Concept:Plants remove certain metabolic waste products as gases through stomata and lenticles.Explanation:Carbon dioxide (CO2) is produced during respiration in plants.This gas diffuses out through stomata on leaves and lenticles on stems.Alkaloids, tannins, and anthocyanins are not excreted in this way.Instead, they are stored in vacuoles or cell walls.Thus, the waste product excreted through stomata and lenticles is carbon dioxide.Answer:A. carbon dioxide