BIOS 1108 Final Exam Questions and Answers 2025

BIOS 1108 Final Exam Questions and Answers 2025

1. 1.01 Identify and use the most recent common ancestor (MRCA) to evaluate the relatedness of taxa: Long answer: The MRCA is the most recent individual from which two or more taxa have descended. Taxa with a more recent MRCA (closer to the tips of a phylogenetic tree) are more closely related than those whose MRCA is deeper in the tree. In short: In order to find relatedness, you need to see which MRCA has lived closer to present - The more recently 2 lineages diverged from common ancestor, the more closely related they are 2. 1.01 How do you identify the MRCA on a phylogenetic tree?: Locate the node where the branches of the taxa in question meet. The position o shows how recently they shared a common ancestor and indicates t relatedness. 3. 1.02 What are the four eons of geologic time in chronological order?: - H.A.P.Phan - Hadean, Archean, Proterozoic, & Phanerozoic 4. 1.02 What major biological events define each geologic eon?: - Hadean (4.6-4.0 billion years ago): Earth forms; no life yet No fossils due to extreme conditions Violent environment: volcanic activity, meteor impacts, and intense storms Formation of Earth's crust begins - Archean (4.0-2.5 billion years ago): Earth's crust stabilizes; oceans begin to form Atmosphere mostly carbon dioxide with little to no oxygen First life appears: unicellular prokaryotes, including cyanobacteria Evolution of oxygenic photosynthesis in cyanobacteria, releasing oxygen into oceans - Proterozoic (2.5 billion-541 million years ago): Oxygen levels rise significantly (Great Oxygenation Event) Early life flourishes: appearance of unicellular eukaryotes and simple multicellular organisms Photosynthetic bacteria continue altering the atmosphere First known multicellular algae and animals (e.g., soft-bodied organisms like sponges) - Phanerozoic (541 million years ago-present): Explosion of visible life (fossil record expands dramatically) Major diversification of animals and plants Life colonizes land; appearance of insects, vertebrates, flowering plants, and mam- mals Includes all major extinction and radiation events (e.g., Cambrian Explosion, age of dinosaurs, rise of humans) 5. 1.02 Why are prokaryotes (Bacteria and Archaea) important for human health and the environment?: - Human Health: Support digestion and nutrient absorption (gut microbiome). Synthesize essential vitamins (e.g., B12, K). Compete with and suppress harmful pathogens. Used in medicine and biotechnology: antibiotics, vaccines, CRISPR gene editing. Some are pathogens causing diseases (e.g., tuberculosis, strep throat). - Environmental Roles: Nutrient cycling: Fix nitrogen (e.g., Rhizobium), decompose organic material, and recycle carbon, sulfur, and phosphorus. Oxygenation: Cyanobacteria evolved oxygenic photosynthesis, leading to the Great Oxygenation Event. Bioremediation: Break down pollutants like oil and heavy metals. Extremophiles (mostly Archaea) survive in extreme environments, expanding our understanding of life. Capable of multiple metabolic pathways: photoautotrophs, chemoautotrophs, het- erotrophs, etc. 6. 1.03 Explain the endosymbiotic theory for the origin of eukaryotes: Eukary- otes arose during Proterozoic eon as a result of the fusion of Archean cells with bacteria; ancient archean engulfed ancient aerobic bacteria forming mutualistic relationship where engulfed bacterium allowed host archaean cell to use O2 to release stored energy as host cell protected bacterial cell from predators - Infoldings in plasma membrane of ancestral prokaryote gave rise to nucleus + ER - Loss of cell wall - In a first endosymbiotic event, the ancestral eukaryote consumed aerobic bacteria that evolved into mitochondria - In a second endosymbiotic event, early eukaryote consumed photosynthetic bac- teria (cyanobacteria) that evolves into chloroplasts 7. 1.03 What evidence supports the origin of eukaryotes through the endosym- biotic theory?: - Evidence for endosymbiotic theory - Size: mitochondria and chloroplasts are approx same size as prokaryotic cells - Genome: mitochondria and chloroplasts have own DNA organized in circular chromosome (genetic sequences similar to specific bacteria) - Reproduction: mitochondria and chloroplasts reproduce by binary fission - Cell membrane: mitochondrial membrane contains phospholipid characteristic of bacte- rial membranes (similar membrane composition to prokaryotes) - If removed from eukaryotic cells, eukaryotes cannot make new mitochondria and