Humans, frogs, and worms all have different circulatory systems, although the grasshopper is the only one without a closed transport system. Worms are classified as annelids, which have 5 aortic arches. Their aortic arches are pumped once and the pumped blood travels to the ventral vessel. The ventral vessel branches out into smaller vessels that lead to organs and tissues. There, gas is exchanged between the organs/tissues and blood. Blood carries oxygen to the body’s cells (blood is enriched with oxygen as oxygen diffuses through the worm’s skin, straight into circulatory vessels near the skin’s surface), while carbon dioxide is deposited into the blood. Then, the carbon dioxide diffuses through the skin, into the environment, as the worm’s deoxygenated blood travels through vessels under the skin’s surface. Therefore, gas is exchanged from the worm’s blood through the worm’s skin- something that frogs and humans cannot do. Worms also carry oxygen around with a pigment. Grasshoppers, on the other hand, have an open circulatory system, meaning that blood flows into open spaces (sinuses), rather than through blood vessels. The blood only carries food and waste, and is not used in gas exchange at all. The grasshopper’s tubular heart pumps blood through the aorta to the head. In this system, the blood moves much more slowly than in closed circulatory systems. Frogs are amphibians, which have one 3-chambered heart which pumps twice (incomplete). Deoxygenated blood is pumped from the heart to the lungs, where carbon dioxide is released into the lungs, and oxygen is taken (this gas exchange takes place on the site of the alveoli). Then, the oxygenated is pumped back into the heart, as it mixes with deoxygenated blood. This blood is then pumped throughout the body, as it delivers oxygen to body cells. Then, it flows back to the heart, and the cycle repeats. Humans, on the other hands, are classified under birds and mammals, which have one 4-chambered heart, which pumps twice (complete). Our hearts have separated chambers, one for oxygenated blood (which flows in one direction), and one for deoxygenated blood (which flows in the other direction). Our hearts pumped deoxygenated blood from the heart to our lungs, where gas exchange takes place. Then, the oxygenated blood gets pumped back to the heart, where it is separated from the deoxygenated blood. The oxygenated blood is then pumped throughout the body, delivering oxygen to body cells. Once the blood is deoxygenated, it is pumped back to the heart, and the cycle continues.
Worms, grasshoppers, frogs, and humans all have tube arrangement digestive systems. They are also all open tubes, which means that all four organisms have a mouth and an anus. However, worms and grasshoppers lack some organs (and possess some organs) that do not coincide with humans and frog anatomy. The worm and grasshopper possess a mouth, pharynx, esophagus, crop, gizzard, intestine, and anus. Worms use tough lips to break dead leaves and other foods into small pieces, while grasshoppers use saliva to help them break down the food. Then, the food passes from the mouth to the pharynx, where the food is lubricated by mucous. The food slides down the esophagus, and is mixed and stored in the crop. Then, it enters the gizzard, where the real digestion begins. The gizzard churns to break up the food into a paste with the help of stones (for worms) or teeth-like plates (for grasshoppers). Then, the food is sent to the intestine, where nutrients are absorbed into the blood. Waste is excreted out through the anus. Frog and human digestive systems have more in common with each other than with the worm and grasshopper digestive systems. However, frogs have a bony plate in their mouth, called maxillary teeth, as well as two studs, called vomerine teeth to trap their food (insects). The frog’s food moves down the esophagus via a series of slow contractions where it also gets lubricated. Then, the food enters the stomach, where stomach acid, bile (produced by the liver and stored by the gall bladder), pancreatic juice (produced by the pancreas), and enzymes break the food down. Then, the food moves into the small intestine, where nutrients are absorbed into the bloodstream. The semi-solid waste is then moved into the large intestine, where excess water is absorbed back into the frog’s body. Waste exits through the cloaca. The human digestive system basically works in the same way, except for a few differences. Unlike the frog mouth, the human mouth gnashes food into small particles, because we have more teeth to thoroughly chew with and mechanically break down the food. Humans also have an esophagus, stomach, liver, gall bladder, pancreas, small intestine, and large intestine, which serve the same purpose as with the frogs. However, frogs have longer stomachs than humans, and a shorter large intestine and esophagus than humans. They also have a cloaca, while humans have rectums and anuses to excrete waste.