This document provides an introduction to microbiology. It defines microbiology as the study of microorganisms including bacteria, algae, and fungi. It describes the structures of prokaryotic and eukaryotic cells and the growth cycle of bacteria. The document outlines several factors that influence bacterial growth such as temperature, pH, oxygen concentration, water availability, pressure, radiation, and nutritional supplements. It provides details on how each of these environmental conditions can impact microbial growth and metabolism.