Membranes Maintain Salt Balance

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Biological Strategy

Crab-eating frog

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Maintain Homeostasis

When a living system is in homeostasis, it means that internal conditions are stable and relatively constant. For example, a human’s internal temperature is approximately 37 degrees Celsius (98.6 degrees Fahrenheit) unless there’s an illness. The human body maintains this temperature despite external ambient temperature. However, as with all physiological processes, maintaining homeostasis requires communication and coordination. So living systems have ways to detect changes from the norm, mechanisms to cause an adjustment, and negative feedback connections between the two. A desert lizard called the Gila monster offers a good example of maintaining homeostasis. The lizard goes from eating large meals to fasting for extended time periods. To maintain its blood sugar levels at a steady level, when food is scarce, its endocrine system releases a hormone that raises its blood sugar levels.

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Amphibians

Class Amphibia (“to live a double life”): Frogs, salamanders, toads

Amphibians live a “double life” by being able to survive both on land and in water. Unlike reptiles with dry, scaly skin, amphibians have smooth skin that needs to be kept moist. Many live in the water through development and start life with gills, and then transition to breathing with lungs. They can get even more oxygen through cutaneous respiration, or breathing through their skin. This class represents the first animal group to be able to efficiently walk on land—aided by the well-defined limbs that gave them a “leg up” on their finned competitors.

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Membranes of crab-eating frog tadpoles allow them to survive in salt water via active ion transport.

Image: W.A. Djatmiko (Wie146) / Wikimedia Commons /

''Fejervarya cancrivora'', from Darmaga, Bogor, West <a href=http://commons.wikimedia.org/wiki/Java title=Java>Java</a>

Image: W.A. Djatmiko (Wie146) / Wikimedia Commons /

''Fejervarya cancrivora'', from Darmaga, Bogor, West <a href=http://commons.wikimedia.org/wiki/Java title=Java>Java</a>

“Tadpoles are effective osmoregulators: that is, they maintain their internal osmotic concentration relatively constant over a wide range of external salinities (Fig. 3.3). This is probably achieved by the active transport of ions out of the body at high environmental salinity, and by the retention of ions and elimination of water when the surrounding salinity is lower than that of the body fluids. Whatever the physiological mechanisms involved, young tadpoles can survive in concentrations of 40 per cent that of sea water (14 parts per thousand, ppt) and older ones to 50 percent sea water or higher. At 80 percent sea water (28 ppt) approximately 50 per cent of tadpoles still survive, and some still live at greater ion concentrations than that of full sea water (Gordon and Tucker 1965).” (Hogarth 1999:63)

Last Updated August 18, 2016

References

Book

The Biology of Mangroves and Seagrasses (Biology of Habitats Series)

Oxford University Press | 31/05/2007 | Peter Hogarth

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Reference

Journal article

Osmotic regulation in the tadpoles of the crab-eating frog (Rana cancrivora)

Gordon, M.S.; Tucker, V.A.

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