Protozoans are organisms usually made up a single cell and are all microscopic. All protozoans are eukaryotes. They have different responses when faced with adverse or unfavorable environmental conditions. Examples include:
Amoeba: During adverse environmental conditions, many amoeba undergo encystment that is they become cysts. The amoeba becomes circular, loses most of its water and secretes a thick membrane that serves as a protective covering. When the environment is again suitable, the covering of the cyst ruptures and the amoeba emerges.
Bacteria: In unfavorable environmental conditions some bacteria such as clostridium form spores, specifically endospores. An endospore is an extremely resistant, tough, dormant, non reproductive cell structure that can withstand desiccation, extreme temperatures, chemical disinfectants and starvation. The bacteria survive in this mode until better growth conditions return