1. What are the three domains of life based on molecular phylogeny? How do they differ from each other in terms of cell structure, metabolism, and gene expression? The three domains of life are Bacteria, Archaea, and Eukarya. Bacteria and Archaea are prokaryotes, meaning they lack a nucleus and other membrane-bound organelles. Eukarya are eukaryotes, meaning they have a nucleus and other membrane-bound organelles. Bacteria and Archaea differ in their cell wall composition, ribosomal RNA sequences, and lipid structures. Eukarya have more complex and diverse metabolism and gene expression than prokaryotes, involving multiple chromosomes, histones, and introns. 2. What is the endosymbiotic theory? What evidence supports this theory? - The endosymbiotic theory is the idea that some organelles in eukaryotic cells, such as mitochondria and chloroplasts, originated from ancient prokaryotes that were engulfed by larger cells and established a symbiotic relationship. The evidence for this theory includes the presence of circular DNA, ribosomes, and double membranes in these organelles, as well as their ability to replicate independently of the host cell. 3. What are the main types of microscopy used to study microscopic organisms? What are the advantages and limitations of each type? - The main types of microscopy are light microscopy, electron microscopy, and fluorescence microscopy. Light microscopy uses visible light to illuminate specimens and can be used to observe living cells, but has a limited resolution of about 0.2 micrometers. Electron microscopy uses beams of electrons to create images of specimens and can achieve a much higher resolution of about 0.2 nanometers, but requires the specimens to be fixed, dehydrated, and coated with metal. Fluorescence microscopy uses fluorescent molecules or proteins to label specific structures or molecules in specimens and can reveal their location, distribution, and interactions, but requires specialized equipment and reagents. 4. What are the main differences between gram-positive and gram-negative bacteria? How does this affect their susceptibility to antibiotics? - Gram-positive and gram-negative bacteria differ in their cell wall structure. Grampositive bacteria have a thick layer of peptidoglycan that retains the purple dye in the