2 3 8 Define Enantiostasis As The Maintenance Of Metabolic A

Some organisms live in environments which experience extreme fluctuations in conditions, to survive some plants and animals evolved adaptations which allow them to cope physiologically with these fluctuations – this survival mechanism is called enantiostasis. Enantiostasis is the maintenance of metabolic ad physiological functions in response to variations in the environment. The survival of species in estuaries, whom have to deal with constantly changing salt and water concentrations, depends on their ability to avoid or tolerate the changes. Enantiostasis is not limited to fluctuations in salt levels, for example extreme changes in environmental pressure are experienced by diving birds.

Estuarine organisms

At high tide the sea water flows into the river mouth, creating an environment with a higher salt concentration (a higher osmotic pressure) than the cytoplasm of the cells in the organism. This sea water has the tendency to draw water out of the tissues in the organism through osmosis. At low tide, sea water flows out of the river mouth and fresh water flows in. This creates a high water potential and water tends to flow into the bodies of plants and animals. Osmoregulation is challenging in an estuary as the organism needs to maintain metabolic function along with withstanding the extreme changes in conditions.

Osmoconformers: are organisms that tolerate the changes in the environment by altering the concentration of their internal solutes, to match the external environment. Their metabolism is able to tolerate changes in salinity in their own body fluids and cells.

Osmoregulators: are organisms that avoid changes in their internal environment and have the ability to keep the solutes at an optimal level (regulate solute concentrations within the body) regardless of the differing external environment. These organisms are unable to tolerate a range of salt concentrations n their body fluids and hence they have mechanisms to exclude salt to keep the internal fluid concentrations constant.