Non-vascular plants excrete excess gases produced by cellular respiration and photosynthesis through diffusion, the movement of molecules from a concentrated area to an area of low concentration. Mosses and algae excrete and take in oxygen and carbon dioxide with the environment through this process.
Normal plants excrete oxygen and waste through their leaves, but non-vascular plants lack vascular tissues, so they can't retain and deliver water to their other parts. They thrive in moist or wet places and also absorb water from an outside source. Like vascular plants, they release extra water to the atmosphere and its environment through transpiration. Non-vascular plants found in the ocean, such as algae and seaweeds, excrete about 70 to 80 percent of the oxygen in the atmosphere.