assignment2

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University of Texas, Rio Grande Valley *

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1407

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Biology

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Apr 3, 2024

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docx

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ASSIGNMENT 2 BIOL 1407 1. Fill in the blanks (2 points each, 4 total): Fungi have multicellular, threadlike forms called _ hyphae _, which are made up of _ fungal cells _, which are single cells joined end-to-end and surrounded by a common cell wall. 2. Fill in the blanks (2 points each, 4 total): Plasmogamy is the fusing to two __ haploid __ hyphae and forms __ dikaryotic __ mycelium. 3. In the below diagram, label each stage of Basidiocarp fungi (a-c) with either dikaryotic, monokaryotic, or diploid (2 points each, 6 total). a. _ dikaryotic__ stage b. _ monokaryotic_ stage c. __d iploid__ stage a) b) c)

4. Explain how Zygomycota triggers the formation of the gametangia. Be sure to include the words trisporol, 4-dehydrotrisporic acid, trisporic acid, and positive and negative strains (6 points). In Zygomycota, the formation of gametangia is triggered by a pheromone called trisporol, which is synthesized by positive (+) mating strains. The trisporol diffuses into the environment and is detected by negative (-) mating strains, which respond by producing the complementary pheromone 4-dehydrotrisporic acid. The interaction of the two pheromones leads to the formation of a bridge between the two hyphae of opposite mating types. This bridge is called a gametangial contact bridge or conjugation tube, and it allows the transfer of haploid nuclei from the (+) strain to the (-) strain. Once the haploid nuclei are transferred, the two nuclei fuse in a process called karyogamy, forming a diploid zygote. The zygote undergoes meiosis, and the resulting haploid nuclei develop into a resistant structure called a zygosporangium. The zygosporangium is a thick-walled structure that protects the enclosed haploid nuclei from adverse environmental conditions. Inside the zygosporangium, the haploid nuclei undergo mitosis, forming a diploid nucleus in each cell. The resulting dikaryotic mycelium grows and eventually produces sporangia that release haploid spores. During this process, trisporic acid is produced as a byproduct of trisporol synthesis. This compound has been shown to be involved in regulating mating behavior and gametangial induction in some species of Zygomycota. 5. In the image below, label the bilateral symmetry body plan with anterior, posterior, dorsal, and ventral (2 points each, 8 total). dorsal

6. Fill in the blanks (2 points each, 6 total): The 3 different germ layers include the _ endoderm __, which is the inner layer that forms the digestive system and intestines, the intermediate layer _ mesoderm _, which usually forms skeletons and muscles, and the outer layer _ ectoderm __, which forms the outer covering of the body and nervous system. 7. Sponges lack tissues, but what do they have that serves as a precursor to tissues and classifies them as animals (instead of a colony)? (4 points) Sponges lack true tissues and organs, but they possess specialized cells that perform specific functions. These cells are organized into two layers: an inner layer of flagellated collar cells called choanocytes, and an outer layer of flattened cells called pinacocytes. The presence of specialized cells that perform specific functions is what distinguishes sponges from colonies of unicellular organisms. These specialized cells represent a precursor to true tissues and allow sponges to be classified as animals. In addition to choanocytes and pinacocytes, sponges also possess other specialized cells, such as amoeboid cells called archaeocytes that are involved in digestion and can differentiate into other cell types, and spicule-producing cells that synthesize the structural elements of the sponge's skeleton. 8. Cnidarians take animal evolution to the next step with digestion occurring in a _ gastrovascular cavity _, the starting step to the complex digestive system. (4 points) 9. Briefly explain why flatworms are flat. What do they lack that necessitates having a thin body? (6 points) Flatworms are flat because they lack a circulatory system and respiratory system, which limits the distance that oxygen and nutrients can diffuse from their outer surface to their inner tissues. Having a flattened body increases the surface area-to-volume ratio, which allows for more efficient gas exchange and diffusion of nutrients. Flatworms also lack a coelom, a fluid-filled body cavity that cushions and protects internal organs. Instead, their mesoderm is filled with muscle fibers that allow for movement and coordination. This also contributes to their flattened body shape, as the muscle fibers are arranged in a longitudinal and circular pattern that can contract and bend the body in various directions. In addition to the functional reasons for their flat shape, flatworms may have also evolved their body plan to aid in camouflage and avoid detection by predators. The flattened body shape allows them to blend in with their surroundings, making them less conspicuous and vulnerable to predation. 10. Fill in the blanks (2 points each, 4 total): In the mollusk body plan, the _ coelom __ is highly reduced and limited to small spaces around some organs and the __ gills _ , which extract dissolved O 2 from the water, project in to the mantle cavity. 11. Briefly explain the difference between open and closed circulatory systems. (6 points) Open and closed circulatory systems are two different ways that animals transport oxygen, nutrients, and other essential substances throughout their bodies. In an open circulatory system, the circulating fluid, or hemolymph, is not contained in vessels and directly bathes the organs and tissues. The heart pumps

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