1) While the brine-shrimp cannot survive in freshwater (do your data agree?), they can adapt to media which vary from about 1/10 sea water to saturated brine (published data). Explain, explicitly, the osmoregulatory mechanism(s) they posses to deal with such extreme environments or propose what mechanism would work.
Our data agrees that the brine-shrimp unable to sustain in freshwater. But the can adapt to such extreme environment high to saturated brine. They can tolerate varying levels of salinity. Brine shrimp are able to regulate the amount of salt they allowed to enter their body tissues with the help from their skin lining of the stomach, and the gills. The outer layer of shrimp is impermeable to water; instead the salt water will enter during feeding via the mouth. As the shrimp ingest water, it is absorbed through the stomach lining. Salt will then be pumped out from the gills, other than going through the digestive tract. Other than that, the neck gland is also thought to be as a salt pump, specially vital in immature shrimp when other excretory organs are under-developed. Brine shrimp use these two pumps to maintain a relatively stable salt concentration within their bodies one during the surrounding water is highly salty, the pumps work harder and have a higher output. And when the surrounding water is less saline, the pumps slow in order to retain some salts within the shrimp.
2) Many animals that conform to the osmolarity of its surroundings may still regulate its internal composition of ions. Why do they have to do this?
Whenever animals sustain an osmolarity difference between the body and the external surroundings, osmoregulation has an energy cost. Other than that, most animals whether they are osmoconformers or osmoregulators, they cannot tolerate substantial changes in external osmolarity and is considered as stenohaline. A part from that, for instance most marine invertebrates are osmoconformers which their osmolarity is the same as seawater. However, they are difference in considerably from seawater in their concentrations of most specific solutes.
1) What are your conclusions regarding the tolerance of fish to variations in ionic composition as compared to osmotic pressure of its's environment?
The osmotic pressure and ionic composition can be differs from the environment it be put. Even in concentrated media, the haemolymph osmotic pressure can be less that of typical invertebrates in sea water. This will enable the animal to colonize in an extreme condition.
2) What are important physiological characteristics of the ions that resulted in increased death of the animals that could account for this activity?
It is prove that, artemia only sustain in potassium salt for less than two days. Recent studies states that potassium ion has high toxicity to Artemia. Eventhough, the brine shrimp able to live over a wide concentration range, it does not mean it is not senstitive towards chemical and ionic composition of its environment. Prolonged survival is only possible in media where sodium ion predominate. A part from that, certain ion or substance are found to be highly toxic. Besides, high toxicity of potassium ions can be antagonized by sodium ions.
1. The Survival of Artemia salina in Various Media by P.C Croghan , Deaprtment of Zoology, University of Cambridge (July10,1957)
2. The Osmotic And Ionic Regulation of Artemia salina by P.C Croghan , Deaprtment of Zoology, University of Cambridge (July10,1957)
3. The Mechanism of Osmotic Regulation in Artemia salina : The Physiology of The Branchiae by P.C Croghan , Deaprtment of Zoology, University of Cambridge (July10,1957)
1. Brine Shrimp: How Do They Survive In Such Extreme Environment? (March 12, 2011)
2. Course Notes : Chapter 44 – Osmoregulation and Excretion ( March 12, 2011)