What is a common characteristic of single-cell microorganisms?

Single-cell microorganisms, such as bacteria and protozoa, commonly reproduce by cell division, which is a fundamental characteristic of these organisms. This process, known as binary fission, allows a single cell to split into two identical daughter cells, enabling rapid population growth under suitable conditions. This characteristic is essential for the survival and adaptability of microorganisms in diverse environments.

In contrast, the other options do not accurately describe single-cell microorganisms. For instance, while some microorganisms can have complex nutritional requirements, many are capable of thriving in simpler environments or utilizing basic nutrients. Additionally, the idea that they do not reproduce is incorrect, as reproduction is a central function of all living organisms. Finally, while most single-cell microorganisms are microscopic and cannot be seen with the naked eye, they play crucial roles in ecosystems and human health. Understanding these characteristics is important for those studying or working in water treatment and management, as it directly impacts microbial analysis and control strategies.