Which plant cell type regulates gas exchange by adjusting stomatal aperture?

• A. Sclerenchyma
• B. Guard cells
• C. Parenchyma
• D. Phloem

Answer: (B)

Gas exchange happens through stomata, tiny openings on the leaf surface, and the opening and closing of these pores are controlled by guard cells that surround each stoma. When guard cells accumulate ions like potassium, water follows by osmosis, they swell, and the pore opens to let in CO2 for photosynthesis (while also releasing water vapor). When ions exit the cells and water leaves, the guard cells become flaccid and the pore closes to reduce water loss. This makes guard cells the match to the question: they actively regulate gas exchange by adjusting stomatal aperture. Other cell types don’t regulate this opening—sclerenchyma provides structural support with thick walls, parenchyma is a general tissue involved in storage and metabolism, and phloem transports sugars.