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Microorganisms differ in their preferred temperature and pH, their relationship with oxygen, and their ability to withstand changes in water availability, osmotic pressure, pressure, or radiation. Growth also depends on access to nutrients and growth factors, as well as on usable energy sources and electron donors or acceptors. Redox conditions can affect the survival of anaerobes, while moisture supports growth and dormant forms such as spores and cysts can endure desiccation. Biofilms create local gradients in oxygen and nutrients, adding another layer to the environmental conditions microorganisms experience. Together, these factors explain why different organisms thrive under different conditions and how environmental adaptation supports microbial survival.