Excretion is the process by which waste products are eliminated from organisms. In plants, waste is excreted through various methods like releasing oxygen during photosynthesis, transpiration of excess water, and shedding of waste-containing leaves. Vacuoles can also store waste. In animals, the main excretory products are carbon dioxide, ammonia, urea, uric acid, guanine, and creatine. Aquatic animals excrete ammonia directly into water, while terrestrial animals convert ammonia into other compounds due to less water. Birds excrete uric acid paste for efficient water retention. Insects use Malpighian tubules to excrete waste into intestines and release it with fecal matter