Planet Earth and Its Environment A 5000-million year Journey

Biology in Focus, HSC CourseGlenda Childrawi, Margaret Robson and Stephanie Hollis

Maintaining a BalanceTopic 20: Enantiostasis and Estuarine Organisms1DOT POINTDefine enantiostasis as the maintenance of metabolic and physiological functions in response to variations in the environment and discuss its importance to estuarine organisms in maintaining appropriate salt concentrationsEnantiostasisSome organisms live in environments where they experience extreme fluctuations in conditions. To survive, these plants and animals have evolved adaptations that allow them to cope physiologically with these fluctuations, a survival mechanism called enantiostasis.

EnantiostasisEnantiostasis is the maintenance of metabolic and physiological functions in response to variations in the environment. The survival of species that live in an environment such as an estuary, where salt and water concentrations fluctuate broadly on a daily basis, depends on their ability to either avoid these changes or tolerate them. legacy.owensboro.kctcs.edu

EnantiostasisOrganisms that move freely between the sea and rivers experience similar fluctuations in environmental conditions, and they too have developed mechanisms of avoidance or tolerance.

EnantiostasisEnantiostasis is not limited to fluctuations in salt levels. For example, extreme changes in environmental pressure are experienced by diving birds and so these animals must also rely on enantiostasis for their survival. telegraph.co.uk

Estuarine OrganismsIn estuaries, the daily change in tides affects the salinity of the environment. At high tide, sea water flows into the river mouth, creating an environment with a high salt concentration (a higher osmotic pressure) than the cytoplasm of cells and body fluids in organisms. This salt water has the tendency to draw water out of cells by osmosis. flickr.com

Estuarine OrganismsAt low tide, sea water flows out of the river mouth and fresh water flows into the estuary. Plants and animals in the estuary which are subjected to this predominantly fresh water environment with a high water potential face the challenge of water tending to move into living tissue. tripwow.tripadvisor.com

Estuarine OrganismsOsmoregulation in organisms inhabiting an estuary is a challenge they need to maintain normal metabolic functioning, despite these enormous fluctuations within the environment. Living organisms employ one of two strategies in enantiostasis. treknature.com

Handout Table 3.2Estuarine OrganismsOsmoconformers are organisms that tolerate the changes in the environment by altering the concentration of their internal solutes to match the external environment. Their body fluids conform to that of the environment. Their metabolism is able to tolerate changes in salinity in their own body fluids and cells.gatheringhisblessings.blogspot.com

Estuarine OrganismsOsmoregulators are organisms that avoid changes in their internal environment and have the ability to keep the solutes at an optimal level. They regulate solute concentrations within the body, regardless of the differing external environment. absolutedivers.com

Estuarine OrganismsThese organisms are unable to tolerate a range of salt concentrations in their body fluids and cells and so they have mechanisms to exclude salt to keep the internal fluid concentration constant, despite fluctuations in the environment. guardian.co.uk

Activity-Use ALARM Scaffold to answer DOT Point Question:Define enantiostasis and discuss its importance to estuarine organisms in maintaining appropriate salt concentrations