IB Biology Option H.5: Transport of Respiratory Gases Student Cards | IB 生物选修 H.5：呼吸气体运输学生卡片

📚 IB Biology Option H.5: Transport of Respiratory Gases Student Cards | IB 生物选修 H.5：呼吸气体运输学生卡片

These student cards summarise the key ideas in IB Biology HL Option H.5, the transport of respiratory gases. You will learn how oxygen and carbon dioxide move between alveoli, blood and tissues, and how haemoglobin's affinity for oxygen changes with partial pressure, pH and temperature. Each card gives a concise, exam-ready statement to help you revise efficiently.

这些学生卡片归纳了 IB 生物 HL 选修 H.5“呼吸气体的运输”的核心要点。你将学习氧气和二氧化碳如何在肺泡、血液和组织之间移动，以及血红蛋白对氧的亲和力如何随分压、pH 和温度变化。每张卡片都提供简洁、适合考试的表述，帮助你高效复习。

1. Partial Pressure Gradients Drive Gas Exchange | 分压梯度驱动气体交换

Oxygen and carbon dioxide move by diffusion down their partial pressure gradients. In the alveoli, P_O₂ is high (about 13.3 kPa) and P_CO₂ is low (about 5.3 kPa). In deoxygenated blood entering pulmonary capillaries, P_O₂ is low (about 5.3 kPa) and P_CO₂ is high (about 6.1 kPa). Therefore oxygen diffuses from alveolar air into blood, while carbon dioxide diffuses from blood into alveolar air.

氧气和二氧化碳沿各自的分压梯度通过扩散移动。在肺泡中，P_O₂ 较高（约 13.3 kPa），P_CO₂ 较低（约 5.3 kPa）。进入肺毛细血管的缺氧血中，P_O₂ 较低（约 5.3 kPa），P_CO₂ 较高（约 6.1 kPa）。因此，氧气从肺泡气扩散进入血液，而二氧化碳从血液扩散进入肺泡气。

In respiring tissues, the gradient is reversed: cells consume oxygen (lowering tissue P_O₂) and produce carbon dioxide (raising tissue P_CO₂). Oxygen leaves the blood, and carbon dioxide enters the blood.

在呼吸组织中，梯度相反：细胞消耗氧气（降低组织 P_O₂）并产生二氧化碳（升高组织 P_CO₂）。氧气离开血液，二氧化碳进入血液。

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2. Haemoglobin Structure and Oxygen Binding | 血红蛋白的结构与氧结合

Haemoglobin is a globular protein made of four polypeptide chains, each with a haem group containing an Fe²⁺ ion. Each Fe²⁺ can reversibly bind one O₂ molecule, so one haemoglobin molecule can carry up to four O₂ molecules.

血红蛋白是一种球状蛋白，由四条多肽链组成，每条链含有一个含 Fe²⁺ 的血红素基团。每个 Fe²⁺ 可逆地结合一个 O₂ 分子，因此一个血红蛋白分子最多可携带四个 O₂ 分子。

The reaction can be summarised as:

该反应可概括为：

Hb + 4O₂ ⇌ Hb(O₂)₄

Binding is reversible, allowing oxygen to be loaded in the lungs and unloaded in respiring tissues.

这种结合是可逆的，因此氧气可以在肺部装载，并在呼吸组织中卸载。

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3. Cooperative Binding and the Oxygen Dissociation Curve | 协同结合与氧解离曲线

Haemoglobin shows cooperative binding: binding of the first oxygen molecule changes the shape of haemoglobin, making it easier for the next oxygen molecules to bind. This produces a sigmoid (S-shaped) oxygen dissociation curve.

血红蛋白表现出协同结合：第一个氧分子的结合会改变血红蛋白的构象，使后续氧分子更容易结合。这产生了 S 形（sigmoid）的氧解离曲线。

At low P_O₂, haemoglobin has low affinity for oxygen and releases oxygen readily. At high P_O₂ (e.g. in the lungs), haemoglobin becomes nearly saturated. This shape allows efficient loading in the lungs and unloading in tissues.

在低 P_O₂ 下，血红蛋白对氧的亲和力低，容易释放氧气。在高 P_O₂ 下（如肺部），血红蛋白接近饱和。这种形状使得氧气在肺部高效装载，在组织中高效卸载。

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4. The Bohr Shift | 玻尔效应

Increased carbon dioxide concentration lowers blood pH. This reduces haemoglobin's affinity for oxygen, shifting the oxygen dissociation curve to the right. This is called the Bohr shift.

二氧化碳浓度升高会降低血液 pH。这会降低血红蛋白对氧的亲和力，使氧解离曲线右移。这称为玻尔效应（Bohr shift）。

The Bohr shift is beneficial because respiring tissues produce CO₂ and H⁺; the rightward shift promotes oxygen release exactly where it is needed. In the lungs, CO₂ is removed, pH rises, affinity increases, and oxygen is loaded more readily.

玻尔效应是有益的，因为呼吸组织产生 CO₂ 和 H⁺；曲线右移正好在需要的地方促进氧气释放。在肺部，CO₂ 被排出，pH 升高，亲和力增加，氧气更容易被装载。

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5. Carbon Dioxide Transport: Three Forms | 二氧化碳运输的三种形式

Carbon dioxide is carried in the blood in three ways: dissolved in plasma (about 7-10%), bound to haemoglobin as carbaminohaemoglobin (about 20-23%), and as hydrogen carbonate ions HCO₃⁻ in plasma (about 70%).

二氧化碳以三种方式在血液中运输：溶解在血浆中（约 7-10%）、与血红蛋白结合形成氨基甲酰血红蛋白（约 20-23%）、以及在血浆中形成碳酸氢根离子 HCO₃⁻（约 70%）。

Inside red blood cells, the enzyme carbonic anhydrase catalyses the conversion of CO₂ and water to carbonic acid, which dissociates:

在红细胞内，碳酸酐酶催化 CO₂ 和水转化为碳酸，碳酸再解离：

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻

The HCO₃⁻ diffuses out of the red blood cell into plasma, while chloride ions move in to maintain charge balance.

HCO₃⁻ 从红细胞扩散到血浆中，同时氯离子进入红细胞以维持电荷平衡。

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6. The Chloride Shift | 氯转移

The chloride shift (also called the Hamburger shift) is the exchange of HCO₃⁻ out of red blood cells and Cl⁻ into red blood cells across the membrane. This maintains electrical neutrality because the outward movement of negatively charged HCO₃⁻ is balanced by the inward movement of negatively charged Cl⁻.

氯转移（又称 Hamburger 转移）是指 HCO₃⁻ 出红细胞、Cl⁻ 入红细胞的跨膜交换。这维持了电中性，因为带负电的 HCO₃⁻ 向外移动由带负电的 Cl⁻ 向内移动平衡。

In the lungs, the reverse occurs: HCO₃⁻ enters red blood cells, Cl⁻ leaves, and CO₂ is regenerated and exhaled.

在肺部则发生相反过程：HCO₃⁻ 进入红细胞，Cl⁻ 离开，CO₂ 重新生成并被呼出。

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7. Foetal Haemoglobin vs Adult Haemoglobin | 胎儿血红蛋白与成人血红蛋白

Foetal haemoglobin (HbF) has a higher affinity for oxygen than adult haemoglobin (HbA). Its oxygen dissociation curve is shifted to the left. This allows the foetus to pick up oxygen from the maternal blood in the placenta, where P_O₂ is relatively low.

胎儿血红蛋白（HbF）对氧的亲和力高于成人血红蛋白（HbA）。其氧解离曲线左移。这使得胎儿能够在胎盘处从母体血液中获取氧气，尽管那里的 P_O₂ 相对较低。

After birth, HbF is gradually replaced by HbA, which has a lower affinity and is better suited for oxygen delivery to tissues.

出生后，HbF 逐渐被 HbA 取代。HbA 的亲和力较低，

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