Osmoregulation is an important process in both plants and animals as it allows organisms to maintain a balance between water and minerals at the cellular level despite changes in the external environment. Osmoregulators take up both minerals and water from the environment and have methods of expelling what they do not need and conserving what is in short supply.
In arid climates, plants develop special mechanisms to conserve water in order to maintain homeostasis through osmoregulation. Cactuses store water in specialized tissue. Other plants develop specialized leaves with waxy exteriors to slow transpiration. Plants adapt to wet environments by increasing transpiration to eliminate excess water.
Freshwater fish collect minerals and water from their environment through their gills. They excrete excess water through the kidneys. Saltwater fish collect minerals and water in the same way. However, because their environment has a higher mineral content, they expel the unneeded minerals through their gills.
In humans, the kidneys play a major role in osmoregulation. They filter waste while retaining the minerals required for homeostasis. If the human does not drink enough water, the kidneys reduce the amount excreted from the body in an attempt to maintain hydration. If a person drinks more water than needed, the kidneys increase the fluid output in more urine. The kidneys serve as filters to maintain the salts the body needs while expelling any excess.