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KS3 CIE Breathing and Gas Exchange | KS3 CIE 呼吸与气体交换