Skeletal System

The skeletal system gives shape, structure and allows the organism to move. In class we learned the three types of skeletons are Hydrostatic Skeleton, Exoskeleton, and Endoskeleton. A hydrostatic skeleton mostly found in organisms with soft bodies which is cavities filled with fluids surrounding by muscles. The Exoskeleton, found on shelled fish and insects, it provides a tough outside to protect the soft insides of the organism. Endoskeletons is internal skeleton, such as the bony or cartilaginous skeleton of vertebrates.

Worm

Worms do not have bones, only a hydrostatic skeleton, that means that it can easily stretch and squeeze into places without their bones breaking. When it comes to pushing heavy things around, it is very hard without the hard bones to help out, so instead the muscles try their best to help out with the movements. Without the bones to help move, the worm has bristles on each segment called setae that help the earthworm move. 

Crayfish

The shells that the crayfish has are called exoskeleton, it protects the organs and tissue of the crayfish, but if it creaks all of the insides will be exposed. Even though the exoskeleton gives protection and support, it can also limit somethings. For example, the crayfish being cold-blooded, it has to move to different environments to maintain homeostasis, such as colder places. The other way around, if the crayfish is too cold, it must move to a more suitable  climate for themselves. The crayfish's exoskeleton must molt. Like how a snake must replace it's skin every so often. So when the crayfish just molted out of it's old shell, the crayfish is vulnerable to it's predators due to not having a shell yet. There is also a disadvantage when gills are attached to the legs, if any of the legs were torn off, it may slow the breathing rate down. That is why the crayfish have multiple legs.


Frog 

The frog's skeletal system is very different from the humans even though they both have a endoskeletons. The endoskeleton forms a supporting framework for the body, it can be well know as an appendicular skeleton and an axial skeleton. Appendicular skeleton consists of the pectoral, pelvic, and the limb bones. Axial skeleton consists of skull, vertebrae, and sternum. Frogs do not have necks and cannot turn, lift or lower their heads like humans can. Another thing that is different in the frog's skeletal system is that the frog does not have ribs. The reason for that is because when ever they jump, half of the time they land on their bellies, so if they ribs there it would crack every time. A frog's pelvis can also slide up and down its spine.

Rat

Like the frog, the rat also has an endoskeleton with 223 bones that are distributed into the axial skeleton and the appendicular skeleton. The rat is also the only organism that we have studied that has a ribcage that covers most of its body. Unlike the frog that did not have the ribcage to protect the organs, the rat has a ribcage to protect the internal organs. 

Circulatory System

The purpose of the circulatory system is to carry blood throughout the body, transporting gasses and nutrients to the organs that need it. It is also needed to carry gas waste so the respiratory system can get rid of it. There are different circulatory systems, such as open and closed ones, as we will see below.

Worm

The circulatory system of an earthworm is very similar to other mammals. Earthworms have a closed circulatory system. This means that their blood flows through blood vessels. Not to mention, their blood vessels help process oxygen from breathing through their skin. Oxygen is drawn in by the dorsal blood vessel. It travels to the five hearts it has, called aortic arches. Once there, it travels to the ventral blood vessel, and the process repeats.

Crayfish
The circulatory system of a crayfish is different from the other organisms we studied in this unit. They have an open circulatory system. In an open circulatory system, there are no veins or arteries, but instead, blood-like fluid is pumped from vessels to cavities in the body. If the blood has no oxygen, then it go to the lungs to retrieve some oxygen and returns to the heart to keep it running. If the blood is oxygenated, then the blood leaves the heart through the sinus arteriole opening and travels through the body to find a cell in need of oxygen and returns to the heart to repeat this process.

Frog

The circulatory system of the frog is a closed circulatory system. It consists of a single ventricle and two atria. The single ventricle is not splint into two, but it is apart enough so that the blood will not mix. This is a disadvantage of the evolutionary system. The blood may get caught and huge issues will occur in the frog's circulatory system. The left atrium receives oxygen-laden blood and enters the ventricle. The oxygen-poor blood at the bottom of the ventricle prevents the oxygen-laden blood from sinking to the bottom. After, the oxygen-poor blood flows into the vessels leading the the lungs and the oxygen-laden blood is forced into arteries.

Rat
The circulatory system of the rat is very similar to a human's circulatory system. It's heart is divided into 4 sections, 2 on the top and 2 on the bottom: the left atrium, the right atrium, the left ventricle, and the right ventricle. Oxygen-poor blood is carried by veins that terminate into 3 main veins: the right superior vena cava, left superior vena cava, and inferior vena cava. Oxygen-poor blood is brought to the heart by the inferior vena cava. They enter the right atrium of the heart and from the right atrium, the blood is pumped into the right ventricle. The blood circulates through the rat's body, just like a human's. It's 4-chambered heart is an advantage because the oxygen-laden blood and oxygen-poor blood are not in risk of mixing in that type of heart.

Respiratory System

The respiratory system performs exchange between gases. The molecules of oxygen and carbon dioxide are exchanges, this process changes oxygen to carbon dioxide. Our respiratory system is responsible to clean out the bacteria or dust we breath in. Every living organism has that system, but in different shape and form, like how some have lungs while others have gills.

Earthworm

The earthworms' respiratory system is very different compared to other mammals, but the purpose is the same, get the oxygen and take out the carbon dioxide. Earthworms do not have lungs or gills like other mammals, but instead they breathe by using their moist skin. By diffusing air through their skin, worms are able to breathe like every other mammal. Their moist skin is need, so that diffusion can happen without a problem. The skin covers the whole body of the worm, so it is much more easy for the worm to take in oxygen an give out carbon dioxide.  

Crayfish 

The crayfish has evolutionary advantage of being able to breathe underwater because of their gills, which it helps the crayfish to breathe. Also most of what crayfish eats is in the water, so it is easier for the crayfish. The crayfish's gills are located on the outside of the body between the crayfish body wall and carapace. When one of the swimmerets were pulled out, you can see that the crayfish's gills is attached to the walking leg. So whenever the crayfish walks the gills will spread out giving space so that oxygen can enter them. The gills are attached therefore when the crayfish walks, it can breathe at the same time. In the crayfish, there is a pocket like thing that lets the crayfish store its water so that when it walks on land and still breath because it needs water in order to survive.

Frog 

There are three main components to a frog's respiratory system. The First is the lungs, for pulmonary respiration. The second is the skin, for cutaneous. Finally the third one is the mouth, for buccal respiration. The most oxygen they get is from their skin. The frog have lungs that help them breathe. Once the nostrils of the frog breathes in the oxygen, it goes through the windpipe and down to the lungs. The frog can use its' mouth to breathe too. The skin of the frog is also is not really for protection, but instead it is for taking in oxygen. A lot of blood vessels are running through the skin of the frog and can help take in oxygen, which goes to the red blood cells. Whenever the frog swims, the oxygen in the water is instantly collected by the skin, so it  can stay underwater for a long period of time.  

Rat 

The rat's respiratory system  only has two lungs. The rat does not need anything else, like the human. Unlike the frog, the rat does not have to hold its breathe or get oxygen from its' skin. Rats use only their lungs to breathe, but when something bad happens, they on have one source to help them live. When the rat breathes the oxygen taken in are transported throughout the body by the red blood cells and at the same time the red blood cell  tries to rid of the carbon dioxide. 

Digestive System

The digestive system allows an organism to take in nutrients. It breaks the food down into particles that can be absorbed by the body. Aside from that, most organisms have different digestive systems that work differently depending on the organism. Each one has their own evolutionary advantages and disadvantages.

Earthworm

An earthworm's digestive system is very simple. It's digestive tract is divided into several different organs. The first is the pharynx, which sucks in the food. Next is the esophagus, which carries it to the crop. The crop stores the food and the gizzard grinds the food. Finally, the intestine digests and absorbs the nutrients and the waste it let out through the anus of the worm. This is the digestive system at it's simplest. However, it has it's disadvantages. The earthworm's intestine is very short, limiting the amount of food it can take in at once. The longer the intestine, the more food that organism can take in.

Crayfish

A crayfish's digestive system is slightly more advanced than the earthworm's. It's digestive tract consists of the foregut, midgut  and hindgut  The foregut conatins an enlarged stomach and the hindgut leads to the anus. With the digestive system, the crayfish is able to take in nutrients and let waste out.

Frog

The frog's digestive system begins with the mouth. First, they use their tongue to catch their prey. Then, their front teeth is used to grind their food before swallowing. The food moves through the esophagus and into the stomach, and shortly after, the small intestine. The small intestine digests the food and extracts the nutrients. When the food passes into the large intestine, the water and wastes are lead to the cloaca, where all wastes exit the frog. The frog has a slightly more advanced digestive system than the simpler organisms of earth, but it is still not as advanced as the rat's or human's digestive system.

Rat

The rat's digestive system is the most advanced out of all of the organisms. Like the frog, the rat begins digestion in it's teeth, where it crushes and tears food into smaller teeth. The food goes down the esophagus and into the stomach. The food then moves into the small intestine, where the intestine takes in nutrients from the ingested food. The villi and microvilli that covers the inside of the small intestine greatly increases the surface area of the small intestine and as a result, absorbs greater amounts of nutrients. At the end of the small intestine, the food travels to the large intestine, where the remaining water from waste material is removed by the large intestine. The waste leaves the rat from the anus and into the outside environment. The rat's digestive system is much like a human's digestive system. It can also absorb in a lot more nutrients at a time than rats can, giving it an evolutionary advantage.

Muscular System

The muscular system is an organ system that allows the body's movement and helps regulate the blood throughout the body. There are three kinds of muscles, the skeletal muscles, cardiac muscles, and the smooth muscles. Muscles in the organisms body usually provide balance, movement, strength, posture, and heat for the body to be warm.

Earthworm

The earthworm has two sets of strong muscles that help them move; the longitudinal and circular. When longitudinal muscles contract the worm's body will become shorter. When the circular muscles contract the body of the worm will become thinner. When the segments of the worm contract and relax, the notion of the longitudinal and circular movement is shown. The muscular system also help the worm defend its self and helps it move around. Earthworm does not have limbs so it has setae, hair like structures that allows the organism to grasp the soil to help move its self. 
Crayfish

The crayfish has powerful abdominal muscles to help them swim backwards and also in their tail because they swim a lot. There is also muscles on the pincers, walking legs, mandibles, and stomach. The claws are full of muscles so when it is protecting its self it can do serious damage to the other organism. 

Grass Frog 

The muscles of the frogs' legs enable hem to jump pretty far. They also have muscles in their stomach because every time they jump, sometimes they would not land on their hind legs, instead on their stomach. The frog has muscles on the arms but because they do not use them a lot there is only a little bit of muscle. the jaw is also filled with muscles because the frog has to eat its prey alive, so the muscles can help prevent the prey for getting away. 

White Rat 

 

The rat has strong muscles in their short and tiny legs because it uses them a lot, like to run after their prey or to climb up a tree. The mouth of the rat is really small so it would be constantly chewing on something, which has a lot of muscles to help. Sometimes the rat uses their short hand to help them eat food. 

Integumentary System

The integumentary systems of the four organisms, the earthworm, crayfish, grass frog, and the white rat are all different, their integumentary system need to help them adapt to the different enviornment. This system is something that covers the body, such as fur, skin or shell. Those covering can help prevent damage such as the loss of water, can also have a lot of different functions. The Integumentary System is the largest body organs and protects the organism for its unknown surroundings
   

Earthworm

The earthworm's skin has two layer. The skin can allow oxygen to get to the blood and carbon dioxide exchange. Its body also has a lot of segments, with a head section and a anus section. The worm is also very rubbery but very moist.The worm's skin is also sensitive to light and touch so it knows where to go. There is also very ting things on the worm that are called setae, the setae are there to help the worm move. The band aid looking thing is called the clitellum and is used for reproduction. the worm are very defensiveness because it does not have legs of hands like other organisms, instead it is really slimmy and squishy.

Crayfish 

The crayfish has an orange-brown shell that is great for protection when predators are near and also give the crayfish its' structure. The many segments on the crayfish allow them to swim more flexibly. The cray fish also has a pair of claws to help them when there are other organisms trying to eat them. They also have other small legs called swimmerets that help them swim. They have two antennas on the crayfish, the antennas are sensory structure, they help the crayfish to touch and feel things. 

Grass Frog

The grass frog has a brownish-greenish skin that is held loosely on the frog and is very slimmy like the worm. Their skin allows the frog to get oxygen and water. The colors are for the frog to camouflage with their environment or it can be used to warn predators of toxin poisons. The frog also has front legs and hind legs with webbed feet to help jump and swim. The head had two bulging eyes to see outside the water and has a 3rd eyelid to protect the eyes.

White Rat 

The white rat has three layers of skin, the epidermis, dermis, and subcutaneous tissue. They have white fur nails, and a tail. Due to their poor eye sight, the rats have whiskers to help them tell what is around them. The rat is warm blooded, its tail is there to help regulate the temperature. The rat's fur can sometimes attract fleas, lice, or mites. their ear, nose, and mouth are also very good. The rat's two front teeth are very sharp so it is easier for them for eating different kinds of food.