C4 Plants: The Hatch-Slack Pathway and Kranz Anatomy | C4植物：哈奇-斯莱克途径与花环结构

📚 C4 Plants: The Hatch-Slack Pathway and Kranz Anatomy | C4植物：哈奇-斯莱克途径与花环结构

C4 plants are a group of species that have evolved a special photosynthetic adaptation to reduce photorespiration and maintain high rates of photosynthesis in hot, bright, and often dry environments. They first fix carbon dioxide into a four-carbon compound before the Calvin cycle, and they show a distinctive leaf structure called Kranz anatomy. This article explains the C4 pathway step by step, compares C4 with C3 photosynthesis, and highlights the key points needed for Cambridge A-Level Biology.

C4植物是一类进化出特殊光合适应机制的植物，能够在高温、强光和干旱环境中减少光呼吸并保持较高的光合速率。它们先将二氧化碳固定为一种四碳化合物，再进入卡尔文循环，并且具有称为花环结构的特殊叶片结构。本文将逐步解释C4途径，比较C4与C3光合作用，并突出剑桥A-Level生物考试所需的关键要点。

1. What Are C4 Plants? | 什么是C4植物？

C4 plants are species that initially fix carbon dioxide into a four-carbon compound, oxaloacetate, before the Calvin cycle operates. The name C4 comes from this first stable four-carbon product. Well-known examples include maize, sugarcane, sorghum, and many tropical grasses. In these plants, photosynthesis is spatially separated between two different cell types: mesophyll cells and bundle sheath cells.

C4植物是指二氧化碳首先被固定为四碳化合物草酰乙酸，然后才进入卡尔文循环的植物。C4这一名称来自最初的稳定四碳产物。常见例子包括玉米、甘蔗、高粱和许多热带禾本科植物。在这些植物中，光合作用在两种不同的细胞类型之间实现空间分离：叶肉细胞和维管束鞘细胞。

2. The Problem: Photorespiration in C3 Plants | 问题：C3植物的光呼吸

In C3 plants, rubisco fixes CO₂ directly into 3-phosphoglycerate in the Calvin cycle. However, rubisco can also use O₂ as a substrate when the leaf temperature is high and the CO₂ concentration inside the leaf is low. This oxygenase reaction produces phosphoglycolate, which must be recycled through a process called phot

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