Soil respiration refers to the production of carbon dioxide when soil organisms respire. The fungi will respire these sugars for energy thereby increasing soil respiration. Some species that lack lungs respire through gills. They are heterotrophs that normally respire by aerobic means. Without them, a cell ceases to respire aerobically and quickly dies. "F. hepatica" has no respiratory organs&colon; the adult flukes respire anaerobically (without oxygen). Of extant lungfish, only the Australian lungfish can respire through its gills. With very few exceptions, animals respire aerobically. Methanogens do not use oxygen to respire; in fact, oxygen inhibits the growth of methanogens. Plants respire some of the carbon compounds which were generated by photosynthesis. Amphibians use this process to respire, whereby they use positive pressure to inflate their lungs. Small-bodied invertebrates of aquatic or continually moist habitats respire using the outer layer (integument). Other species can respire through their skin, intestines, and/or stomach. These worms live in deep burrow systems and require water in their environment to respire. They instead respire through a series of gill slits that perforate the body wall.