Final answer:
Protozoans have two cellular states: the active trophozoite and the protective cyst. The transition between these states, encystment and excystment, is triggered by environmental conditions, usually in response to unfavorability for the trophozoite form.
Step-by-step explanation:
Protozoans exhibit two main cellular states: the trophozoite and the cyst. The trophozoite is the active, feeding, and growing stage where the protozoan utilizes nutrients from its environment, or, if parasitic, from a host organism. In contrast, the cyst is an inactive, dormant stage encased in a protective wall, which allows the protozoan to survive harsh environmental conditions such as extreme temperatures or dehydration.
Transitions between these states are triggered by environmental cues. Encystment occurs when conditions become unfavorable for the trophozoite, allowing the protozoan to preserve itself until circumstances improve. The return to the trophozoite state, known as excystment, is induced when conditions again become favorable for growth and feeding.
Among the protozoans, Eimeria is a genus known for its ability to form cysts. These protective stages are crucial for disease-causing protozoans, to ensure their survival outside the host and to facilitate the spread to new hosts