Psychrophrynella wettsteini species without known major threats. Psychrophrynella wettsteini Psychrophrynella wettsteini is a species of frog in the family Craugastoridae. It is endemic to Bolivia and only known from the region of Unduavi in the Unduavi Valley, Sud Yungas Province, La Paz Department. Common name Wettstein's Andes frog has been coined for it. It is named for Otto von Wettstein, Austrian zoologist. "Psychrophrynella wettsteini" is a comparatively large species (maximum snout–vent length ) and has a robust body and long limbs. The snout is rounded. The tympanic membrane is absent, whereas the tympanic annulus is visible through the skin. Tips of the
Cell membrane concentration in order to equilibrate the membrane. It is considered a passive transport process because it does not require energy and is propelled by the concentration gradient created by each side of the membrane. Such a concentration gradient across a semipermeable membrane sets up an osmotic flow for the water. Osmosis, in biological systems involves a solvent, moving through a semipermeable membrane similarly to passive diffusion as the solvent still moves with the concentration gradient and requires no energy. While water is the most common solvent in cell, it can also be other liquids as well as supercritical liquids and