Dissections
January 2015
Invertebrate Comparative Anatomy: For the past two weeks, my biology class has been studying the evolution of organisms from the beginning of the Cambrian Explosion that sparked the new adaptations that formed diverse branches of organisms. The main topics we focused on were the specialization of cells, complexity of the body plan and symmetry, new formations of organs and systems, appendages, and skeletons. We observed the differences between phylum in each category and discovered the importance of the new changes that helped the organism survive in the conditions. We compared the functions of the organisms to track the evolutionary process, such as contrasting the digestive, reproductive, excretory, respiratory, circulatory, and nervous systems as well as recording the diverse methods of movement. We achieved this by dissecting one organism from separate phylum. For example, we cut sponges, jellyfish, worms, squid, and grasshoppers.
We were presented with the task to compile a book with information and diagrams that easily describe the differences between each phylum and the ways evolution contributed to these differences. This file would be able to assist future biology classes while studying the topic of invertebrates.* This unit is followed up by the frog dissection that will occur next week and the update will be at the bottom of the page.
*I will try to scan photos of my groups completed booklet or post a link(it is not uploaded yet).
We were presented with the task to compile a book with information and diagrams that easily describe the differences between each phylum and the ways evolution contributed to these differences. This file would be able to assist future biology classes while studying the topic of invertebrates.* This unit is followed up by the frog dissection that will occur next week and the update will be at the bottom of the page.
*I will try to scan photos of my groups completed booklet or post a link(it is not uploaded yet).
The information contained within these paragraphs is organized by each phylum with the corresponding pictures. The paragraphs hold information concerning the changes and adaptions for each phylum compared to the previous more simple organisms we observed.
Phylum Porifera Dissection: The very first organism we observed was a simple sea sponge. Sponges don't have the ability to move and generally stay in on place, attached to the sea floor, once they form. Sponges can reproduce through budding off in asexual reproduction or releasing eggs and sperm into the water until they meet up in external sexual fertilization. Sponges host bacteria, algae, and plant-like protists in a mutual beneficial relationship. These creatures use sunlight to produce food for the sponge and the sponge uses its spicules to magnify the amount of sunlight that reaches the plants. The plants give off oxygen and nutrients that are essential because sponges filter it through the water and uses it for energy. The thriving plants can be consumed by marine animals that find shelter in the sponge.
Phylum Cnidaria Dissection: Although jellyfish evolved past the sponge, it is still a relatively simple organism, making it the perfect subject for our next dissection. Unlike the asymmetrical sponge, the jellyfish has radial symmetry and several stages in their life. Digestion is also more complex; they have a mouth and are carnivorous. Jellyfish also have digestive tissues like the gastrovascular cavity and the gastroderm. Specialization of cells inculde the advancements of the sensory cells, such as the oceli and statocyst. A nerve net the is spaced throughout the entire creature also assists in detecting stimuli. Another major progression is the fact that jellyfish have the ability to control their movement unlike the stable sponge that was fixed in one place. Jellyfish also reproduce sexually with the development of gonads and this creates a greater genetic variety.
Phylum Annelida Dissection: In order to observe major changes in the evolutionary path, we dissected a roundworm and view both the internal and external features and the difference between simpler organisms. Cnidarians have specialized cells called statocytes, epidermal cells, and cells lining the gastrovascular cavity that helps digestion. Although the jellyfish has a more complex digestive mechanism than the filter-feeding sponges, worms have a closed digestive tract that has two separate openings. Worms have specialized cells that make up the sex organs (clitellum and seminal vesicle), heart, and the digestive intestine and track. They also have specialized cells that make up their circulatory system and brain. They have all of the following organs: pharynx, esophagus, seminal receptacle and vesicle, heart, crop, gizzard, intestine, dorsal vessel, ventral vessel, and small ring vessels. The worm’s overall body plan involves a segmented, bilaterally symmetrical plan, with a one-way digestive track that goes from the posterior end to the anterior end, which is unlike the cnidarians who contain radial symmetry, a central gastrovascular cavity, and are hydrostatic. Annelids also have a dorsal side, which has evolved to become a darker color in order to camouflage with surrounding dirt. The ventral side is lighter, and has setae, which help it grip and move in the dirt. Each segment is separated by a septum. Unlike the sponges, both the cnidaria and annelids have control of their movement.
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Phylum Mollusca Dissection: Continuing on the path of advancements, we compared a squid from the molllusca phylum to the previous animals. It has specialized sensory cells and structural cells that form organs and cannot be found in the previous phylums. They have chromatophors, mottled pigment cells, that can change color in order to camouflage with the environment. Several of the organs and complex structures include: branchial hearts, systemic heart, ovaries, testicles,
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seminal vesicles, pancreas, liver, kidney, brain, mantle shell, gills, ink sac. It also has a centralized nervous system and has cephalization. Unlike all the previous organisms, squids have two separate sexes and are not hermaphrodites. They reproduce sexually.
Phylum Anthropoda Dissection: The final organism we dissected in the invertebrate unit was the grasshopper. This animal showed many distinctions in their body that proved this phylum is much more complex than the original sponge. Anthropods have the ocelli, a sensory organ that detects light. They also have specialized internal organs such as ones used for respiration, unlike the previous phylums grasshoppers have a network of branching tracheal tubes that extend through the body. Specialized malpighian tubules are present to extract waste from the blood and add them to feces. They also have a specialized exoskeleton made of chiton. Like the annelida, the grasshopper has segments, but is more complex because it has appendages that are specialized. These appendages include the antenna, claws, walking legs, jumping legs, wings, mouthparts, and aquatic animals can have flippers. The grasshopper has three distinct segments, the head, the thorax, and the abdomen. More modern nervous system that have two nerves that encircle the esophagus and connect the brain to a ventral nerve cord. Ganglia, or groups of nerve cells, coordinate the movement of individual legs and wings to help the animal move efficiently. The grasshopper is further along the evolutionary path than the simpler animals.
Reflection: This series of labs gave me the opportunity to explore invertebrates in depth, both internally and externally. I really enjoyed participating in dissection because it made the learning from notes applicable and relatable to real life organisms. I thought it was very interesting to determine the adaptations made by each phylum as organisms progressed in order to survive on Earth. For example, I liked viewing the changes of the respiration system. The simple sponges used diffusion to exchange gases through their pores and the grasshoppers were able to breathe through a network of branching tracheal tubes that are located all over the body. Even though this process takes millions of years, I still find it fascinating that organisms can change drastically enough to form completely new phylum and groups of animals. I also thought it was amazing that we have all evolved from the same basic organism from the Cambrian Period the occurred over five hundred million years ago. It surprised me that humans are closely related to fish, in fact, as an embryo, fish and humans looked the same and only the types of genes holding DNA determined the final outcome of our structures and functions of systems. In biology class.
This project made me learn a lot about the process of organisms evolving, but there are still concepts I would like to explore more. One of the major questions that came up throughout the entire dissection process was what do other species or subcategories of this phylum act like? I wonder about the changes in organisms that are closely related to the specimen we observed and I am curious about how these adaptations could aid or impinge on their ability to survive. Another thing I was curious about was the small changes that don't make the organism diverse enough to form a new species, but eventually these minute modifications lead to new specialized organs. I want to research more about the types of changes and the time it takes to pass down these genes to the future generations. Finally, I am curious about new possible species that become more complex than humans. Unfortunately, I will not live long enough to actually discover the physical changes in people, but currently, I have the chance to speculate about the advancements.
This project made me learn a lot about the process of organisms evolving, but there are still concepts I would like to explore more. One of the major questions that came up throughout the entire dissection process was what do other species or subcategories of this phylum act like? I wonder about the changes in organisms that are closely related to the specimen we observed and I am curious about how these adaptations could aid or impinge on their ability to survive. Another thing I was curious about was the small changes that don't make the organism diverse enough to form a new species, but eventually these minute modifications lead to new specialized organs. I want to research more about the types of changes and the time it takes to pass down these genes to the future generations. Finally, I am curious about new possible species that become more complex than humans. Unfortunately, I will not live long enough to actually discover the physical changes in people, but currently, I have the chance to speculate about the advancements.
Perch Dissection: The body of the perch is long and streamlined to aid in fast swimming and the fins and scales are adapted to balance while maneuvering through the water. Gill rakers help filter things and protect the gill arches. The pectoral and pelvic fins help steer during side to side movement; the dorsal fin contains the spine and maintains balance; the caudal fin is used for propelling. The perch's scales are clear and face towards the tail. This positioning helps the fish move quickly through the water by cutting down the amount of drag. The fish has two nostrils and it differs from humans because it doesn't have an external nose. Gills have adapted to assist the perch by having the ability to fan out and create more surface area for respiration. The lateral lines, a sensory organ that catches vibrations and feels pressure changes, is located near the top of the fish. Without an external skeleton, fish have the opportunity to grow and they have a larger range of movement. Guppies fertilize eggs internally, but the perch leaves eggs exposed on rocks to have them externally fertilized. The guppy would produce fewer eggs because the perch doesn't need to carry eggs inside them until development and the perch must compensate for the possibility of most of the eggs not being fertilized or being protected until adulthood. The swim bladder increases or decreases the amount of air inside to change the fish's density to move the fish to deeper or shallower water. Luminescent fish use light to attract prey in the dark because it is too dark to search for food.