Oxygen and carbon dioxide from the air enter through the stoma. 氧和二氧化碳从空气中进入气孔。
Each stoma is surrounded by two crescent-shaped GUARD CELLS, attached to each other at their ends, which regulate the opening and closing of the pore by changes in their turgidity. 每个气孔被两个新月形的保卫细胞头尾相接围绕而成。