Essay on Osmoregulation as a Homeostatic Mechanism using the Comparitive Melting-Point Method for two Crab Species.

Words: 1827
Pages: 8

Osmoregulation as a Homeostatic Mechanism using the Comparitive Melting-Point Method for two Crab Species.

Two crab species, Plagusia and Cyclograpsus, were collected from a local estuary in the littoral and deep water zone for osmoregulation studies. To examine differences in osmoregulatory mechanisms among the species, haemolymph of the specimens was extracted once they were acclimated to varying concentrations of seawater. Using the comparative melting-point, capillary tubes were filled with small samples of seawater and blood then frozen and melted in a -15˚C ethanol bath. The melting time of each was observed thereafter. Subject’s time range fell over 17 minutes of which the majority of the most salinated samples melted
…show more content…

Figure 1. The Melting Points of Seawater, Cyclograspus Blood and Plagusia Blood as a Function of the Ionic Concentration (Percentage Seawater) of the Solution.

Figure 2. Hypothetical Graph of a Osmoregulating and Osmoconforming Species.
Osmotic regulation is the maintenance of a difference in the osmotic pressure of the organisms’ water environment and its body fluid (Jones, 1941). Therefore based on this definition, the Plagusia crab is considered as the osmoconformer, whilst the Cycograspus crab is osmoregulator.
Figure one showed both the curves of the Plagusia and Cycograspus to have a downward trend. The first noticeable change occurred in the 70% seawater and Plagusia blood sample. This was unusual as we expected the 100 % seawater to melt first due the high saline content and instability of the crystalline structure (Brittain, 2009). To follow was the sample containing Plagusia blood in 60% seawater.
A slight trend was followed, as shown in figure 1. All the Plagusia samples melted regularly quickly, approximately between “time zero” and 1 minute, 20 seconds. The standard curve sample was the next data set to melt with the varying percentages of seawater, however they didn’t melt chronologically, between approximately 1 minute, 83 seconds and 2 minutes, 67 seconds. The samples containing the Cyclograspus blood was the last data set to melt, approximately between 5 minutes, 92 seconds and 13