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Evaluate the phrase, "the circulatory system of the crocodile is "more evolved" than the circulatory system of the locust

The above phrase is a complex one to consider, because the word "evolved" can be interpreted in two different ways. The first way (and the obvious one) is simply to take it as a synonym for "complex", "sophisticated", or another such word. However, some biologists would argue that by the mere fact that the crocodile and the locust both exist on Earth in the present day, they are both equally "evolved", regardless of sophistication. In the same way, a worm, despite being capable of almost no cognitive thought, is "as evolved" as a human being. If we take this definition of "evolved" to be true, there is little left for me to write, so I shall use the first definition. Locusts, like other arthropods, have what is known as an "open" circulatory system. Within the exoskeleton, the organs float freely in a fluid called "haemolymph", which is circulated by a tube that runs along the back of the body. The fluid is pumped out at one end and in at the other. Since arthropods are much smaller than mammals or reptiles, they can breathe directly through holes in their exoskeletons called spiracles, which lead to tubes known as trachea, which constantly branch off, becoming smaller and smaller, eventually leading directly to respiring cells where gas exchange occurs. In larger organisms, such a system would drastically reduce stability, or else, the amount of muscle required to draw air all the way through a system of one size, would itself require a system of a much larger size. The function of the haemolymph is akin therefore to the other functions of blood, namely transport of mineral ions and proteins to cells. Since insects are so small, these solutes do not need to be directed across large distances to the specific target organs or tissues, as there is no doubt that within such a small aqueous environment, they will reach their target cells. Crocodiles however are of course, much larger than locusts. If they had only an exoskeleton for stability, then any kind of blow could still cause damage to internal organs due to the shockwave created. More stability is required therefore, in the form of a skeleton, along with connective tissue, separating organs and providing rigidity. An open circulatory system therefore would not work, as it would require extremely high pressure to push the blood through, in, around and between all the different organs and tissues. Instead, there is a complex network of vessels carrying blood to specific regions of the body, and blood can even be diverted to organs requiring more oxygen for respiration. Rather than simple muscular contractions of vessels, which would not create enough pressure to force the blood through tight capillaries, there is an organ which serves as a pump, known as the blood, consisting of a special kind of muscular tissue, and several chambers, allowing it to pump the blood at extremely high pressures. Crocodiles have lungs, where gas exchange occurs. Oxygen diffuses from the alveoli to the adjacent blood vessels, and Carbon Dioxide diffuses from the blood vessels into the alveoli. Since the alveoli are so small (each about 200µm in diameter), the adjacent blood vessels are also very small. Since they are small, they blood loses pressure as it passes through them. Therefore, once the blood has been pumped to the lungs to become oxygenated, it needs to be pumped again in order to have enough pressure to make its way round the whole of the crocodile's body. This is concordant with double circulatory systems in humans; however the system of the crocodile is even more complex. The aorta, which receives oxygenated blood from the left ventricle, divides into the right and left systemic arch. Unlike in humans however, the left systemic arch can also be supplied with deoxygenated blood from the right ventricle. Usually this does not occur - a valve prevents it from happening - but when the crocodile dives below the surface of the water, the valve opens, allowing deoxygenated blood from the right ventricle to pass into the left systemic arch instead of the pulmonary artery. This prevents unnecessary flow of blood to the lungs. To conclude, the circulatory system of a crocodile is more sophisticated than that of a locust in order to accommodate for the size difference. It is closed, and is a double system. However, whether the difference in sophistication corresponds to a difference in how "evolved" the two organisms are is another matter. Certainly, the circulatory system of a crocodile has undergone more evolution.