Form and Function

            One aspect that is essential in gaining a better understanding of an organism is their form and function. The loggerhead sea turtle is the largest hard-shelled turtle in the world. Adult turtles tend to grow to be around 3 feet long and weigh approximately 200 pounds (U.S. Fish and Wildlife Service, 2013). Distinctive characteristics include the turtle’s large head and extremely strong jaws used to crush hard shelled prey (MarineBio, 2014). An interesting fact about the loggerhead turtle's head is that it can't be withdrawn like many other turtle's can. But to make sure their head is still well protected, the Caretta caretta have very thick and scaly skin covering both their head and neck (MarineBio, 2014). A turtle's coloring and shell shape is also unique to the species. The loggerhead underbellies, also known as plastron, are usually a monochromatic yellow color. The turtle’s heart-shaped shells, also known as carapace, tend to have a red/brown coloring (Department of Energy and Environmental Protection, 2013). It is important to note that a turtle’s shell is not an exoskeleton; it is actually a bony covering and a source of protection to the dorsal area of the turtle (MarineBio, 2014). Parts of the epidermal layer of the shell are the scutes, or ridges, on the shell (U.S. Fish and Wildlife Service, 2013). Turtles are motile animals in both water and on land by use of their four flippers. In fact, they can swim up to 24 kph since their flippers are designed similar to paddles used in a rowboat (MarineBio, 2014).
            Loggerhead turtles spend a majority of their time in water; in fact they spend less than 2% of their life at the surface (Lutcavage et al., 1987). In order to survive in these conditions, the loggerhead’s lungs have actually adapted to spending a majority of their time underwater. Their lungs are divided in to multiple chambers, which provides them with a larger surface area for gas exchange. Their increase of gas exchange allows for a higher intake of oxygen (Lutcavage et al., 1987). Loggerhead turtles actually store and transport their oxygen for when they are submerged for long periods of time, which minimizes the amount of times they need to go up to the surface for air. The stored oxygen is mostly used to supply their brain, heart and lungs while the rest of their body undergoes anaerobic respiration; meaning they undergo cellular respiration without oxygen (Lutcavage et al., 1987). Loggerhead turtles will usually dive for four to five minutes before spending only one to three seconds on the surface for air (MarineBio, 2014). Since loggerheads can dive to fairly deep depths, their lungs are lined with smooth muscles and fibers. These muscles and fibers increase the stability of the loggerhead’s lungs without hindering the efficiency of gas exchange (Lutcavage & Lutz, 1991). Another fascinating fact about loggerhead turtle’s diving patterns is that their gas exchange system actually differs depending on if their dive is voluntary or forced. If their dives are forced the turtles they are less likely to appropriately respond, thus possibly leading to mortality (Lutcavage et al., 1987).

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