The Comparison of Norway Rats and Humans and the Dissection of Animals

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The purpose of this lab is to discover and learn about the external features, digestive system, respiratory system and circulatory system of a Norway rat. This lab is to help teach students about the external characteristics of a rat. Specifically, where features are positioned, what functions they have and how they appear. This experiment is also meant to analyze the rat's digestive system and how each organ participates in the digestion of food. When it comes to the respiratory system, this experiment helps observe how the rat's organs are displayed, their functions and where the parts are positioned. Finally, this lab presents the circulatory system and the detailed components of the heart and identifying the specific blood vessels. The Norway rat can be described, as large in size. They are able to increase in sizes up to 500 grams. It is possible for them to reach lengths of 40cm, their tail alone could measure up to 21cm. The body of the Norway rat is known to be covered in very shaggy fur that could vary in colours like brown or gray. The tail and ears of this rat are covered in textured scales. The tail is usually shorter than the head and body.

These Rats usually nest in underground burrows which allows them to be able to enter buildings to search for food. They typically tend to come out in the night and stay in their burrows during the daytime. Norway rats are omnivorous and feed on many different types of foods. They will eat anything from meat, fruit, grains or nuts. If the rats come across another dead animal, they can serve as a food source for these type of rats as well. They are also very capable of catching small fish and other rodents. As like any other animal, they also need to drink water in order to survive. The Norwegian rat typically lives in communities with both dominant and subdominant members. These type of rats are also most commonly found throughout North America. They are able to live in a large variety of human habitats. They are extremely adaptive and thrive comfortably in densely populated cities. Outside, they can be found burrowing in the soil beneath buildings, near tree roots and even river banks. They also commonly live in basements, crawl spaces, attics and sewers. Norway rats are known to be carriers of various diseases.

The rat and human have many similarities. They both share the same kingdom, phylum and class, but have a different order, family, genus and species. As the taxa get more specific, there are fewer similarities between the two. The kingdom is the largest taxa, making it the easiest to put two organisms in one group. The human and rat both belong in the Animalia kingdom. Some characteristics of the Animalia kingdom include Cells that organize into tissues which create organs and make organ systems that have specific functions. The organisms in this category are also multicellular, eukaryotic, heterotrophic and are motile. Another taxa level that the human and rat are both in is the phylum, specifically the Chordata. There are four main aspects of a Chordata which consists of having a notochord, a dorsal hollow nerve cord, pharyngeal slits and post-anal tail. The notochord was present when the human and rat were in an embryo stage but changed into bone and cartilage of the vertebral column. The dorsal hollow nerve is also changed when out of the embryo period and is mainly in the central nervous system and is the nervous tissue of the brain and spinal cord. The pharyngeal slits are opening in the pharynx that reaches out to the outside surface of the body, usually these turn into gills but for the human and rat, they turned into parts of the ear and tonsils. The final component of being a Chordata is the post-anal tail which the rat has this that extends past the end of its body, on the other hand, the humans used to be more visible but ended up reducing size.

The last similar taxa between the rat and human are the class: Mammalia. The major features that Mammalia share is hair to keep the organism warm and the rat has whiskers which have sensory functions to detect nearby items. Mammalia also has sweat glands to prevent getting overheated and are warm-blooded which allows them to be wherever they want and they will stay warm. Some systems are also similar to humans and rats like the circulatory, respiratory and skeletal system: they both have a four-chambered heart, a diaphragm and specialized teeth to perform different tasks. The sex of an embryo can be determined by Y and X chromosomes and when the baby is being produced, they connect with the mom with the placenta and when the infant is born it feeds off the mother's milk.

Subsequently, the rat and human divide paths and start to have differences between their taxa because it begins to become more specific. The first taxa they split order, the human is in the Primates category and the rat is in the Rodentia. The difference between the two groups is the brain because the Rodentia have eyes on the side of their head, unlike Primates that have eyes on the front of the head which allows better hand-eye coordination and has an amazing sense of depth due to two photos at different angles. The teeth are also a large difference because Rodentia major in incisors meant for gnawing on items, but Primates have multiple different types of teeth like incisors, canine and molars. The final thing that Primates have is opposable thumbs, other than those few aspects, they are partially similar because they both can have collarbones, nails instead of claws and have five-toed feet.

The next taxa level is family which the two organisms go into Hominidae and Muridae. These family characteristics are similar to the order but with more specific measurements and amount of body parts. Some new characteristics of humans in the family Hominidae means that they don’t have tails, they stand more vertically, and their nostrils are close together, forward and downward. The only differences for Muridae are the specific amount of no more than 3 molars on each side of the mouth and four claws are on the forelegs and five on the back legs, but could possibly have a nail. The final two taxa work together to specify one organism in the whole world, the human genus and species is Homo sapiens and the rats are Rattus norvegicus. At this point, humans are capable of staying vertical and have an average height of around 160 cm for females and 175 cm for males. Their skulls have also changed because the base is small and the surrounding of the brain is high along with the back being rounded which reduces neck muscle. A few smaller features are that the face is vertical and Homo sapiens are the only organism to have a chin that sticks out. Compared to the rat, the human is large, but the rat is quite large and reaches 400 mm from nose to tail. A couple of other characteristics is that it is covered in fur although the ears and tail are bald and the head is more horizontal. Overall, the similarities and differences between the human and rat can get challenging when the requirements to stay in the same category get more detailed and specific.

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There are many differences and similarities between rats and humans including the cells, systems and diet. The two organisms have the same cell, the animal cell, they share the same organelles and they are both in the Animalia kingdom so they do have these cells. Some structures in the animal cell include plasma membrane, nucleus, cytoplasm, rough/smooth endoplasmic reticulum (ER), mitochondria, Golgi apparatus, ribosomes, lysosomes and others. There is a difference though if people specifically look in the nucleus because the chromosome count is different between rats and humans. A paper that was published in April describes the creation of a draft sequence for Rattus norvegicus, this draft includes 21 pairs of chromosomes while humans have 23 pairs.

Diseases can also impact both rats and humans and can even be tested on rats to help further the research of the cure. The same paper that talks about the draft of sequence for rats, also mentions the diseases tested that they helped advance medical research for cardiovascular diseases like hypertension, mental disorders, nerve regeneration, diabetes, surgery, transplants, cancer, the healing of bones and injuries and motion sickness. Although there are a few tests that have negative results that show that not all diseases can be shared between rats and humans. There was an arthritis experiment and the results were that the rats were dragging their swollen limbs, this proves that not all diseases match for rats and humans. The reasoning could differ between the difference in pH value, rats not capable of vomiting or even the small differences in systems.

Further, in the development of cells, they create systems which may have certain similarities and differences between rats and humans. They share similar circulatory systems since they both have a closed system and 4 chambered hearts. Both systems have the same function of carrying blood through the lung for gas exchange then back to the heart and both organisms have certain major blood vessels like superior vena cava, pulmonary arteries and veins, aorta, inferior vena cava, descending aorta. Although, a few systems are not the same between rats and humans like the digestive system. Two main differences between the human digestive system and rat are that the rat does not have a gallbladder and the large intestine has an enlarged cecum. The rat does not need the gallbladder due to the lack of fatty foods which means that there is no need for stored bile that breaks down fat. The reason that the rat needs a larger cecum is that it digests more seeds and grains so having a larger cecum helps digest these certain foods. Therefore, the rat has many similarities to humans that have helped advance research, but they do have differences that make them unique because, without these special characteristics, they would basically be humans.

A rat matures sexually at two to five months of age. They are able to breed any month of the year. It is known that a female rat is able to mate as many as 500 times with various males. Each litter numbers can vary from anywhere between four to 22. A female can have 3 to 12 litterers per year. This means that a pair of rats can produce as many as 2,000 offspring in a year if left to breed in unrestricted conditions. The Gestation period for Norway rats is 21 to 24 days. The typical lifespan for a wild Norway rat is about 2 years. There are hundreds of alternatives for teachers and students to use in place of dissection specimens. Some of them include the use of CD-ROMs, models, videos, charts, and much more. With these technologies and programs made available in schools to aid with virtual dissections, the money spent on buying dissection sets can clearly be put to better use. These type of alternatives are readily available at every educational level. With interactive and comprehensive alternatives, students are able to gain a far greater understanding and respect for animals than with traditional dissection. For example, some programs that can be used in the alternative are Digital Frog 2.5, V-FrogTM, DissectionWorks, and many more.

Many people believe that animal dissection labs are an unethical and an unnecessary part of the secondary school biology curriculum. Millions of animals that are dissected each year in education systems are subjects of severe animal abuse. Many of these animals are sold to schools from fur companies, pet stores and, many times, slaughterhouses. Animals are often stockpiled on top of one another and shipped in crowded containers with no temperature regulation, food, or water. Animals get treated unjustly, and by buying these dissection sets, it is funding and promoting the abuse of animals. Millions of frogs are harvested every year from the wild for dissection purposes. This means that, along with all of the other ways humans are impacting frog populations, such as global climate change and pollution, humans are also destroying their populations. In the school curriculum, children are taught about the biodiversity crisis and all of its negative aspects. But, yet, students are encouraged to contribute to it. Many animals taken for school dissections, especially fetal pigs, are by-products of the meat industry. Almost all of the pigs slaughtered for human consumption are raised in horrible crowded and confined conditions. Not only are their lives extremely shortened, but they are also deprived of space, fresh air, and fresh food. The fetuses used for dissections are taken from pregnant pigs at the slaughterhouse. School boards are promoting the mistreatment of the animals raised for the meat industry. Another point that many people believe is that it’s not necessary for students to dissect animals in order to see what the insides of the animals look like. If a student were to pursue a career in a field where this is needed, they would have the opportunity to dissect human cadavers in University. When honestly, realistically, very few students who participate in these labs in high school will actually go down these career paths. Another point would be that buying animals for biology classes can be quite costly. The cost for a high school dissection set can be over $1000.00. However, with technology, there are so many alternative educational, interactive dissection programs that can be used instead, like the ones I mentioned before.

While most people are strongly against dissection in the classroom, there are still a whole bunch of people who are totally all for it. Some reasons that people are in favour of dissections are that many people find it much easier to learn when they are able to do hands-on projects and activities. Dissection shows that the animals that were put on this earth aren't there to be mutilated or demolished but to teach us of the complexity of life. It allows us to be curious and exposes us to the reality of life. There are many people that believe that only thing that an animal dissection lab teaches students is that an animal’s life is disposable and unimportant, But, it helps us understand things we need to know about body systems and prepares many students for real life hands on experiences along with actually teaching us to have respect for all living things. For example, veterinarians that save lives go through dissections that help them to learn and one day in the future to save animals lives. I personally think that doing dissections in Biology class is a super fun experience. It’s a fun and interesting way of helping students learn about the different body systems and how each of them work. As I mentioned before, some people argue that it is 'gross' and 'cruel', Well I believe that if you can't handle it, request that you be excused from the dissection. Just because one or even a few students don’t want to participate in the dissection, it doesn't mean that the entire school can't.

After doing the dissection of the rat, several observations were discovered. Identifications of organs in the circulatory, respiratory and digestive system, as well as the external features of the rat, were examined throughout the dissection. These observations provided a detailed understanding towards the anatomy of a rat and human body. In order to observe the organs of the circulatory, respiratory and digestive system, precise incisions were made. Seeing organs in a body positioned in order according to the process of each system, gave a kinesthetic understanding to not only how the systems of a rat function, but of a human too. All organs within the rat have its own purpose, and during the dissection, the process of when these organs are used and where the food, blood, or oxygen goes after it leaves or before it enters these organs became more visible.

There are many ways to improve the effectiveness and results of the lab. I believe using fingers opposed to the tools when appropriate is extremely beneficial because fingers aren't sharp and powerful like the tools, such as the probe, so there will be a decreased chance of damaging organs. Another method for improvement is to cut open the chest cavity of the rat more with precise cuts from scissors. If cuts are made above the lungs and heart, the trachea and esophagus will become more visible. My group members and I could have had a more detailed visual if we continued the cut from the ribcage up the neck of the rat. In conclusion, there was room for improvement found in the lab.


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