The Light Dependent Reactions of Photosynthesis | 光合作用的光依赖反应

📚 The Light Dependent Reactions of Photosynthesis | 光合作用的光依赖反应

The light dependent reactions of photosynthesis convert light energy into chemical energy in the forms of ATP and reduced NADP. These energy-rich molecules are then used in the Calvin cycle to fix carbon dioxide into sugars. In the Cambridge A-Level syllabus, understanding these reactions requires linking the structure of the thylakoid membrane to the processes of light absorption, electron transport, photolysis and chemiosmosis.

光合作用的光依赖反应将光能转化为ATP和还原型NADP中的化学能。这些富含能量的分子随后在卡尔文循环中用于固定二氧化碳生成糖类。在剑桥A-Level大纲中，理解这些反应需要将类囊体膜的结构与光吸收、电子传递、光解和化学渗透等过程联系起来。

1. Overview of the Light Dependent Reactions | 光依赖反应概述

The light dependent reactions are the first stage of photosynthesis. They occur in the thylakoid membranes and convert absorbed light energy into chemical energy carried by ATP and reduced NADP. These products are essential for the light independent reactions, the Calvin cycle, that assemble sugars from CO₂.

光依赖反应是光合作用的第一阶段。它们发生在类囊体膜上，将吸收的光能转化为ATP和还原型NADP所携带的化学能。这些产物对于从CO₂组装糖类的光独立反应（卡尔文循环）至关重要。

The term ‘light dependent’ means that the reactions stop if light is removed, because they require a continuous supply of light energy to drive electron excitation and proton pumping.

「光依赖」一词意味着如果移除光照，反应就会停止，因为它们需要持续供应光能来驱动电子激发和质子泵送。

The overall outcome of the non-cyclic pathway is the production of O₂, ATP and NADPH. Oxygen is released as a waste product, while ATP and NADPH are used in the stroma.

非循环途径的总体结果是产生O₂、ATP和NADPH。氧气作为废物释放，而ATP和NADPH则在基质中使用。

2. Location: The Thylakoid Membrane | 发生场所：类囊体膜

The light dependent reactions are located mainly on the thylakoid membrane, a folded internal membrane system in chloroplasts. The membrane encloses an inner compartment called the thylakoid lumen or thylakoid space.

光依赖反应主要发生在类囊体膜上，这是叶绿体内折叠的内部膜系统。该膜包围着一个称为类囊体腔或类囊体空间的内部区室。

Thylakoid membranes may be stacked into grana or remain unstacked as stroma lamellae. Stacking increases the density of photosystems and electron carriers, which improves the efficiency of energy transfer.

类囊体膜可堆叠成基粒或作为基质片层保持非堆叠状态。堆叠增加了光系统和电子载体的密度，从而提高了能量传递效率。

The compartmentalisation of the thylakoid is crucial because it allows protons to be pumped into a small lumen, producing a steep H⁺ concentration gradient across the membrane.

类囊体的区室化至关重要，因为它允许质子被泵入体积较小的腔内，从而在膜两侧产生陡峭的H⁺浓度梯度。

3. Photosystems and Light Harvesting | 光系统与光捕获

A photosystem is a multi-protein supercomplex containing light-harvesting antenna pigments and a reaction centre. The antenna pigments include chlorophyll a, chlorophyll b and carotenoids.

光系统是一个多蛋白超复合体，含有光捕获天线色素和反应中心。天线色素包括叶绿素a、叶绿素b和类胡萝卜素。

When a photon hits an antenna pigment, the energy is transferred from one pigment molecule to another by resonance energy transfer. This rapid transfer eventually delivers energy to the reaction centre chlorophyll a.

当光子击中天线色素时，能量通过共振能量传递从一个色素分子传递到另一个。这种快速传递最终将能量送到反应中心叶绿素a。

PSII has a reaction centre chlorophyll a called P680 because its absorption peak is at 680 nm. PSI has a reaction centre chlorophyll a

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