Biology Assessment

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2) The differences in urine concentration of terrestrial mammals, marine fish and fresh water fish:

- Within terrestrial mammals, marine and freshwater fish the urine is composed of multiple constituents, including urea, chloride, sodium, potassium, creatine and other dissolved ions, organic compounds and inorganic compounds. All of the constituents are obtained as undesirable bodies within the blood and were removed by the kidney in order to maintain homeostasis as the nitrogenous wastes, over compositions of both glucose and dissolved ions can be potentially harmful. The concentration and similarly the volume of terrestrial mammal urine varies significantly depending on the climate and circumstances under which they subside. Mammals that live in the desert have highly concentrated urine, due to a large amount of the water is used quite rapidly (whilst the body is working in relatively high temperatures with low humidity) through perspiration and respiration. However dissolved ions must be supplemented accordingly as they too are lost through the sweating mechanism. The opposite configuration applies for mammals who live under opposite conditions. But the main issue associated with living in an atmosphere is the conservation of water and the removal of nitrogenous wastes.

- Within marine fish, with the primary excretory organ still being the kidney, they still face the distinct issue associated with the concentrations of sodium/potassium ions outside the body being higher than that within the fish’s blood. This can be harmful as the concentrations outside are far higher than the required amount in order to sustain life, so as a result the fish is constantly trying to eliminate the dissolved ions from within its blood. Similarly the fish is also trying to retain as much water as possible due to the loss of water via osmosis as surrounding water has a higher dissolved ion concentration, along with the excretion of nitrogenous wastes is completed through the gills via active transport. So therefore marine fish have higher concentrations of solutes within their urine, as they have to remove as much salt from their body as possible, containing low amounts of water as the fish must attempt to retain as much water which is known as Scant urine, this is done in order for homeostasis.

- Freshwater fish attempt to remove as much water as they possibly can, and similarly to retain as higher concentration of dissolved solids as possible. Due to the low dissolved ion concentration in the surrounding water, salt is constantly trying to move out into the water and additionally the surrounding water is trying to diffuse into the body of the fish. So in this case freshwater fish are trying to remove as much water as possible, whilst retaining the appropriate concentration of ions possible. As a result of the large amounts of water that diffuse into the fish, they must urinate copious amounts of dilute urine in order to achieve homeostasis.

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